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Alcatel-Lucent GSM
BSS System Description
BSS Document
Concept Guide
Release B10
3BK 21222 AAAA TQZZA Ed.08
Status RELEASED
Short title System Description
All rights reserved. Passing on and copying of this document, useand communication of its contents not permitted without writtenauthorization from Alcatel-Lucent.
BLANK PAGE BREAK
2 / 304 3BK 21222 AAAA TQZZA Ed.08
Contents
Contents
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1.1.1 Alcatel-Lucent Radio Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171.1.2 Extended GSM Band (E-GSM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171.1.3 GSM 850 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171.1.4 Frequency Band Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181.1.5 GPRS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
1.2 BSS Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191.2.1 Call Set Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191.2.2 Call Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201.2.3 Call Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201.2.4 Operations & Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
1.3 BSS Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211.3.1 Base Station Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211.3.2 Base Transceiver Station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221.3.3 Transcoder And Transmission Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251.3.4 The Multi-BSS Fast Packet Server . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
1.4 Extended GSM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291.4.1 E-GSM Mobile Station Recognition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291.4.2 E-GSM Management After Initial Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . 301.4.3 E-GSM Determination at Handover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301.4.4 TCH Allocation for E-GSM and P-GSM Mobile Stations . . . . . . . . . . . . . . . . . . . . 31
1.5 External Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321.5.1 Network Subsystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331.5.2 Mobile Stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341.5.3 Phase 2 Mobile Support in a Phase 1 Infrastructure . . . . . . . . . . . . . . . . . . . . . . . 381.5.4 Operations and Maintenance Center-Radio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
1.6 Network Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391.6.1 Telecommunications Management Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391.6.2 Q3 Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
1.7 BSS Telecommunications Layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401.7.1 Call Management Sub-layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411.7.2 Mobility Management Sub-layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411.7.3 Radio Resource Management Sub-layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411.7.4 The A Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431.7.5 The Ater Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441.7.6 The Abis Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441.7.7 HSL Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451.7.8 Satellite Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451.7.9 The Air Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 461.7.10 System Information Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511.7.11 Dynamic SDCCH Allocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
1.8 Networks Interworking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561.8.1 2G and 3G Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561.8.2 2G to 3G Handover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 571.8.3 2G to 3G Reselection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581.8.4 GAN System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 591.8.5 Number of BCCH Frequencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
2 GPRS in the BSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 622.1.1 Packet Switching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 622.1.2 GPRS Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
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2.2 GPRS Channels and System Information Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 662.2.1 Logical Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 662.2.2 Virtual Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 662.2.3 System Information Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
2.3 GPRS Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 682.3.1 The Gb Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 682.3.2 The BSCGP Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 692.3.3 The GCH Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702.3.4 Specific LCS Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
2.4 GPRS Network Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 712.4.1 MAC and RLC Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 712.4.2 Temporary Block Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 712.4.3 Mobility Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 722.4.4 Enhanced Packet Cell Reselection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 732.4.5 Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 762.4.6 Radio Power Control and Radio Link Measurement . . . . . . . . . . . . . . . . . . . . . . . . 77
2.5 Resource Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 782.5.1 Timeslot Allocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 792.5.2 Autonomous Packet Resource Allocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 802.5.3 Packet Flow Context . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 812.5.4 Dynamic Abis Allocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 822.5.5 Enhanced Transmission Resource Management . . . . . . . . . . . . . . . . . . . . . . . . . . 852.5.6 Frequency Hopping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 852.5.7 PCM Link Sharing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 862.5.8 TBF Resource Re-allocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 862.5.9 Dynamic Allocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 872.5.10 Extended Dynamic Allocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
2.6 Traffic Load Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 882.6.1 Smooth PDCH Traffic Adaption to Cell Load Variation . . . . . . . . . . . . . . . . . . . . . . 882.6.2 Congestion Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 892.6.3 M-EGCH Statistical Multiplexing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 892.6.4 GPRS Overload Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
2.7 Data Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 912.7.1 GPRS Attach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 912.7.2 Packet Data Protocol Context Activation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 922.7.3 Data Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 952.7.4 Packet Data Protocol Context De-activation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1032.7.5 GPRS Suspend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1072.7.6 GPRS Resume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1082.7.7 GPRS Detach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
2.8 Location Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1122.8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1122.8.2 Logical Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1132.8.3 LCS Positioning Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1142.8.4 LCS Scenario in Circuit-Switched Domain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1152.8.5 Physical Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1152.8.6 SMLC Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1162.8.7 BSS and Cell Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1162.8.8 LCS O&M . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
2.9 High Speed Data Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1182.9.1 HSDS Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1182.9.2 GPRS CS3/CS4 and EGPRS Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1192.9.3 Transmission Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1212.9.4 Cell/GPU Mapping Modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
2.10 Gb over IP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
3 Call Set Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1273.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
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3.1.1 Call Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1283.1.2 Call Set Up Phases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
3.2 Mobile-Originated Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1303.2.1 Radio and Link Establishment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1303.2.2 Authentication and Ciphering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1393.2.3 Normal Assignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
3.3 Mobile-Terminated Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1463.3.1 Radio and Link Establishment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1473.3.2 Authentication and Ciphering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1473.3.3 Normal Assignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1483.3.4 Off Air Call Set Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1493.3.5 IMSI Attach-Detach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
3.4 Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1503.4.1 Paging Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1523.4.2 Discontinuous Reception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
3.5 Congestion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1553.5.1 Queueing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1553.5.2 In-queue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1563.5.3 Pre-emption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
3.6 Classmark Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1593.6.1 Classmark IE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1603.6.2 Classmark Updating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1623.6.3 Location Updating with Classmark Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
3.7 Authentication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1653.7.1 IMSI/TMSI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1653.7.2 Authentication Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
3.8 Ciphering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1673.8.1 Mobile Station Ciphering Capability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1673.8.2 BSS Ciphering Capability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1683.8.3 Ciphering Keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1683.8.4 Ciphering Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
3.9 Tandem Free Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1713.9.1 TFO Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1723.9.2 TFO Functional Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1733.9.3 TFO Optimization and Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
4 Call Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1754.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1764.2 In-Call Modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
4.2.1 In-Call Modification Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1784.2.2 Circuit-Switched Group 3 Fax Data Rate Change . . . . . . . . . . . . . . . . . . . . . . . . . 1794.2.3 Error Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
4.3 Frequency Hopping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1804.3.1 Baseband Frequency Hopping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1814.3.2 Synthesized Frequency Hopping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
4.4 Speech Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1824.4.1 Continuous Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1824.4.2 Discontinuous Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1834.4.3 Voice Activity Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1834.4.4 BSS Discontinuous Transmission Towards Mobile Station . . . . . . . . . . . . . . . . . 1844.4.5 Mobile Station Discontinuous Transmission Towards BSS . . . . . . . . . . . . . . . . . 185
4.5 Radio Power Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1864.5.1 BTS Radio Power Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1874.5.2 Mobile Station Radio Power Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1874.5.3 Radio Link Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1884.5.4 Power Control Decision and Handover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1894.5.5 Change Power Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
4.6 Handover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
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4.6.1 Principal Handover Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1934.6.2 Radio Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1954.6.3 Handover Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1964.6.4 Target Cell Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2024.6.5 Synchronous and Asynchronous Handover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2054.6.6 Circuit-Switched Telecom Handovers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
4.7 Overload Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2104.7.1 BTS Overload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2104.7.2 BSC Overload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
4.8 Call Re-establishment by the Mobile Station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
5 Call Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
5.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2145.2 Call Release Procedures in Normal Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
5.2.1 Normal Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2155.2.2 Calls Terminated Following a Channel Change . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
5.3 Call Release - Special Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2225.3.1 Call Release Following Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2225.3.2 BSC-Initiated Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2245.3.3 BSC-Initiated SCCP Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2265.3.4 BTS-Initiated Call Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2265.3.5 Mobile Station-Initiated Call Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2305.3.6 Remote Transcoder Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
5.4 Preserve Call Feature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2325.4.1 Normal Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2325.4.2 Abnormal Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
6 Handling User Traffic Across the BSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2356.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2366.2 Speech . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236
6.2.1 Analog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2376.2.2 Interleaving and Forward Error Correction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2376.2.3 Speech Data Bursts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2376.2.4 Digital Speech . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2386.2.5 Digital 64 kbit/s A-law Encoded Speech . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2386.2.6 Enhanced Full-Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2396.2.7 Half-Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2406.2.8 Adaptive Multiple Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2406.2.9 Channel Mode Adaptation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2446.2.10 VGCS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
6.3 Circuit-Switched Data Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2466.3.1 Transparent Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2466.3.2 Non-Transparent Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248
6.4 Short Message Service - Cell Broadcast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2496.4.1 SMS-CB Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2496.4.2 Phase 2+ Enhancements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250
6.5 Support of Localized Service Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2516.6 PLMN Interworking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252
7 Cell Environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2537.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
7.1.1 Rural and Coastal Coverage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2567.1.2 Urban Coverage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
7.2 Concentric Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2567.3 Sectored Site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2577.4 Extended Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258
7.4.1 Standard Extended Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2597.4.2 Enlarged Extended Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2597.4.3 PS in Extended Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260
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7.5 Umbrella Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2607.5.1 Mini Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2607.5.2 Microcell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2617.5.3 Indoor Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264
7.6 Cell Shared by Two BTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2657.7 Unbalancing TRX Output Power per BTS Sector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
8 Operations & Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2678.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
8.1.1 Subsystem O&M Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2698.1.2 System O&M Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
8.2 O&M Control - Subsystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2718.2.1 LMTs and IMT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2718.2.2 OML Auto-Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2728.2.3 Managed Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2728.2.4 Security Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
8.3 O&M Control via OMC-R . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2738.3.1 Multiple Human-Machine Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2738.3.2 ACO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2748.3.3 Connection from BSC to OMC-R . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2758.3.4 Electronic Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
8.4 Configuration Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2788.4.1 Hardware Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2798.4.2 Logical Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2798.4.3 Default Parameter Customization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2808.4.4 Software Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2808.4.5 Auto-Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2808.4.6 OML Auto-Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2828.4.7 Network Element Provisioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283
8.5 Fault Management - Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2838.5.1 Alarm Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2858.5.2 Alarm Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2858.5.3 BSC Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2878.5.4 BTS Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2918.5.5 Alarms Detected by the TSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2938.5.6 MFS Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2938.5.7 Recovery Example: Carrier Unit Failures with BCCH . . . . . . . . . . . . . . . . . . . . . . 2948.5.8 Automatic Power-Down . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2978.5.9 BSC Alerter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297
8.6 Performance Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2988.6.1 Traces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2988.6.2 Performance Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2998.6.3 Radio Measurements Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2998.6.4 Results Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
8.7 Audits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3028.7.1 Audit Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3028.7.2 Audit Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303
8.8 Remote Inventory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304
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Figures
FiguresFigure 1: BSS in the PLMN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Figure 2: Logical Position of External Components Associated with BSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Figure 3: Location Update . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Figure 4: TMN System Hierarchy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Figure 5: Timeslot 4 of a TDMA Frame Supporting Access Grant Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Figure 6: Model LLC Packet Data Unit used in GPRS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Figure 7: The Alcatel-Lucent GPRS Solution in the PLMN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Figure 8: Mobile Station-Originating Packet Data Protocol Context Activation . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Figure 9: GGSN-Originating Packet Data Protocol Context Activation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
Figure 10: Mobile-Originating Packet Data Protocol Context De-activation . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Figure 11: Network-Originating Packet Data Protocol Context De-activation Processes . . . . . . . . . . . . . . . 105
Figure 12: Radio and Link Establishment for Mobile-Originated Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
Figure 13: Connection for Mobile-Originated Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
Figure 14: Normal Assignment for Mobile-Originated Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
Figure 15: Radio and Link Establishment for Mobile-Terminated Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
Figure 16: CCCH with Three Blocks Reserved for AGCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
Figure 17: Four TDMA Frame Cycles Providing 24 Paging Sub-channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
Figure 18: Location Update with Mobile Station Sending Location Area Identity of Previous VLR . . . . . . . 165
Figure 19: Example of TFO Establishment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
Figure 20: Different Forms of Discontinuous Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
Figure 21: Power Output Balancing Based on Received Quality and Signal Levels . . . . . . . . . . . . . . . . . . . . 190
Figure 22: Umbrella Cell Load in Mobile Velocity Dependent Handover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
Figure 23: Mobile Station Disconnecting a Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
Figure 24: Normal Call Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
Figure 25: Initiation of Normal Release by MSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
Figure 26: BSC/BTS/Mobile Station Interactions in Normal Call Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
Figure 27: Normal Release Final Steps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
Figure 28: Call Release Following Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
Figure 29: BSC-initiated Call Release Toward the MSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
Figure 30: BTS-initiated Call Release following LAPD Failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
Figure 31: Call Release due to Mobile Station-Initiated Radio Link Failure . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
Figure 32: Call Release Due to Communication Failure Detected by Transcoder . . . . . . . . . . . . . . . . . . . . . . 231
Figure 33: Encoded Speech Transmission Across the BSS with 9120 BSC . . . . . . . . . . . . . . . . . . . . . . . . . . . 236
Figure 34: Multiplexed Ater Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238
Figure 35: Data Transmission Across the BSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246
Figure 36: Example: Cell Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
Figure 37: Sectored Site Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
Figure 38: Example of Extended Cell Topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258
Figure 39: Umbrella Cell with Mini Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260
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Figures
Figure 40: Indoor Cell Example Network Hierarchy with Three Layers and Two Bands . . . . . . . . . . . . . . . . 264
Figure 41: Multiple HMI Access to OMC-Rs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
Figure 42: ACO Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274
Figure 43: X.25 Without Redundancy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275
Figure 44: X.25 With Redundancy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
Figure 45: RSL Correlation on the Abis Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288
Figure 46: Example Alarm Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290
Figure 47: Example: Loss of Carrier Unit Holding BCCH. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296
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Tables
TablesTable 1: System Information Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Table 2: Network Operation Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Table 3: Cell List Identifier and Paging Performed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
Table 4: Paging Request Message and Mobile Station Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
Table 5: Downlink Discontinuous Transmission Status in Channel Activation . . . . . . . . . . . . . . . . . . . . . . . . . 184
Table 6: Operator Discontinuous Transmission Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
Table 7: Mobile Station Maximum and Minimum Power Ranges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
Table 8: Software Version versus Hardware Board/Feature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
Table 9: Circuit-Switched Data Rate Conversions Across the Air Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
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Preface
Preface
Purpose This document provides detailed descriptions of the functions and features ofthe Alcatel-Lucent BSS. Note that some of the functions and features may notbe available on the system installed at your location.
The technical information in this document covers:
Mobile Communications SupportThese sections describe how the BSS handles communications between amobile station and the NSS. It follows a call through the Alcatel-Lucent BSS,and describes how each element in the system functions individually, andwith other elements, showing how the BSS and its units react as a system.
Operations and Maintenance (O&M).These sections describe the O&M functions within the system, and inparticular, both local and distributed O&M functions in the BSS.
What’s New In Edition 08Updated section 2G and 3G Cells (Section 1.8.1) due to rapport 2G and3G cells.
Updated section Extended Cell (Section 7.4) due to 3 extended cells allowanceon BTS.
Updated section System Information Messages (Section 1.7.10)due to systemimprovement.
In Edition 07Improve section 2G to 3G Reselection (Section 1.8.3) due to system evolution.
In Edition 06Improve section BTS Radio Power Control (Section 4.5.1)due to adjustmentof BTS power level
Improve section LMTs and IMT (Section 8.2.1)due to several IMT sessionwith admin acces possible per MFS
In Edition 05
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Preface
Introduce the max number of BCCH frequencies for the set of all target cells,in Number of BCCH Frequencies (Section 1.8.5).
In Edition 04Update with the new equipment naming.
In Edition 03Overall document quality was improved following a quality review.
Illustrations and layout were checked and improved.
In Edition 02Overall document quality was improved following an editorial review.
Information concerning GAN interoperability was added in GAN System(Section 1.8.4).The following sections were updated:
Transcoder And Transmission Function (Section 1.3.3)
Mobile Station Multislot Class Handling (Section 2.9.2.3).
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The following sections were modified:
Information concerning GAN was added in GAN System (Section 1.8.4)
Information concerning GboIP was introduced in Gb over IP (Section 2.10)
Information concerning EDA was introduced in Extended DynamicAllocation (Section 2.5.10)
Information concerning AMR-WB and TFO was added in Adaptive Multiple
Rate (Section 6.2.8)
Information concerning TC IP supervision and STM-1 was added inTranscoder And Transmission Function (Section 1.3.3) and Remote
Inventory (Section 8.8).
In Edition 01The following sections were updated after a review:
Extended GSM (Section 1.4)
GPRS Channels and System Information Messages (Section 2.2)
Results Analysis (Section 8.6.4).The following sections were updated:
Information concerning compressed messages in the call setup step was
added in 2G to 3G Handover (Section 1.8.2)
Information concerning the TDSCDMA feature was added in 2G to 3GReselection (Section 1.8.3)
Information concerning availability in the case of NC2 was added in 2Gto 3G Reselection (Section 1.8.3)
Information concerning the NC2 related restriction was added in Cell
Reselection Modes (Section 2.4.3.1)
Information concerning the recommendation on IR activation was added inModulation and Coding Schemes (Section 2.9.2.2)
Information concerning one GSL configured on GPU was added inMulti-GPU per BSS (Section 1.3.4.3).
The following sections were modified:
Information concerning MX capacity improvements was added in HSLLinks (Section 1.7.7)
Information concerning MCCCH was added in Control Channels (Section
1.7.9.4)
Information concerning DTM was added in Dual Transfer Mode (Section1.7.9.5)
Information concerning MCS reduction on the flight and WRR was added inMAC Algorithm (Section 2.7.3.8).
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Preface
Audience This manual is for people requiring an in-depth understanding of the functionsof the Alcatel-Lucent BSS:
Network decision makers who require an understanding of the underlying
functions of the system, including:
Network planners
Technical design staff
Trainers.
Operations and support staff who need to know how the system operates in
normal conditions, including:
Operators
Support engineers
Maintenance staff
Client Help Desk personnel.
Assumed Knowledge The document assumes that the reader has an understanding of:
GSM
GPRS
Mobile Telecommunications
Network Management concepts and terminology.
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1 Introduction
1 Introduction
This section gives a brief overview of the Alcatel-Lucent BSS, its functionsand features.
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1 Introduction
1.1 OverviewThe BSS provides radio coverage for GSM subscribers in a defined area. Itsprincipal role is to provide and support signaling and traffic channels betweenmobile stations and the NSS.
The following figure shows the BSS within the PLMN, and its links to the PSTNand the PSDN in a fixed network.
Base Station Subsystem
Mobile Stations
NetworkSubsystem
FixedNetwork
PLMN
OMC−R
NMC
MFS
BTS
SGSN
MSC PSTN
TC
BSC
PSDN
MFS : Multi-BSS Fast Packet Server
NMC : Network Management Center
PSDN : Packet Switched Data Network
PSTN : Public Switched Telephone Network
SGSN : Serving GPRS Support Node
Figure 1: BSS in the PLMN
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1 Introduction
1.1.1 Alcatel-Lucent Radio Solutions
To respond to the swiftly evolving needs in the BSS, Alcatel-Lucent offersspecific Radio Solutions.
The Alcatel-Lucent Radio Solutions include the following BSS equipment:
9120 BSC
9130 BSC
G2 Transcoder
9125 Transcoder
BTS 9100
BTS 9110
9135 MFS
9130 MFS.
Note: BTS G1 and BTS G2 are still supported by Alcatel-Lucent.
1.1.2 Extended GSM Band (E-GSM)
The Alcatel-Lucent BSS supports the E-GSM band. E-GSM consists of:
The 900 MHz primary band, called the P-GSM band. This uses 890-915
MHz for uplink, and 935-960 MHz for downlink
The 900 MHz extended band, called the G1 band. This uses 880-890 MHzfor uplink, and 925-935 MHz for downlink.
This corresponds to a total number of 174 addressable frequencies.
1.1.3 GSM 850
The GSM 850 MHz band was introduced in Release 1999 of the 3GPPStandard in 1999 to allow operators to progressively replace the D-AMPS andCDMA technologies that were using these frequencies. Besides certain Asiancountries, the GSM 850 MHz band concerns in particular the Latin Americancountries where many operators already use the GSM system in their networkwith GSM 1900 MHz to extend or replace their existing D-AMPS network. Theterm GSM 850 applies to any GSM system which operates in the 824 MHz to849 MHz band for the uplink direction and in the 869 MHz to 894 MHz band forthe downlink direction. The GSM 850 band is defined by 124 absolute radiofrequency channel numbers (ARFCN) among the 1024 ARFCNs available inthe GSM standard.
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1 Introduction
1.1.4 Frequency Band Configurations
The Alcatel-Lucent BSS supports the following multiband networkconfigurations:
BSS with a mix of GSM 850 and GSM 1900 cells
BSS with a mix of GSM 850 and GSM 1800 cells
BSS with a mix of GSM 900 and GSM 1800 cells
BSS with a mix of GSM 900 and GSM 1900 cells.
For more information, refer to the Basic GSM System Specifications.
1.1.5 GPRS
GPRS, the solution chosen by European Telecommunication StandardsInstitute (ETSI) in response to the demand for increased data transmissionrates, is available in the Alcatel-Lucent BSS.
This means there are now two parallel systems in the PLMN:
Circuit-switched transmission for voice
Packet-switched transmission for data.
For information about how GPRS functions in the BSS, see GPRS in theBSS (Section 2).
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1 Introduction
1.2 BSS FunctionsFunctions are defined by the International Telecommunications Union andEuropean Telecommunication Standards Institute recommendations.
This section provides an overview of the BSS functions with a system-wideview; that is, how the BSS functions work together within the system. Networkelements and functional units are indicated where applicable, but are notdescribed. For more information, refer to the specific network elementdescription manuals, such as the BTS Functional Description.
The BSS provides signaling and traffic channels between the mobile stationand the NSS. To ensure a high level of service to the subscribers, the BSSoffers the following functions:
Call Set Up
Call Handling
Call Release
Operations & Maintenance.
1.2.1 Call Set Up
Call Set Up is used for speech and data calls. The following tables shows threebasic types of call.
Type of Call Description
Mobility Management Mobility Management calls, such as location updates, are used by thesystem to gather mobile station information. The exchanges are protocolmessages only. Therefore, only a signaling channel is used.
Supplementary Service Supplementary service calls, such as SMS, allow the mobile station to sendand receive messages to and from the BTS. These calls pass small amountsof information. Therefore, only a signaling channel is used.
User Traffic User traffic calls, such as speech or data calls to a correspondent, can passlarge amounts of information. Therefore, they require greater bandwidththan a signaling channel. These calls use traffic channels.
Call set up processes include:
Radio and Link Establishment to assign a signaling channel betweenthe mobile station and the NSS
Classmark handling to manage different mobile station power and ciphering
capabilities
Ciphering to ensure data security on the Air Interface
The normal assignment process to assign a traffic channel between the
mobile station and the NSS.
For more information, refer to Call Set Up (Section 3).
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1.2.2 Call Handling
The call handling function supervises and maintains calls which are in progress.Call handling involves:
In-call channel modification during a call
Maintenance of call integrity and quality through features such as Frequency
Hopping, Discontinuous Transmission or Radio Power Control
Handover to change channels when a mobile station moves from onecell to another
Handover when the quality of the current channel drops below an acceptable
level
Ciphering to ensure data security on the Air Interface
Overload control to manage the call load on the system.
For more information, refer to Call Handling (Section 4).
1.2.3 Call Release
The call release function ensures that resources allocated to a call are free forreuse when they are no longer required by the current call.
Specifically the Call Release function includes:
Call Release in normal service:
Calls terminated by call management
Calls terminated following a channel change.
Special cases:
Call release following a reset
BSC-initiated release
BTS-initiated release
Mobile station-initiated release.
For more information, refer to Call Release (Section 5).
1.2.4 Operations & Maintenance
O&M provides the operator interface for the management and control of theBSS, and its interconnection to the NSS. O&M is divided into three principalareas:
Configuration Management
Fault Management
Performance Management.
For more information, refer to Operations & Maintenance (Section 8).
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1.3 BSS ComponentsThere are three main units in the BSS:
The BSC, which acts as the controller of the BSS. The BSC provides
control of the BTS and their resources, and performs switching functionswithin the BSS
The BTS, which provides the radio transmission and reception functions
for a cell
The Transcoder, which performs rate adaptation and encoding/decoding ofspeech and data between the MSC and the BSC.
The BSS, as shown in Figure 1, is supervised by the OMC-R. In a largenetwork, one or more high-level supervisors, such as NMCs, can exist tocentralize network management activities. The NMC has the authority to senddirectives to the OMC-R.
For more information about the NMC, refer to documentation supplied withthe NMC.
1.3.1 Base Station Controller
The BSC provides control of the BTS and manages radio resources and radioparameters. From a transmission point of view, the BSC also performs aconcentration function if more radio traffic channels than terrestrial channels areconnected to the MSC. A single BSC can control a large number of BTS. Theexact number is a function of the BSC equipment and the configurations used.
The BSC provides:
Resource management
Database management
Radio measurement processing
Channel management
Operations and maintenance functions within the BSS
Communication with the OMC-R
Switching between the Air Interface channels (and their associated Abis
channels), and the A Interface channels.
For more information about these interfaces, refer to:
The A Interface (Section 1.7.4)
The Abis Interface (Section 1.7.6)
The Air Interface (Section 1.7.9).
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The 9120 BSC also incorporates the following transmission equipment:
The Base Station Interface Equipment (BSIE), which performs signaling and
submultiplexing on the Abis Interface
The Transcoder Submultiplexer Controller (TSC), which collects andprocesses transmission data. It also provides an operator interface to
certain transmission functions via a Local Maintenance Terminal.
For a more detailed description of the 9120 BSC, refer to the BSC/TC OverallDescription.
In the 9130 BSC, the transmission equipment is replaced by virtualtransmission processes, to ensure the same functions as in the 9120 BSC.For a more detailed description of the 9130 BSC, refer to the 9130 BSCEvolution Functional Description.
1.3.2 Base Transceiver Station
The BTS provides the radio transmission, control and baseband functionsfor a cell. The BTS also supports the Air Interface with the mobile stations.Alcatel-Lucent provides two families of BTS:
BTS G1 or G2
BTS 9100 or BTS 9110.
These families of BTS have different architectures, and are not functionallyidentical, (e.g., only the BTS 9100 or BTS 9110 can support GPRS).
The BTS performs the following functions under the control of the BSC:
Transmit and receive functions
Antenna diversity
Frequency hopping
Radio channel measurements
Radio frequency testing.
The BTS also includes BIEs which enable it to communicate with the BSC overthe Abis Interface. In the BTS 9100 and BTS 9110, the BIE is integratedinto the SUM.
For a more detailed description of the BTS, refer to the:
BTS Functional Description
BTS 9100/9110 Functional Description.
For the BTS name, it is possible to use any combination of the followingcharacters: a-z, A-Z, 0 - 9, -, _ (hyphen, underscore). Blank spaces are alsopermitted in the BTS name. For more information about naming rules, referto the O&M Parameters Dictionary.
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1.3.2.1 Antenna DiversityAntenna Diversity is a BTS feature that protects against multipath fading. Thisis achieved by duplicating the receive antenna and receive path up to the FrameUnit of the BTS (or the TRE for a BTS 9100 or BTS 9110). The Frame Unit(or TRE) uses the data burst which has the fewest errors. This increases thelow-power mobile station range, thereby allowing larger cells.
1.3.2.2 G1 and G2 BTS Antenna DiversityAntenna diversity on G1 and G2 BTS duplicates the receive antenna andreceive path up to the Frame Unit. The Frame Unit uses the data burst whichhas the fewest errors. This increases low-power mobile station range, thereforeallowing larger cells and lowering infrastructure investment.
The following figure shows the antenna diversity path through the G1 andG2 BTS.
BASEBANDCONTROL
CONTROL
BASEBAND RADIO COUPLING
OMU
BIE
FHU
Other Antennae
TX
CUFU
aaa
b bb
abBest of a&b
COUPLING
UNIT
aRX
RX
(Option)b
BIE : Base Station Interface Equipment
CU : Carrier Unit
FHU : Frequency Hopping Unit
FU : Frame Unit
OMU : Operations and Maintenance Unit
RX : Receiver
TX : Transmitter
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1.3.2.3 BTS 9100/9110 Antenna DiversityAntenna diversity on the BTS 9100 or BTS 9110 follows the same principle asin the G1 and G2 BTS. The antennae are used for both transmit and receive,and the receive path is duplicated up to the TRE, providing the same gain inefficiency and low-power mobile station range.
The following figure shows the antenna diversity path through the BTS 9100.
TRE 1
TRE 2
TRE 3
TRE 4
BASEBAND
CONTROL
RADIO
SUM
ANy ANx
RADIO
COMBINING DUPLEXING
ANT a
ANT b
ab
Tx / Rx
Tx / Rx
b
b
b
a
a
a
Best of a&b
Best of a&b
Best of a&b
Best of a&b
b
a
b
a
b
a
b
a
ab
ab
ab
ab
BASEBAND
ANC
ANT : Antenna
ANx : Antenna Network Type x
ANy : Antenna Network Type y
SUM : Station Unit Module
TRE : Transmitter/Receiver Equipment
Note: The configuration shown above (1 Sector, 3X4 Transceivers) is one exampleonly. Other combinations of Antennae and TREs are possible. There is no ANyin the BTS 9110, and ANy is not needed if the sector has two TREs.
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1.3.3 Transcoder And Transmission Function
The Transcoder is the key component for the transmission function, whichprovides efficient use of the terrestrial links between the equipment of the BSS.In addition to the Transcoder, Submultiplexers are also used for transmissionfunctions.
The Transcoder provides:
Conversion between A-law and Radio Test Equipment-Long Term Predictionencoded traffic (speech)
Conversion between A-law and Algebraic Code Excited Linear Prediction
encoded traffic (speech)
Rate adaptation (data)
O&M control of the transmission function.
The Transcoder is normally located next to the MSC.
The Submultiplexer performs submultiplexing on the Ater Interface, betweenthe MSC and the BSC. When submultiplexing is used, a Submultiplexer islocated at each end of the link.
The following figure shows how transmission components are distributed inthe BSS with an 9120 BSC.
BTS BSC
MSC
BSC
TC
TCBTS
BTSTSC
BIE
BIE
BIE SM SM
TSC
BIE
OMC−R
BIE : Base Station Interface Equipment
SM : Submultiplexer
TSC : Transcoder Submultiplexer Controller
TC : Transcoder
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BSS with the 9130 BSC differs from BSS with the 9120 BSC, in that thetransmission components are replaced by virtual transmission processors.
There are two types of transcoders:
G2
There are 2 types of G2 TC:
G2 TC equipped with ASMC and TRCU
G2 TC equipped with ASMC/TRCU + MT120 boards (in the case
of an extension).
9125The 9125 TC can be equipped with up to 48 sub-units (referred to as MT120boards). Each MT120 offers an Atermux connection to a BSC and up to 4Atrunk connections to the MSC.The 9125 Compact TC can have 2 9125 TC STM-1 boards, active andstandby. They are inserted in a dedicated 9125 TC STM-1 subrack, whichis located in the bottom part of the TC rack. Each TC MT120 board isconnected to both TC 9125 STM-1 boards (dual star).
1.3.4 The Multi-BSS Fast Packet Server
The MFS is preferably located at the Transcoder/MSC site.
It is internal to the BSS and provides the following functions:
PCU (Packet Control Unit) functions:
PAD (packet assembly/disassembly) function
Scheduling of packet data channels
Automatic Retransmission Request functions
Channel access control functions
Radio channel management functions.
The Gb Interface protocol stack.
The MFS converts GPRS frames, carried on multiple 16 kb/s links from multipleBTS, to one or more frame relay channels connected to the SGSN on the GbInterface. For more information, refer to The Gb Interface (Section 2.3.1).
The set up of Packet Data Channels is controlled by the MFS. It also negotiatesresources with the BSC and routes GPRS packets. When an additional channelis required on a BTS, the MFS asks the BSC to allocate a channel and toconnect it to an Ater channel which the MFS controls.
The Alcatel-Lucent solution also supplies two dedicated GPRS interfacesbetween the MFS and the BSS:
The BSCGP Interface supplies routing of GPRS messages and resource
negotiation between the BSC and the MFS
The GCH Interface routes user data traffic and signaling between the MFS
and the BTS transparently (to the BSC).
The IMT ensures the hardware and software management of the MFS.
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1.3.4.1 GPRS Processing UnitsThe MFS is divided into GPRS processing units (GPU) which areinterconnected via an Ethernet bus and controlled by a control station. TheGPU handles the O&M and telecom functions of several cells, but a cell cannotbe shared between several GPUs.
A GPU cannot be connected to more than one BSC, which means that eachGPU cannot manage several BSSs simultaneously. Even so, the use of severalGPUs per BSS is required for traffic capacity reasons. The MFS is in charge ofassociating each cell with a GPU. This is referred to as GPU cell mapping.
The GPU is in charge of:
O&M functions:
Initialization of the MFS
Software download
Software configuration
Performance monitoring.
Telecom functions:
Radio and transmission resource control
Radio link control of packet connections
Common control channels management
MS radio resource control
Logical Link Control (LLC)
Protocol Data Unit (PDU) transfer
Multiframe management
Congestion control
Gb Interface management
Signaling management on the GSL Interface.
1.3.4.2 GPU Protocol ManagementThe GPU is split into two sub-units, the Packet Management Unit (PMU)and the Packet Traffic Unit (PTU).
The protocols handled by a GPU are split in the following manner:
Protocols handled by the PTU:
Radio Interface protocols (RLC and MAC)
GCH Interface protocols (L2-GCH and L1-GCH).
The PTU manages the corresponding GCH Interface (for more information,refer to The GCH Interface (Section 2.3.3)).
Protocols handled by the PMU:
Gb Interface protocols (BSSGP, Network Service, and Full Rate)
BSC Interface protocols (BSCGP, L2-GSL, and L1-GSL)
RRM protocol.
The PMU manages the corresponding Gb and GSL interfaces.
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1.3.4.3 Multi-GPU per BSSTo increase the GPRS capacity of the BSS in terms of the number of PDCH,several GPU boards can be connected to the BSC to support the PCU function.This feature is applied regardless of the BTS type.
For one BSC, in the case of a multi GP configuration, if the last GSL of anyGPU is lost, all GPUs assigned to the BSS will be reset (reset_data) andPS outage occurs.
The only exceptions are the following:
GSL loss on GPU which have all cells locked
GSL loss on GPU and the other GPU have also their GSL down.
1.3.4.4 Cell MappingMapping a cell means that a cell is associated with a GPU. Remapping acell means that a cell, already linked to a GPU, is moved to another GPU.The mapping of cells onto GPUs is performed by the MFS, which actuallydefines the mapping of cells onto LXPUs (logical GPU). An LXPU is eitherthe primary GPU, or the spare GPU in the case of switchover. All the GPRStraffic of one cell is handled by only one GPU. The following figure shows anexample of cell mapping.
MFS
GPU1
GPU2
GPU3
GPU4
BSC
Cell 1
Cell 2Cell 4
Cell 3
Cell 8
Cell 9Cell 12
Cell 11
Cell 5
Cell 6
Cell 7
Cell 14
Cell 13
Cell 10
GPU : GPRS Processing Unit
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1.4 Extended GSMTwo 10 MHz extended bands for GSM 900 in the range 880-890 MHz/925-935MHz are specified as an option on a national basis. The reason for this ismainly due to the lack of primary band frequencies in countries outside Europe.The term "G1" is used for the extended band. The term "P-GSM" is usedfor the primary band. The term "E-GSM" is used for the whole GSM 900frequency band, i.e., the primary band (890-915 MHz/935-960 MHz) plusthe extended band (880-890 MHz/925-935 MHz). This corresponds to 174addressable carrier frequencies and leads to an increase of 40% against the124 frequencies in the primary band.
With the Enhanced E-GSM Band Handling feature, which is supported byAlcatel-Lucent BTS only, (E)GPRS and all types of signaling channelsare carried on the frequencies in the entire E-GSM band (e.g., primaryand extended), when the EGSM_RR_ALLOC_STRATEGY parameter is setto 1 (same behavior for E-GSM capable mobile stations). When theEGSM_RR_ALLOC_STRATEGY parameter is set to the default value of 0 (differentbehavior for E-GSM capable mobile stations), the OMC-R does not allow theoperator to define the BCCH, CCCH, SDCCH and CBCH on an E-GSM TRX.
Both P-GSM only and E-GSM mobile stations are supported in thenetwork, but are handled differently, depending on the value towhich the EGSM_RR_ALLOC_STRATEGY parameter is set. When theEGSM_RR_ALLOC_STRATEGY parameter is set to the default value of 0, theBSS handles E-GSM capable mobiles stations differently from P-GSM onlymobile stations. When the EGSM_RR_ALLOC_STRATEGY parameter is set to 1,the BSS handles P-GSM only and E-GSM capable mobile stations in E-GSMcells in the same way, that is, the BSS assumes that all GSM 900 mobilesare E-GSM capable.
E-GSM TRXs are preferred to support (E)GPRS in E-GSM cells, and only whenthe EGSM_RR_ALLOC_STRATEGY parameter is set to 0. An E-GSM cell is one inwhich FREQUENCY_RANGE = EGSM or EGSM-DCS1800.
An E-GSM TRX is a TRX configured with:
Frequencies in the G1 band only, or
Frequencies in both the P-GSM and G1 bands.
For information about radio resource allocation with Enhanced E-GSM BandHandling, refer to TCH Allocation for E-GSM and P-GSM Mobile Stations(Section 1.4.4).
1.4.1 E-GSM Mobile Station Recognition
From messages sent by the mobile station, the BSS determines if a mobilesupports the E-GSM band.
The mobile station is determined to be E-GSM if:
The FC bit of Classmark 2 is set to 1 (regardless of the value of the Band
2 bit of Classmark 3) or
The FC bit of Classmark 2 is set to 0, and the Band 2 bit of Classmark3 is set to 1.
If the information is not available, the mobile station is considered as notsupporting the G1 band. The BSS never triggers a Classmark Interrogationprocedure to obtain the E-GSM ability of a mobile station.
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1.4.2 E-GSM Management After Initial Determination
Once the E-GSM ability is initially determined as described above, the mobilestation radio characteristics might change during a transaction. If the BSCreceives a classmark change message, it takes this into account and updatesthe E-GSM ability according to the content of the received message.
1.4.3 E-GSM Determination at Handover
In the case of internal handover, the E-GSM ability of a mobile station isstored in the BSC memory. In the case of external incoming Handover, thehandover request message includes either Classmark 1 or Classmark 2 IE,and optionally Classmark 3 IE. If Classmark 1 is present and Classmark 3 isnot present or Classmark 3 is present but does not contain the Band 2 bit,the mobile station is not considered as E-GSM. If both Classmark 1 andClassmark 3 are present, and Classmark 3 contains the Band 2 bit, the BSCgets the E-GSM ability of the mobile station from Classmark 3. If Classmark2 is present and Classmark 3 is not present, or Classmark 3 is present butdoes not contain the Band 2 bit, the BSC gets the E-GSM ability of the mobilestation from Classmark 2 ("FC" bit).
If both Classmark 2 and Classmark 3 are present, the mobile station is seenas E-GSM:
If the FC bit of Classmark 2 is set to 1 (whatever the value of the band 2
bit of Classmark 3)
If the FC bit of Classmark 2 is set to 0 and the band 2 bit of Classmark
3 is set to 1.
After an incoming external handover, if a classmark change message isreceived from the mobile station, the BSC ignores any subsequent classmarkupdate message received from the MSC.
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1.4.4 TCH Allocation for E-GSM and P-GSM Mobile Stations
The allocation of G1 band channels can be done for Normal Assignment(NASS), Internal Channel Change (ICC), or External Channel Change (ECC).Each TRE has the capability to support the P-GSM or the E-GSM band. EachTRX is configured as a P-GSM TRX or an E-GSM TRX. As enhanced E-GSMband handling allows P-GSM and G1 frequencies to be mixed in the FHS, whena TCH is needed, the BSC first checks the frequencies in the FHS. If at leastone frequency belongs to the G1 band, the related TRX is considered as anE-GSM TRX. TCHs are then allocated as described below.
In an E-GSM cell, when the EGSM_RR_ALLOC_STRATEGY parameter is set to 0 ,when allocating a TCH to serve circuit-switched requests, the BSC selects theTCH in the following order:
For E-GSM capable mobile stations
First, a radio timeslot which IS E-GSM capable but NOT PS capable
Next, a radio timeslot which is NEITHER E-GSM capable NOR PS
capable
Thirdly, a radio timeslot which is NOT E-GSM capable but IS PS capable
Lastly, a radio timeslot which is E-GSM capable and PS capable.
For P-GSM capable only mobile stations
First, a radio timeslot which is NEITHER E-GSM capable NOR PS
capable
Next, a radio timeslot which is NOT E-GSM capable but IS PS capable.
When the EGSM_RR_ALLOC_STRATEGY parameter is set to 1, the BSS assumesthat all GSM 900 mobile stations are E-GSM capable, and handles P-GSM onlyand E-GSM capable mobile stations in E-GSM cells in the same way.
In multiband concentric cells, the above allocation only applies to the outer zone.
When the EGSM_RR_ALLOC_STRATEGY parameter is set to 0, in an E-GSMcell, when allocating a PDCH to serve packet-switched requests and basedon the TRX ranking provided to the MFS, the BSC selects the TCH in thefollowing order:
First, a radio timeslot which is E-GSM capable AND PS capable
Next, a radio timeslot which is NOT E-GSM capable but IS PS capable.
When the EGSM_RR_ALLOC_STRATEGY parameter is set to 1, the BSS handlesP-GSM only and E-GSM capable mobile stations in E-GSM cells in the sameway.
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1.5 External ComponentsThe BSS communicates with three external components:
The NSS on the A Interface
The mobile station on the Air Interface
The OMC-R on the BSS/OMC-R Interface.
The following figure shows the logical position of the External Components.
Base Station Subsystem
MobileStations
NetworkSubsystem
FixedNetwork
PLMN
OMC−R
NMC
MFS
MSCTranscoder
PSDN
HLR
AbisInterface
Ater Interface
Gb Interface
AInterfaceBTS
BTS
BTS
BSC
PSTN
GGSNSGSN
GGSN : Gateway GPRS Support Node
HLR : Home Location Register
MFS : Multi-BSS Fast Packet Server
NMC : Network Management Center
PSDN : Packet Switched Data Network
PSTN : Public Switched Telephone Network
SGSN : Serving GPRS Support Node
Figure 2: Logical Position of External Components Associated with BSS
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1.5.1 Network Subsystem
Managing communication within the PLMN and external networks is the primaryrole of the NSS. The NSS manages the subscriber administration databases.
It contains the following components.
Component Description
MSC Performs and coordinates the outgoing and incoming Call Set Up function.The MSC is a large capacity switch used for passing mobile traffic tomobile subscribers, or to subscribers of external networks. This part ofthe NSS interfaces with the BSS.
Home Location Register The HLR is the central database within a given network for mobilesubscriber specific data. It contains static data such as accessauthorization, information about subscribers and supplementary services.It also controls the dynamic data about the cell in which the mobile stationis located.
Visitor Location Register The VLR temporarily stores information about mobile stations entering itscoverage area. Linked to one or more MSCs, the VLR transmits data to anew VLR when a mobile station changes areas.
Authentication Center The AuC manages the security data used for subscriber authentication.
Equipment Identity Register The EIR contains the lists of mobile station equipment identities.
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1.5.2 Mobile Stations
Mobile stations provide radio and processing functions which allow subscribersto access the mobile network via the Air Interface. Subscriber-relatedinformation is stored on a specific device called a SIM.
The SIM is a removable smart-card that conforms to internationally recognizedstandards. It contains the IMSI. This is used by the Network Operator toidentify the subscriber in the network and to provide security and protectionagainst misuse.
Each mobile station has its own IMEI. The IMEI is used by the NetworkOperator to prevent stolen or non-type approved mobile stations from accessingthe network.
There are three types of mobile station in GSM:
Phase 1
Phase 1 extended
Phase 2.
For information about GPRS mobile stations, refer to GPRS Elements (Section2.1.2).
Mobile stations have different capabilities according to the class of mobilestation and the purpose for which the mobile station was designed. Thesedifferences include power output and ciphering.
Only phase 2 mobile stations can turn off ciphering, or change the cipheringmode, during a channel change procedure such as a handover. The cipheringcapability of a mobile station is signalled to the BSS in the mobile stationclassmark.
Ciphering is used to protect information transmitted on the Air Interface. Thisis performed between the BTS and the mobile station (i.e., Air Interface).Transmission ciphering does not depend on the type of data to be transmitted(i.e., speech, user data, signaling), but on normal transmission bursts. Formore information about mobile station ciphering capabilities, refer to Ciphering(Section 3.8).
1.5.2.1 Mobile Station Idle ModeA mobile station is in idle mode when it is switched on but not communicatingwith the network on an SDCCH or a traffic channel.
The BSS supports four idle mode functions:
Cell selection and cell reselection
GSM/GPRS to UMTS cell reselection
Location updating
Overload control.
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1.5.2.2 Mobile Station Cell Selection and ReselectionA mobile station monitors the broadcast messages from the BTS. This includesmonitoring the FCCH and SCH.
The mobile station chooses the best cell on which to camp. If this cell is in alocation area other than that stored in the mobile station memory, then themobile station initiates a location update procedure. For a mobile station tocamp on a cell, it has to synchronize with the cell.
The BTS broadcasts an FCCH and an SCH at a defined time in the BCCHcycle. These channels are used as reference points for the mobile station tosynchronize with the BCCH. Once synchronized, the mobile station continuesto monitor these channels to stay synchronized.
This type of synchronization, along with cell configuration and channelfrequency information, enables the mobile station to calculate where channelsoccur in the multiframe sequences.
Timing advance information is sent to the mobile station when an SDCCH isassigned. The mobile station uses the channel configuration informationto calculate which part of the CCCH contains its paging message, andtherefore which timeslot to monitor for paging messages. When the mobilestation is camped on a cell, it continues to monitor the BCCH transmissionsfrom neighboring cells. The BCCH frequencies of the neighboring cells aretransmitted on the BCCH of the home cell (sys_info 2). The mobile station candecide to camp on a new cell if it receives a better signal from an adjacent cell.
Reasons for moving to a new cell include:
A problem in the existing cell
The mobile station moving.If the mobile station moves to a new cell which is in the same location areaas the one currently in its memory, it does not initiate a location update. Itrecalculates its paging group and monitors the new paging channel. Pagingmessages are broadcast from all cells in a particular location area.
1.5.2.3 GSM/GPRS to UMTS Cell ReselectionThe reselection of a UTRAN cell is triggered by a multi-RAT mobile stationin circuit-switched idle mode, packet-switched idle mode, or packet-switchedtransfer mode. In NC0 mode, a multi-RAT mobile station can reselect aUTRAN cell in any GMM state. In dedicated mode, the multi-RAT mobilestation follows the GSM handover procedures. The BSS then broadcasts theset of UTRAN cell parameters which allows the multi-RAT mobile station toreselect a UTRAN cell on its own.
For more information about 2G to 3G cell reselection, see GSM-to-UMTSCell Reselection (Section 2.7.3.7).
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1.5.2.4 Location UpdatingThe location update procedure is always initiated by the mobile station.Location update is performed after the call has finished (cell reselection).
Reasons for location updates include:
A periodic updateThe mobile station performs a periodic location update after a lack ofsignaling activity for a specific time. If the timer expires, the mobile stationinitiates a location update, even if it has not changed location area. Theduration of the mobile station timer is defined by the network and sent to themobile station as system information messages on the BCCH. The time canbe between six minutes and 25 hours.
A handover to a cell in a new location area.When a mobile station is handed over to a cell in a new location area, thereis no automatic location update in the network. A new Location Area Identityin the BCCH (sys_info 3 and sys_info 4) is detected by the mobilestation when the current call is finished, and initiates the location updateprocedure. This saves the system performing several location updates if themobile station is handed over several times during a call.
The mobile station camps on a cell with a different location area code to the onein the mobile station memory. The mobile station initiates the location updateprocedure by sending a Channel_Request message indicating that the call isfor a location update. The BSS assigns a dedicated signaling channel andestablishes a signaling path between the mobile station and the MSC. SeeMobile-Originated Call (Section 3.2) for more information.
When a signaling path is established, the mobile station sends the LocationArea Identity of the old cell on which it was camped to the MSC. The new VLRinterrogates the old VLR for authentication and subscriber information. Formore information, see Location Updating with Classmark Procedure (Section3.6.3) and Authentication (Section 3.7).
The Location Area Identity comprises:
Mobile Country Code
Mobile Network Code
Location Area Code.
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The BSS adds the cell identity of the mobile station’s current location to themessage sent to the MSC. This information is sent in a Mobility Managementsub-layer message and is transparent to the BSS. The NSS stores thisinformation either in its HLR or its VLR. Following a location update procedure,the VLR can assign a new Temporary Mobile Subscriber Identity (TMSI) to themobile station. For more information about the TMSI, refer to Authentication(Section 3.7). The following figure shows a mobile station as it moves to anew location area.
MSC
MSCBSCBTS
BSC
Mobile Station connectingin a new location area
VLR
VLR
MobileStation
MobileStation BTS
BSC
BSCProtocol Messages
VLR : Visitor Location Register
Figure 3: Location Update
1.5.2.5 Overload ControlTo protect itself against overload, the system can bar access to mobile stationsby changing the RACH control information in the system information messagesdescribed in Table 1.
For more information, refer to:
GPRS Overload Control (Section 2.6.4)
Overload Control (Section 4.7).
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1.5.3 Phase 2 Mobile Support in a Phase 1 Infrastructure
When a phase 2 mobile station is used in a phase 1 infrastructure network,the BSS functions as phase 2 on the Air Interface and has the capability offunctioning as phase 1 or phase 2, depending on the MSC capabilities. Theinfrastructure (BSS and MSC) remains phase 1. This conforms to updatedGSM recommendations for phase 1.
Problems that may occur when using phase 2 mobile stations on a phase1 network include:
The implementation rules for phase 1 are not strictly defined, therefore some
implementations cannot function with phase 2 mobiles.For example, some of the spare bits in phase 1 are now used by the phase2 protocol. However, some phase 1 infrastructures reject the message asspare bits are used.
Some protocol changes in phase 2 changed or replaced a phase 1 protocolFor example, power and quality measurements sent by phase 2 mobilestations have a finer range of power control, which the phase 1 infrastructuremust process.
Phase 2 mobile stations send some phase 2 messages even though theyare in a phase 1 environment.For example, phase 2 mobile stations send either new messages or newelements in messages, which the phase 1 infrastructure could reject. Thisblacklists the mobile station due to an invalid protocol message for phase1. Depending on what these messages are, the updates to the phase 1infrastructure would accept these messages/elements. The messages canbe either ignored or only partially treated. This is based on informationcontained in the messages or elements.
1.5.4 Operations and Maintenance Center-Radio
The OMC-R supervises one or more BSSs.
It performs the following functions:
Manages the BSS software versions
Acts as the central repository for configuration data
Manages fault and performance measurement reports
Handles supervision of alarms and events
Manages the MFS.
The reported data is available to the operator from the OMC-R’s centraldatabase. The OMC-R only performs O&M activities. It does not perform usertraffic processing or call establishment and control activities. Refer to theOperations & Maintenance Principles for more information.
Operator actions via the terminal interface trigger commands throughout theBSS. The OMC-R provides object-oriented management information, andsupports a Manager/Agent scheme to perform and control managementactivities. The terminal interface supports different user profiles with differentaccess rights.
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1.6 Network ManagementNormally the OMC-R provides all the network management and controlfunctions required by the BSS. However, the management and controlfunctions are proprietary to the system supplier. In keeping with InternationalTelecommunications Union and European Telecommunication StandardsInstitute recommendations, the Telecommunications Management Network(TMN) model standardizes the Network Management function. NetworkManagement is compatible with all equipment, even that of differentmanufacturers. Network Management is controlled from one or several NMCs.
1.6.1 Telecommunications Management Network
The ability to transfer management information across the TelecommunicationsManagement Network environment is defined by a protocol suite, the QInterfaces. The following figure shows the hierarchical structure of the TMN. Itgraphically defines the respective management responsibilities in the threemain levels of the Management Information Tree (MIT).
For more information about the Telecommunications Management Network,refer to the BSS/MFS and TMN Functions section of the Operations &Maintenance Principles document.
NMC
OMC−R
BSC
BTS BTSBTS
Q3
BSS
OSS
NMC Operator (Resource Management)
OMC−R Operator (Resource and Equipment
Management)
Security Block (SBL) Management
Network Management
&Network Element
Management
Mediation Function
Network ElementMFS
OSS : Operation Support System
MFS : Multi-BSS Fast Packet Server
NMC : Network Management Center
Figure 4: TMN System Hierarchy
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1.6.2 Q3 Interface
Communication between the NMC and the OMC-R takes place across theQ3 Interface (see Figure 4).
The Q3 protocols can be divided into:
Association connection and disconnection mechanisms
Message format and structure
Command types.
For more information about Network Management and the Q3 Interface, seethe Operations & Maintenance Principles.
1.7 BSS Telecommunications LayersThe telecommunications functions of a GSM network are split into layers.
These layers are split into two basic categories, Application and Transmission:
The Application layer is split into sub-layers, to control:
Call Management
Mobility Management
Radio Resource Management.
The Transmission layers, which provide transmission between the various
components.
Note: These Transmission layers relate to the OSI layers, that is, the Physical Layer(i.e., Layer 1) and the Data Layer (i.e., Layer 2). The protocols used for theselayers are standard.
The following figure shows the general distribution of the telecommunicationfunctions within a GSM network.
MS BTS BSC NSS
CM
MM
RRM
GSM Application Layers
TRANSMISSION
CM : Call Management
MM : Mobility Management
MS : Mobile Station
RRM : Radio Resource Management
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1.7.1 Call Management Sub-layer
The Call Management sub-layer performs Call Control to establish, maintainand release calls. SMS within Call Management allows the mobile station tosend and receive messages of up to 160 characters. The SupplementaryService functions are also provided to the mobile stations as part of CallManagement.
1.7.2 Mobility Management Sub-layer
The Mobility Management sub-layer is used by the NSS to manage thesubscriber database, including information about subscriber location andauthentication. It is also used by the mobile stations to send location updateswhen they move to new location areas.
1.7.3 Radio Resource Management Sub-layer
The Radio Resources Management sub-layer establishes, maintains andreleases stable connections between the mobile station and the MSC for theduration of a call. This includes functions such as managing the limited radioresources, to ensure high service availability. It also performs handoverswhen a mobile station moves during a call, or the channel quality falls belowan acceptable level. RRM functions occur mainly between the mobile stationand the BSC.
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The following figure shows the application layers, transmission layers andInterfaces of the BSS.
MS BTS BSC MSC
MM
RRM
GSMApplicationLayers
Layer 2
Air Interface Abis Interface A Interface
Layer 1 Layer 1
TC08.60
CM
LAPDm LAPD LAPD SCCP
SS7
SCCP
SS7
LAPDm
BSSAP BSSAP BSSAP
Layer 1Layer 1Layer 1Layer 1
}}
BSSAP : BSS Application Part
CM : Call Management
LAPD : Link Access Protocol on the D Channel
LAPDm : Link Access Protocol on the Dm Channel
Layer 1 : Physical Layer
Layer 2 : Data Link Transfer Layer
MM : Mobility Management
RRM : Radio Resource Management
SCCP : Signal Connection Control Part
SS7 : Signaling System No. 7
TC : Transcoder
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1.7.4 The A Interface
The A Interface is used for communication between the BSC and the MSC.The connection between the BSC and MSC can be either terrestrial lines ora satellite link.
The A Interface includes the:
Physical Layer 1The physical layer provides a physical connection to transport the signals.It supports a 2 Mbit/s link divided into 32 x 64 kbit/s channels by TimeDivision Multiplex. The actual physical link used depends on NetworkOperator implementation.
Data Link Layer 2Layer 2 provides the frame handling functions for the interface. It is also usedto pass signaling messages using the International TelecommunicationsUnion (ITU) SS7 protocol.
This comprises the:
Message Transfer Part, which provides the mechanism for reliable
transfer of the signaling messages
Signaling Connection Control Part, which provides the mechanism to
identify transactions relating to a specific communication.
Application Sub-Layer 3 RRM
To transfer Layer 3 messages relating to a transaction, the SCCP uses theBSS Application Part. This is divided into two parts:
Direct Transfer Application Part, which transfers messages directlybetween the MSC and the mobile station. These messages are not
interpreted by the BSS. The BSS must read and recognize the initialmessage as a DTAP message.
BSS Management Application Part which supports procedures between
the MSC and the BSC, such as resource management and handover
control.
On the A Interface, the process is terminated at the BSC. Messages for theBSS, passed by the BSSMAP, are interpreted by the BSC Layer 3.
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1.7.5 The Ater Interface
The part of the A Interface between the Transcoder and BSC is known as theAter Interface. It is a set of 2Mbit/s PCM/E1 links.
Ater Mux InterfaceThe Ater Mux Interface is the result of multiplexing four Ater Interfaces.Transcoding is a Layer 1 process, therefore the difference between the twointerfaces is at the physical level.
Optimized Ater Interface MappingThis feature improves efficiency on the Ater Mux PCM connection betweenthe 9120 BSC and the G2 Transcoder.Four Ater Interfaces are submultiplexed onto the Ater Mux connection. Thisinterconnects four Digital Trunk Controllers and four Transcoder RateAdaption Units, achieving a 4:1 mapping.The 4:1 mapping of the 9120 BSC and G2 Transcoder allows up to 116traffic channels.
1.7.6 The Abis Interface
The Abis Interface is used for communication between the BSC and the BTS.
The Abis Interface includes:
Physical Layer 1The physical layer provides a physical connection to transport the signals. Itsupports a 2 Mbit/s link divided into 32 x 64 kbit/s channels by TDM.The physical link used depends on the Network Operator implementingthe interface.
Data Link Layer 2The data link layer provides frame handling and signaling functions usingthe LAPD.
This layer supports three types of signaling links:
The Radio Signaling Link for signaling to the mobile station (includingSMS)
The O&M Link for O&M informationThe OML Auto-detection feature (see OML Auto-Detection (Section8.4.6)) allows the timeslot reserved for the O&M Link to be used forsignaling (if there are no G1/G2 BTS on the Abis Interface). This providesfor an increase in the amount of telecom traffic on the Abis Interface.
The Layer 2 Management Link for the Layer 2 management functions
such as frame checking and error correction.
Application Layer 3: BTS Management Sub-layerThe BTS management sub-layer carries Layer 3 messages between theBSC and the BTS. Some of these messages are transparent to the BTS.These are passed directly to the mobile station using the BTS RRMsub-layer 3 on the Air Interface. Non-transparent messages includemessages for radio link layer control and channel management.
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1.7.7 HSL Links
The 9130 BSC capacity depends on a High Speed Signaling Link (HSL)introduction, between the BSC and the MSC. The ports where HSL arephysically connected cannot be used for other purposes. The HSL is similar tothe Low Speed Signaling Link (LSL) (N7). The same operations are allowedon their SBL. The mixed mode, HSL + LSL, is not allowed. These links areexclusive.
1.7.8 Satellite Links
The Abis and Ater interfaces were designed to use terrestrial transmission links.However, in developing countries, the terrestrial transmission infrastructuredoes not exist and in many cases is difficult and costly to provide. There is alsoa need in the developed world to provide temporary GSM coverage for transientmobile population density increases, for example at sporting events. Usinggeostationary earth orbiting satellites is a simple and relatively low-cost solutionto these problems. Unfortunately, there is one major drawback: transmissiondelay. The Geostationary orbit is located at an altitude of 35,786 km abovethe equator, therefore propagation delay of radio signals can vary between119 ms at the equator to a maximum delay of 139 ms. The delay for one hop(the path from one point on earth to another point, via one satellite link) variesbetween 238 and 278 ms. This delay degrades speech quality, but although thedegradation is worse than experienced in the PSTN, it is usable. The delay alsohas an effect on signaling messages.
Satellite links can be used on the Abis Interface or on the Ater Interface, butnot both.
Parameter modification is done from the OMC-R and propagated to the BSCand the concerned BTS. A new connection type parameter is associated witheach Abis link. The operator can set the parameter at Abis creation time. Ifthe satellite link is made using the Ater Interface, the new connection typeparameter associated with the Ater as a whole is used. Both Abis and Aterconnection types can be either terrestrial or via satellite. The default value foreach is terrestrial.
Note: This is not a standard GSM feature and Alcatel-Lucent cannot guarantee theperformance because there are so many unknown factors, such as error rateand mobile population variations, which have significant effects because ofthe delay.
1.7.8.1 Abis Interface Using Satellite LinksThis feature is available only for Alcatel-Lucent BTS and later. When the link isinstalled on the Abis Interface, for those BTS where the satellite link is installed,the following features are not available:
Closed multidrop
PCM synchronization (the BTS must be configured as free running).
Synchronous handovers, fax and data (in circuit-switched mode, transparentand not transparent) are supported.
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1.7.8.2 Ater Interface Using Satellite LinksOn the Ater Interface, the satellite link can be installed either on the Ater(between the BSC and the Transcoder), or on the A Interface (between theTranscoder and the MSC). Because the latter case is rare, the wording Ateris used for both cases. When only some of the timeslots are routed via thesatellite, at least the Qmux and the X.25 (if the satellite link is on the A Interface)must be routed. Channels that are not routed must be blocked, either fromthe MSC or from the OMC-R. If only one link is forwarded, there is no longerredundancy on the following: SS7, X.25, and Qmux.
1.7.9 The Air Interface
The Air Interface is the radio interface between the BTS and the mobile station.
The Air Interface includes:
Physical Layer 1
Data Link Layer 2
RRM sub-layer 3 of the application layer.
1.7.9.1 Air Interface LayersThe Air Interface layers comprise:
Physical Layer 1 is a radio link where channels are divided by time and
frequency
Data Link Layer 2 provides frame handling and signaling functions, using amodified version of the LAPDm
Application Sub-Layer Radio Resources Management. On the AirInterface, most of the Layer 3 messages are transparent to the BTS. The
BTS uses Layer 3 to extract certain information from some messages before
passing on the equivalent message.For example, when the BTS receives an encryption_command messagefrom the BSC, it reads the Ki value and the algorithm to be used, beforepassing on the cipher_mode_command message. For more informationabout this procedure, refer to Ciphering (Section 3.8).
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1.7.9.2 Air Interface ChannelsThe Air Interface is divided by frequency and time, using Frequency DivisionMultiplex Access (FDMA) and Time Division Multiple Access (TDMA). Thisprovides frames of eight timeslots for each frequency supported by thecell. The channels of the cell are then assigned to specific timeslots withinthe TDMA frames.
GPRS traffic uses the same radio resources as circuit-switched traffic, andis carried on the same type of physical channel. Refer to GPRS in the BSS(Section 2) for information about GPRS channels.
However, not all channels require the full capacity of a timeslot at eachoccurrence of a frame. Channels are configured to share timeslots by onlyusing certain occurrences of the frame. The cycle of frame occurrences isknown as a multiframe. A multiframe can be 26 or 51 occurrences of a frame,depending on the channels configured within it. Within a multiframe, the samephysical channel can support more than one logical channel.
The following figure shows timeslot four of a TDMA frame supporting AccessGrant Channels.
AGCH
AGCH
AGCH
AGCH
AGCH
Frame 1 Frame 2 Frame 3 Frame 4 Frame 5AGCH : Access Grant Channel
Figure 5: Timeslot 4 of a TDMA Frame Supporting Access Grant Channels
Channels can be divided into traffic channels and control channels.
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1.7.9.3 Traffic ChannelsA traffic channel can be used for speech or data. The Alcatel-Lucent BSSsupports the following types of traffic channels.
TrafficChannel
Types
Speech Speech
Full-rate speech traffic channel
Enhanced full-rate speech traffic channel
Half-rate speech traffic channel.
Data Data
Full-rate data traffic channel (9.6 Kbit/s)
Full-rate data traffic channel (4.8 Kbit/s)
Half-rate data traffic channel (4.8 Kbit/s)
Full-rate data traffic channel (<2.4 Kbit/s)
Half-rate data traffic channel (<2.4 Kbit/s).
Note: A timeslot that is configured as a TCH timeslot can be used as a PDCH, aVGCH (Voice Group Call Services Channel), or a standard CS TCH. In terms ofradio resource management, there is no practical difference between VoiceGroup Call Services (VGCS) traffic and standard point-to-point CS traffic, andthe operator only configures the TCH.
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1.7.9.4 Control ChannelsCCHs control communications between the BSS and the mobile stations. Thefollowing table describes the four types of CCH.
ControlChannel
Description
BCCH The BCCH broadcasts cell information to any mobile station in range. Three channels usethe BCCH timeslot:
FCCH: used on the downlink for frequency correction of the mobile station with the BTS
SCH: used on the downlink for frame synchronization of the mobile station with the BTS
BCCH: used to broadcast system information to the mobile stations on the downlink, togive the cell configuration, and how to access the cell.
CCCH The CCCH communicates with mobile stations in the cell before a dedicated signalingchannel is established. Three channels use the CCCH timeslot:
RACH: used on the uplink by the mobile station for initial access to the network
PCH: used on the downlink for paging messages to the mobile station
AGCH: used on the downlink to give the mobile station access information before adedicated channel is assigned.
The multiple CCCH feature allows the operator to use only one additional CCCH, so twoTimeslots TS0 and TS2 are used. The operator decides to configure either 1 or 2 TS formCCCH, i.e. no dynamic allocation by the BSS depending on the load is foreseen.
DCCH The DCCH passes signaling information for a specific mobile station transaction. Twochannels use the DCCH timeslot:
SDCCH: used for signaling and short message information
CBCH: uses an SDCCH channel for Short Message Service - Cell Broadcasts.
ACCH The ACCH passes signaling information for a specific mobile station transaction. An ACCHchannel is always associated with a traffic channel. Two channels use the ACCH timeslot:
FACCH: associated with a traffic channel, and can steal slots out of 24 or 26 slots which arenormally dedicated to the traffic channel for signaling purposes as well as the SACCH slot.
SACCH: associated with a traffic channel, which uses one out of 26 slots for signalingpurposes.
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1.7.9.5 Dual Transfer ModeA dual transfer mode capable MS uses a radio resource for CS traffic andsimultaneously one or several radio resources for PS traffic.
The following DTM principles apply:
DTM allocation means 1 TCH (established in FR) and at least 1 PDCHallocated by MFS
In DTM, no PS measurements are done (no cell reselection while in DTM,
only emergency CS HO)
CS has priority over PS (direct transition from PTM to DTM is not possible,
direct transition from DTM to PTM is not possible, direct transition from Idlemode to DTM is not possible, transition from DTM to dedicated mode, and
from dedicated mode to DTM are possible)
Allocated TCH and PDCH are contiguous
Multi slot allocation (3GPP): MS class 5 (1 TCH, 1 PDCH), MS class 9 (1TCH, 2 PDCH DL, 1 PDCH UL), MS class 3x: up to 5 TS in DL, max 6 TS
UL+DL, MS class 4x: up to 6 TS in DL, max 7 TS UL+DL
(2+3) configuration is supported (requires EDA)(1PDCH DL, 2PDCH UL,1TCH UL, 1TCH DL)
DTM TBFs are always allocated in NRT
TCH changes must be avoided due to PS outage (only emergency HO areallowed, all PS reallocation triggers are forbidden in first step, in second
step for EDA, T3 is mandatory).
Specific constraints apply for PS resources to be allocated in DTM:
The PDCH must be allocated in the MFS (i.e. the PDCH is in an "allocated"state, but not in the "not allocated" or "de-allocating" state)
The PDCH must be located in the "non preemptable PS zone" of the cell
The PDCH must not be in the "Full" state in the considered direction
The PDCH must not be "locked" due to a CS preemption process.
Specific constraints apply for CS resources to be allocated in DTM :
The RTS must be allocated in the MFS (i.e. the PDCH is in an "allocated"
state, but not in the "not allocated" or "de-allocating" state)
The RTS must be located in the "non preemptable PS zone" of the cell
The RTS position must be compatible with the DTM multislot class of the MS
The RTS does not support any RT PFC
The RTS does not support any PACCH channel (when considering all the
DL and UL TBFs established on this RTS and all the RT PFCs createdon this RTS)
The basic Abis nibble mapped onto the RTS is "available" (i.e. it is either free
or it is used in an M-EGCH link from which it is possible to release one GCH).
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1.7.10 System Information Messages
System information messages transmit information about the cell to the mobilestation. System information messages 2 and 5 have several variations to avoidcompatibility problems with phase 1 mobile stations.
The following table shows the system information messages, the channel onwhich they are transmitted and the type of information in each message.
Message Channel Information
Sys_info 1 BCCH Cell channel description
RACH control information
Sys_info 2 BCCH Neighbor cell BCCH frequency list
Indication of which Network Color Code it is allowed tomonitor
RACH control information
Sys_info 2bis
(multiband systemsonly)
BCCH Extended Neighbor cell BCCH frequency list in the sameband as the serving cell. This message is only sentif Sys_info 2 is not sufficient to encode all availablefrequencies.
RACH control information
Spare bits
Sys_info 2ter
(multiband systemsonly)
BCCH Extended Neighbor cell BCCH frequency list in different bandas serving cell
The minimum number of cells, if available, to be reported ineach supported band in measurement results.
RACH control information
3G cell description
Spare bits
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Message Channel Information
Sys_info 3 BCCH Specific Cell Identity
Location Area Identity
Control channel description
Cell options:
Power central information
Discontinuous Transmission (mechanism) information
Radio link time out
Cell selection parameters:
Cell reselect hysteresis for Location Area reselection
Maximum transmit power allowed in cell
Additional reselection parameter
Allows/forbids new establishment causes (phase 2 mobilestations)
Minimum receive level to access cell.
RACH control information
Spare bits setting flags and timers
Sys_info 4 BCCH Location Area Identity.
Cell selection parameters:
Cell reselect hysteresis for Location Area reselection
Maximum transmit power allowed in cell
Additional reselection parameter
Allows/forbids new establishment causes (phase 2 mobile
stations)
Minimum receive level to access cell.
RACH control information
CBCH channel description
CBCH Mobile Allocation
Spare bits setting flags and timers
Sys_info 5 SACCH Neighbor cell BCCH frequency list
For VGCS, only VGCS capable neighbor cell BCCHfrequency list
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Message Channel Information
Sys_info 5bis
(multiband systemsonly)
SACCH Extended Neighbor cell BCCH frequency list
This message is only sent if:
The serving cell is a GSM 1800 cell and Sys_info 5 is not
sufficient to encode all GSM 1800 neighbor frequencies
The serving cell is a GSM 900 cell, andThe mobile station is phase 2, andThere are neighboring GSM 1800 cells, andSys_info 5ter is not sufficient to encode all of the GSM1800 cells.
For VGCS, only VGCS capable neighbor cell BCCHfrequency list
Sys_info 5ter
(multiband systemsand phase 2 mobilestations only)
SACCH Extended Neighbor cell BCCH frequency list in different bandas serving cell
The minimum number of cells, if available, to be reported ineach supported band in measurement results
For VGCS, only VGCS capable neighbor cell BCCHfrequency list
Sys_info 6 SACCH Specific Cell Identity
Location Area Identity
Cell options:
Power control information
Discontinuous Transmission information
Radio link time out
Indication of which Network Color Code it is allowed tomonitor.
For VCGS, status of the NCH, and an indication of
whether paging channel restructuring has taken place
Sys_info 7
Sys_info 8
BCCH SI 7 Rest Octets
SI 8 Rest Octets
SI 4 Rest Octets_S
LSA Parameters
LSA ID information
LSA identity
Sys_info 10 SACCH $(ASCI)$ message providing information for cell reselectionin group receive mode
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Message Channel Information
Sys_info 13 BCCH SI 13 Rest Octets without PBCCH configured in the cell:
SI 13 Rest Octets
GPRS Mobile Allocation
GPRS cell options
GPRS Power Control parameters.
SI 13 Rest Octets with PBCCH configured in the cell:
SI 13 Rest Octets
GPRS Mobile Allocation
PBCCH description.
Sys_info 16
Sys_info 17
BCCH SI 16 Rest Octets
SI 17 Rest Octets
LSA Parameters
LSA ID information
LSA identity
Table 1: System Information Messages
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1.7.11 Dynamic SDCCH Allocation
Dynamic SDCCH allocation is a specific timeslot used for signaling (SDCCH) orfor traffic (TCH), depending on the overload. The operator configures:
A set of static SDCCH/x timeslots to handle normal SDCCH traffic
A set of dynamic SDCCH/8 timeslots, used for TCH traffic, or for SDCCH
traffic.
The general principles for dynamic SDCCH are:
Automatic allocation of SDCCH/8 timeslots (minimum and maximum)on a cell basis
Only SDCCH/8 timeslots are concerned. It is not necessary to add or delete
a SDCCH/3, or a SDCCH/4, or a SDCCH/7 timeslot
The set of static SDCCH/x and dynamic SDCCH/8 timeslots represents themaximum number of allocatable SDCCH timeslots
The static SDCCH/8 timeslots cannot be used for TCH purposes
The dynamic allocatable SDCCH/8 timeslots are allocated for SDCCH whenall the static SDCCH/8 timeslots are busy
A TCH call cannot free a timeslot for SDCCH/8 allocation
A TCH is preferably not allocated dynamic SDCCH/8 timeslots.
Note: VGCS calls cannot use dynamic SDCCH allocation.
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1.8 Networks Interworking
1.8.1 2G and 3G Cells
Cells references
A 2G cell is completely defined in the BSS by:
Absolute Radio Frequency Channel Number (ARFCN)
Base Station Identity Code (BSIC).
A 3G cell is completely defined by:
UTRAN ARFCN (UARFCN)
Primary scrambling code. Like the BSIC in GSM, the primary scramblingcode allows the UE/MS to discriminate UTRAN FDD cells having the
same UARFCN.
Identification 2G cells 3G cells
Complete radio reference ARFCN + BSIC UARFCN + Primary scrambling code
Partial radio reference Only ARFCN Only UARFCN or (UARFCN + Scramblingcodes per scrambling code group)
Cell Global Identifier CGI = MCC + MNC +LAC +CI
MCC + MNC + RNC-ID + C-ID
Partial identifiers LAC + CI, CI UC-ID = RNC-ID + C-ID, C-ID
O&M cell identifier Local Cell Identifier
Cells rapport:
The max number of 2Gto3G Adjacency for one cell is 12
In case of 9120 BSC:
The max number of 3G external cell per BSC is 450
The max number of 2Gto3G Adjacency per BSC is 980
In case of 9130 BSC:
The max number of 3G external cell per BSC is 850
The max number of 2Gto3G Adjacency per BSC is 1850
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1.8.2 2G to 3G Handover
The following rules apply for 2G to 3G handover:
A 2G to 3G handover is based on the measurements reported by the UE/MS.
As soon as measurements above a given threshold are reported for oneor several 3G cells, those cells are candidate for handover. The averaged
measurements received along a given time must be above a given threshold.
The only measurements requested by the UE/MS are the CPICH Ec/No.
Nevertheless, an internal parameter (FDD_REP_QUANT) is defined to
choose the type of measurement.
The feature can be activated (or deactivated) on a per cell basis, by an O&M
parameter (EN_3G_HO)
When a dual mode UE/MS enters the RR dedicated mode, it sends aCLASSMARK CHANGE message and/or a UTRAN CLASSMARK CHANGE
message which contains the INTER RAT HANDOVER INFO. There is noacknowledgement from the network at layer 3
If the UTRAN CLASSMARK CHANGE is to be sent by the MS, the
CLASSMARK CHANGE message is sent first
If a condition is met to perform handover from 2G to 3G, the BSS does not
perform an intersystem handover via directed retry. The BSS proceeds with
the normal assignment procedure
If a condition is met to perform handover from 2G to 3G on the SDCCH, the
BSS does not perform an intersystem handover. The BSS proceeds with thenormal assignment procedure on the allocated SDCCH
When handover to 3G occurs, the LAC can also be used as additional
information but it is not part of the cell identifier.
There are two types of lists to describe the neighbor cells in the serving cell:
Distribution listsThe list is shared between all the MS of the serving cell and consequentlybuilt from information sent within the SYSTEM INFORMATION familymessages on the BCCH or PACKET SYSTEM INFORMATION familymessages on the PBCCH.
Non-distribution listsThe list is given to an individual UE/MS camping on the servingcell and consequently built from information sent in the dedicatedSYSTEM INFORMATION family, MEASUREMENT INFORMATION andPACKET MEASUREMENT INFORMATION messages on the SACCH orPACCH/PCCCH.
For 2G to 3G CS handover, in the call setup step of dual mode mobiles, the
INTER RAT HO INFO element via the UTRAN CLASSMARK CHANGEmessage is not segmented and it is compressed. There is a gain of 700ms
and a reduction of SDCCH load during call setup.
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The following dimensioning and support constraints apply:
In the Alcatel-Lucent UTRAN, 2G to 3G handover is supported from Rel-4
This feature is limited to TCH/2G to TCH/3G handover
SDCCH/2G to SDCCH/3G handover will not be implemented
SDCCH/2G to TCH/3G handover will not be implemented
When both 2G and 3G candidate cells are determined, the 3G cell(s) prevail
A dual mode UE/MS only in dedicated transfer mode can be handed over
to UTRAN
Maximum number of outgoing 2G to 3G adjacencies at the most per 2Gcell: 8
Maximum number of outgoing 2G to 3G adjacencies at the most per BSC:
980
Maximum number of 3G (external) cells at the most per BSC: 450
Maximum number of distinct 3G FDD_ARFCN neighboring one 2g cell: 3
MEASUREMENT REPORT message is limited to 6 measurements.
1.8.3 2G to 3G Reselection
2G to 3G reselection in PTM and NC2 in medium radio condition is notpermitted. NC2 2G to 3G reselection is allowed in good coverage conditions.
2G to 3G/TDSCDMA cell reselection is available and optional, lockableat the OMC-R.
The parameters EN_2G_TO_3GTDD_CELL_RESELECTION andEN_2G_TO_3G_CELL_RESELECTION cannot be enabled at the same time.
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1.8.4 GAN System
GANs extends the radio coverage of 2G and 3G networks by allowing adapteddual mode (GSM/UMTS and GAN) mobiles to be connected to a 2G or 3GMSC through an unlicensed radio access (WIFI, Bluetooth).
GANC (GAN Controller) is connected to a legacy GSM/GPRS Core Network.
In the GSM system, the GANC system interoperates with the 2G, throughpseudo GAN cells.
Each pseudo GAN cell allows the handover between the 2G to GANC (in chargeof the real GAN system). A pseudo GAN cell must be adjacent to the 2G cell.
The MS decides when it is relevant to perform a handover and then the BSSexecutes the handover.
There are no requirements on the packet side.
Handover from a GAN cell to 2G has no impact on the BSS:
Incoming External from GSM or from GANThe counters related to incoming external handovers take into accounthandovers coming from GAN and from GSM. No specific counters areprovided for incoming handover from GAN.
Outgoing External to GSM or to GANThe counters related to outgoing external handovers take into accounthandovers to GAN in the same way as for GSM handovers. No specificcounters are provided for outgoing handover to GAN.
1.8.5 Number of BCCH Frequencies
The max number of BCCH frequencies for the set of all target cells must becontrolled as follow:
Serving cell is:
Non-Evolium cell
For Reselection adjacencies, if the neighbourhood of the serving cell is:
2G onlyThere are up to 32 different BCCH 2G frequencies for the set of alltarget cells
Mixed 2G and 3GThere are up to 31 different BCCH 2G frequencies for the set of alltarget cells
Evolium cell
For reselection adjacencies
If the neighbourhood of the serving cell is:
2G onlyThere are up to 32 different BCCH 2G frequencies for the set of alltarget cells
Mixed 2G and 3GThere are up to 32 different BCCH 2G frequencies for the set of alltarget cells
For handover adjacencies
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If the neighbourhood of the serving cell is:
2G onlyThere are up to 32 different BCCH 2G frequencies for the set of alltarget cells
Mixed 2G and 3GThere are up to 31 different BCCH 2G frequencies for the set of alltarget cells.
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This section provides an introduction to GPRS and describes:
Packet Switching
GPRS Elements
GPRS Channels and Interfaces
GPRS Network Functions
GPRS Data Transmission.
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2.1 OverviewThe success of GSM runs parallel to the explosion of interest in the Internetand related data services. Presently, data transmission over the Air Interfaceis limited to 9.6 kb/s, too slow for use of graphic-intensive services suchas the World Wide Web and personal video conferences. In addition, thecircuit-switched method used for data transmission makes inefficient use ofradio resources, which are under increasing pressure from the growth inGSM subscribers and use.
The solution chosen by the ETSI for the double challenge of increased demandfor data service and pressure on radio resources is called General PacketRadio Service (GPRS). The ETSI recommendations establish a standard forinserting an alternative transmission method for data in the PLMN (packetswitching instead of circuit switching).
The Alcatel-Lucent GPRS solution follows the ETSI GSM phase 2+recommendations closely.
2.1.1 Packet Switching
In circuit switching, a connection is established and maintained during the entirelength of the exchange, whether data is being transmitted or not. Resourcesare dedicated to a single end-to-end connection, and a radio channel in a cell,with its associated transmission channels, may be unavailable for use evenwhen little or no information is passing across it at a given moment.
In packet-switched systems, data is transmitted over virtual circuits, which existonly while data is actively being transmitted over them. This means that duringidle time, timeslots can be used for carrying other data.
Packet-switching systems operate according to the following generalprocedures:
1. The PAD function disassembles data into "packets" of a predefined size.
2. The PAD encloses the packets in a data envelope (headers and footers).This data envelope includes information about origin and destination points,and the order in which the packet’s contents are to be reassembled at thedestination. The figure below shows a model of a GPRS Packet DataUnit at the LLC layer.
3. Packets move from origin to destination point by different routes and canarrive at the destination in a different order than that in which they were sent.
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4. At the destination, another PAD reads the envelope information, strips it off,and reassembles the data in the proper order.
DATA Footer
ENVELOPE
Address Field Contains:Protocol discriminatorCommand/response SAPI (mobility management,QoS, SMS)
Control Field − 4 possible types:Confirmed information transferSupervisory functionsUnconfirmed information transferControl functions
HeaderAddress Field
Control Field FCSInformation Field
FCS : Frame Check Sequence
SAPI : Service Access Point Indicator
Figure 6: Model LLC Packet Data Unit used in GPRS
Examples of packet-switching protocols include X.25 and Internet Protocol.Since GPRS is compatible with these widely used protocols, it is suitable foraccess to public or custom packet data services, or to the Internet. Mobiletelephones using packet data services must be connected to a portablecomputer or an electronic organizer.
2.1.2 GPRS Elements
The different elements shown in the figure below represent a parallel system tothe circuit-switched system used in GSM until now.
BTS
MS
BSC
To PSTN
BSS
GGSN
BTS
BSCGP
GCH
Ater
Gb
Packet
GCH
Abis
SGSN
To Public DataNetworks
GCH
Traffic
Switched
FRDN Gb
MSC/VLR
OMC−R
MFS
Circuit
Traffic
SwitchedTranscoder
BSCGP : BSC GPRS Protocol
FRDN : Frame Relay Data Network
GCH : GPRS Channel
GGSN : Gateway GPRS Support Node
MFS : Multi-BSS Fast Packet Server
PSTN : Public Switched Telephone Network
SGSN : Serving GPRS Support Node
VLR : Visitor Location Register
Figure 7: The Alcatel-Lucent GPRS Solution in the PLMN
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In the Alcatel-Lucent solution, the MFS with its associated interfaces is the BSSelement. All other components are external to the BSS.
This section describes the following internal and external components:
GPRS mobiles
The Serving GPRS Support Node
The Gateway GPRS Support Node
The Multi-BSS Fast packet Server.
2.1.2.1 GPRS MobilesThere are three classes of GPRS capable mobile stations: Class A, Class B,and Class C.
Currently, only Class B and C mobile stations are supported:
Class AClass A mobile stations can handle circuit-switched voice and GPRStraffic simultaneously.
Class BClass B mobile stations can be IMSI attached and GPRS attached at thesame time, but use only one service (circuit switched or packet switched)at a time.
A GPRS-attached Class B mobile station can initiate an IMSI connectionand suspend its GPRS service in the following cases:
When the user is not engaged in any GPRS data transfer, and either:
A mobile station-originated call is initiated
The mobile station receives a mobile-termination call.
When the user is engaged in a GPRS session (e.g., an Internet session),
and either:
A mobile station-originated call is initiated
The mobile station receives a mobile-termination call.
The mobile station performs a LAU procedure in network mode II ornetwork mode III.
Class CClass C mobile stations can be either IMSI-attached or GPRS-attached, butnot both, and can use circuit-switched or GPRS services alternately.
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2.1.2.2 The Serving GPRS Support NodeThe SGSN is a GPRS network entity at the same hierarchical level as theMSC. It is external to the BSS and communicates with it via Frame Relayover the Gb Interface. The SGSN is involved in requesting specific networkresources for GPRS traffic. It performs GPRS paging, authentication, andcipher setting procedures based on the same algorithms, keys and criteriaas in circuit-switched GSM traffic.
When a mobile station wants to access GPRS services, it makes its presenceknown to the network by performing a GPRS Attach procedure. Thisestablishes a logical link between the mobile station and the SGSN. The mobilestation is then available for SMS over GPRS, paging from the SGSN, andnotification of incoming GPRS data.
The SGSN also participates with other network elements in the routing andrelaying of packets from one node to another.
One SGSN can be connected to many MSCs and many MFSs.
2.1.2.3 The Gateway GPRS Support NodeThe GGSN is connected to SGSNs via an IP-based backbone. It providesinterworking between the GPRS network and external packet-switchednetworks. It is external to the BSS.
When the mobile station sends or receives GPRS data, it activates the PacketData Protocol address that it wants to use. This has the effect of making themobile station known to the GGSN. User data is transferred transparently fromthe mobile station and external data systems by the GGSN using encapsulationand tunnelling. This allows data packets equipped with GPRS-specific protocolinformation to be transferred between the mobile station and GGSN, in turnreducing the requirement for the GPRS system to interpret external dataprotocols.
The GGSN also works with other network elements in the routing and relayingof packets from one node to another.
2.1.2.4 The Multi-BSS Fast Packet ServerFor more information about the MFS, refer to the The Multi-BSS Fast PacketServer (Section 1.3.4).
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2.2 GPRS Channels and System Information MessagesGPRS traffic uses the same radio resources as circuit-switched traffic, andis carried on the same type of physical channel. When a physical channel isallocated to carry packet logical channels (using TDMA frames, as doescircuit-switched traffic), it is called a Packet Data Channel, or PDCH.
2.2.1 Logical Channels
The types of logical channels which can be carried on a PDCH are the:
Packet Traffic Channel
This channel is analogous to a circuit-switched traffic channel, and isused for user data transmission and its associated signaling. It has twosub-channels:
Packet Data Traffic Channel which contains the user data traffic
Packet Associated Control Channel (bi-directional) which contains
the signaling information.
If multiple PDTCHs are assigned to one mobile station, the PACCH is alwaysallocated on one of the PDCHs on which PDTCHs are allocated.The function of these sub channels is analogous to their circuit-switchedcounterparts.
Packet Timing Advance Control Channel.This bi-directional channel is used for maintaining a continuous timingadvance update mechanism.
2.2.2 Virtual Channels
Packet switching is a mode of operation adapted to transmission of "bursty" data- that is, data which comes in intense "bursts" separated by periods of inactivity.The network establishes a connection during the transmission of such a "burst"of data. If there is no activity on this connection, the connection is taken down.
When the original user needs to send or receive another burst of data, a newtemporary connection is set up. This can be on another channel in the samecell, or in another cell if the mobile station is in motion. The routing of one burstof data may be different from the routing of another.
The establishment and disestablishment of temporary connections istransparent to the user. The user sees an exchange of data that seems to bea continuous flow, unless the network is over congested. This semblance ofcontinuous flow is a Virtual Channel.
A virtual channel can be represented as the flow of data between two terminalsduring a user session. The user has the impression of a single continuousconnection, but in the network, this is not the case.
A single data transfer, either in the uplink or in the downlink direction, canpass between the MFS and the mobile station via one or more PDCH. APDCH is shared between multiple mobile stations and the network. It containsasymmetric and independent uplink and downlink channels.
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2.2.3 System Information Messages
GPRS system information messages, like their GSM counterparts, transmitinformation about the cell to the mobile station. GSM BCCH messages, shownin Table 1 , are also used in GPRS. In addition, GPRS also uses the messagesshown in the following tables.
Message Channel Information
SI 13 BCCH The SI 13 message is sent on the BCCH andcontains all the necessary information requiredfor GPRS. It also indicates the presence andthe location of the PBCCH in the serving cell.The SI 13 message is broadcast only if GPRSis supported in the cell.
SI 2quater BCCH The SI 2quater message is sent on the BCCHduring 2G to 3G cell reselection and containsinformation about:
3G cells
3G measurement parameters
GPRS 3G measurement parameters, when
there is no PBCCH.
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2.3 GPRS InterfacesThis section describes the GPRS interfaces, and in particular, the newinterfaces introduced for GPRS needs. These interfaces link the MFS andthe SGSN, the BTS, and the BSC.
2.3.1 The Gb Interface
The Gb Interface uses frame relay techniques to link the PCU function of theMFS and the SGSN.
Physically, it can be routed in a variety of ways:
A direct connection between the MFS and the SGSN
Via a public Frame Relay Data Network
Via the MSC
Via the Ater Mux Interface through the Transcoder to the MSC. In this
case, it carries a combination of packet-switched and circuit-switchedtraffic and signaling.
Combinations of these methods are also possible. See Figure 7 for the positionof the Gb Interface in the system.
The Gb Interface provides end-to-end signaling between the MFS and theSGSN, and serves as the BSS-GPRS backbone. Its principal functions areshown in the following table.
Function Description
Transfer of BSSGP-PDUs between the BSS andthe SGSN
Allocation and load sharing of PDUs amongVirtual Channels
Network services
Access to intermediate Frame Relay Data Network
Radio resource information
Quality of Service Information
Routing information
Transfer of LLC-PDUs between the BSS and theSGSN
BSS-GPRS Protocolservices
Suspend and Resume procedures for Class Bmobile stations
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2.3.2 The BSCGP Interface
The BSCGP Interface provides communication between the BSC and the MFS(see Figure 7). The BSC GPRS Protocol controls two LAPD connections (forredundancy) using 64 kb/s timeslots. The BSCGP Interface carrier followinginformation.
Function Description
Circuit-switched and packet-switched paging(MFS to BSC)
Channel Requests from BSC to MFS
Common radio signaling
Uplink and downlink channel assignment (MFSto BSC)
Allocation/de-allocation of resources (MFS toBSC)
Release indication (BSC to MFS)
GPRS radio resourcemanagement
Load indication: this limits the allocation for GPRStraffic (BSC to MFS)
Note: The common radio signaling functions of the BSCGP are handled on the GPRSSignaling Link, which is carried inside the Ater Interface.
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2.3.3 The GCH Interface
The GCH Interface provides a synchronous connection between the MFS andthe BTS, using one to five 16 kb/s timeslots. The GCH links pass transparentlythrough the BSC (see Figure 7). Its functions are as follows:
Transfer of PDUs between the MFS and the BTS. (Therefore, packet data
is not directly handled by the BSC but passes transparently through it onthe GCH interface.)
Synchronization with the radio interface at GCH link establishment
Correction of clock drifts between Abis and BTS clocks.
The protocol for the GCH Interface uses the two layers described below:
L1-GCH LayerL1-GCH is the physical layer based on ITU-T recommendations G.703.The L1-GCH layer uses digital transmission at a rate of 2048 kbit/s with aframe of 32 x 64 kbit/s timeslots. An L1-GCH channel has a transmissionrate of 16 kbit/s.
L2-GCH LayerL2-GCH is the data link layer which is an Alcatel-Lucent proprietaryprotocol. This layer is in charge of the data transfer of the GCH framesbetween the MFS and the BTS.The L2-GCH layer offers a service of data transport for the RLC/MAClayers located in the MFS.
Its main functions are:
GCH link establishment and release
Synchronization with the radio interface
RLC/MAC PDUs transfer.
For more information about GSM transmission, refer to Call Set Up (Section 3).
The M-EGCH (Multiplexed-EGCH) link is available. The M-EGCH is a linkestablished between the MFS and the BTS and is defined per TRX. AnM-EGCH is made up of one to 36 GCHs.
The M-EGCH link of a TRX carries:
TBF traffic when TBFs are established on the PDCHs of the TRX
TBF signaling messages on the TBF PACCH
MFS-BTS control messages
Uplink signaling messages after one-block allocation (in UL two-phase
access).
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2.3.4 Specific LCS Interfaces
For LCS, the following specific interfaces are used:
SAGISupports the exchange of messages between SMLC and the external GPSserver following an Assisted GPS positioning request in the circuit-switcheddomain
RRLP(BSCLP)Supports the exchange of messages between BSC and the SMLC (i.e.,MFS) in the circuit-switched domain.
2.4 GPRS Network FunctionsThis section describes various GPRS-specific network functions necessaryfor successful packet data transfer. This includes paging, cell reselection,error checking and re-establishment, as well as radio power control and linkmeasurement.
2.4.1 MAC and RLC Functions
Since multiple mobile stations can be competing for the same physicalresource(s), an arbitration procedure is necessary. This is provided by theMedium Access Control (MAC) function.
The MAC function operates between the MFS and the mobile station, andworks in conjunction with the Radio Link Control (RCL) function. RCL definesthe procedures for retransmission of unsuccessfully delivered data blocks (errorcorrection) and for the disassembly and reassembly of PDUs.
2.4.2 Temporary Block Flow
When PDUs need to be transferred between the MFS and the mobile station,a temporary point-to-point physical connection is set up to support theunidirectional transfer of PDUs on one or more PDCHs. This connection iscalled a Temporary Block Flow (TBF).
A TBF is maintained only for the duration of the data transfer. The TBF isallocated radio resources on one or more PDCHs and comprises a numberof RLC/MAC blocks carrying one or more PDUs.
A typical user session, in which data is exchanged bi-directionally, requiresthe establishment of one TBF in each direction. The path of each TBF can bedifferent.
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2.4.3 Mobility Management
The GPRS Mobility Management (GMM) activities related to a GPRSsubscriber are characterized by the following states:
State Description
Idle In idle mode, the subscriber is not attached to the GPRS MM and therefore not known tothe different GMM entities. The GMM context holds no valid location or routing informationfor the subscriber.
GMM Ready When the mobile station starts the GPRS attach procedure, the mobile station enters theGMM Ready state to request access to the network.
GMMStandby
When the GMM Ready timer expires or is de-activated by the network, the mobile stationreturns to GMM Standby state.
2.4.3.1 Cell Reselection ModesNetwork-controlled reselection modes are defined below.
Mode Description
NC0 A GPRS mobile station performs autonomous cell reselection without sending measurementreports to the network.
NC1 A GPRS mobile station performs autonomous cell reselection. Additionally, when it is in theGMM Ready state, it periodically sends measurement reports to the network.
NC2 A GPRS mobile station in GMM Ready state does not perform autonomous cell reselection.When in GMM Ready state, it sends measurement reports to the network that controlsthe cell reselection.
NC2 is used only from R’4 MS.
2.4.3.2 Error CheckingSince the integrity of the data transmitted is crucial, packet-switched networksemploy a method of error checking. This confirms that the data receivedcorresponds exactly to the data transmitted.
In GPRS, an LLC-PDU includes a Frame Check Sequence used to detect errorsin the header and information fields of the PDU (see Figure 6). The FrameCheck Sequence uses the Cyclic Redundancy Check method of error checking.
Most of the mobile stations use non-acknowledged LLC transmission (whichcan be incompatible with TCP). Error detection is done at the RLC level. In thecase of cell reselection, the Alcatel-Lucent BSS retransmits the last LLC-PDU ifall its RLC blocks were not acknowledged.
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2.4.3.3 Mobility Management ProcessMobility Management in GPRS can be accomplished by the combination ofautonomous cell reselection by the mobile station and packet error correction.
The process is as follows:
1. The mobile station performs an autonomous cell reselection. The process isbased on average measurements of received signal strength on the BCCHfrequencies of the serving cell and the neighbor cells as indicated in theGPRS neighbor cell list. This refers to NC0.
The cell reselection procedure is the same as for circuit-switched traffic,but based on GPRS reselection parameters that can be configured bythe operator.
If the cell does not have a PBCCH, the mobile station applies existing circuitswitching parameters using the BCCH.
2. Once the mobile station is camped on the new cell, the data transfer isresumed. If an LLC-PDU has not been correctly received, it is re-emitted.
This process produces a slight overhead on throughput but has the advantageof greatly simplifying the cell change process.
2.4.3.4 Link Re-establishmentIf the mobile station detects a radio link failure, it will re-establish the link withthe SGSN. The BSS transmits the reselection configuration parameters to beused by the mobile station. Mobile-controlled reselection is equivalent tocircuit-switched call re-establishment. Refer to Call Re-establishment by theMobile Station (Section 4.8) for more information.
2.4.3.5 Full Intra-RA LLC-PDU ReroutingThis feature is implemented for a cell handled by another GPU when there is anabsence of information about the target cell to which the mobile station moves.
The BSS links the old and new cells, using the information they have incommon for that mobile station, namely the TLLI and the RAI. Once this link isset up, the BSS reroutes data from the old cell to the new cell.
The BSS autonomously decides to perform LLC-PDU rerouting on a cell changewhen the SGSN does not support the Inter-NSE Rerouting (INR) R4 option. Ifthe SGSN supports this option, then autonomous rerouting does not occur.
2.4.3.6 NC2 for Mobile Stations in Packet Transfer ModeTo reduce the number of cell reselections, the mobile station in packet transfermode does not make autonomous reselections. It sends measurement reportsto the network, therefore NC2 mode is selected.
2.4.4 Enhanced Packet Cell Reselection
In addition to enhanced cell reselection for R97-onwards MS, packet cellreselection is further improved with the following new features:
Network Assisted Cell Change
Packet SI Status and Packet PSI Status procedures
NC2 Cell ranking with load criteria.
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2.4.4.1 Enhanced Cell Reselections for R97 Onwards Mobile StationsNC2 mode is activated when the mobile station enters the packet transfer modeand NC2 mode is de-activated either at the end of the packet transfer mode orat GMM Ready timer expiry (O&M parameter) This reduces the number of cellreselections triggered during GPRS sessions. When this feature is activated,the BSS prevents multi-RAT mobile stations from monitoring 3G cells whilein packet transfer mode. This allows network control of mobile station cellreselection in packet transfer mode.
NC2 for mobile stations in packet transfer mode is activated by O&M. Whenactivated, the network controls cell reselection of each mobile station in apacket data transfer. Each of these mobile stations periodically reports itsmeasurements to the serving cell and on the six strongest neighbor cells.This enables the network to decide whether or not an NC cell reselection isperformed and which neighbor cell is the best candidate for reselection.
This feature reduces the number of cell reselections triggered when the mobilestation is in packet transfer mode.
2.4.4.2 Network Assisted Cell ChangeNetwork Assisted Cell Change (NACC) is a one of the new featuresimplemented to reduce the duration of packet cell reselection. With NACC,control of cell reselection can be managed by the either the MS or the network,if NC2 mode is not being used. NC2 has priority over NACC.
NACC takes place in the serving cell and consists of the following independentprocedures:
Cell Change Notification
Cell System Information Distribution.
NACC is enabled/disabled by the EN_NACC parameter.
An MS supports Cell Change Notification (CCN) under the following conditions:
CCN is activated in the (P)SI
The MS is not in Dedicated Mode or Dual Transfer Mode
The MS is in NC0 mode
The MS is in packet transfer mode.
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If the MS fulfills these conditions, when it detects a best new cell, using CCN:
1. The MS informs the BSS it wants to move from serving cell A to target cell B.
2. The BSS sends the required system information for the target cell on thePACCH.
For a target cell without PBCCH, the SI13, SI1 and SI3 messages containthe required information. For a target cell with PBCCH, system informationis contained in PSI14, PSI1 and PSI2.
3. The BSS also returns either a Packet Cell Change Continue or a Packet
Cell Change Order message to the MS.
4. If the MS receives a Packet Cell Change Continue message, it switchesto the previously selected target cell B.
If the MS receives a Packet Cell Change Order message, the CCNprocedure is ended and the BSS (in NC2 mode) takes control of cellreselection using the Cell System Information Distribution procedure.The Packet Cell Change Order message is sent to the MS when theMS-selected target cell does not correspond to the target cell selectedby the BSS.
5. Upon receipt of the Packet Cell Change Order message, the MS startsa timer and sends a Channel_Request message to the network-selectedtarget cell.
6. When the MS receives a successful response to its Channel_Request
message, along with the necessary system information, the MS switches tothe new target cell.
2.4.4.3 Packet PSI Status and Packet SI Status MessagesThe Packet PSI and Packet SI Status feature is implemented to reduce theamount of time required for GPRS cell reselection. This feature allows an MS toaccess a new cell without first receiving the full set of (P)SI messages sent onthe BCCH (for SI messages) or the PBCCH (for PSI messages). The MS onlyhas to read the information needed for GPRS operations in the target cell.
The necessary GPRS information is contained in the following (P)SI messages:
SI13
SI3
SI1 (for SI, only if present; for PSI only if the PBCCH is hopping)
PSI1
PSI2
After receiving the necessary information, the MS sends the appropriatestatus message (PACKET PSI STATUS or PACKET SI STATUS) to the BSS. Thisstatus message tells the BSS what information the MS received in the earlier(P)SI messages. The BSS then sends the remaining SI messages neededby the MS on the PACCH if the MS has not returned to the packet idle state.If the MS has returned to the packet idle state, the MS can read the missingSI messages itself.
The new EN_PSI_STATUS parameter is used to enable/disable:
Packet SI Status in cells without BCCH
Packet PSI Status in cells with PBCCH.
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2.4.4.4 Cell Ranking with Load CriteriaIn NC2, cell ranking with load criteria avoids directing mobile stations towardshigh loaded cells. This reduces the possibility of an MS being served withnon-optimum resources or being rejected due to congestion. The following twoparameters control cell ranking with load criteria.
This parameter... Is used to...
EN_NC2_LOAD_RANKING Enable/disable ranking the load of the target cell during NC2 cell ranking.
THR_NC2_LOAD_RANKING Set the threshold above which a cell is considered to be in a PS highload situation for NC2 cell reselection.
2.4.5 Paging
Paging is the procedure by which the network contacts a mobile station.The network can co-ordinate circuit-switched and packet-switched paging ifthere is a Gs Interface between the MSC and the SGSN. This means thatcircuit-switched paging messages can be sent on the channels used forpacket-switched paging messages, and vice-versa. Three modes are defined.
Mode Description
Network Operation Mode 1 Circuit-switched paging messages are sent via the SGSN and MFS.
The circuit-switched paging message for the GPRS-attached mobilestation is sent on the PPCH or CCCH paging channel, or on the PACCH.This means that the mobile station only needs to monitor one pagingchannel. It receives circuit-switched paging messages on the PACCHwhen the mobile station is in packet transfer mode.
Network Operation Mode 2 Circuit-switched paging messages are sent via the MSC and BSC, butnot the MFS.
The circuit-switched paging message for the GPRS-attached mobilestation is sent on the CCCH paging channel. The channel is alsoused for packet-switched paging messages. This means that themobile station only needs to monitor the PCH. Circuit-switched pagingcontinues on the PCH even if the mobile station is assigned a PDCH.
Network Operation Mode 3 Circuit-switched paging messages are sent via the MSC and BSC, butnot the MFS.
The circuit-switched paging message for the GPRS-attached mobilestation is sent on the CCCH paging channel. The packet-switchedpaging message is sent on either the PPCH (if allocated) or on theCCCH paging channel.
Table 2: Network Operation Modes
Packet-switched paging does not use the Local Area for paging, but a GPRSRouting Area (RA). The RA is smaller, and fewer cells are involved.
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For VGCS, Notification messages are broadcast periodically in the cell, onNCH, and optionally on FACCH, for ongoing point-to-point calls, to notify theVGCS mobile station of a new VGCS call being established.
This process is similar to the Paging procedure used for standard calls.Different notification procedures are applied, depending on the mode of themobile station to be notified:
Idle Mode Notification messages are broadcast on the NCH of thecell for new or ongoing VGCS calls
Group Receive Mode or Group Transmit Mode Notification messages
are broadcast on the FACCH of other ongoing VGCS calls to notify the newVGCS calls that are being setup in the cell
Dedicated Group Transmit Mode Notification messages are broadcast
on the FACCH of the dedicated TCH allocated to the talker
Dedicated Mode Notification messages are broadcast on the FACCH of
all ongoing point-to-point calls in the cell to notify the new VGCS calls thatare being setup in the cell.
2.4.6 Radio Power Control and Radio Link Measurement
In order to decrease the level of interference in a network, the uplink anddownlink transmissions are constantly measured and a balance is maintainedbetween transmission power and the actual quality of the link. In GPRS,power control is implemented in an open loop on the uplink path. Thismaintains speech quality in the network and keeps a low bit error rate fordata transmission.
The BSS broadcasts the configuration parameters necessary for the mobilestation. When it first accesses a cell, the mobile station sets its output power asdefined in the system information. It then resets its power output according tothe parameters broadcast, and to an evaluation of the uplink path loss.
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2.5 Resource ManagementIn order to provide flexibility to the operator in managing the use of resourcesby circuit-switched and packet-switched traffic, resources are shared betweenthe MFS and the BSC. Use of these resources by one system or the other canbe controlled by a variety of parameters to meet operators’ needs. The MFSand BSC co-ordinate resource management over the BSCGP Interface.
In GPRS, resource management refers principally to the allocation of PacketData Channels. PDCHs are dynamically allocated according to criteria thatcan be defined by the user.
When a TBF request is made, resources are allocated on one or more PDCHfor the transfer of PDUs. The allocation process takes place as follows:
1. A TBF establishment request is received through a Packet Channel requestfor the uplink, or through a downlink LLC-PDU for the downlink.
2. The number of PDCHs is determined by the:
Mobile station multislot class. This is not always known in the uplink case
O&M parameter (MAX_PDCH_PER_TBF). This defines the maximum
number of allocatable PDCHs per TBF.
3. If the requested number of PDCHs is not available, a request to establish aTBF is sent to the BSC.
4. PDCHs are allocated to the TBF.
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2.5.1 Timeslot Allocation
GPRS allows bandwidth to be shared between several mobiles. On a radiotimeslot, bandwidth can be shared between up to nine users on the downlinkpath and six on the uplink path, or up to 16 GPRS requests within one timeslot.Circuit-switched data services require at least one timeslot per user.
The radio blocks on each timeslot are equally distributed among the usersassigned to the channel. For example, on the uplink path when coding scheme2 is used, the minimum raw bit rate per user is 1.9 kbit/s (13.4/7) instead of 13.4kbit/s. The following table describes the parameters for timeslot allocation.
This parameter: Is used to:
MAX_UL_TBF_SPDCH Define the maximum number of users (between one and six) that share aPDCH in the uplink direction.
MAX_DL_TBF_SPDCH Define the maximum number of users (between one and nine) that share aPDCH in the downlink direction.
N_TBF_PER_SPDCH Define the optimum number of shared users per direction and per PDCH. Thisensures a good bit rate as long as the GPRS load is normal.
However, setting the N_TBF_PER_PDCH parameter ensures a compromisebetween resource efficiency and quality of service. For example, ifN_TBF_PER_PDCH = 2 and coding scheme 2 is used, the preferred raw bit rateper user will be 6.7 kbit/s/s (13.4/2). When the number of users on the PDCHreaches the N_TBF_PER_PDCH value (2), the PDCH is declared "busy" and willpreferably not accept a third user. But if the GPRS load is such that all PDCHsare busy, the BSS will override the number of users set in N_TBF_PER_PDCH
and increase the number of shared resources to the maximum, using theMAL_XL_TBF_SPDCH value.
For VGCS, a timeslot configured as a TCH timeslot is considered by the BSC tobe a TCH timeslot reserved for VGCS and normal traffic when it is identifiedas TCH/SPDCH. When there are VGCS only timeslots available (configuredbut currently free) in the cell, these timeslots are used for VGCS. If there areno VGCS only timeslots available, the other free VGCS capable timeslots areused. Otherwise, VGCS calls are handled as normal calls and are managedusing the same timeslot allocation strategy as for standard calls.
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2.5.2 Autonomous Packet Resource Allocation
Autonomous Packet Resource Allocation introduces a new way of sharing radioresources between the MFS and the BSC. With this feature, the MFS no longerneeds to request radio timeslots from the BSC. Instead, the MFS is alwaysaware of all the available timeslots. This speeds up PDCH establishment anddecreases the BSC and MFS CPU loads.
Because the MFS is aware of all available timeslots, the choice of the bestallocation to serve the TBFs in the MFS is simplified. The SPDCHs areordered by the BSC to ensure consistent circuit-switched and packet-switchedallocation. The BSC ranks the PS TRXs and sends this ranking to the MFSon the BSCGP interface at cell creation and if the cell is modified during anO&M operation. The BSC defines the number of SPDCHs allocated to theMFS by computing the MAX_SPDCH_LIMIT. The resulting SPDCH allocationis based on the whole BSS load (CS plus PS load), with the PS load beingprovided periodically by the MFS. The BSC informs the MFS of the numberof PS timeslots with the highest priority for PS traffic in the Radio ResourceAllocation Indication message.
Autonomous Packet Resource Allocation works as follows:
1. The MFS periodically sends the BSC a Radio Resource Indication
Usage message. This message contains the number of SPDCHs in theMFS and their use.
2. Upon receipt of this message, the BSC estimates the PS traffic load. Then,the BSC sends a Radio Resource Allocation Indication message providingthe number of radio resources allocated to the MFS.
3. The MFS updates its SPDCH allocation table. If necessary, the MFSpre-empts a few SPDCHs in order to release them to the BSC.
4. The MFS sends a new Radio Resource Indication Usage message tothe BSC acknowledging the new SPDCHs and indicating the de-allocatedSPDCHs (if any).
The following table shows the how the Autonomous Packet Resource Allocationuses a CS/PS resource-sharing concept with radio resources.
A Timeslot Defined as.... Is...
Reserved for PS Reserved for PS traffic only. The number of Reserved for PS timeslots isdefined by the MIN_SPDCH parameter.
Priority for PS Used for either CS or PS traffic, but PS traffic has priority. The numberof Priority for PS timeslots is defined by the MAX_SPDCH_HIGH_LOAD andMIN_SPDCH parameters.
Priority for CS Used for either CS or PS traffic, but CS traffic has priority. The number ofPriority for CS timeslots available is the difference between the MAX_SPDCH
and MAX_SPDCH_HIGH_LOAD parameters.
Reserved for CS Reserved for CS traffic only. The number of Reserved for CS timeslots isdefined by the MAX_SPDCH parameter.
This feature introduces a new parameter, MAX_SPDCH_LIMIT. It defines thenumber of SPDCHs that can be granted by the BSC to the MFS, and replacesthe MAX-SPDCH_DYN parameter.
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2.5.3 Packet Flow Context
The Packet Flow Context (PFC) provides end-to-end QoS management. Itallows the BSS to differentiate between different types of traffic on the radiointerface, by reading the QoS profiles listed in each PDP context defined bythe subscriber.
A PFC describes the QoS characteristics of ongoing data transmission. TheBSS recognizes three QoS classes:
The streaming classThis class is a real-time stream and enforces jitter constraints. Videostreaming and Push over Cellular (PoC) are typical applications.
The interactive classThis class corresponds mainly to traditional Internet applications like webbrowsing.
The background classThis class corresponds to Best Effort services such as e-mail downloading,SMS and ftp downloading.
When the PFC is activated, the BSS can reject or negotiate the QoSparameters in order to provide an optimum level of service by:
Favouring conversational and streaming traffic over interactive and
background traffic by reserving resources for these types of trafficThis is particularly useful for subscribers who request a specific quality ofservice (QoS) profile for each PDP context, according to their requirements(for example, contexts associated with e-mail can tolerate lengthy responsetimes, while other applications such as interactive real-time applicationsrequire a very high level of throughput).
Defining a flow aggregate based on the lifetime of the flows, in order todetermine admission control and QoS based resource allocation in the BSS.
In a basic case of mobile station initiated PDP context , PFC works as follows:
1. The mobile station defines the required QoS parameters and sends anActivate_PDP_Context_Request or a Modify_PDP_Context_Request
message to the SGSN.
2. The SGSN determines the QoS it wants, based on:
The QoS requested by the mobile station
The subscribed QoS stored in the HLR
Network QoS constraints.
The SGSN then performs internal call admission control and resourceallocation.
3. The SGSN asks the GSGN to create the PDP context.
4. The GSGN performs internal call admission control and can eventuallydowngrade the QoS requested by the SGSN.
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5. The SGSN uses the PFC feature to read and, if necessary, manage theQoS (for example, to downgrade resources when there is a cell change toa congested cell).
6. The SGSN informs the GSGN of any changes and informs the mobilestation of the PDP context creation or modification, including the finalQoS established in the network.
Note: PFC can only be used if both the BSS and the SGSN support the feature.
For more information about PDP context management, refer to Packet DataProtocol Context Activation (Section 2.7.2).
2.5.4 Dynamic Abis Allocation
This feature dynamically allocates Abis nibbles among the different TREs usedfor PS traffic in a given BTS. That is, the telecom mapping of the Abis nibbles tothe TREs in the BTS is done dynamically. This means that unused Abis nibbleson one timeslot can be switched to another timeslot as needed. Dynamic Abisallocation reduces the average number of Abis nibbles used for PS traffic. Itallows a higher average Abis bandwidth per PDCH and increased BSC capacityin terms of TREs. With dynamic Abis allocation, some BTS configurations donot need a second Abis link. This feature simplifies the dimensioning of theAbis interface since TRX-level dimensioning is no longer needed.
Dynamic Abis allocation works with M-EGCH statistical multiplexing (seeM-EGCH Statistical Multiplexing (Section 2.6.3)). As a reminder, a GCHchannel in an M-EGCH link corresponds to a 16k link between the MFS andthe BTS and uses one Abis nibble plus one Ater nibble switched together inthe BSC. When needed for PS traffic, the GCH channel is activated. Whenno longer in use, the GCH channel is de-activated. In order to activate GCHchannels at the BTS, TREs must listen to the Abis nibbles to detect the GCHactivation messages. With dynamic Abis allocation, the BSC, when requestedby the MFS, performs Abis-Ater switching / de-switching. Abis-Ater switchingallows the BSC to switch N 16k Abis nibbles to N 16k Ater nibbles (n > 1).Abis-Ater de-switching does the reverse, i.e., N 16k Ater nibbles are switchedfor N 16k Abis nibbles.
In conjunction with dynamic Abis allocation, the process also uses Abis NibblePools (Section 2.5.4.1) and a new Abis Resource Manager (Section 2.5.4.2).
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2.5.4.1 Abis Nibble PoolsDynamic Abis allocation uses logical pools of Abis nibbles. An Abis nibble poolis a set of basic and extra Abis nibbles which can be dynamically allocatedamong TREs. The nibbles of a given pool can only be used by a fixed set ofTREs. That is, there is a one-to-one logical association between a pool of Abisnibbles and a set of TREs. The basic and extra Abis nibbles in the pool are notshared among TREs in the same way.
The different types of Abis nibbles in a pool are shared as follows:
Extra Abis nibbles are shared at BTS level (e.g., among all TREs of the BTS)
Bonus basic Abis nibbles are also shared at BTS level
Basic Abis nibbles are shared at cell level (among all the TREs of the samesector in a shared cell). Note that in a cell shared over two BTS, only
one BTS sector supports PS traffic.
To build Abis nibble pools, each basic Abis nibble is statically mapped on anAbis timeslot. There are two 64k Abis timeslots reserved per TRE. This isimportant for CS traffic because a TCH always uses the basic Abis nibble thatwas initially mapped on its timeslot. For the extra Abis nibbles, a number of 64kExtra timeslots (EXTS) are defined for each BTS.
2.5.4.2 Abis Resource ManagerThe Abis resource manager handles the pools of basic and extra Abis nibblesassociated with a given BTS. There is one Abis resource manager per BTS.The manager acts upon requested received from a higher-level transmissionresource manager at GCH level. The Abis resource manager is located inthe MFS since the MFS must manage the Abis nibbles in order to managepre-emption due to CS traffic. Because there is a manager for each BTS, theAbis resource manager for a given BTS is located on one unique GPU in theMFS. Abis nibbles are allocated to a TRE using the GSL-RSL interfaces. Abisnibbles are identified in the BSS by a physical identifier. The Abis resourcemanager must be able to address an Abis nibble at both the BSC and BTSsides. A physical identifier for the nibble means that no BSC Abis nibbleid-to-BTS Abis nibble id conversion is necessary. This avoids complexity andBSC load-related problems.
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2.5.4.3 Abis Nibble Pool ManagementThe Abis resource manager uses the following input messages to managethe Abis nibble pools:
Cell State Response / Cell State Change messages (the contents of the twomessages are the same)
Extra Abis Pool Configuration messages, indicating the list of extra Abis
timeslots available for PS traffic in a BTS
RR Allocation Indication messages, indicating which radio timeslots areavailable for PS traffic (i.e., which radio timeslots whose basic Abis nibbles
can be used / can no longer be used for PS traffic)
Cell Deletion messages.
Depending on the message and its contents, the Abis resource manageracts as described below.
For a Cell State Change message:
When a PS capable TRE is removed, the corresponding basic Abis nibblesare immediately removed from the Abis pool. The Abis resource manager
triggers the release of the current GCHs of the TRE and the release of theGCHs currently using the basic Abis nibbles initially mapped to the TRE (if
any). All the basic nibbles associated with the TRE are de-allocated from
the TREs using them. The Abis and Ater nibbles of the concerned GCHsare then de-switched in the BSC.
When a PS capable TRE is added, the resource manager does nothing.
If the basic Abis nibble-to-timeslot mapping for a TRE has changed, the oldbasic Abis nibbles are immediately removed from the pool. The manager
triggers the release of the current GCHs of the TRE and of the GCHscurrently using the old basic Abis nibbles of the TRE (if any). The Abis and
Ater nibbles of the impacted GCHs are then de-switched in the BSC.
If some basic Abis nibbles used for the BCCH or the static SDCCH are nolonger present in the Cell State Change message, the corresponding
basic Abis nibbles are immediately removed from the Abis pool. Thecorresponding GCH links (if any) are released.
If there are new basic Abis nibbles available for PS traffic due to BCCH /
static SDCCH channels in the Cell State Change message, these basicnibbles are added to the Abis nibble pool.
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Upon receipt of an Extra Abis Pool Configuration message, the resourcemanager:
Deletes from the Abis pool any EXTSs indicated as removed from the list of
available EXTSs. The corresponding GCHs are released and the Abis andAter nibbles are then de-switched in the BSC.
Adds new EXTSs to the Abis pool. From that moment on, the new EXTSsare available to any M-EGCH in the BTS.
Upon receipt of an RR Allocation Indication message, the Abis resourcemanager:
Pre-empts any basic Abis nibbles whose timeslots are no longer availablefor PS traffic. The corresponding GCHs (if any) are released and Abis-Ater
de-switching is done in the BSC.
Adds any basic Abis nibbles whose timeslots are newly available for PStraffic to the Abis pool.
When a Cell Deletion message is received by the MFS, the Abis resourcemanager immediately removes all the basic nibbles of the cell (TREs BCCH,static SDCCH) from the pool. All the GCHs using these nibbles are released(but they can be used in another cell). Then Abis-Ater de-switching is done inthe BSC.
2.5.5 Enhanced Transmission Resource Management
With the M-EGCH Statistical Multiplexing and the Dynamic Abis Allocationfeatures, better management of transmission resources (Ater and Abisnibbles) is possible. This reduces the consumption and waste of transmissionresources. A dedicated transmission resource manager operating at MFS /GPU level is also added. This resource manager handles both Abis and Aterresources at the GCH level.
The transmission resource manager is in charge of:
Creating and removing the M-EGCH links
Selecting, adding, removing and redistributing GCHs over the M-EGCH links
Managing transmission resource pre-emptions
Managing Abis and / or Ater congestion states
Optionally, monitoring M-EGCH link use, according to the (M)CS of their
supported TBFs (UL and DL).
2.5.6 Frequency Hopping
Frequency hopping improves the bit error rate and therefore contributesto overall network quality. Frequency hopping, already provided forcircuit-switched channels, is extended to the packet-switched channels forGPRS implementation. The BSS sends the hopping law when setting upa connection. All GPRS channels then use the same hopping law in asynchronized scheme.
For more information about frequency hopping, refer to Call Set Up (Section 3).
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2.5.7 PCM Link Sharing
Resource allocation is made easier by the use of a shared 2048 kb/s PCM link.GPRS signaling and traffic channels can be multiplexed with circuit-switchedtraffic channels on this link between the MFS and the BSC.
Traffic on the Ater Mux Interface between the MFS and the Transcoder is eitherprocessed by the MFS as GPRS traffic, or passed transparently through thecross-connect in the MFS to the BSC as circuit-switched traffic.
2.5.8 TBF Resource Re-allocation
Resource re-allocation is enabled using the EN_RES_REALLOCATION parameter.The feature provides radio and transmission resources for a TBF following anuplink request received from the mobile station, or following one or moredownlink LLC-PDUs received from the SGSN, when there is no establishedTBF for the mobile station. More than one TRX can be allocated to GPRSservices in any given cell. Resource allocation must be prioritized, so priority isset on PDCH groups. The allocation is granted to the PDCH group with thehighest priority. This avoids PDCH groups in a congested state and PDCHgroups that are dual-rate capable.
The requested throughput is served by the:
Maximum number of slots allowed by the mobile station multislot class
GPRS service constraints (the operator gives the maximum number ofallowed slots for one GPRS connection)
Network constraints (resource availability).
The allocation strategy consists of maximizing the allocated PDCH(s) use and,if necessary, requesting additional PDCH(s) from the BSC. EGPRS traffic haspriority over GPRS traffic. For example, TRXs with high throughput are used forEGPRS traffic. Although GPRS throughput is optimized using TRXs with highthroughput, this occurs only when there is no conflict with EGPRS traffic.
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The following table describes the four types of TBF re-allocations.
This type ofre-allocation...
Is used to...
T1 Maintain a TBF alive despite a pre-emption.
T2 Re-allocate an ongoing TBF when establishing a concurrent TBF when:
A downlink TBF is established concurrent with an existing uplink TBF, which is
allocated with the maximum number of timeslots supported in the direction of thebias, re-allocation cannot be given to the mobile station
An uplink TBF is established concurrent with a downlink TBF.
T3 Offer better throughput to ongoing TBFs when:
A TBF cannot be served with the maximum number of PDCHs it supports because:
Of lack of resources at the time of the request
The EGPRS class is used to establish a GPRS TBF, where the GPRS mobilestation class allows a greater number of allocated PDCHs with better PDCH
allocation available to serve the TBF.
"Signaling traffic" becomes "data traffic"
An EGPRS TBF is served on a TRX which offers a higher throughput (i.e., a betterTRX class).In this case, "Signaling traffic" becomes "data traffic", and an EGPRS TBF is servedon a TRX which offers a higher throughput (i.e., a better TRX class).
T4 Move an uplink GPRS TBF sharing one PDCH with a downlink EGPRS TBF ontoPDCHs which do not support a downlink EGPRS TBF. When one PDCH is sharedbetween an uplink GPRS TBF and a downlink EGPRS TBF, the downlink EGPRS TBFis limited to GMSK (i.e., MCS4). Consequently, after a T4 re-allocation the downlinkEGPRS TBF is able to use 8-PSK (i.e., up to MCS9).
T4 re-allocation is not used with dual transfer mode mobile stations.
2.5.9 Dynamic Allocation
When an uplink TBF is established for a mobile station, the network provides tothe mobile station the list of the uplink PDCHs assigned for that TBF and the listof the USF identifiers of this TBF.
One unique USF is assigned per TBF per assigned PDCH. During the lifetimeof the TBF, the mobile listens to the downlink PDCHs corresponding toits uplink assigned PDCHs.
On one assigned PDCH, whenever the mobile station detects its USF (notethat in this example, there is only one TBF established per mobile station perdirection, i.e. that there is no “multiple TBF” feature), which means that it isallowed to transmit on the same uplink PDCH in the next Block Period.
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2.5.10 Extended Dynamic Allocation
The Extended Dynamic Allocation (EDA) is an extension of the basic DynamicAllocation (E)GPRS MAC mode to allow higher throughput in uplink for type 1mobile stations (supporting the feature) through the support of more than tworadio transmission timeslots.
With EDA mode, the mobile station detects an assigned USF value for anyassigned uplink PDCH and allows the mobile station to transmit on that PDCHand all higher numbered assigned PDCHs.
The mobile station does not need to monitor all the downlink PDCHcorresponding to its uplink PDCH allocated, which allows the type 1 mobilestation to support configurations with more uplink timeslots (and thereforewith less downlink timeslots).
The feature is mainly used only whenever the mobile station relies on itsown resources.
2.6 Traffic Load ManagementTraffic load conditions affect PDCH allocation, as described in CongestionControl (Section 2.6.2).
A PDCH can have one of four possible states, as shown in the following table.
State Explanation
Empty No established TBFs.
Active At least one established TBF and the total number of established TBFs is smallerthan a defined threshold (O&M parameter N_TBF_PER_SPDCH).
Busy The number of established TBFs is greater than or equal to O&M parameterN_TBF_PER_SPDCH but smaller than the maximum allowed (O&M parameterMAX_UL/DL_TBF_SPDCH).
Full The number of established TBFs is equal to the maximum set by O&M parameterMAX_UL/DL_TBF_SPDCH.
2.6.1 Smooth PDCH Traffic Adaption to Cell Load Variation
To avoid wasting GPRS traffic resources when entering a high load situation(with the ability to allocate GPRS traffic on multiple TRXs, the gap betweenMAX_PDCH and MAX_PDCH_HIGH_LOAD can be much bigger than in release B6.2),the BSC evaluates the total (circuit and packet-switched) traffic per cell andindicates the number of PDCHs that can be granted for GPRS traffic to the MFS.
The BSC notifies the MFS about any change in the number of available GPRSresources. Therefore, the GPRS traffic is constantly adapted to the actualtraffic situation in the cell.
The Load_EV_Period_GPRS parameter controls smooth PDCH trafficadaptation. It calculates the number of load samples (calculated everyTCH_INFO_PERIOD) for the PDCH traffic adaptation load averaging algorithm.
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2.6.2 Congestion Control
Capacity on demand allows operators to both reserve a number of PDCH forGPRS traffic and reserve other PDCH for shared traffic, according to the realtraffic load in the cell at any given moment. The actual GPRS traffic load isdynamically matched by allocating or de-allocating PDCH after negotiationbetween the MFS and the BSC.
The BSC is the master in the negotiation process, which means ifcircuit-switched traffic is heavy in a cell, there is no guarantee a GPRS mobilestation can establish a call. To ensure GPRS calls are possible at any time,the MIN_PDCH parameter can be set at the OMC-R to define the number ofPDCH permanently allocated to GPRS in a cell. Using this parameter to set theminimum number of PDCH allocated to GPRS traffic also sets the maximumnumber of radio timeslots allocated to circuit-switched traffic. For GPRS calls, itis also necessary to get an Ater resource. The function "fast GPRS access" (atleast one PDCH always established in a cell) fulfills this requirement.
2.6.3 M-EGCH Statistical Multiplexing
M-EGCH Statistical Multiplexing provides a means of sharing Ater and Abisnibbles between the radio timeslots of a TRX. With this feature, transmissionresources left available by a PDCH can be re-used by other PDCHs belongingto the same TRX. This avoids wasting transmission bandwidth on both the Aterand Abis interfaces.
The feature reduces the amount of GCH resources used, especially on the Ater.It multiplexes the blocks of all the PDCHs of a TRX on a single transmissionlink, the M-EGCH (Multiplexed-EGCH) link. This link is established between theMFS and the BTS. M-EGCH links are defined per TRX (instead of as a singleEGCH link per PDCH). This allows the (M)CS variations of the TBFs mappedon a TRX to compensate each other without requiring more transmissionresources. With M-EGCH statistical multiplexing, in the downlink, the TBF isselected first and then the PDCH.
For more information about the M-EGCH link, see The GCH Interface (Section2.3.3).
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2.6.4 GPRS Overload Control
To prevent traffic overload conditions, the SGSN and the BSS constantlyexchange traffic load information. This exchange of information, or flow control,regulates the downlink traffic between the SGSN and the BSS. The BSS sendsmobile station and BSSGP Virtual Connection radio status information to theSGSN, which then regulates the output traffic to the BSS when needed.
Flow control is therefore applied at two levels:
Mobile station, and
BVC.
Because more than one Network Service Virtual Connection can be usedbetween the BSS and the SGSN, the traffic load can be shared and smoothlydistributed over the Gb Interface. During data transfer uplink initialization, aNetwork Service Virtual Connection is selected and the uplink bandwidth isreserved. If a Network Service Virtual Connection is unavailable, traffic is thenput on another Network Service Virtual Connection. The reserved bandwidthon the Network Service Virtual Connection is released at the end of the transfer.Load sharing allows different data transfers within the same cell to be carriedby different Network Service Virtual Connection.
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2.7 Data TransmissionThis section describes the GPRS data transmission process, andexplains Attach/Detach procedures, Packet Data Protocol ContextActivation/De-activation, and mobile-originated and mobile-terminated datatransfer.
2.7.1 GPRS Attach
To access GPRS services, the mobile station performs a GPRS Attach orcombined GPRS/IMSI Attach to the SGSN. For more information about themobility feature IMSI Attach-Detach, see IMSI Attach-Detach (Section 3.3.5)).This procedure establishes a logical link between the mobile station and theSGSN, and allows the mobile station to be available for paging from the SGSNand notification of incoming GPRS data.
This is shown in the following figure.
MS BTS BSC MFS SGSN
Update Location
Subscriber
Data
SubscriberData ACK
Update
Location ACK
GPRS Attach Complete
HLR
GPRS Attach Request
Authentication
GPRS Attach Accept
HLR : Home Location Register
MFS : Multi-BSS Fast Packet Server
MS : Mobile Station
GPRS : General Packet Radio Service
SGSN : Serving GPRS Support Node
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In the GPRS Attach process:
1. The mobile station sends a GPRS Attach Request to the SGSN.Thisrequest contains:
The mobile station identity (IMSI or P_TMSI)
The mobile station Routing Area Identity
The type of Attach procedure requested (GPRS Attach, or combined
GPRS/IMSI Attach)
The mobile station classmark.
2. The SGSN verifies the mobile station identity, sends a location update tothe HLR, (if the attach requested is a combined GPRS/IMSI Attach, theMSC/VLR is also updated), and requests a subscriber data profile.
3. The HLR sends a location acknowledgment back to the SGSN with thesubscriber data inserted.
4. The SGSN then assigns a P_TMSI to the mobile station.
5. The mobile station acknowledges the P_TMSI, and the Attach procedureis complete.
Once the GPRS Attach procedure is performed, the mobile station is in Standbyand can activate Packet Data Protocol contexts.
2.7.2 Packet Data Protocol Context Activation
A Point-To-Point GPRS subscription contains one or more Packet Data Protocoladdresses. Each Packet Data Protocol address is defined by an individualPacket Data Protocol context in the mobile station, the SGSN, and the GGSN.Before a mobile station can send or receive data, a Packet Data Protocol contextmust be activated. Only the GGSN or a mobile station in Standby or Readycan activate Packet Data Protocol contexts. The process for mobile-stationoriginating activation and GGSN-originating activation are described separately.
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2.7.2.1 Mobile Station-Originating ActivationThe following figure illustrates Mobile Station-Originating Activation.
MS BTS BSC MFS SGSN
Activate PDP Context Request
Create PDP Context Request
Create PDP
Context Response
GGSN
Activate PDP Context Accept
GGSN : Gateway GPRS Support Node
MFS : Multi-BSS Fast Packet Server
MS : Mobile Station
PDP : Packet Data Protocol
SGSN : Serving GPRS Support Node
Figure 8: Mobile Station-Originating Packet Data Protocol Context Activation
For Mobile Station-originating Packet Data Protocol context activation:
1. The mobile station sends an Activation Request to the SGSN.This requestcontains:
Transaction Identifier
Packet Data Protocol type
Packet Data Protocol address
Access Point Name
Quality of Service requested
Packet Data Protocol configuration options.
2. The SGSN verifies the mobile station subscriber data, creates a TunnelIdentifier (TID - a logical bi-directional tunnel between the mobile station andthe GGSN), and sends the new Packet Data Protocol type and addressto the GGSN.
3. The GGSN creates a context, sends an acknowledgment to the SGSN,which sends an acknowledgment to the mobile station.
4. The GGSN can now send data through the SGSN, and billing begins.
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2.7.2.2 GGSN-Originating ActivationThe following figure shows the GGSN Packet Data Protocol context activationprocess.
MS BTS BSC MFS SGSN
Routing InfoACK
PDP PDU
HLR
PDU Notification Request
GGSN
Routing Info
Request
PDU Notification ResponseRequest PDP Context Acitvation
PDP Context Activation
GGSN : Gateway GPRS Support Node
HLR : Home Location Register
MFS : Multi-BSS Fast Packet Server
MS : Mobile Station
PDP : Packet Data Protocol
PDU : Protocol Data Unit
SGSN : Serving GPRS Support Node
Figure 9: GGSN-Originating Packet Data Protocol Context Activation
For GGSN-originating Packet Data Protocol context activation:
1. When the GGSN receives data, it sends a message to the HLR requestingthe mobile station location.
2. The HLR sends the GGSN location information and the current SGSN IPaddress.
3. The GGSN sends a PDU Notification Request to the SGSN, which indicatesthat a Packet Data Protocol context needs to be created.
4. The SGSN returns a PDU Notification Response to the GGSN, and sendsa Request Packet Data Protocol Context Activation message tothe mobile station. This message contains the Packet Data Protocol typeand address.
5. The mobile station then begins a Packet Data Protocol context activationprocedure as described above.
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2.7.3 Data Transfer
When the mobile has data to transfer through the network, data transferscan be mobile originated or mobile terminated. This section describes eachtransfer type.
2.7.3.1 Mobile-Originated Data TransferThe following figure illustrates the data transfer process when it is mobileoriginated.
MS BSS SGSN
Packet UL TBF
Assignment
Packet ChannelRequest
UL LLC PDU
RLC PDU
ACK/NACK
RLC PDU
RLC PDU
ACK/NACK
1
5
2
3
4
6
LLC : Logical Link Control
MS : Mobile Station
PDU : Protocol Data Unit
RLC : Radio Link Control
SGSN : Serving GPRS Support Node
TBF : Temporary Block Flow
UL : Uplink
When the mobile station has data to send:
1. An Uplink Temporary Block Flow is requested (either on the PRACH, if thereis a master PDCH, or on the RACH).
2. An Uplink Temporary Block Flow is established.
3. Data is sent to the network through the Radio Link Control Protocol DataUnits.
4. RLC PDUs are acknowledged by the network.
5. RLC PDUs are re-assembled into Logical Link Control PDUs and sentto the SGSN.
6. On receipt of the last RLC PDUs, an acknowledgment is returned and theUplink Temporary Block Flow is released.
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2.7.3.2 Mobile-Terminated Data TransferThe following figure illustrates the data transfer process when it is mobileterminated, that is, when the network originates the data transfer.
MS BSS SGSN
Paging PS
PPCH or PCH
Packet ChannelRequest
STAND BY
Packet UL TBF
Assignment
LLC PDU
UL − LLC PDU
READY
DL − LLC PDU
Packet DL TBF
Assignment
1
2
3
4
5
6
DL : Downlink
MS : Mobile Station
LLC : Logical Link Control
PCH : Paging Channel
PDU : Protocol Data Unit
PPCH : Packet Paging Channel
PS : Packet Switched
SGSN : Serving GPRS Support Node
TBF : Temporary Block Flow
UL : Uplink
When the network has data to send to the mobile:
1. The SGSN receives a downlink Packet Data Protocol PDU for a mobilestation, and sends a paging request to the BSS.
2. The BSS sends packet paging requests to all the cells in the routing area, onthe PPCH if there is a master PDCH in the cell, or on the PCH.
3. The mobile station requests the establishment of an uplink TBF from theBSS.
4. The uplink TBF is established, which allows the mobile station to senda Logical Link Control PDU to the SGSN in order to acknowledge thepaging message.
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5. The SGSN sends the data LLC-PDUs to the BSS.
6. The BSS establishes a Downlink TBF on receipt of the first LLC-PDU, andreleases after sending of the last LLC-PDU.
2.7.3.3 Delayed Downlink TBF ReleaseDelaying the release of downlink TBFs allows enhancement of the datathroughput served to mobile station end users. It also significantly reduces theGPRS signaling load. GPRS RLC/MAC procedures were designed for nonreal-time data transfer where the data arrives as one large block. However,the true nature of packet traffic is usually different from this assumption. Forexample, TCP-based applications often send small packets between peerentities before the actual data transfer starts. This leads to a high number ofTBF establishments and releases. Consequently, resource use is far fromoptimal and transmission delays unnecessarily long. The problem can beavoided by delaying TBF release for a short period (e.g., 0.5-2s) after thetransmission buffer becomes empty.
Delayed downlink TBF release can occur in either of the following modes:
Acknowledged ModeWhen the network wishes to delay the release of the TBF, it sends the lastRLC data block but does not set the Final Block Indicator (FBI) bit. Thenetwork only sets the FBI bit when it wishes to permanently end the TBF.Once the network has sent the RLC data block containing the last octets ofthe most recent LLC frame to the mobile station, the network maintains thedownlink TBF by occasionally sending dummy downlink RLC data blocks tothe mobile station, incrementing the BSN with each dummy data block sent.When the network receives a new LLC frame, it begins to transmit new RLCdata blocks to the mobile station, beginning with the next available BSN.When the network wishes to poll the mobile station for a Packet DownlinkAck/Nack when it has no LLC data to send, the network sends a dummydownlink RLC data block. The dummy downlink RLC data block is formed byinserting an LLC Dummy UI Command into a CS1 downlink RLC data block.The LLC Dummy UI Command is an invalid LLC-PDU and is discarded bythe LLC entity in the mobile station.
Unacknowledged Mode.In RLC unacknowledged mode, the mobile station detects the end of theTBF by detecting the Final Block Indicator (FBI) bit set to 1. The mobilestation then transmits a Packet Control Acknowledgement, acknowledgingthe end of the TBF. The procedure for delayed release of downlink TBFin RLC acknowledged mode applies except that no retransmission ofdata blocks is done.
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2.7.3.4 Extended Uplink TBF ModeIn normal TBF release, a countdown procedure is used to release the TBF.Once the countdown is started, PDUs received after the start of the countdowncannot be transmitted in the current TBF. A new TBF must be requestedand established, causing release and establishment delays. Extended ULTBF Mode avoids these delays and increase data throughput by extendingthe duration of an UL TBF. With Extended UL TBF Mode, the existing TBF ismaintained so data transmission can be quickly restarted without having tore-establish a new UL TBF even though the countdown has started.
Extended UL TBF Mode allows the network to initiate the sending of datato the MS without performing a DL TBF establishment on the CCHs. Withthis mode, the MS can send data from newly-arrived LLC frames after thecountdown procedure starts. In other words, the MS can restart an existingcountdown procedure when there is new data. In the delayed state, thenetwork occasionally allocates some radio blocks to the MS to see if the MShas data to transmit. But if radio resources are requested by the BSC andthis request involves the PDCH carrying the PACCH of the TBF, then T1allocation is performed. The re-allocated TBF keeps the same mode it hadbefore the re-allocation.
Extended UL TBF Mode is used whenever allowed by the MS capabilities. If anMS does not support Extended UL TBF Mode, the BSS uses the normal TBFrelease procedure. If the BSS does not know the MS capabilities at UL TBFestablishment, the BSS can switch to the new mode if the MS capabilities arereceived before the start of the UL TBF release procedure.
2.7.3.5 TBF Establishment Time ImprovementTBF Establishment Time Improvement reduces the TBF setting duration inthe following ways:
Downlink TBF establishment protocol alignment, reducing downlink TBFestablishment on PACCH by about 160 ms
Immediate uplink TBF establishment to avoid waiting for the establishment
of some GCHs before serving an incoming UL request. An UL TBF isestablished immediately if one of the TRXs of the cell already owns n
M-EGCH link
Downlink TBF extension is an enhancement of the delayed downlink TBFrelease feature (re-activation of the delayed downlink TBF release when an
uplink TBF is established)
Mobile station context handling (called Handling of mobile station
session/enhanced mobile station context in the System Features
Description) to keep mobile station characteristics as long as possible
Modification of Dummy UI command period when a concurrent uplink TBF is
ongoing (to avoid the 10% throughput waste in case of uplink FTP transfer).
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2.7.3.6 GPRS Fast AccessThe M-EGCH resource guarantees fast access in a cell when combined with theImmediate uplink TBF establishment feature (described in TBF EstablishmentTime Improvement (Section 2.7.3.5)). By implementing both features, the firstuplink TBF establishment in a cell is sped up by 300 to 400 ms.
Initial M-EGCH resource establishment, combined with the Immediate uplinkTBF establishment, optimizes TBF establishment times. Initial M-EGCHresource establishment guarantees that a first uplink TBF establishment requestin a cell is served immediately. It also guarantees the availability of minimumresources in a cell and speeds up the first uplink TBF establishment time.
This ensures that a given cell always has at least one established TRX (i.e., aTRX with an associated M-EGCH link) allowing the "Immediate uplink TBFestablishment" sub-feature to take full advantage of the initial reservationand perform well in all cases (except congestion). Additionally, with a highpacket-switched load, the blocking probability because of unavailable Aterresources is reduced.
A flag in the OMC-R is set to guarantee, or not, at least one established SlavePDCH in a given cell, usable for GPRS and EGPRS traffic.
The user chooses the best compromise between short access times andresource consumption. Typically, a user reserves terrestrial resources for denseurban cells, where there is often GPRS traffic, in order to minimize accesstimes. In rural areas, the user can chose to optimize the Ater consumption andnot reserve any terrestrial resources.
When disabled, no M-EGCH link is established by anticipation for a TRX ofthe cell. M-EGCH link establishment is done as soon as a TBF needs to beestablished. The Immediate uplink TBF establishment does not show itsbest performance.
When enabled, one TRX is established (i.e., one TRX of the cell has anassociated M-EGCH link) even without GPRS traffic. The number of GCHsto be established is indicated by N_GCH_FAST_PS_ACCESS. The need for TRXestablishment is evaluated at cell start, when EN_FAST_INITIAL_GPRS_ACCESS
is set from disabled to enabled. Accordingly, a TRX is then established or not.
A periodic background mechanism verifies every T_CANDIDATE_TBF_REALLOC
seconds that at least one TRX is established in the cell.
The EN_FAST_INITIAL_GPRS_ACCESS parameter is set according to overallsystem dimensioning. These initial resources are statically established andcannot be pre-empted for packing switching needs (intra-cell or inter-cellGCH pre-emption).
Note that for G2 DRFU BTS, a slave PDCH is established for GPRS fastaccess, since M-EGCH statistical multiplexing is not supported in DRFU BTS.
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2.7.3.7 GSM-to-UMTS Cell ReselectionThe three 3G-neighbor frequencies are set at cell level, enabling networkoperators to declare different 3G neighborhoods per GSM cell. The PacketSystem Information is updated in order to lighten mobile station processing,and de-activates 3G measurements when the mobile station switches fromPBCCH to circuit-switched dedicated mode. A new feature, Improved 3G CellReselection is implemented to further reduce MS processing time.
This feature contains the following improvements for broadcasting 3G FDDneighboring cell information:
3G neighboring cell information broadcast in the SI2quarter messageSending this information in an SI2quarter message allows the MS to receiveand refresh its knowledge of 3G neighboring cells more quickly. SI2quartermessages are sent on the Extended BCCH, if enabled. Otherwise they aresent on the BCCH.
3G neighboring cell information instantiated at GSM cell levelThis improves 3G cell detection by the MS as only frequencies which arereally covered are broadcast. In addition to the 3G search parameters,instantiation includes the 3G local cell ID.
Complete 3G neighboring cell description broadcastWhen enabled, the cell description includes the Primary Scrambling codesand the diversity parameter of the neighboring 3G cells, in addition to theUTRAN frequencies. The operator can define the 3G cell so that when ascrambling code is changed in that 3G cell, the code is also changed in allservicing cells with an adjacent link to the 3G cell.
UTRAN frequencies instantiated at BSS levelTo enable operators to keep their existing 3G cell planning, the UTRANfrequencies can be instantiated at the BSS level instead of at cell level.However, only one instantiation level is allowed. Therefore, the operatormust choose either BSS level or cell level.
Alcatel-Lucent BTS support these improvements.
The 3G search de-activation ensures that no 2G-to-3G cell reselection istriggered when the mobile station is in Packet Transfer mode.
If NC2 or NC0 is activated, the mobile station cannot perform a cell reselectiontowards 3G or measure 3G signal strength during the transfer. The mobilestation stops receiving the declared 3G frequencies as soon as it receives thePacket Measurement Order message, ceasing the search for 3G cells whenin Packet Transfer mode.
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2.7.3.8 MAC AlgorithmThe following rules apply for MAC algorithm scheduling:
TBFs are ordered in queues
The TBF is selected, then a PDCH for this TBF
TBF round robin and PDCH round robin per TBF
Each time a TBF gets a block/USF scheduled on a PDCH, it is movedat the end of the queue
A TBF which cannot get a block/USF scheduled remains at the sameposition in the queue
RT TBFs are scheduled according to their credit, then NRT TBFs are
scheduled
Credit management for RT TBFs (decrease, reset)
Extra scheduling of RT TBFs
TDM mode: scheduling of TBFs according to available MEGCH capacity
(both in DL and in UL)
T_MAX_FOR_TBF_SCHEDULING timer in RLC
The weight, a parameter to control scheduling of NRT TBFs: no more
absolute scheduling of NRT TBFs
Reduce the number of TBF queues in MAC 5 queues instead of 16 queuesfor QoS (P0 to P15)
P0 for PNCD/PSCD messages
P1 for GMM signalling
P2: not used
RT (GBR traffic): note that this is not really real time traffic as there is no
constraint on the transfer delay to the mobile
NRT TBF: all NRT TBS in the same queue whatever the priority P4 to P15
Extra scheduling now applies to NRT TBFs also (with a small change inRT TBF extra scheduling)
DL and UL TBFs are put in the same queue: no more separate scheduling
processes for the DL, then the UL TBFs
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GPRS faulty management: no DL Dummy TBF created for UL GPRS TBF
The following rules now apply during the TBFs scheduling in each RT andNRT queue:
A DL EGPRS block (whatever the MCS) can be scheduled on a PDCH if
and only if there is no UL GPRS USF already scheduled or reservedblock on this PDCH in this 20 ms period
An UL GPRS USF can be scheduled on a PDCH if and only if no DLEGPRS block is scheduled on this PDCH in this 20 ms period
A PDDCB can be sent on a PDCH with an UL GPRS USF but no useful
DL CS block.
The main principles of MAC algorithm are as follows:
For any DL or UL TBF, RT or NRT TBF, there are 2 scheduling phases:
The basic scheduling for which the credit or weight of the TBF must be
greater or equal to the basic_scheduling_limit (current assumption =1)
The extra scheduling for TBFs which credit or weight can be below the
basic_scheduling_limit
This leads to 4 scheduling phases for TBFs:
RT basic scheduling
NRT basic scheduling
RT extra scheduling credit of RT TBF is decreased by 1 when scheduled
in this phase
NRT extra scheduling
A basic scheduling phase stops:
Either when all resources (radio & transmission) are consumed
Or when all the RT (resp. NRT) TBFs have a credit (resp. weight) <
scheduling_limit
Or when no RT (resp. NRT) TBF is schedulable anymore (e.g their
(M)CS is higher than the available transmission resources)
The scheduling of P0 to P2 TBF is not restricted by any credit nor weight(i.e still absolute).
The following principles concerning the enhanced PDDCB solution apply:
All NRT UL and NRT DL TBFs are managed in the same TBF queue, which
leads to the TBF round robin applied between DL TBF and UL TBF
All the RT UL and RT DL TBFs are managed in another common TBF queue
No need to insert virtual dummy DL TBF for the UL GPRS TBF.
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Weight management for NRT TBF:
The current_weight is initialized to the init_weight when the TBF is activated
(or re-activated)
The current_weight is decreased by 1 each time the corresponding TBFis scheduled on one PDCH, unless the current_weight has reached the
minimum limit
The current_weight is set to null when an UL NRT TBF enters the extendedmode or when a DL TBF enters the delayed mode
Reset of current_weight" means the following:current_weight = MIN(current_weight + init_weight, maximum_credit_weight)
Reset of DL NRT TBFs and UL NRT TBFs weights performed independently:
reset of DL current_weights is performed when all the conditions areverified for DL NRT TBFs, even if the conditions are not satisfied for UL
NRT TBFs; and vice versa
Reset conditions are checked at the beginning of every 20 ms period (e.g totake into account the status change of a NRT TBF that may occur after the
scheduling in the previous block period).
2.7.4 Packet Data Protocol Context De-activation
Before a GPRS Detach procedure can be initiated, the Packet Data Protocolcontext must be de-activated. The de-activation can be done by the mobilestation or by the network.
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2.7.4.1 Mobile-Originating De-activationThe following figure illustrates this process.
MS BTS BSC MFS SGSN
De−Activate PDP Context Request
Delete PDPContext Request
Delete PDP
Context Response
GGSN
De−Activate PDP Context Accept
1
2
34
GGSN : Gateway GPRS Support Node
MFS : Multi-BSS Fast Packet Server
MS : Mobile Station
PDP : Packet Data Protocol
SGSN : Serving GPRS Support Node
Figure 10: Mobile-Originating Packet Data Protocol Context De-activation
For Mobile-originating Packet Data Protocol context de-activation:
1. The mobile station sends a De-activate Packet Data Protocol ContextRequest to the SGSN.
2. The SGSN sends a Delete Packet Data Protocol Context Request to theGGSN, which contains the TID.
3. The GGSN deletes the Packet Data Protocol context, and sends a DeletePacket Data Protocol Context Response with the de-activated TID to theSGSN.
4. The SGSN sends a De-activate Packet Data Protocol Context
Accept message to the mobile station, confirming the de-activation.
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2.7.4.2 SGSN-Originating De-activationThe following figure shows the network-originated Packet Data Protocol contextde-activation processes.
MS BTS BSC MFS SGSN
Delete PDPContext Request
Delete PDP
Context Response
GGSN
De−Activate PDP Context Request
SGSN−Originating
De−Activate PDP Context Accept
GGSN−OriginatingDelete PDP
Context Request
De−Activate PDP Context Request
De−Activate PDP Context Accept
Delete PDPContext Response
1
2
3
4
1
2
3
4
GGSN : Gateway GPRS Support Node
MFS : Multi-BSS Fast Packet Server
MS : Mobile Station
PDP : Packet Data Protocol
SGSN : Serving GPRS Support Node
Figure 11: Network-Originating Packet Data Protocol Context De-activation Processes
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For network-originated Packet Data Protocol context de-activation processes:
1. The SGSN sends a Delete Packet Data Protocol Context Request to theGGSN, which contains the TID.
2. The GGSN de-activates the Packet Data Protocol context and sends aDelete Packet Data Protocol Context Response to the SGSN.
3. The SGSN sends a De-activate Packet Data Protocol Context Request tothe mobile station.
4. The mobile station de-activates the context, and returns a De-activatePacket Data Protocol Context Accept.
2.7.4.3 GGSN-Originating De-activationFor GGSN-originating de-activation:
1. The GGSN sends a Delete Packet Data Protocol Context request to theSGSN, which contains the TID.
2. The SGSN sends a De-activate Packet Data Protocol Context Request tothe mobile station.
3. The mobile station de-activates the context and returns a De-activatePacket Data Protocol Context Accept.
4. The SGSN sends a Delete Packet Data Protocol Context Response to theGGSN, which deletes the context.
Figure 11 shows this process.
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2.7.5 GPRS Suspend
The following figure shows the GPRS suspend processes.
MS BTS BSC MFS SGSN
RR Suspend
Suspend
Suspend
Suspend Ack
Suspend Ack
T3
1
2
3
4
5
MFS : Multi-BSS Fast Packet Server
SGSN : Serving GPRS Support Node
For the GPRS Suspend process:
1. The mobile station sends an RR Suspend (TLLI, RAI, suspension cause)message to the BSC. This is sent as soon as possible after entering thededicated mode. If the GPRS suspension procedure was initiated during aGPRS transfer, the mobile station releases all its GPRS resources.
2. The BSC sends a Suspend (TLLI, RAI, suspension cause) message to theMFS, via the GSL link. The BSC stores TLLI and RAI in order to be ableto request the SGSN (via the MFS) to resume GPRS services when themobile station leaves dedicated mode. A timer is not necessary to monitorthe Suspend Ack reception. If this acknowledgment is not received (i.e., noSuspend Reference Number (SRN) reception, see step 4), the Resume willnot be sent at circuit-switched call completion.
3. The MFS sends a Suspend (TLLI, RAI) message to the SGSN.
4. The MFS receives aSuspend Ack from the SGSN, in which there is aSuspend Reference Number which is used in the GPRS resume process.The acknowledgment of the SGSN is supervised by a timer (T3).
5. The MFS sends a suspend acknowledgment to the BSC, with the SuspendReference Number information.
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2.7.6 GPRS Resume
The following figures shows the GPRS resume processes.
MS BTS BSC MFS SGSN
Resume
Resume
Resume Ack
Resume Ack
T4
RR Channel Release
T_GPRS_Resume
1
2
3
5
4
6
MFS : Multi-BSS Fast Packet Server
MS : Mobile Station
RR : Radio Resource
SGSN : Serving GPRS Support Node
For the GPRS Resume process:
1. The BSC determines that the circuit-switched radio channel must bereleased (typically upon circuit-switched call completion). If the BSC is ableto request the SGSN to resume GPRS services (i.e., the suspend proceduresucceeded and the BSC received the Suspend Reference Number, andno external handover has occurred), the BSC sends a Resume (TLLI, RAI,Suspend Reference Number) message to the MFS. After sending theResume message, the BSC starts a guard timer (T_GPRS_Resume) andwaits for a Resume Ack message from the MFS. The guard timer is set asshort as possible, so as to be compatible with the usual RR connectionrelease procedure, and therefore not delay the procedure. However, thismessage is not sent in the case of successful completion of an externalhandover. In this case, the BSC deletes any stored data or suspend/resumecontext related to that mobile station.
2. On receipt of a Resume message from the BSC, the MFS sends a Resume
(TLLI, RAI, Suspend Reference Number) message to the SGSN, starts aguard timer (T4) and waits for a Resume Ack message from the SGSN.
3. The MFS receives a Resume Ack from the SGSN.
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4. On receipt of the Resume Ack from the SGSN, the MFS stops the guardtimer (T4) and sends a Resume Ack message to the BSC. If no Resume
Ack is received from the SGSN before expiry of the guard timer (T4), theMFS sends a Resume Nack to the BSC. On receipt of the Resume Ack orResume Nack message from the MFS, the BSC stops the guard timer(T_GPRS_Resume).
5. The BSC sends an RR Channel Release (GPRS Resumption) messageto the mobile station and deletes its suspend/resume context. GPRSResumption indicates whether the BSS has successfully requested theSGSN to resume GPRS services for the mobile station, (i.e., whether theResume Ack was received in the BSS before the RR Channel Release
message was transmitted). The mobile station then exits dedicated mode.If the guard timer expired, or if a Resume Nack message was received bythe BSC, the Channel Release message includes the GPRS Resumptionindication equal to NOK.
6. The mobile station resumes GPRS services by sending a Routing Area
Update Request message in the following cases:
Reception of a Channel Release with GPRS Resumption = NOK
Reception of a Channel Release without GPRS Resumption IE
T3240 expiry.
2.7.7 GPRS Detach
After the Packet Data Protocol Context is de-activated, the mobile station or thenetwork can perform a GPRS Detach procedure.
Whether the detach is initiated by the mobile station or the network, the resultsare the same:
The mobile station leaves the Ready mode and enters the Idle mode
All Packet Data Protocol contexts are deleted
The mobile station returns to the circuit-switched system.
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2.7.7.1 Mobile Station-Originating DetachThe following figure illustrates this process.
MS BTS BSC MFS SGSN
Delete PDPContext Request
Delete PDP
Context Response
GGSN
GPRS Detach Accept
Detach Request
1
2
3
4
GGSN : Gateway GPRS Support Node
MFS : Multi-BSS Fast Packet Server
MS : Mobile Station
PDP : Packet Data Protocol
SGSN : Serving GPRS Support Node
For the Mobile-originating GPRS Detach processes:
1. The mobile station sends a GPRS Detach Request to the SGSN. Thismessage contains:
The type of Detach (GPRS or GPRS/IMSI)
An indication if the Detach is due to a mobile station switch off.
2. The SGSN tells the GGSN to de-activate the Packet Data Protocol context.
3. The GGSN responds to the SGSN with a message that it has de-activatedthe Packet Data Protocol context.
4. The SGSN sends a Detach Accept message to the mobile station.
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2.7.7.2 Network-Originating DetachThe following figure shows the Network-originating GPRS Detach procedures.
MS BTS BSC MFS SGSN
Delete PDPContext Request
GGSN HLR
GPRS Detach Request
Cancel Location
Delete PDP
Context Response
Detach Accept
Cancel Location ACK
1
12
3
2
4
GGSN : Gateway GPRS Support Node
HLR : Home Location Register
MFS : Multi-BSS Fast Packet Server
MS : Mobile Station
PDP : Packet Data Protocol
SGSN : Serving GPRS Support Node
A GPRS Detach can be initiated by both the SGSN and the HLR.
An SGSN Detach is the most common network Detach.
In this procedure:
1. The SGSN sends a Detach Request to the mobile station, which containsthe Detach type. The Detach type tells the mobile station if it needs tore-attach and re-activate the Packet Data Protocol context previously used.
2. The SGSN tells the GGSN to de-activate the Packet Data Protocol contexts.
3. The GGSN responds to the SGSN with a message that it has de-activatedthe Packet Data Protocol context.
4. The mobile station sends the Detach Accept message to the SGSN.
If the Detach is requested by the HLR:
1. The HLR sends a Cancel Location message to the SGSN, which initiatesthe above process.
2. The SGSN confirms the Packet Data Protocol context deletion by sending aCancel Location Acknowledgment to the HLR.
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2.8 Location Services
2.8.1 Introduction
Location Services (LCS) provide mobile station geographical location (i.e.,longitude, latitude). LCS is applicable to any target mobile station whetheror not the mobile station supports LCS, but with restrictions on positioningmethod when LCS or individual positioning methods are not supported bythe mobile station.
LCS clients make requests to the PLMN LCS server for location informationabout one or several target MSs with a set of parameters such as LCS ClientType, LCS Priority, LCS Quality of Service (QoS), which includes requestedposition accuracy and allowed response time. LCS clients reside in an entity(including the mobile station) within the PLMN or in an entity external to thePLMN. The target mobile station is positioned by the LCS. Depending on thepositioning techniques, some LCS functions reside in the mobile station.
LCS in the packet-switched domain is not supported.
Network Measurements Results (NMR) are not supported with LCS.
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2.8.2 Logical Architecture
LCS Services support requires new network elements in the networksubsystem and optionally, depending on positioning techniques and networksynchronization, on the radio side.
These network elements are:
Gateway Mobile Location Center (GMLC)
Serving Mobile Location Center (SMLC).
MFS
BTS
BTS BSC
CBC
SMLC
MSC
SGSN
LSN1 LSN2
A Interface
Gs Interface
LbInterface HLR
GMLC
Router A−GPSserver
SAGI
Gb Interface
Lg
Lg
LCS Client
LhMS
BTS(LMU Type B)
LMUType A
As depicted in the above figure:
The GMLC is the first network element for external Location Application
(LA) access in a GSM PLMN. The GMLC requests routing information fromthe HLR via the Lh Interface. After performing registration authorization, it
sends positioning requests to the MSC or to the SGSN and receives finallocation estimates from the MSC or the SGSN via the Lg Interface
The SMLC is the network element serving the mobile station. The SMLC
manages the overall co-ordination and scheduling of resources required toperform positioning of a mobile station. It also calculates the final location
estimate and accuracy. The SMLC controls to obtain radio Interfacemeasurements enabling mobile station location in the service area. The
SMLC is connected to the BSS (via the Lb Interface). It dialogs with otherSMLCs (via the Lp Interface) to obtain measurements managed by another
SMLC when the mobile station is at the border of the SMLC-covered area.
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2.8.3 LCS Positioning Methods
In LCS, the SMLC, a functional network element in the BSS, is integrated in theMFS and is configured by the OMC-R, if the MFS also provides the GPRSservices to several BSCs. The SMLC performs locations services for this set ofBSCs. Location requests are received on the A Interface from the NSS.
The LCS uses an Alcatel-Lucent proprietary interface, BSCLP, for signalingprotocol between the BSC and the SMLC.
LCS supports the following positioning methods:
TA Positioning
Conventional GPS Positioning
Assisted GPS (A-GPS) Positioning.
2.8.3.1 TA PositioningTA Positioning delivers Cell ID, Timing Advance, and, optionally, MeasurementReport information to the SMLC. TA Positioning regroups several distinctmethods, depending on the availability and the relevance of the elementaryinformation:
The Time Advance (TA)
Cell Id (CI), only in omnidirectional cells, the geographic co-ordinates of the
BTS is returned instead of the real mobile station position. The TA value isused to determine the region as a circle or a ring
Cell Id + Timing Advance (CI+TA).
With the TA positioning method, no signaling exchange is required between theSMLC and the mobile station. The TA positioning applies to all mobile stations,whether they support LCS or not.
2.8.3.2 Conventional GPS PositioningConventional GPS Positioning is based on the GPS location estimateperformed in the mobile station and provided to the SMLC.
2.8.3.3 Assisted GPS (A-GPS) PositioningAssisted GPS (A-GPS) Positioning is split into Mobile Station-Assisted A-GPSand Mobile Station-Based A-GPS positioning methods, depending on wherethe location calculation is processed: in the network or in the mobile station.
For Mobile Station-Assisted A-GPS, the mobile station receives GPS AssistanceData from the SMLC, performs GPS measurements and returns the GPSmeasurements to the SMLC. The SMLC provides these GPS measurements tothe external GPS server, which computes the mobile station location estimate.
For Mobile Station-Based A-GPS, the mobile station receives GPS AssistanceData from the SMLC, performs GPS measurements and location calculation,and returns its location estimate to the SMLC.
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2.8.4 LCS Scenario in Circuit-Switched Domain
In the circuit-switched domain, an LCS scenario is as follows:
1. An external LCS Client requests the current location of a target mobilestation.
2. This request is handled by the GMLC, which verifies the LCS Client identityand authorizations, and determines the MSC of the target mobile station.
3. The MSC receives the location request containing the type of locationinformation requested (current location, assistance data for the mobilestation), the mobile station subscriber’s IMSI, LCS QoS information(accuracy, response time). In idle mode, the MSC performs circuit-switchedpaging, authentication and ciphering to establish an SDCCH with the mobilestation. The mobile station subscriber is only aware of circuit-switchedpaging when a GPRS mobile station in Packet Transfer Mode suspendsGPRS traffic to answer circuit-switched paging.
4. When the mobile station is in dedicated mode (after a specific SDCCHestablishment for location, or during an ongoing call), the MSC sends thelocation request to the BSC in the existing SCCP connection for the currentcall, which forwards it to the SMLC.
5. The SMLC chooses a positioning method and triggers the appropriateprocedure to locate the mobile station. Some message exchanges takeplace between the SMLC and the BSC.
6. The MSC then sends a response to the GMLC. The LCS-related messagesexchanged between the BSC and the MFS are conveyed through currentGSLs (same SAPI as for GPRS-related messages).
2.8.5 Physical Implementation
The GPU software supports both GPRS and SMLC, and is handled as a whole.For a BSC connected to several GPUs, the SMLC is supported by the pilotGPU (the pilot GPU is the GPU handling procedures at the BSS level). Whenthe pilot GPU is reselected, the SMLC function restarts on the new pilot GPU.The LCS-related configuration data is downloaded from the control station tothe new pilot GPU. The former pilot GPU clears all the LCS-related telecomcontexts as well as the LCS-related configuration data.
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2.8.6 SMLC Functions
The SMLC performs the following functions:
Handles LCS protocols towards the BSC and the mobile station, and
towards the external GPS server
Manages call-related location context per mobile station
Selects a positioning method
Triggers the position calculation process for the TA positioning method and
presents the location estimate of the mobile station in a standard format.For Conventional GPS or Mobile Station-Based A-GPS, the calculation is
performed in the mobile station
Requests and receives GPS Assistance Data destined for the mobile
station, when Mobile Station-Assisted and Mobile Station-Based A-GPS
Provides GPS measurements performed by the mobile station to theexternal GPS server, for Mobile Station Assisted A-GPS, to retrieve the
mobile station location estimate
Uses O&M information present in the MFS or SMLC, provided by the OMC-R
Handles errors.
2.8.7 BSS and Cell Configuration
LCS is an optional feature of the Alcatel-Lucent BSS. It can be blocked by themanufacturer, and enabled or disabled by the operator at the OMC-R level.For LCS cell support, the user activates LCS on the BSS handling this cell,and also activates GPRS for this cell. For example, setting MAX_PDCH toa value greater than zero is mandatory; the cell is locked for GPRS if theoperator does not want GPRS running on this cell. The user configures therequired transmission resources (Ater and Gb resources) on the GPU(s)connected to this BSC.
The O&M characteristics of the serving cell are:
Enabled LCS positioning method in the cell
Preferred GPS method when several GPS methods are candidates for the
location procedure
Configuration data availability
SMLC and GPS server interface state.
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2.8.8 LCS O&M
The OMC-R provides LCS centralized management.
Two alarms are used:
An alarm indicating the concerned LSN.
This alarm’s attributes are:
alarm label: "GPS server not reachable through LSN"
alarm type: communicationsAlarm
probable cause: lan error
perceived severity: minor.
An alarm with the following attributes:
alarm label: "GPS server not reachable"
alarm type: QoS
probable cause: underlying resource unavailable
specific problem: alarmId translation, component translation (identifying
Fabric)
perceived severity: major.
The user correlates this information with the current router state and withthe Ethernet links state between GPUs and hubs.
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2.9 High Speed Data Service
2.9.1 HSDS Description
High Speed Data Service (HSDS) supports CS1 to CS4 in GPRS and supportsEGPRS with MCS1 to MCS9. The coding scheme and the radio modulationare modified to increase the data traffic throughput of a given radio timeslot,resulting in an increase of throughput on the Abis and Ater interfaces.
On the Ater Interface, several Ater nibbles are allocated dynamically by MFStelecom to handle throughput higher than 16kbit/s
On the Abis Interface, a group of 16k nibbles is associated with each radio
timeslot. Depending on the coding scheme or the MCS, from one to five 16kchannels are necessary per PDCH between the MFS and the BTS.
The following table explains HSDS terminology.
Term Explanation
M-EGCH Set of n-associated multiplexed 16k channels used to transport PS traffic.There is one M-EGCH per TRX (and not per PDCH).
GCH Any of the n 16k channels composing an M-EGCH.
Nibble 16k channel.
Basic Abis nibble 16k Abis channel either used for circuit-switched or packet-switched traffic.
Extra Abis nibble 16k Abis channel exclusively used for packet-switched traffic.
PS capable TRX TRX which can be used for packet-switched traffic, at least for GPRS traffic,characterized by TRX_Pref_Mark = 0.
8-PSK capable TRX TRX which is EGPRS capable and with n > 1. At least two GCHs arenecessary for 8-PSK (MCS5).
TRX class n For a TRX class n, the MFS will use n GCHs to establish one M-EGCH.
TRX EGPRS capability Possibility for the TRX to support EGPRS or not and if it is able to supportEGPRS, its maximum MCS.
Established TRX The corresponding radio and transmission resources are allocated and thecorresponding M-EGCH is activated.
Allocated PDCH The corresponding radio resource is allocated by the BSC, but no associatedAter resources are allocated.
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2.9.2 GPRS CS3/CS4 and EGPRS Protocol
2.9.2.1 EGPRSFor HSDS, EGPRS enables data transmission support at a bit rate exceedingGPRS capabilities and uses new modulation and coding schemes on the AirInterface. Data throughput is optimized in concordance with radio propagationconditions (Link Adaptation).
2.9.2.2 Modulation and Coding SchemesNine modulation and coding schemes enhance packet data communications(EGPRS), providing raw RLC data rates ranging from 8.8 kbit/s (minimum valueper timeslot, under the worst radio propagation conditions) up to 59.2 kbit/s(maximum value achievable per timeslot under the best radio propagationconditions). Data rates above 17.6 kbit/s require that 8-PSK modulation areused on the A Interface, instead of GMSK.
Link adaptation changes Modulation and Coding Schemes (MCS) according toradio conditions. When radio conditions worsen, a protected MCS with moreredundancy is chosen, leading to a lower throughput. Inversely, when radioconditions improve, a less protected MCS (less redundancy) is chosen forhigher throughput.
The following table describes the three families of coding schemes and theirunit payloads.
This Family... Contains... Payload Unit
Family A MCS3, MCS6 and MCS9 37 bytes
Family A padding MCS3+padding, MCS6+padding and MCS8 34 bytes
Family B MCS2, MCS5 and MCS7 28 bytes
Family C MCS1 and MCS4 22 bytes
When a block is retransmitted with a given MCS, it can be retransmitted (ifneeded) via ARQ with a more robust MCS of the same family.
Two selective ARQ mechanisms are used for the transfer of EGPRS RLC datablocks in the acknowledged RLC/MAC mode:
Type I ARQ mechanismWith this mechanism, when a RLC data block is retransmitted, the same oranother MCS from the same family is selected.
Type II ARQ mechanism (also called Incremental Redundancy (IR)In this case, a different "puncturing scheme" is applied to the same MCS, ifan error is detected.IR and re-segmentation are activated on a per cell basis.
Note: Ensure that the two features are not activated at the same time.
Four Coding Schemes are used for GPRS (CS1 to CS4).
GPRS and EGPRS signaling always uses CS1.
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MCS1 to MCS4 are based on GMSK modulation, while MCS5 to MCS9 arebased on 8-PSK modulation. The Alcatel-Lucent BSS supports MCS5-MCS9 inboth the uplink and the downlink direction.
Coding Scheme Modulation Maximum rate [kbps]per radio timeslotbasis
MCS9 8-PSK 59.2
MCS8 8-PSK 54.4
MCS7 8-PSK 44.8
MCS6 8-PSK 29.6
MCS5 8-PSK 22.4
MCS4 GMSK 17.6
MCS3 GMSK 14.8
MCS2 GMSK 11.2
MCS1 GMSK 8.8
CS4 GMSK 21.55 (UL)
20 (DL)
CS3 GMSK 15.75 (UL)
14.4 (DL)
CS2 GMSK 13.455 (UL)
12 (DL)
CS1 GMSK 9.2 (UL)
8 (DL)
2.9.2.3 Mobile Station Multislot Class HandlingWith GPRS/EGPRS, an GPRS/EGPRS mobile station multislot class isintroduced.
The multislot classes 30-33 are considered for GPRS and EGPRS:
PTM (Packet Transfer Mode): 30-33 classes mobile
DTM (Dual Transfer Mode): 31-32 classes mobile. Class 33 terminals are
supported as MS class 32 in DTM mode.
The available throughputs are:
In PTM mode: Up to 5 DL PDCHS instead of 4 (5 + 1 vs 4 + 1)
In DTM mode: Up to 3 DL PDCHs instead of 2 (4 + 2 vs 3 + 2).
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2.9.2.4 Incremental Redundancy in ULWith EGPRS, performance in terms of maximum user throughput decreasesquickly when the distance between the MS and the antenna increases. Thismeans that for the end user the quality of service depends on the positionof the MS relative to the antenna. Therefore, it is important to improve themaximum user throughput under these conditions. By improving the decodingperformances of the BTS with EGPRS, incremental redundancy increase themaximum user throughput in the uplink, particularly when the MS is far from theantenna. This is especially useful when the MS is at the border of to cells.
Incremental redundancy uses a type II hybrid ARQ mechanism and is onlyused with EPGRS data blocks sent in RLC acknowledge mode, using MCS1 toMCS9. Incremental redundancy is not used with RLC unacknowledged mode.
Incremental redundancy is based on the reception of RLC data blocks codedwith different puncturing schemes. This lets the BTS enhance the decoding ofthe data blocks using soft combining. By taking into account the erroneousRLC data blocks and combining them with the retransmitted data blocks, theBTS increases the probability of decoding the blocks correctly. This reducesthe number of times the BTS uses a slower coding scheme compared tosituations where incremental redundancy is not used. As a result, the averagethroughput is increased.
The BTS supports incremental redundancy with RLC data blocks transmittedwith the same MCS and with data blocks retransmitted with the followingMCS combinations:
MCS7 / MCS5
MCS9 / MCS6
MCS8 / MCS6 with padding.
Incremental redundancy is enabled / disabled with the Enable_IR_UL
parameter. By default, the feature is disabled.
2.9.3 Transmission Handling
The following sections describe transmission handling.
2.9.3.1 TRX Hardware Configuration ManagementThe Abis timeslots are connected to the TCUs through the BIUA. TheBTS connects each radio timeslot to one Abis nibble. All the nibbles forcircuit-switched traffic (basic nibbles) for a given TRE are connected to thesame TCU.
The extra 16k nibbles are connected to any TSU TCU carrying the primaryAbis, or any TSU TCU carrying the secondary Abis.
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2.9.3.2 Logical Configuration Management and TRX/RSL MappingIn standard configurations, TRXs are mapped to TREs using the currentalgorithm.
After mapping, the following adjustment occurs:
TREs are classified according to their packet switching capability and FullRate/Dual Rate usage, from the highest to the lowest priority: from G4 High
Power Full Rate, G4 High Power Dual Rate, G4 Medium Power Full Rate,G4 Medium Power Dual Rate, Alcatel-Lucent 9100 Full Rate, and finally
to Alcatel-Lucent 9100 Dual Rate
If PS_Pref_BCCH_TRX = True (i.e., the BCCH TRX has the highest priority forPS traffic), the TRX with BCCH is mapped to the highest priority TRE
TRXs with TRX_Pref_Mark = 0 are mapped to the TREs with the highest
priority, beginning with the TRXs which have the biggest PDCH-group size.
2.9.3.3 TRX RankingThe BSC determines the ranking of packet switch capable TRXs forcircuit-switched and packet-switched calls to ensure consistent allocation. Bythis ranking, the TRXs selected first by the BSC for circuit-switched calls arethose selected last by the MFS for packet-switched calls.
Packet switch capable TRXs are ranked according to the following criteria, fromthe highest to the lowest:
TRX supporting the BCCH, if PS_Pref_BCCH_TRX = True
TRX capability (G4 High Power, then G4 Medium Power, and then
Alcatel-Lucent 9100)
Dual Rate capability (Full Rate TRXs have a higher priority than DualRate TRXs)
The number of radio timeslots available for PS traffic.
Circuit switch only TRXs are not provided to the MFS.
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2.9.3.4 Connection of Extra Abis Nibbles to TREs in the BTSExtra Abis nibbles are connected to the BTS TREs as follows, enabling a givenradio timeslot to be connected to n nibbles overall in the BTS:
1. The BSC informs the BTS via the OML of the static mapping of each extra16k nibble on the Abis to each TRX.
2. The BSC groups extra Abis nibbles so that 8 x (n-1) extra Abis nibblesare mapped on BTS, on top of the already-mapped basic Abis nibbles( n = 1 to 5).
3. Extra Abis timeslots are only mapped on a TCU supporting TRE Full Rate.A Dual Rate TCU does not support extra Abis TS. The same constraintexists between Full Rate TRE and Dual Rate TRE as between Extra Abistimeslot and Dual Rate TRE.
4. To perform Full Rate TRE or extra Abis timeslot extension, the operatortriggers a compact reshuffling to group all Dual Rate TRE to free TCU forFull Rate TRE or extra Abis timeslot.
2.9.3.5 Second Abis LinkWhen there are insufficient Abis timeslots on one Abis link, a second Abiscan be attached to the BTS.
In this case, the OML, RSL, and basic timeslots are always mapped to the firstlink and extra timeslots for the TRX transmission pools are split over the twoAbis links and the second Abis link supports extra 16k nibbles for packet traffic.
This link does not carry circuit-switched traffic and cannot cross-connect onthe secondary Abis.
Only Alcatel-Lucent BTS with SUMA boards or Alcatel-Lucent 9110-E supportthe second Abis link. Alcatel-Lucent BTS with SUMP boards must be upgraded.
An Alcatel-Lucent BTS can manage two termination points. It is thereforeimpossible to do the following:
Connect a BTS in chain after a BTS with two Abis
Change the Abis from chain to ring if there is a BTS with two Abis
Attach a second Abis to a BTS that is not at the end of an Abis chain
Attach a second Abis to a BTS that is in an Abis ring.
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2.9.3.6 Transmission PowerThe three types of transmission power are:
GMSK Output PowerThe BTS sets all TRE transmit GMSK output power to the same level, theminimum value among the maximum TRE output power in a sector and ina given band.
8-PSK Output PowerFor one given TRE, the maximum output power is lower in 8-PSK thanin GMSK because of the 8-PSK modulation envelope which requires aquasi-linear amplification. The TRE transmit power in 8-PSK does notexceed the GMSK transmit power in the sector and in the band. In 8-PSK,the applicable leveling aligns, when necessary, the 8-PSK transmit power tothe GMSK transmit power in the sector and in the band.
Modulation Delta Power.The Modulation Delta Power is the difference between the GMSK outputpower of the sector for the TRE band and the 8-PSK output power ofthe TRE.8-PSK High Power Capability is true if Modulation Delta Power is less than 3dB, else it is an 8-PSK Medium Power Capability type TRE.
2.9.4 Cell/GPU Mapping Modification
The algorithm which maps the cells on the GPUs takes into account the numberof extra Abis nibbles allocated per TRX. This avoids all cells having staticGCHs, mapped on the same GPU and thus limits the risk of Ater blocking.
The cell/GPU mapping process includes:
A new parameter (Nb_Extra_Abis_TS) per cell to the MFS in order to steer
the cell - GPU mapping. Nb_Extra_Abis_TS is the number of auxiliary 64kchannels in the TRX Transmission pools of the cell
The number of GCHs used by the initial PDCH, when
En_Fast_Initial_GPRS_Access = True
One GCH, if Nb_Extra_Abis_TS = 0
Two GCHs, if Nb_Extra_Abis_TS differs from 0.
After a change of pools configuration, the cell is "misaligned" and the operatormust resynchronize the MFS.
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2.10 Gb over IPWith the introduction of GBoIP, the telecom traffic, towards/from the SGSN,goes through the router from/in the MFS.
The following rules apply
For an 9130 Evolution MFS:
O&M one LAN:O&M/Telecom flows are using the same IP interface. This is the defaulttopology.O&M/Telecom flows use a different IP interface.
O&M two LAN:The case of a same IP interface used for O&M/Telecom flows is notsupported.The case of different IP interfaces used for O&M/Telecom flows isnot recommended.
For an 9135 MFS:
O&M one LAN:O&M/Telecom flows use the same IP interface. This is the nominal case.O&M/Telecom flows use a different IP interface.
O&M two LAN:Not applicable.
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3 Call Set Up
3 Call Set Up
This section provides an overview of how a call is set up between the NSS andthe mobile station. It describes the various kinds of calls that can be set up. Italso describes the type of teleservice and bearer service required.
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3.1 OverviewCall set up is required to establish communication between a mobile stationand the NSS. The NSS is responsible for establishing the connection with thecorrespondent. Different types of calls require different teleservices. Theseteleservices are defined in the GSM specifications. The type of teleserviceand bearer service to be used is negotiated before the normal assignmentprocedure. See Normal Assignment (Section 3.2.3) for more information.
3.1.1 Call Types
The following table shows the three basic types of call.
Type of Call Description
Mobility Management Calls These calls, e.g., location update, are used bythe system to gather mobile station information.The exchanges are protocol messages only;therefore, only a signaling channel is used.Figure 3 illustrates the location updateprocedure.
Service Calls These calls, e.g., SMS and SS calls, passsmall amounts of information. Therefore, onlya signaling channel is used.
User Traffic Calls These calls, e.g., speech or data calls to acorrespondent, can pass large amounts ofinformation. Therefore they require greaterbandwidth than a signaling channel. Thesecalls use traffic channels.
The channels used for calls are the SDCCH for signaling (static SDCCH), fortraffic and signaling (dynamic SDCCH), and the traffic channel for user traffic(see The Air Interface (Section 1.7.9) for more information). These channelsare associated with FACCH/SACCH. An SDCCH is always assigned for call setup, even if a traffic channel is later required for the call.
The role of the BSS in call set up is to assign the correct channel for thecall, and to provide and manage a communications path between the mobilestation and the MSC.
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3.1.2 Call Set Up Phases
The following table shows the phases involved in call set up.
Phase Composition
Radio and LinkEstablishment
Paging (for mobile-terminated calls only) informs the mobile station that it is beingcalled.
If attach_detach_allowed is activated, the mobile station IMSI_detach messagecan eliminate the need for paging. See IMSI Attach-Detach (Section 3.3.5).
The immediate assignment procedure allocates a resource to the mobile stationand establishes a Radio Signaling Link between the BSS and the mobile station.
A Interface connection, to assign an SCCP signaling channel between the BSCand MSC
Assignment of a switching path through the BSC.
Authentication andCiphering
Classmark handling.
Authentication.
Ciphering.
Normal assignment Teleservice/bearer service negotiation.
Channel allocation.
Physical context procedure.
Traffic channel assignment, if required.
Call connection.
For more information about the phases, refer to:
Mobile-Originated Call (Section 3.2)
Mobile-Terminated Call (Section 3.3).
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3.2 Mobile-Originated CallA call initiated by a mobile station can either be a subscriber call, wherespeech and/or data is passed across the network, or a location update callfrom a mobile station in idle mode. Location update information is passedon the signaling connection. Therefore, the initial call set up procedure issimilar to a subscriber call. The location update does not require allocationof a traffic channel.
3.2.1 Radio and Link Establishment
When a connection with a mobile station is required, the following must happen:
A radio channel must be assigned to permit communication between the
mobile station and the BSS
A terrestrial link must be established in order to signal the presence of
the mobile station to the network.
The procedure for obtaining these initial connections is called radio and linkestablishment.
The radio and link establishment procedure establishes signaling links between:
The BSS and the mobile station via the SDCCH channel
The BSS and the MSC via the SCCP link.
These links pass the information for call negotiation, and set up a trafficchannel, if required.
Figure 12 shows radio and link establishment for a mobile-originated call.
Note: A VGCS call initiated by a mobile station uses the same general call set upprocedures as a standard mobile call; any exceptions are described in therelevant procedure descriptions below.
3.2.1.1 Channel RequestThe mobile station initiates a call by sending a Channel_Request message,with an REF. The REF includes an establishment cause and a RAND (used forauthentication). It is transmitted on the RACH channel. The RACH channelis associated with the CCCH channel which the mobile station is monitoringwhile in idle mode.
The establishment cause field of the REF specifies:
An emergency call
Call re-establishment
Response to paging
Mobile station-originating speech call
Mobile station-originating data call
Location update
Service call (SMS, etc.).
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The mobile station notes the random number and frame number associatedwith each Channel_Request message. These are used by the mobile station torecognize the response sent from the BSS. This response is sent on the AGCH,which can be monitored by many mobile stations. The mobile station decodesall messages sent on this AGCH, and only accepts a message with a randomnumber and frame number matching one of the last three requests sent.
MS BTS BSC MSC
SDCCHAllocation
Switch toSDCCH
REF stored in MS memory
Service Request must match original sent by MS in the SABM
MS compares message with REF in memory
Channel Request (RACH)REFChannel RequiredREF+RFN+TA
Channel Activation
TA+SDCCH+power
Channel Activation Ack
Immediate assign command
TA+SDCCH+power+RFN+REF
Immediate assignment (AGCH)
REF+RFN+TA+SDCCH
SABM+ cm + Service Request
UA
Service Request
Establish Indicationcm + Service Request
SCCP Connection Requestcm + Service Request
SCCP Connection Confirm
cm : Classmark
ID : Mobile Station identity
power : Mobile Station power or BTS power
REF : Random access information value
RFN : Reduced frame number
SDCCH : Description of the allocated SDCCH (Standalone Dedicated Control Channel)
ServiceRequest
: Initial Layer 3 message
TA : Timing advance
UA : Unnumbered acknowledgment
Figure 12: Radio and Link Establishment for Mobile-Originated Call
The mobile station continues to transmit Channel_Request messages until itreceives a response.
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If no response is received before the mobile station has transmitted apredefined number of retries, the mobile station:
Displays a network error message for all calls except location updates
Performs automatic reselection for location update calls. This means thatthe mobile station attempts random access on a different cell.
On receipt of the Channel_Request message from the mobile station, the BTSsends a Channel_Required message to the BSC. This message contains therandom number sent by the mobile station, and the timing advance measuredby the BTS.
Note: Under peak load conditions, resources may be over allocated due to thisprocess. See below for details on how the Immediate Assignment Extendedfeature works to alleviate this problem.
In order to establish a radio connection on a VGCH between a mobilestation which is in group receive mode on that channel and theBTS, the mobile station sends an Uplink_Access message with theSubsequent_Talker_Uplink_Request parameter on the voice group callchannel. The Uplink_Access message is similar to a Channel_Request
message but is sent only on the group call channel uplink.
The mobile station sends an Uplink_Access message when:
A subsequent talker uplink is requiredThe BTS performs any necessary contention resolution and grants theuplink to one mobile station by sending a VGCS_Uplink_Grant messageto the mobile station in unacknowledged mode on the main signallinglink. The BSS sends Uplink_Busy messages on the main signalling linkin all cells of the group call area.
There is a reply to an uplink access request.
Note: For emergency VGCS calls, the Channel_Request message contains theEmergency_VGCS_Channel_Request parameter, which indicates that thefast call set up procedure should be initiated. See Immediate Assignment(Section 3.2.1.3).
3.2.1.2 SDCCH Channel ActivationThe BSC checks the Channel_Required message to ensure it can accept therequest. It allocates an SDCCH channel if one is available. The resourcemanagement software of the BSC allocates the SDCCH on the basis of whichtraffic channel has the most available SDCCHs. This ensures the load isspread between the traffic channels.
The BSC then sends a Channel_Activation message to the BTS. It alsosets a timer to wait for an acknowledgment from the BTS, indicating thatit is ready to activate the channel.
The Channel_Activation message contains:
A description of the SDCCH to be used
The timing advance
Mobile station and BTS power commands. The mobile station and BTS
power are set to the maximum allowed in the cell.
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The BTS initiates the physical layer resources for the channel and sets theLAPDm contention resolution ready for the first mobile station message on theSDCCH. It then sends a Channel_Activation_acknowledgment message tothe BSC. The BSC stops its guard timer.
Note: Contention resolution prevents two mobile stations connecting to the sameSDCCH.
The following figure shows the Channel Activation procedure.
MS BTS BSC MSC
SDCCHAllocation
Channel Activation Ack
Channel Activation
TA+SDCCH+power
power : Mobile Station power or BTS power
SDCCH : Description of the allocated SDCCH (Standalone Dedicated Control Channel)
TA : Timing advance
For emergency VGCS calls, the immediate call set up procedure is used. If theO&M flag En_FAST_VGCS_SETUP is set to "disabled", when the BSC receivesthe Emergency_VGCS_Channel_Request message, it ignores the message.If the O&M flag En_FAST_VGCS_SETUP is set to "enabled", when the BSCreceives the Emergency_VGCS_Channel_Request message, it allocates theSDCCH. Once the SDCCH is established, the mobile station uses it to send anImmediate_Set_Up message to core network (this message is transparentfor the BSS).
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3.2.1.3 Immediate AssignmentThe BSC builds and sends an Immediate_Assign_Command message repeatingthe information given in the Channel_Activation message. This messagealso includes the random number and frame number of the original mobilestation request to which the BSC is replying. It also instructs the BTS to informthe mobile station of the SDCCH channel assignment. The BSC starts a guardtimer for the mobile station to respond.
The following figure shows the Immediate Assignment procedure.
MS BTS BSC MSC
Switch toSDCCH
Immediate assignment (AGCH)
REF+RFN+TA+SDCCH
Immediate assign command
TA+SDCCH+power+REF+RFN
REF : Random access information value
RFN : Reduced frame number
SDCCH : Description of the allocated SDCCH (Standalone Dedicated Control Channel)
TA : Timing advance
The BTS sends the Immediate_Assignment message to the mobile stationon the AGCH.
The mobile station checks the random number and frame number in theImmediate_Assignment message. If it matches those from one of its lastthree Channel_Request messages, the mobile station switches to theindicated SDCCH and sets its timing advance to the value indicated in theImmediate_Assignment message.
When a mobile station requires an emergency VGCS call, it sends anImmediate_Setup message. When the BSC receives this message, it sendsa SCCP_Connection_Request message to establish the dedicated SCCPconnection. The user data field of this message contains the Immediate_Setup
message.
The call is then set up as for a standard voice and/or data calland a SCCP_connection_confirm message is sent, containing theAssignment_Request message in the user field.
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3.2.1.4 Immediate Assignment RejectWhen there is congestion on the SDCCH, the mobile station could retryrepeatedly without success to access a channel.
This produces the following undesired effects:
Undesirable messages on the mobile station screen
The subscriber has to restart his call attempt manually
Repeated futile attempts to connect overload the RACH and Abis Interface
"Ping-pong" cell reselection by the mobile station.
Therefore, the system implements a special Immediate_Assignment_Rejectmessage when the following conditions are met:
The BSC flag EN_IM_ASS_REJ is set to true. This flag is set on a BSC basis,and can be viewed but not modified from the OMC-R
All SDCCHs in the cell are busy
The BSC receives a Channel_Required message from the BTS with one ofthe following establishment causes:
Emergency call
Call re-establishment
Mobile station-originating call
Location update
Service Calls.
The Immediate_Assignment_Reject message is contained in the informationelement of the Immediate_Assign_Command message. This message starts atimer in the mobile station which causes it to wait in idle mode until the timerexpires, before sending new Channel_Request messages. The length of thetimer is dependent upon the establishment cause, and can be set by the user.
If an Immediate_Assign_Command message is received before expirationof the timer, it has priority and the mobile station will respond to it, therebyconnecting the call.
Note: This message cannot be used when the mobile station is responding to paging,i.e., in the case of a mobile-terminated call.
For VGCS emergency calls, when all SDCCH sub-channels in the cell arebusy, the BSC sends an Immediate_Assignment_Reject message with"Wait Indication" corresponding to the GSM timer T3122, the value of whichdepends on the establishment cause in the Channel_Required message. Thecorresponding value for T3122 is usually equal to 2 seconds (which is thesame value as for the establishment cause "emergency call" for the normal apoint-to-point call).
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3.2.1.5 Immediate Assignment ExtendedUnder peak load conditions, it is likely that the mobile station will send severalChannel_Request messages before receiving an Immediate_Assignment
message indicating that a channel is allocated to it. At this stage, the BSCis unable to identify the mobile station which sent a given Channel_Request
and so it will grant several SDCCHs to the same mobile station, thus wastingresources and reducing throughput on the AGCH.
If several Immediate_Assignment messages are queued on the AGCH, theBTS will try to build an Immediate_Assignment_Extended message, passedto the mobile station on the Air Interface, constructed from pieces of twoImmediate_Assignment messages as follows:
The first Immediate_Assignment message in the queue (i.e., the oldest)
The first of the remaining Immediate_Assignment messages in the queue,which are able to be merged according to one of the following criteria:
At least one of the two allocated channels is non-hopping
If both allocated channels are hopping, they share the same MobileAllocation (see Baseband Frequency Hopping (Section 4.3.1) for more
information about Mobile Allocation).
If there are several Immediate_Assignment messages in the AGCH queue,but the first one cannot be merged with any other in the queue (using theabove criteria), a "classic" Immediate_Assignment message is sent on the AirInterface.
3.2.1.6 Set Asynchronous Balanced ModeThe first Layer 2 frame sent on the SDCCH is a standard LAPDm type frame,known as the Set Asynchronous Balanced Mode. This is equivalent to theSet Asynchronous Balanced Mode Extended frame in the LAPD. On the AirInterface, it establishes the LAPDm connection with the BTS. This framecan also contain Layer 3 messages.
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3.2.1.7 Contention ResolutionThe mobile station starts its LAPDm connection and sends a Layer 3 messagein its first frame. The BTS uses this message for contention resolution. TheBTS sends an acknowledgment to the mobile station containing the sameLayer 3 message. Therefore, only the mobile station that sent the message canaccept the acknowledgment from the BTS and consider itself connected.
The following figure shows the establishment of the connection for a mobileoriginated call.
MS BTS BSC MSC
SABM+ cm + Service Request
UA
Service Request
Establish Indicationcm + Service Request
SCCP Connection Requestcm + Service Request
SCCP Connection Confirm
cm : Classmark
ServiceRequest
: Initial Layer 3 message including the mobile station identity and classmark
UA : Unnumbered acknowledgment
Figure 13: Connection for Mobile-Originated Call
For a mobile-originated call, the Layer 3 message from the mobile stationcontains:
An Information Element indicating:
CM service request (speech/data, SMS, emergency call)
Location updating request (location updating procedure)
CM re-establishment request (after a failure)
IMSI detach indication (mobile station power off - see IMSI Attach-Detach
(Section 3.3.5) for more information).
The mobile station identity (see Authentication (Section 3.7) for moreinformation)
The mobile station classmark (see Classmark Handling (Section 3.6) for
more information).
The network uses this message to decide which call negotiation procedures arerequired and whether to assign a traffic channel.
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For VGCS calls, the BSS considers that there are three levels of contentionresolution:
At cell levelThe BTS immediately sends a VGCS_Uplink_Grant message as soonas it receives the first correctly decoded Uplink_Access message.Further Uplink_Access messages are ignored. The BTS sends only oneTalker_Detection message to the BSC.
At BSC levelThe BSC sends an Uplink_Busy message to all BTS (except the BTS thatsent the first Talker_Detection message) in the BSC area involved inthe VGCS call as soon as the BSC receives the first Talker_Detectionmessage, in order to prevent too many incoming Talker_Detection
messages.If another BTS receives an Uplink_Access message between thetime the Talker_Detection message was received by the BSC andan Uplink_Busy message was received by other BTS, then the BSCmanages a queue with an initial fixed size of 5. If the queue is full (the sixthTalker_Detection message is received), an Uplink_Release message isimmediately sent to the respective BTS.The BSC sends an Uplink_Release message after the firstTalker_Detection message is received from any of the BTS.An Uplink_Release message is sent to all the BTS that have aTalker_Detection message in the queue (possibly 0 to 4), with theexception of the first BTS which sent the Talker_Detection message. TheBSC then sends an Uplink_Request_Confirmation message to the MSC.
At the network levelIf uplink requests have been made by more than one BSC, the contentionresolution is performed by the MSC.
3.2.1.8 Establish IndicationThe BTS sends an Establish_Indication message to the BSC to indicatethat the mobile station has connected. The BSC stops the guard timer, extractsthe classmark information, and initiates an SCCP connection with the MSC.
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3.2.1.9 SCCP ConnectionFor standard calls:
The BSC sends an SCCP_Connection_Request message to the MSC
The MSC replies with an SCCP_Connection_Confirm message. This
message can contain a classmark request or a cipher mode command.
The signaling link is established between the mobile station and the MSC.
For VGCS calls:
The MSC sends a SCCP_Connection_Request message to the BSC
establish the VGCS call controlling SCCP connection. The user data field ofthis message contains the VGCS/VBS_Setup message
When the BSC receives the SCCP_Connection_Request containing the
VGCS/VBS_Setup , it allocates the necessary resources for the requestedcall.
The BSC then sends a SCCP_Connection_Confirm message to the MSC.
The user data field of this message contains the VGCS/VBS_Setup_Ack
message.
Note: When a mobile station makes an emergency VGCS call, it sends anImmediate_Setup message. When the BSC receives this message, it sendsa SCCP_Connection_Request message to establish the dedicated SCCPconnection. The user data field of this message contains the Immediate_Setup
message.
3.2.2 Authentication and Ciphering
The content of the classmark IE sent during radio and link establishmentdepends on the type of mobile station. The classmark information is used formobile station power control and to set ciphering. The MSC can request aclassmark update to ensure that it has the correct information. Classmarkprocedures are described in Classmark Handling (Section 3.6).
The authentication procedure:
Authenticates the mobile station identity
Checks the mobile station has the correct Individual Subscriber
Authentication Key value on the SIM for the ciphering procedure
Sends the Random Number for the ciphering and authentication procedures.
For more information about this procedure, refer to Authentication (Section 3.7).
Information passed on the Air Interface must be protected. The MSC canrequest that the BSS set the ciphering mode before information is passed onthe SDCCH. Ciphering is described in Ciphering (Section 3.8).
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3.2.3 Normal Assignment
Figure 14 shows the normal assignment process for a mobile originated call.
Once the Radio and Link Establishment procedure is successfully completed,the mobile station has a signaling link with the network. If the call requires atraffic channel to communicate with a called party, the mobile station sends asetup message. This indicates the teleservice and bearer service required,and the called party number. The information is sent transparently through theBSS. This message can contain more than one bearer service element, anda parameter indicating that the subscriber may request a change of service(In-Call Modification) during the call. See In-Call Modification (Section 4.2)for more information.
The MSC sends a Call_Proceeding message to the mobile station. Thisindicates that the call parameters have been received, and that attempts toestablish communication with the called party are under way.
3.2.3.1 Channel RequestThe MSC initiates the assignment of the traffic channel by sending theAssignment_Request message and sets a timer to supervise the responsefrom the BSC.
The BSC checks the message which must contain a channel type (for a trafficchannel this is speech or data plus data rate). This message also containsthe mobile station classmark which the BSC uses if it has not received theclassmark from the mobile station.
The Assignment_Request message may contain a codec list, giving, in order ofpreferences, the type of codec it prefers to use (for example, one that supportsenhanced full-rate speech). In this case, the BSC checks the list against thosesupported by the cell, and chooses the preferred codec type that can be usedby both the BTS and by the mobile station.
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If the BSC finds an error in the Assignment_Request message, it sends anassignment_failure message. If no error is detected, it starts the normalassignment procedure towards the mobile station.
MS BTS BSC MSC
SetTranscoder
ReleaseSDCCH
TCHallocation
Set switchingPath
Initiate SDCCHRelease
set up (SDCCH)
tele/bearer servicecalled party no.
layer 3 CC
layer 3 CC
layer 3 CC layer 3 CC call proceeding
assignment request
channel type+cm
physical context request
physical context confirm
power + TA
channel activation
TCH + TA + cipher
+ DTX + power
channel activation acknowledge
assignment command
assignment command (SDCCH)
establish indication
SABM (FACCH)
UA (FACCH)
assignment complete (FACCH)
assignment complete
connect acknowledgement
layer 3 CC
layer 3 CC
layer 3 CC
layer 3 CC
layer 3 CC
alerting
connect
(SACCH)
TA + power updates
+ sys info 5 e 6
cipher : Encryption algorithm + ciphering key
cm : Classmark
DTX : Discontinuous transmission flags
TA : Timing advance
Figure 14: Normal Assignment for Mobile-Originated Call
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3.2.3.2 Traffic Channel AllocationThe BSC ensures that it is not running any other procedures for the mobilestation and then allocates resources for the traffic channel. The resourcesallocated are calculated using an algorithm in the BSC. The BSC can receivean Assignment_Request message in various situations.
Therefore, it has traffic channel resource allocation algorithms for:
Normal assignment
In-call modification
Intercell handover
Intracell handover
Directed retry
Concentric cells
Microcells.
In normal conditions (mobile-originated call, normal assignment), the normalassignment algorithm is used. The BSC keeps a table of idle channels in whichthe channels are classified by their interference level (1 = low, 5 = high).
The interference level of all free channels is monitored by the BTS. Thisinformation is periodically sent to the BSC in the RF_resource_indication
message. The BSC does not automatically allocate a channel from the lowestinterference level, as a number of channels can be reserved for handover.After all reserved channels are accounted for, the channel allocated is fromthe lowest interference level. If the number of reserved channels exceedsthe number of free channels, then the BSC allocates a channel from thehighest interference level. If no channels are available, the BSC sends anassignment_failure message to the MSC indicating the cause of the failure.
3.2.3.3 TCH Allocation for VGCSA channel used for VGCS is referred to as VGCH. A VGCH is simply a normalTCH timeslot that is used for VGCS. One VGCH channel is allocated by theBSS in each cell involved in a VGCS call. If the MSC asks the BSC forimmediate allocation of a VGCH, allocation is performed just after the VGCSsetup procedure and is based on the Resource Controlling SCCP connectionassociated with the VGCH.
For VGCS calls, the BSS can allocate one VGCH for each cell involvedin the VGCS.
If immediate allocation of a VGCH is required (for example, for an emergencycall), then VGCS allocation is performed immediately after call set up, and isbased on the Resource Controlling SCCP connection associated with theVGCH.
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3.2.3.4 Traffic Channel ActivationThe BSC sends a Physical_Context_Request message to the BTS, to findout the current power and timing advance being used by the mobile station onthe SDCCH. The BTS responds with a Physical_Context_Confirm message,containing the relevant information. If no channel is available, and queuing isenabled, the call is placed in the queue. Refer to Congestion (Section 3.5)for more information about queuing.
The following figure shows the channel activation process for the traffic channel.
MS BTS BSC MSC
TCHallocation
physical context confirm
power + TA
physical context request
channel activation
TCH + TA + cipher
+ DTX + power(SACCH)
TA + power updates
+ sys info 5 & 6channel activation acknowledge
assignment command
assignment command (SDCCH)
cipher : Encryption algorithm + ciphering key
DTX : Discontinuous transmission flags
MS : Mobile Station
TA : Timing advance
TCH : Traffic Channel
The BSC sends a Channel_Activation message to the BTS.
This contains:
A description of the traffic channel to be used
The mobile station timing advance to be applied
The encryption algorithm and ciphering key (same as for SDCCH
assignment)
A Discontinuous Transmission indicator for uplink (not used) and downlink(see Speech Transmission (Section 4.4) for more information)
The mobile station power to be used (see Radio Power Control (Section
4.5) for more information)
The BTS power to be used.
The BSC starts a timer, and waits for the BTS to acknowledge that it hasactivated the channel.
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The BTS initializes its resources for the traffic channel, sets the cipheringmode, sends timing advance and power information to the mobile stationon the SACCH associated with the traffic channel, which is constantlymonitored by the mobile station. At the same time, the BTS sends aChannel_Activation_Acknowledgment message to the BSC. The BSC stopsits timer and sends an Assignment_Command message on the SDCCH to themobile station. This instructs the mobile station to change to the traffic channel.
When the mobile station receives the Assignment_Command message, itdisconnects the physical layer, and performs a local release to free the LAPDmconnection of the SDCCH.
For VGCS calls, when the BSC receives aChannel_Activation_Acknowledgment message from the BTS, the BSCsends a VGCS_Assignment_Result message.
3.2.3.5 Traffic Channel AssignmentThe following figure shows the channel assignment process for the trafficchannel.
MS BTS BSC MSC
SetTranscoder
ReleaseSDCCH
Set SwitchingPath
SABM (FACCH)
UA (FACCH)
assignment complete (FACCH)
establish indication
assignment complete
FACCH : Fast Associated Control Channel
MS : Mobile Station
SABM : Set Asynchronous Balanced Mode
UA : Unnumbered Acknowledgment
The mobile station then establishes the LAPDm connection (via the SABM onthe FACCH) for the traffic channel. The BTS sends an Establish_Indication
message to the BSC. It also sets the Transcoder and its radio link failuredetection algorithm. The BTS sends a Layer 2 acknowledgment to the mobilestation. The mobile station sends an Assignment_Complete message tothe BSC.
When the BSC receives the Establish_Indication message, it establishesa switching path between the allocated Abis and A Interface resources.When it receives the Assignment_Complete message, it sends anAssignment_Complete message to the MSC and initiates release of theSDCCH (see Call Handling for more information).
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For VGCS, a dedicated TCH is allocated:
To the first calling mobile station
To subsequent calling mobile stations
To listening mobile stations moving into a cell where a VGCH has notbeen allocated.
3.2.3.6 Connecting the CallOnce communication with the called party is established (but before the call isanswered), the MSC sends an alerting message to the mobile station. Themobile station generates a ring tone.
When the called party answers, the MSC sends a connect message to themobile station. The mobile station responds with a connect_acknowledgment
message. The call is established.
The following figure shows the call connection process for a mobile originatedcall.
MS BTS BSC MSC
initiate SDCCHrelease
connect acknowledgement
layer 3 CC
layer 3 CC
layer 3 CC
layer 3 CC
layer 3 CC
alerting
connect
MS : Mobile Station
SDCCH : Standalone Dedicated Control Channel
3.2.3.7 Off Air Call Set UpOff Air Call Set Up (OACSU) is a method available in the BSS whereby thenetwork assigns a traffic channel only when the called party has answered thecall. This improves the efficiency of traffic channel allocation as unsuccessfulcalls will not take up any traffic channel resources. This feature is controlled bythe MSC.
The Layer 3 alerting message is sent by the MSC just after theCall_Proceeding message. The mobile station then enters the ringing phase.The Assignment_Request message is not sent by the MSC until the calledparty answers. The rest of the Layer 3 exchanges between MSC and BSC takeplace after the mobile station sends the Assignment_Complete message tothe MSC.
When OACSU is in use, the mobile station may provide internally generatedtones to the user (in a Mobile-Originated call) during the ringing phase, as thetraffic channel is not yet available for tones or in-band announcements to besent.
This feature increases the probability of an internal (SDCCH-to-SDCCH)handover being initiated by the BSS while the Normal Assignment procedure isbeing initiated by the MSC.
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3.3 Mobile-Terminated CallA call from the NSS to a mobile station can be either a call routed throughthe NSS from a calling party, or it can be initiated by the NSS for mobilitymanagement.
A mobile-terminated call set up follows the same basic procedures as amobile-originated call. This section describes only those procedures whichare different. The following figure shows radio and link establishment fora mobile-terminated call.
MS BTS BSC MSC
channel request(RACH)
paging request(PCH)
TMSI/IMSI
paging command
TMSI/IMSI paging group +
channel number
paging
TMSI/IMSI + cell list
channel required
IMSI : International Mobile Subscriber Identity
MS : Mobile Station
PCH : Paging Channel
RACH : Random Access Channel
TMSI : Temporary Mobile Subscriber Identity
Figure 15: Radio and Link Establishment for Mobile-Terminated Call
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3.3.1 Radio and Link Establishment
Before the BSS sets up a signaling link, the mobile station has to be paged.This procedure is initiated by the MSC. It sends a paging message to the BSCcontrolling the location area from which the mobile station last performeda location update.
This message is sent in connectionless mode and contains:
The mobile station identity (TMSI or IMSI of the mobile station to be paged)
A cell identifier list which identifies the cells where the paging request is tobe sent. This could be all cells or a group of cells.
The MSC sets a timer to wait for a Paging_Response message from themobile station.
The BSC checks the Paging message and, if valid, calculates the mobilestation paging group and the CCCH timeslot for the paging group.
The BSC sends a Paging_Command message to each BTS, indicating the TMSIor IMSI, the paging group and the channel number.
Each BTS formats the information and broadcasts a Paging_Request messageon the Paging Channel.
The mobile station listens to messages sent to its paging group. Whenit receives a paging message with its mobile station identity, it sends aChannel_Request message on the RACH to the BTS, indicating that therequest is in response to a Paging_Request message.
The BSS then performs the radio and link establishment procedure describedin Mobile-Originated Call (Section 3.2).
Note: When the mobile station sends the SABM, it indicates that the connection isin response to a paging request. For more information about paging, seePaging (Section 3.4).
3.3.2 Authentication and Ciphering
The system handles authentication and ciphering for a mobile-terminated callin the same manner as a mobile-originated call.
For more information, refer to:
Authentication and Ciphering (Section 3.2.2)
Classmark Handling (Section 3.6)
Authentication (Section 3.7)
Ciphering (Section 3.8).
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3.3.3 Normal Assignment
The normal assignment procedure for a mobile-terminated call is initiated bythe MSC. This is shown in the figure below.
The MSC sends a Layer 3 Call Control Set_Up message to the mobile station,indicating the bearer service and teleservice to be used for the call. The MSCcan indicate more than one bearer service.
The mobile station checks this message. If it can accept the call, it sends aCall_Confirmation message which can contain a bearer capability parameterindicating which bearer service is preferred.
The BSS performs the physical context and channel assignment. This isdescribed in Normal Assignment (Section 3.2.3). Once the traffic channelis assigned, the mobile station alerts the user and sends an Alerting
message to the MSC. When the mobile station user answers, the mobilestation sends a Connection message to the MSC. The MSC sends aConnection_Acknowledgment message to the mobile station and connectsthe call.
All these messages are Layer 3 Call Control messages, and are transparent tothe BSS.
MS BTS BSC MSC
ringtone
useranswer
call confirmed (SDCCH)
layer 3 CC
bearer service
layer 3 CC
set up
layer 3 CC
layer 3 CC
tele/bearer service
alerting
layer 3 CC
layer 3 CC
connect
layer 3 CC
layer 3 CC
layer 3 CC
layer 3 CC
connect acknowledge
MS : Mobile Station
SDCCH : Standalone Dedicated Control Channel
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3.3.4 Off Air Call Set Up
If Off Air Call Set Up (OACSU) is in use, it is possible that at one moment thecalled party may have answered the call, but the traffic channel is still notassigned by the network (for example, the call is queued). In this case, themobile station may supply tones to the answering user, so that the user doesnot hang up before the Normal Assignment procedure completes.
3.3.5 IMSI Attach-Detach
IMSI Attach-Detach is a mobility feature which primarily concerns the MSCand the mobile station. Used together with the periodic location updateprocedure, IMSI Attach-Detach allows the network to provide more efficientcontrol and use of resources.
For example, if a mobile-terminated call arrives for a mobile station which is"detached", the MSC knows that the mobile station is not active and does notneed to start a paging request. For the BSS, this can reduce load on the PCH.
Initiation of the IMSI Attach-Detach procedure is controlled by a parameterin the BSS, Attach_Detach_Allowed. When this parameter is set, the BSSbroadcasts system information on all cells indicating that the network supportsIMSI Attach-Detach.
Mobile stations which have successfully connected and logged themselvesonto the network are then obliged to perform IMSI Attach-Detach procedures.
Refer to documentation supplied with mobile stations which support thisfunction.
For more information about the Attach_Detach_Allowed parameter, see the9153 OMC-R Configuration Handbook.
IMSI Attach-Detach is also used for other functions at the MSC. Refer todocumentation for your network’s MSC equipment.
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3.4 PagingPaging is the procedure by which the network contacts a mobile station. Forexample, if the network needs to inform the mobile station of an incoming call, itpages the mobile station to prompt it to request a channel. After the immediateassignment procedure, the Service_Request message from the mobile stationindicates that the connection is in response to a paging message.
Paging messages are sent on the CCCH. The downlink CCCH carries theAGCH and the PCH.
The PCH is divided into sub-channels, each corresponding to a paging group.To save the mobile station from monitoring every occurrence of the PCH,each mobile station is assigned a paging group calculated from the IMSI.Each mobile station calculates its paging group and monitors only that PCHsub-channel. This saves mobile station battery power.
The number of paging groups and the CCCH organization varies for eachconfiguration. The mobile station knows the CCCH organization from theinformation passed on the BCCH (sys_info 3).
The AGCH sends the Immediate_Assignment message to the mobile station.A number of blocks can be reserved for the AGCH using the BS_AG_BLKS_RES
parameter. If this parameter is set to 0, then the Immediate_Assignment
message is sent on the PCH. The following figure shows a TDMA frame withnine CCCH blocks, three of which are reserved for the AGCH and the rest forthe PCH. The parameter to reserve these blocks is set to BS_AG_BLKS_RES = 3.
CCCH0 CCCH1 CCCH2 CCCH3 CCCH4 CCCH5 CCCH6 CCCH7 CCCH8
Reserved for AGCH Available for PCH channels
TDMA Frame Cycle
AGCH : Access Grant Channel
CCCH : Common Control Channel
PCH : Paging Channel
TDMA : Time Division Multiple Access
Figure 16: CCCH with Three Blocks Reserved for AGCH
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In the example shown in the figure above, BS_AG_BLKS_RES is set to three.Every occurrence of the TDMA frame cycle carrying the CCCH has threeAGCHs and six PCHs. However, more than six paging groups can be definedby assigning a different group of six PCHs to a number of TDMA multiframecycles. This is specified using the parameter BS_PA_MFRMS , as shown inthe following figure.
AGCH AGCH AGCH PGR0 PGR1 PGR2 PGR3 PGR4 PGR5
First TDMA Frame cycle
AGCH AGCH AGCH PGR6 PGR7 PGR8 PGR9 PGR10 PGR11
Second TDMA Frame cycle
AGCH AGCH AGCH PGR12 PGR13 PGR14 PGR15 PGR16 PGR17
Third TDMA Frame cycle
AGCH AGCH AGCH PGR18 PGR19 PGR20 PGR21 PGR22 PGR23
Fourth/1 TDMA Frame cycle
These four TDMA frames represent 24 PCHs. The parameter to reserve these is BS_PA_MFRMS = 4
AGCH : Access Grant Channel
PGR : Paging Group
PCH : Paging Channel
TDMA : Time Division Multiple Access
Figure 17: Four TDMA Frame Cycles Providing 24 Paging Sub-channels
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3.4.1 Paging Control
The MSC has to initiate the paging procedure, as it holds the information on thelast mobile station location update.
The MSC sends the Paging message to the BSC(s) and sets a timer forthe Paging_Response from the mobile station, which is sent as part of theservice_request message after the immediate assign procedure.
The Paging message from the MDC contains a cell list identifier IE, identifyingthe cells in which the Paging message is to be transmitted.
The BSC checks the cell identifier list and builds a Paging_Command messagefor the relevant BTS. The following table shows the different cell identificationlists and the paging performed by the BSC.
Cell List Identifier Paging Performance
No IE present Paging performed in all cells controlled by BSC
IE indicates all cells Paging performed in all cells controlled by BSC
Error in IE Paging performed in all cells controlled by BSC
IE indicated specificcell(s)
Paging performed only in those cells specified
IE indicates specificlocation area(s)
Paging performed in all cells of each location areaspecified
Table 3: Cell List Identifier and Paging Performed
The BSC calculates the paging group of the mobile station for each cell andthe CCCH timeslot. It then sends a Paging_Command message to each BTS,indicating the CCCH timeslot number, mobile station paging group and themobile station identity (IMSI/TMSI).
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The BTS builds a Paging_Request_Type_x message to send to the mobilestation. There are three types of paging request messages, as the BTS canpage more than one mobile station at a time. The following table shows therelationship between the paging message type, the number of mobile stationsto be paged and the mobile station ID used.
Paging Request Message Mobile Station Identification
Type_1, identifying up to twomobile stations.
IMSI or TMSI (for one mobile station)
IMSI, IMSI or TMSI, TMSI or IMSI, TMSI(for two mobile stations)
Type_2, identifying three mobilestations.
TMSI, TMSI, TMSI or
TMSI, TMSI, IMSI
Type_3, identifying four mobilestations.
TMSI, TMSI, TMSI, TMSI
Table 4: Paging Request Message and Mobile Station Identification
By using a combination of paging message types, several mobile stations canbe simultaneously paged. This is done even if some mobile stations are pagedusing the IMSI and others are paged using the TMSI.
The Paging_Request messages are stored in a buffer, while waiting to besent on the relevant PCH sub-channel. If this buffer becomes full, the nextPaging_Command message is discarded.
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When the mobile station receives the Paging_Request message, it sends aChannel_Request message to initiate the immediate assign procedure. Theservice request message following the immediate assign procedure indicatesthat the Channel_Request is in response to a Paging_Request message.This is shown in the following figure.
MS BTS BSC MSC
channel request
paging request
TMSI/IMSI
paging command
+ CCCH timeslot
+ paging group
channel requiredREF + RFN + TA
paging
+ cell list IE
SABM
establish indication
+ service request (paging response)
CCCH : Common Control Channel
IE : Information Element
IMSI : International Mobile Subscriber Identity
MS : Mobile Station
REF : Random access information value
RFN : Reduced frame number
SABM : Set Asynchronous Balanced Mode
TA : Timing advance
TMSI : Temporary Mobile Subscriber Identity
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3.4.2 Discontinuous Reception
Discontinuous Reception adds to the power-saving abilities of the system,extending mobile station autonomy under battery operation.
The DRX feature implements a receiver off/on ratio of 98 to 2. When the mobilestation is in idle mode, DRX allows the mobile station to switch off its receiverand data processing. Instead of the mobile station listening continually on thePaging Channel sub-channel of the CCCH for a paging message, it only listensto that part of the PCH which corresponds to its paging group. The PCH issplit into a number of paging sub-channels, each of which serves the mobilestations of a particular paging group.
The mobile station calculates its paging group and the part of the PCH ithas to monitor. It gets the information from its IMSI, and from the ControlChannel description sent on the BCCH (sys_info 3). The paging informationis transmitted at predefined regular intervals. The mobile station only turns onits receiver to listen to its paging group and then turns itself off again. Thisoccurs cyclically, between 0.95 seconds and 4.25 seconds, depending onthe configuration of the cell.
Apart from listening to the PCH, the mobile station monitors the home cell’sBCCH up to once every 30 seconds, and the top six neighboring cells up toonce every five minutes. For more information about Paging, refer to Paging(Section 3.4).
3.5 CongestionTo prevent an Assignment_Request or an external Handover_Requestmessage from being rejected, the BSS allows queueing of traffic channelrequests. Congestion occurs when all traffic channels are busy for a particularcell and the message arrives at the BSC. Queueing is allowed if indicated bythe MSC in the request message.
3.5.1 Queueing
Queueing is used to achieve a higher rate of successful call set up and externalhandover completion in cases of traffic channel congestion. This is achieved byqueueing the request for a defined period of time. During this time a trafficchannel can become available and the traffic channel assignment can thenbe completed.
When all traffic channels of a cell are busy, assignment and external handoverrequests for traffic channel allocation can be queued, if:
Requested by the MSCIf the MSC allows queueing, this information and the priority of the requestfor queueing are sent in the Priority Information Element of the request.
Configured in the BSC.The BTS can perform queueing if specified in the BSC configuration. BTSqueueing can be enabled/disabled by an operator command through theOMC-R. Setting the BTS_Queue_Length parameter to 0 disables queueing.
If either the MSC or BSC does not allow the request to be queued, the requestis immediately rejected and an Assignment_Failure message is sent tothe MSC.
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3.5.2 In-queue
If queueing is allowed, the request cannot be queued if one of the two queuelimits is exceeded. These limits are:
The maximum number of requests that can be queued per BTS if defined bythe O&M parameter BTS_Queue_Length. The range is from 1 to 64. This
can be individually set for each BTS
The global limit of 64 queued requests in the BSS. The sum of all BTSqueue lengths cannot exceed 64.
When one of the queue limits is exceeded, the request may still be queued ifthere is a lower priority request in the queue. If the priority of the incomingrequest is higher than the lowest in the queue, the incoming request is queuedand the oldest lowest priority request is then rejected.
Once a request is queued, the BSC informs the MSC by sending aQueueing_Indication message.
A timer is activated when the request is queued. If the timer expires or therequest is preempted by a higher priority request, the request is rejected.
Once in the queue, the request waits to be either accepted or rejected due toone of the following events: traffic channel availability or Forced Directed Retry.
3.5.2.1 Traffic Channel AvailabilityIf another traffic channel disconnects within the cell, the request at the top ofthe queue is assigned to the newly available traffic channel. The request isremoved from the queue. An Assignment_Complete message is sent to theMSC notifying it of the successful assignment of a traffic channel.
3.5.2.2 Forced Directed RetryThe BSC detects that the call can be supported on another cell, andimplements Forced Directed Retry.
If the BSC detects the possibility of a handover for the queued request, itgenerates an internal or external handover alarm and initiates the appropriatehandover procedure. A handover from an SDCCH in the serving cell to a trafficchannel in a target cell is known as directed retry.
On detection of the handover alarm, the BSC cancels the queued request,stops the timer, and selects a neighbor cell in the target cell list. The target cellmust be able to support the ciphering requirements of the call. Once a cell isselected, a traffic channel is chosen and a handover is attempted (SDCCH totraffic channel). If the handover fails, another cell is chosen from the target celllist. This procedure continues until a successful handover or the handover limit(number of handover attempts allowed) is exceeded.
The MSC is notified of a successful handover by an Assignment_Complete
message. The direct retry finishes if the number of handover attempts isexceeded, or there are no more cells left in the target cell list. Finally anAssignment_Failure message is sent to the MSC indicating that there are noradio resources available.
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3.5.2.3 Queue Pre-emptionIf a higher priority request arrives in the queue, Queue Pre-emption isimplemented.
If one of the queue limits is exceeded and the request is the oldest of the lowestpriority requests in the queue, the request is rejected. An Assignment_Reject
message is sent to the MSC indicating that there are no radio resourcesavailable.
3.5.2.4 Timer ExpiresIf the timer expires, the request is de-queued and rejected. AnAssignment_Reject message is sent to the MSC indicating that there are noradio resources available.
3.5.2.5 Fast Traffic HandoverAnother possibility to save resources in case of traffic peaks is to forcehandovers toward neighbor cells which have less traffic. The fast traffichandover searches in the whole cell for a mobile which can perform a handoverto a neighbor cell with less traffic if the received signal level of the BCCH isgood enough. It is much more efficient than the forced directed retry when theoverlap of adjacent cells is reduced, e.g., in the case of single layer networks,or for deep indoor coverage (if the umbrella cell does not overlap totally themicrocells). Fast traffic handover is enabled on a per cell basis, by setting theEN_FAST_TRAFFIC_HO parameter to TRUE. Setting the EN_FAST_TRAFFIC_HO
parameter to ’False’ disables fast traffic handover for that cell.
Fast traffic handover is enabled when all of the following conditions are met:
A request is queued at the top of the queue. The request is of full-ratetype for assignment or emergency external incoming handover, and is not
in the HOLD state
The parameter EN_FAST_TRAFFIC_HO is set to TRUE.
The queued request is an assignment. If it is an external incoming handover, itis an emergency handover to trigger the algorithm; otherwise the algorithm isnot triggered.
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3.5.3 Pre-emption
Pre-emption is an optional feature and is initiated during congestion periods.The feature allows radio resources in a cell to be allocated to those calls whichare deemed to be the most important. The importance of the connectionis given by the MSC to the BSC via signaling on the A Interface. Duringcongestion periods, the BSC ensures that high priority transactions obtain theresources they require. The BSC performs a release of radio resources in orderto obtain the radio resource for the higher priority call.
For Phase 1 and Phase 2 GSM, the signaling for priority and pre-emption existson the A Interface. The setting of this data on the A Interface is controlled bythe MSC. The conditions under which the information is set is up to operatorchoices. For Phase 2+ GSM, the priority and pre-emption information is basedon subscription data which is stored in the HLR and downloaded to the VLR viaMAP protocols. This information can also be used by the MSC when setting thepriority level and pre-emption attributes for the call.
The pre-emption attributes of a call are defined by three bits:
pci: The pre-emption capability indication indicates if the transaction can
pre-empt another transaction
pvi: The pre-emption vulnerability indication indicates if the transactioncan be pre-empted
prec: The pre-emption recommendation. This is needed in order to defer
pre-emption until a suitable non-congested cell is found in the preferredcell list. The pre-emption recommendation is used when the old BSS
recommends that another connection be pre-empted.
Pre-emption is applied to the TCH only. The pre-emption feature is optionaland controlled by the O&M parameter (EN_TCH_PREEMPT) on a per-BSCbasis. The BSC provides pre-emption of TCH radio resources. This takes intoaccount the priority of the call. The lowest lower priority call with the pvi bitset is pre-empted and thus released. Directed retry and/or forced handover inorder to avoid pre-emption is not supported.
3.5.3.1 eMLPPEnhanced Multi Level Priority and Pre-emption (eMLPP) is a supplementaryservice that allows a subscriber in the fixed or mobile network to initiate callsthat have a priority and pre-emption attribute known to all the network elements.The eMLPP standardization provides the transportation of the subscriptioninformation for priority and pre-emption on MAP. This subscription information isstored in the HLR and the GCR and is transported to the VLR.
This information is used for the following procedures:
Paging
TCH Assignment
TCH Handover.
Only TCH pre-emption is supported (i.e., only for circuit-switched services).
Pre-emption for VGCS is possible for both the VGCH, in transmit and receivemodes, and for the dedicated channel, in dedicated transmit mode.
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3.5.3.2 Pre-emption RulesAn Assignment Request message with pci=1 and priority level=p1 willpre-empt an ongoing call with pvi=1 and priority level=p2 (p2 is lower than p1).A Handover Request message with pci=1 and priority level=p1 will pre-emptan ongoing call with pvi=1 and priority level=p2, except if the prec bit is presentand set to 0 (i.e., the old BSS does not recommend the pre-emption of anongoing call to be performed by the target BSS).
In both cases, the call with the lowest priority level=p2 value is selected first,and if several calls have the same lowest priority level=p2 value, one of themwith the pci bit set to 0 is preferred.
3.6 Classmark HandlingThe mobile station classmark contains information about the mobile stationtype and capabilities. This information is used by the BSS when implementingprocedures that affect a mobile station, such as:
Handover
Power Control
Ciphering
Overload Control
Location Updating.
Mobile stations of different types have different capabilities within the network.It is essential that the network recognizes the mobile station classmark wheninitiating procedures for a specific mobile station.
There are three entities that provide classmark handling, as shown in thefollowing table.
Entity Classmark Handling
BSS Performed by the BSC, which is responsible for collectingthe classmark data needed to perform procedures on themobile station.
MSC Indicates the mobile station classmark data to the BSC forMSC-initiated procedures.
Mobile station The BSS is informed of any classmark changes andinformation is sent on request from the BSS.
Note: The BSS can receive mobile station classmark information from both the MSCand the mobile station. The information from the mobile station overridesinformation from the MSC.
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3.6.1 Classmark IE
The Alcatel-Lucent 900/1800 BSS supports classmark 1, classmark 2 andclassmark 3 IEs. Classmark 1 IE is always sent to the BSS when the mobilestation tries to establish communication.
Classmark 1
The Classmark 1 IE contains:
The revision Level
The RF Power Level
Support of A5/1 Encryption.
Classmark 2The Classmark 2 IE is defined in GSM to allow the coding of phase 2capabilities such as the A5/2 ciphering algorithm and VGCS capability. Theclassmark contains the same elements as Classmark 1 IE, plus supportof A5/2 encryption.
Classmark 3The Classmark 3 IE is defined in GSM to allow multiband mobile stations toindicate their capabilities. The classmark specifies the supported bandsand the respective power classes.
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3.6.1.1 Classmark IE FieldsThe following tables describes the fields contained in a classmark IE.
This field... Indicates...
Revision Level Either a phase 1 or phase 2 mobile station. It does not distinguishbetween phase 1 and phase 1 extended mobile stations. If there is anerror in this field, then a default phase 1 is assumed.
RF Power Level the mobile station power capability.
For Alcatel-Lucent 900:
Class 1 = 20 W
Class 2 = 8 W
Class 3 = 5 W
Class 4 = 2 W
Class 5 = 0.8 W
For Alcatel-Lucent 1800:
Class 1 = 1 W
Class 2 = 0.25 W
The value is not permitted if there is an error in this field. The result ofthis is that the mobile station power capability is assumed to be the sameas the maximum transmit power allowed in the cell.
Support of A5/1 Encryption Whether the mobile station supports the A5/1 encryption algorithm. Ifthe A5/1 encryption algorithm is not supported, there is no indication ofother algorithms being supported.
Support of A5/2 Encryption Whether the mobile station supports the A5/2 encryption algorithm. Ifthe A5/2 encryption algorithm is not supported, there is no indication ofother algorithms being supported.
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3.6.1.2 Impact on BSS and MSCThe main difference between classmarks 1 and 2 for the BSS or MSC is thesupport of the encryption algorithm. For procedures that require ciphering,the BSS and MSC cannot recognize the mobile station ciphering capability ifonly Classmark 1 IE was received. Therefore, there is a classmark updatingprocedure.
Similarly, for classmark 3, the BSS and MSC do not recognize the mobilestations multiband capabilities if only a Classmark 1 IE was received.Therefore, a classmark updating procedure is required.
3.6.2 Classmark Updating
Further classmark information may be required by the BSS or MSC wheninitiating a procedure which needs to encrypt information. The mobile stationcan also send updated information if, for example, its power capability changes.
Therefore, updating of classmark information can be initiated from the:
Mobile station by sending a classmark_change message to the BSC which
sends a classmark_update message to the MSC.
BSC by sending a classmark_enquiry message through the BTS to themobile station. The mobile station responds with a classmark_change
message.
MSC by sending a classmark_request message to the BSC. This promptsthe BSC to send a classmark_enquiry message to the mobile station
which responds with a classmark_change message.
The classmark_change message from the mobile station is passed throughthe BTS to the BSC. The BSC stores the information for its own use andforwards the information to the MSC. Depending on the network type andconfiguration, the classmark update is not always required. Therefore, the BSShas a parameter in the BSC (parameter Send_CM_Enquiry) which can beconfigured. The following table shows the possible configurations.
ParameterValue Action
0 The classmark_enquiry message is never initiated by theBSC.
1 The BSC always initiates a classmark update when it receivesa location update request.
2 The BSC only initiates a classmark update on reception of alocation update request if A5/1 is not available. This is workedout from the classmark 1 IE.
If the system requests a classmark update to a phase 1 mobile station, themobile station is not able to respond. It considers the message an error andsends an RR_status message. This message is ignored by the BSS andis not passed to the MSC.
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3.6.3 Location Updating with Classmark Procedure
If the mobile station is a phase 1 extended or phase 2 mobile station, it cansend classmark update information on request from the BSS or MSC. Becausethe BSS does not know the mobile station ciphering capability from theclassmark 1 IE, updating is required. This is received when the mobile stationestablishes the LAPDm connection, as shown in the following figure.
MS BSC MSC
switch to
SDCCH
channel request
(FACCH/SACCH)
power + TA + sys info 5 & 6
BTS
channel required
(RACH)
establish indication
SABM + rn + fn + cm
SCCP connection
classmark enquiry
SCCP connection
confirm
classmark change
classmark 2IE classmark update
classmark 2IElocation update
(SDCCH)
cm : Classmark
FACCH : Fast Associated Control Channel
IE : Information Element
MS : Mobile Station
RACH : Random Access Channel
SABM : Set Asynchronous Balanced Mode
SACCH : Slow Associated Control Channel
SCCP : Signal Connection Control Part
SDCCH : Standalone Dedicated Control Channel
TA : Timing advance
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For location updates with classmark updates:
1. The mobile station initiates a location update procedure by sending aChannel_Request message on the RACH.
2. The BSS performs the immediate assign procedure, as described inMobile-Originated Call (Section 3.2).
3. The mobile station establishes the LAPDm link and sends the location updaterequest and classmark 1 IE. The BTS sends an Establish_Indication
message to the BSC, containing the location update request and classmark1 IE.
4. The BSC uses the classmark to send mobile station power controlinformation to the BTS to start power control. It stores the classmarkinformation and requests an SCCP connection with the MSC.
5. When the BSC receives an SCCP_Connection_Confirm message, it sends aclassmark_enquiry message to the mobile station.
6. The mobile station responds with a classmark_change messagecontaining the classmark 2 IE. This information is passed to the MSC in aclassmark_updating message. If the mobile station is a phase 1 mobilestation, it responds with an RR_status message which is ignored by theBSS. In this case, the BSS sets ciphering with the information availablefrom the classmark 1 IE.
7. The MSC initiates the authentication procedure and on receipt of theauthentication response message, initiates the ciphering procedure. Referto Ciphering (Section 3.8) for more information about ciphering.
8. When ciphering is set, the MSC can accept the location update.
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3.7 AuthenticationThe authentication procedure ensures that the subscriber identification (IMSI,TMSI) and the IMEI are valid. The system behavior for non-valid identificationsis at the discretion of the Network Operator. The procedure also validatesthe Ki value in the mobile station, and sends the RAND which is used tocalculate the ciphering key.
3.7.1 IMSI/TMSI
When the subscriber accesses the network for the first time, the subscriptionis identified by the IMSI sent in the Location_Updating_Request message.When the NSS has performed authentication and set the ciphering mode, theVLR assigns a TMSI, in an encrypted format over the Air Interface.
The next time the subscriber connects to the system, it uses the TMSI as itsidentification. If the mobile station has changed location area, it includes theold Location Area Identity. The new VLR interrogates the old VLR for theauthentication information (IMSI and Ki value). The new VLR then assigns anew TMSI. This is shown in the figure below.
New TMSIs can be assigned by the serving VLR at any time. The subscriberidentity is secure because the TMSI is always ciphered and changed regularly.
service request + TMSI + old LAI
MSCBSCBTS
MSC
BSCBTS
Mobile Station moving and connectingin a new location area
MobileStation
new TMSI
info request
IMSI +Ki
VLR
VLR
MobileStation
IMSI : International Mobile Subscriber Identity
Ki : Individual Subscriber Authentication Key
LAI : Location Area Identity
TMSI : Temporary Mobile Subscriber Identity
VLR : Visitor Location Register
Figure 18: Location Update with Mobile Station Sending Location Area Identity of Previous VLR
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3.7.2 Authentication Procedure
The following steps describe the authentication procedure:
1. The authentication procedure is initiated by the NSS.It sends an Authentication_Request messageto the mobile station and sets a guard timer.This message contains:
Parameters for the mobile station to calculate the response
A ciphering key sequence number.
The ciphering key is calculated from the authentication Key value assignedto the IMSI or TMSI and the value RAND.
2. The mobile station responds using the RAND and thevalue authentication Key assigned to its TMSI or IMSI.For mobile-originated calls, the mobile station uses:
The TMSI, if available
The IMSI, if no TMSI is assigned.
For mobile-terminated calls, the mobile station uses the TMSIor IMSI as requested in the Paging message from the network.For emergency calls, the mobile station uses:
The TMSI, if available
The IMSI, if no TMSI is assigned
The IMEI, if there is no TMSI or IMSI. This can happen when thereis no SIM in the mobile station.
3. When the mobile station sends the Authentication_Response message,the NSS stops its guard timer and validates the response.If the mobilestation response is not valid, the network response depends on whether theTMSI or IMSI was used:
If the TMSI was used, the network can request that the mobile station
sends its IMSI
If this is a valid IMSI, but is different from the IMSI that the network
associated with the TMSI, the authentication procedure is restarted withthe correct parameters
If the IMSI is invalid, the network sends an Authentication_Reject
message to the mobile station.
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3.8 CipheringCiphering is supported in the Alcatel-Lucent 900/1800 BSS to protectinformation transmitted on the Air Interface.
This includes:
Subscriber information such as the IMSI
User data
SMS and SS data
Information such as called and calling party numbers.
Ciphering protects the information by using encryption. There are threedifferent ciphering modes, the use of which depends on the mobile stationclassmark and the capability of the BTS.
These modes are:
Encryption using algorithm A5/1
Encryption using algorithm A5/2
No encryption.
The two encryption algorithms are defined in GSM. If either is to be used, boththe mobile station and BTS must have the same encryption capability.
3.8.1 Mobile Station Ciphering Capability
The mobile station ciphering capability depends on whether it is a phase 1mobile station, a phase 1 extended mobile station, or a phase 2 mobile station.The following table shows the different mobile station ciphering capabilities.
Mobile Station Type Capability
Phase 1 No encryption and A5/1
Phase 1 Extended No encryption and A5/1 and A5/2
Phase 2 No encryption
No encryption and A5/1
No encryption and A5/2
No encryption and A5/1 and A5/2
Only phase 2 mobile stations can turn off ciphering or change the cipheringmode during a channel change procedure such as a handover.
The ciphering capability of a mobile station is signalled to the BSS in themobile station classmark.
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3.8.2 BSS Ciphering Capability
The Alcatel-Lucent 900/1800 BSS supports both uniform ciphering networkconfigurations and mixed ciphering network configurations.
A cell can be configured to support one of the following:
No encryption
No encryption and the A5/1 algorithm
No encryption and the A5/2 algorithm.
A uniform ciphering network configuration is where all cells have the sameciphering capability.
A mixed ciphering network configuration is where the cells have differentciphering capabilities.
3.8.3 Ciphering Keys
The encryption used on the Air Interface is provided by the physical layerhardware. This means that it does not distinguish between signaling and usertraffic; therefore, the entire bit stream is encrypted.
The encryption pattern added to the bit stream is calculated by the algorithmA5/1 or A5/2, using a ciphering key.
For maximum security, the value of the Ciphering Key is not a fixed value. It iscalculated separately by the HLR, BSC and the mobile station for each call.This means that the value Kc is never transmitted on the Air Interface.
The value Kc must be the same in the HLR, BSC and the mobile station.
It is calculated using:
A value Ki, which is assigned to the IMSI when the user subscribed
to the service
A RAND, sent from the MSC during the authentication procedure.
The resulting value Kc is used to decipher the encrypted bit stream on thedownlink, by the mobile station, and on the uplink, by the BTS.
3.8.4 Ciphering Process
3.8.4.1 Choosing the Ciphering ModeThe ciphering chosen by the BSC for a call depends on:
The algorithms that the Network Operator allows in the network. This
information is sent in the Permitted_Algorithm message from the MSCduring ciphering or external handover procedures.
The ciphering capability of the mobile station. This information is sent to the
BSC in the mobile station classmark
The ciphering capability of the BTS being used to set up the call.
If the mobile station capability is not compatible with that of the BTS or isnot allowed by the Network Operator, then the BSC sets ciphering withno encryption.
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3.8.4.2 Setting the Ciphering ModeThe ciphering mode is set as follows:
1. Ciphering is initiated by the MSC by sending a cipher_mode command tothe BSC. This command contains the Permitted_Algorithm message.
2. The BSC compares the permitted algorithms with the mobile stationclassmark and the BTS capability. If they match, the BSC sends anencryption_command message to the BTS containing the value Kc andthe algorithm to be used. If there is no match and ’no encryption’ ispermitted, the BSC sends the encryption_command to the BTS indicating’no encryption’.
3. If the BTS and mobile station capabilities are not compatible and theMSC does not allow the ’no encryption’ option, then the BSC sends acipher_mode_reject message to the MSC.
4. The BTS sends the ciphering_mode command on the SDCCH to themobile station indicating the algorithm or ’no encryption’. If encryption isto be used the BTS sets its decryption mode ready to receive encryptedframes from the mobile station.
5. The mobile station either:
Starts the encryption and sends an encrypted Layer 2 acknowledgment
message to the BTS. This prompts the BTS to start encryption mode for
frames sent to the mobile station
Sends an unencrypted level 2 acknowledgment to the BTS.
6. The mobile station sends a ciphering_mode_complete message tothe BTS which is passed transparently to the BSC. The BSC sends acipher_mode_complete message to the MSC.
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The following figure shows this process.
MS BTS BSC MSC
algorithm orno encryption
ciphering mode command
(SDCCH)
ciphering mode complete
encryption command
algorithm + Kc or
no encryption
ciphering mode command
permitted algorithms + Kc
cipher mode complete
MS : Mobile Station
SDCCH : Standalone Dedicated Control Channel
3.8.4.3 Ciphering During HandoverOnly phase 2 mobile stations can change ciphering mode during a handover.If a phase 2 mobile station using the A5/1 algorithm is handed over to a cellwhich supports A5/2 and ’no encryption’, the BSC instructs the target BTS toset the new ciphering algorithm and sends the value Kc.
If a phase 1 mobile station using the A5/1 algorithm needs to be handed over,the target cell must support A5/1, as the phase 1 mobile station cannot changeciphering mode. For mixed ciphering networks, it is normal that the initialcipher_mode command from the MSC only allows a phase 1 mobile station touse the ’no encryption’ option, as this is supported by all cells.
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3.9 Tandem Free OperationTandem Free Operation (TFO) provides better voice quality by avoidingunnecessary successive coding and decoding operations in the case ofmobile-to-mobile calls. The importance of TFO is always increasing, as thepercentage of mobile-to-mobile calls increases with the number of subscribers.Take the example of a call involving two mobile stations, MS 1 and MS 2.
With the TFO feature, the same codec will be used on both BSS.
This improves the speech quality of mobile-to-mobile calls, and particularlywhen using the half-rate codec.
Without TFOOne GSM coding and decoding scheme (codec), is used between MS 1and Transcoder 1, then A/law coding is used (at 64 kbit/s) between the twotranscoders and finally one GSM codec is used between Transcoder 2 andMS 2. This means a loss of quality for the speech call.
With TFO.The intermediate transcoding realized by the two involved transcoders isavoided. The same codec is used on both BSS. This improves the speechquality of mobile-to-mobile calls, particularly when using the half-rate codec.This allows a wide use of the half-rate codec, with a good level of speechquality, in order to save resources in BSS.
Note: As VGCS is point to multipoint on the downlink, it is not compatible with TFO.
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3.9.1 TFO Process
TFO can be applied whenever the two mobile stations use the same codec.To satisfy this condition, after TCH allocation, the two BSS negotiate at eachside a common codec (full-rate, half-rate or enhanced full-rate), by using anin-band protocol in the speech frame. The following figure shows an exampleof TFO call establishment.
BTS A BSC A TC A TC B BSC B BTS B
Channel activationTFO enabled
Channel activationTFO enabled
CON_REQ CON_REQ
DL_ACKDL_ACK
TRAU frames
TFO_REQ
Codecs match
1
2
3
4
5TFO REPORT (TFO STATUS= ON)
TFO_ON TFO_ONTFO frames
TRAU frames
PCM samples
TRAU frames TRAU frames
TFO_ACK
TFO REPORT (TFO STATUS= ON)
TFO_ACK
TFO_REQ
PCM : Pulse Code Modulation
TC : Transcoder
TFO : Tandem Free Operation
TRAU : Transcoder Rate Adaptation Unit
Figure 19: Example of TFO Establishment
Referring to the figure above, the call establishment is as follows:
1. At call establishment, the BSC sends the Channel_Activation message tothe BTS, containing information related to TFO.
2. TRAU frames are exchanged between the BTS and the Transcoder. PCMsamples are exchanged between the TRAUs. One TRAU frame is stolenfrom the BTS by the Transcoder, to send TFO configuration information (inthe con_req message).
3. As soon as the TRAUs receive the information that TFO is enabled in thecon_req message, (and also the TFO configuration information), they sendthe tfo_req message, within PCM speech samples, to indicate that theTRAUs are TFO capable. Meanwhile, the TRAUs acknowledge the con_req
message to the BTS with the dl_ack indication.
4. The TRAUs acknowledge that the tfo_req message is received by sendinga tfo_ack indication.
5. The same codecs are then used on both sides. The TRAUs can exchangeTFO frames.
6. The BTS are made aware of the exchange of TFO frames by tfo_on. TheBSC is informed via a tfo_report message on the Abis Interface.
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The Alcatel-Lucent TFO implementation is fully compliant with the GSMstandard and additionally provides:
As an operator choice, the Alcatel-Lucent BSS is able to force the distant
BSS (Alcatel-Lucent or not) to overcome ETSI codec choice rules, inorder to optimize voice quality and load management. This mechanism is
patented by Alcatel-Lucent.
Codec optimization, to take into account that the two mobile stations may
use the same codec, but a better codec is available on both parts.
3.9.2 TFO Functional Architecture
The TFO procedure is defined between two TRAUs. When TFO is possiblebetween two mobile stations, TFO frames (similar to TRAU frames) aretransferred between the two TRAUs on the A Interface. These frames containcoded speech streams, and may also contain embedded TFO messages. Theyare supported by a 0.5 kbit/s signaling channel between two Transcoders,emulated during the TFO negotiation phase. This channel uses one bit (LeastSignificant Bit) every 16 PCM samples, regularly stolen on the 64 kbit/s circuit.Note that when TFO frames are transmitted, speech is nevertheless coded toG.711 law and sent to the A Interface on the remaining MSB bits of the PCMsamples. This allows a faster reversion to normal operation mode if required.Moreover, lawful interception in the MSCs is still possible. The Alcatel-Lucentsolution avoids any Ater supplementary links, because the BSC-TranscoderTFO messages are exchanged through the BTS and the Abis Layer 3 protocol.
When the same codec is used on both sides, no TFO negotiation is neededbetween the TRAUs.
When the same codec is not used on both sides, TFO negotiation is neededbetween the TRAUs. In this case, TFO communication is possible between thetwo BSS, but the TRAUs do not use the same speech codec. TFO negotiationand resolution by the BSS are needed. When detecting the mismatch, eachTRAU sends to the other (using TFO messages) the codec locally used, and thelist of possible codecs. At each side, the BSS determines the matching codec.On each BSS, the same algorithm is implemented. This algorithm attempts tofind a matching codec using the information given by the TRAU. If a commoncodec can be found, an internal intracell handover is performed to change thespeech codec used locally, and TFO exchange of the speech stream begins. Alogical parameter, configurable at the OMC-R, allows the BSC to ignore theload in the cell and to force the handover in order to solve codec mismatchsituations. If no common codec can be found, or internal intracell handover isnot possible, TFO mode is given up, and the system reverts to normal mode.
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3.9.3 TFO Optimization and Management
TFO is managed by the OMC-R operator, on a per cell basis. Several functionsare introduced to provide full control of TFO optimization, load regulation,speech quality, or Adaptive Multiple Rate (Section 6.2.8) codec support.
3.9.3.1 TFO OptimizationFor a better speech quality, TFO optimization allows a new TFO negotiationon an ongoing TFO mobile-to-mobile call, to find a better common codec, interms of speech quality. Therefore, enhanced full-rate coding is consideredbetter than full-rate coding which is considered to be better than half-ratecoding. The Enable TFO Optimization feature can be enabled or disabled percell at the OMC-R.
In some cases, both sides may use the same codec, but a better codec isavailable at each side and may be used (e.g., half-rate is used at both sides,but full-rate is possible). The procedure is then the same as the modification ofspeech codec in mismatch status, except that it takes place only when TFOframes are already exchanged. The TFO messages exchanged between bothTRAUs are then embedded in TFO frames.
3.9.3.2 TFO Negotiation ControlFor better traffic load regulation, Alcatel-Lucent defined the function "ForceTFO half-rate when loaded" to give control of load regulation precedence overTFO to the operator. This function can be enabled or disabled, per cell, at theOMC-R, and allows the BSC to take into account the load in the cell whilebuilding the list of supported codec types. If the cell is loaded, only half-rate (ifpossible) will be included in the list. If the distant BSS supports TFO but nothalf-rate, the function "Force TFO half-rate when loaded" allows the BSC inthis case to recompute the list of supported codec types by inserting full-rateand enhanced full-rate in the list.
Therefore, the function "Force TFO half-rate when loaded" leads to threedifferent behaviors, depending on three possible values of the correspondingflag:
TFO half-rate not forced. No filtering on the load is done. The load is nottested and all the codec types supported by the call and by the cell are listed
in the supported codec type list
TFO half-rate only. Filtering is done on the load, half-rate is forced if the cellis loaded and the mobile station supports half-rate, and if this codec type
is authorized in the cell. The list of supported codec types is restricted tothe half-rate codec type. As a consequence, if the distant side supports
half-rate, then the distant side will do an intracell handover to use half-rate,
and TFO will go on with half-rate. If the distant side does not supporthalf-rate, TFO will not be possible
TFO half-rate preferred. Filtering is done on the load, but TFO is preferredto half-rate. In the case of a load situation, only half-rate is sent in the list of
preferred codecs. But if the distant BSS does not support half-rate, a new
list is computed, without taking into account the load in the cell.
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4 Call Handling
This section provides an overview of Call Handling and describes thesupervision of a call in progress.
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4.1 OverviewIn order to provide effective management of calls in the BSS, it is necessaryto ensure:
Maximum perceived signal quality with minimum perceived interference
Call continuity regardless of changes in propagation conditions or changeof location of the mobile station.
Given that spectrum is limited, this must be accomplished with maximumresource reuse. Another important factor for the customer (and the operator aswell) is power efficiency to reduce overall power consumption and prolong theautonomy of the mobile station under battery operation.
The supervision of calls in progress is provided by the Call Handling function.Call Handling, with associated features, implements needed changes in therequired teleservice to maintain call quality and continuity.
Call Handling functions and features include:
In-Call Modification
Frequency Hopping
Discontinuous Transmission
Radio Power Control
Handover
Overload Control
Call re-establishment by the mobile station.
Note: A VGCS call uses the same general call handling procedures as a standardcall; any exceptions are described in the relevant procedure descriptions below.
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4.2 In-Call ModificationIn-call modification allows the teleservice to be changed during a call. Thismeans that a call does not have to be cleared, and a new call established, ifmore than one teleservice is to be used.
The different types of in-call modification are:
Alternate between speech and a transparent data service
Alternate between speech and a non-transparent data service
Change from speech to a transparent data service
Change from speech to a non-transparent data service
Alternate between speech and transparent fax group 3
Alternate between speech and non-transparent fax group 3
Data rate change for transparent fax group 3
Data rate change for non-transparent fax group 3.
Calls requiring a change of service have to negotiate a ’dual-service’ before thenormal assignment procedure. This is indicated in the Set_Up message, whichis described in Call Set Up (Section 3).
Note: Changing the data rate of a fax call is not a true in-call modification procedure,as the teleservice is not changed (no dual-service negotiation).
The main difference between the in-call modification procedure and a changeof data rate for fax are as follows:
The in-call modification procedure is triggered by a message from the
mobile station
The data rate change for fax is triggered by in-band signaling from the
fax machine to the MSC.
Both procedures use existing resources, therefore no new resources need tobe allocated. All full-rate traffic channels can be used for speech or data at anyof the defined data rates.
Both procedures use the mode ’modify procedure’ to change the transmissionmode. This is basically a normal assignment procedure but instead of a newchannel being assigned, a new mode is assigned.
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4.2.1 In-Call Modification Procedure
In-call modification is initiated from a mobile station. This can occur during acall to a correspondent on the public telephone network or to a mobile station.
For a mobile-station-to-mobile station call, both mobile stations must negotiatea dual service during call establishment.
The process is as follows:
1. The mobile station initiates the procedure by sending a Layer 3 Call Controlmodify message to the MSC, indicating the new mode. If the data calldirection is different from the original call set up, then this message containsan indicator to reverse the call direction. The mobile station starts a guardtimer for the procedure.
2. The MSC checks the modify message. If it can accept the modechange, it starts the normal assignment procedure by sending anAssignment_Request message and starting a guard timer. This messagecontains a channel type (speech or data plus data rate).
3. The BSS handles the normal assignment procedure as if assigning a trafficchannel during call set up (described in Call Set Up (Section 3)), withthe following exceptions:
When the BSC has checked and accepted the Assignment_Request
message, it does not assign a new traffic channel. This is becauseit already has a traffic channel assigned for the transaction. The
transaction is identified by the SCCP connection on which theAssignment_Request message was received
The Channel_Activation and Channel_Activation_Acknowledge
messages are replaced by the mode_modify and mode_modify
acknowledge messages.
4. When the MSC receives the Assignment_Complete message from the BSC,it sends a Layer 3 CC modify_complete message to the mobile station.This informs the mobile station that the procedure is successfully completed,and the mobile station can start transmitting in the new mode.
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4.2.2 Circuit-Switched Group 3 Fax Data Rate Change
Group 3 facsimile equipment can change the data transmission speed toreduce the error rate.
Fax data rates can be:
9600 bit/s
4800 bit/s
2400 bit/s
1200 bit/s.
The Alcatel-Lucent 900/1800 BSS supports both transparent andnon-transparent fax transmission.
The BSS supports the Group 3 fax data rate change by:
In-band signaling for non-transparent faxFor non-transparent fax transmission, the data rate change is handledwithin the BSS, using in-band signaling. This means that the frame size issignalled in the frame by a "frame delimiter" field. The Radio Link Protocol inthe BTS uses this information to control the data flow on the Air Interface.The BSS does not need to change the channel mode
The mode modify procedure for transparent fax.Transparent fax frames are passed transparently through the BSS.Therefore, in-band signaling cannot be used within the BSS. The Group3 fax equipment informs the MSC of a data rate change using in-bandsignaling. The MSC then initiates a mode modify procedure using theAssignment_Request message.This procedure is the same as the mode modify procedure for in-callmodification, except that the MSC does not send a Layer 3 Call Controlmode_modify_complete message. This is because the procedure was nottriggered by a Layer 3 CC modify message from the mobile station. Whenthe MSC receives the Assignment_Complete message from the BSC, itsets the new data rate to the correspondent.
4.2.3 Error Handling
The Alcatel-Lucent 900/1800 BSS tries to provide the highest level of service atall times. In general, if errors occur during an in-call modification, the BSS triesto revert to the old mode to keep the call active.
For example, if the mobile station does not reply to the channel_mode_modify
message from the BSC, it is assumed that it is still active but in the old mode.The BTS, however, has set the new mode. The BSC sends a mode_modify
message to the BTS indicating the old mode. If the BTS acknowledges that ithas reverted to the old mode, the call is kept active.
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4.3 Frequency HoppingFrequency Hopping is a method to increase frequency reuse and improve thesystem’s ability to cope with adjacent channel interference.
The Frequency Hopping algorithm can be either random or cyclic. Associated(i.e., paired) uplink and downlink frequencies are always +/-45 MHz.
There are two major types of frequency hopping:
Baseband Frequency Hopping (Section 4.3.1)
Synthesized Frequency Hopping (Section 4.3.2).
Frequency Hopping improves BSS-mobile station performance by providingtwo types of diversity:
Frequency diversityFrequency diversity averages the effects of signal fading by using severalfrequencies to improve transmission performance. Obstacles such asbuildings produce fading by reflecting the signal out of phase with the mainsignal. Each frequency is affected differently by fading.After error correction information is added to the data, it is encoded so thatthe data is split into packets and the information is repeated. This createsredundant information which is transmitted in bursts on the Air Interface.With Frequency Hopping, each redundant information burst is transmittedon a different frequency. This enables the original data to be reconstructedfrom the received flow, even if errors occur due to fading.In this way Frequency Hopping improves transmission performance.
Interference diversity.Interference diversity spreads the co-channel interference between severalmobile stations. In high traffic areas, the capacity of a cellular system islimited by its own interference; that is, the interference caused by frequencyreuse. Interference Diversity minimizes the time during which a given useron a given mobile station will experience the effects of such interference.
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4.3.1 Baseband Frequency Hopping
A Mobile Allocation is a set of all the frequencies available for frequencyhopping. When the Frequency Hopping procedure is implemented, a group ofmobile stations is assigned to a Mobile Allocation.
When a traffic channel is set up in a cell where Frequency Hopping is active,the traffic channel is assigned:
A particular timeslot
An FHSAn FHS is defined as the subset of frequencies within the MA to be used bya given cell for Frequency Hopping.
A MAIOThe MAIO indicates the initial hopping frequency of the traffic channel withinthe FHS. Use of the MAIO ensures that each traffic channel is assigned adifferent frequency during hopping.
An HSNThe HSN supplies the identifying number of an algorithm which is usedto calculate the next frequency in the FHS on which the traffic channeltransmits. There can be up to 63 different HSN algorithms, all of which arepseudo random. Within a given FHS, only one algorithm is used to avoidcollisions. An HSN of zero means a cyclic use of the frequencies.
An example of Frequency Hopping is shown in the figure below. Because HSN= 0, hopping occurs in a sequential manner. With a non-zero HSN, each ofthe three traffic channels would hop in a random fashion determined by thealgorithm corresponding to the HSN.
TCH1 on TS1
TCH2 on TS2
TCH3 on TS3
MAIO=0
MAIO=1
MAIO=2
Assignmentfor TCH 1:TS=1MAIO=0HSN=0
Frame n
Frame n+1
Frame n+2
Frame n+3
f 1
f 2
f 3
Within this FHS the HSN=0
f 1f 2 f 3
f 1
f 3
f 3f 2
f 2f 1
f : Frequency
FHS : Frequency Hopping System
TCH : Traffic Channel
MAIO : Mobile Allocation Index Offset
HSN : Hopping Sequence Number
TS : Timeslot
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4.3.2 Synthesized Frequency Hopping
Synthesized Frequency Hopping functions in a similar fashion to BasebandFrequency Hopping, but is performed at a different location. Instead ofswitching each timeslot between traffic channels, the channel assigned to atimeslot is assigned to a fixed Carrier Unit (or TRE).
The Carrier Unit/TRE changes frequency with each TDMA frame in accordancewith the HSN algorithm selected, in the same manner as above. Therefore,instead of the channel hopping from one fixed transceiver to another, thetransceiver itself hops from one frequency to another, in both cases, accordingto the algorithm and parameters selected.
Synthesized Frequency Hopping has the advantage of allowing an FHS tocontain one more frequency than the number of Carrier Units/TREs in thesystem. This is particularly useful in some microcellular applications where onlyone transceiver is available for Frequency Hopping.
Note: Normally, in both Frequency Hopping schemes (Baseband and Synthesized),timeslot 0 (TS0) is not available for Frequency Hopping. This is becauseit carries the BCCH, which must always be at maximum power and on afrequency known to mobile stations in Idle mode in the cell.
4.4 Speech TransmissionSpeech is transmitted over the air in the following ways:
Continuous transmission
Discontinuous transmission.
The system also uses Voice Activity Detection (VAD) when transmitting.The two transmission types and VAD are described separately. In addition,discontinuous transmission from the BSS to the MS and from the MS to theBSS is explained in detail.
4.4.1 Continuous Transmission
Sound is continuously encoded into digital information, even when no oneis talking.
In normal conversation, only one participant at a time talks. This is used by thesystem to its advantage, by transmitting only when someone is speaking.
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4.4.2 Discontinuous Transmission
Discontinuous Transmission and VAD work together to decrease the averagetransmission time on a channel. By transmitting only when actual speech ispresent, the system reduces the interference level generated by the network inboth the uplink and downlink directions and saves power.
In tandem with Frequency Hopping, this improves spectrum efficiency withoutjeopardizing the quality of the telephony service.
Only actual speech is digitally encoded and transmitted. During the non-speechphase (silent periods), noise/comfort mode information is sent once every 480ms instead of once every 20 ms for speech.
In this way the system:
Improves spectral interference
Increases power savings.
By transmitting at a reduced rate of 1 in 24 during the silent phases, the powerautonomy of the mobile station improves.
Discontinuous Transmission does not occur during half-rate speech or datamodes. It can be activated for either the uplink or the downlink or both.
The receivers of Discontinuous Transmission information can automaticallydetect that the transmitter is in Discontinuous Transmission mode by thereception of Silence Indication (SID) messages.
During quiet periods SID messages are sent instead of speech bursts. SIDscarry noise information about background noise. This information is used to:
Let the receiver know that the link is still open
Provide comfort noise. Users of telephones prefer to hear background noiserather than silence. Complete silence disturbs the listener.
Provide measurements of the link quality and timing advance. If there are
no bursts of data over the Air Interface for a particular channel, no powerlevel control and quality can be performed.
To eliminate the noise side effects generally known as banjo noise, the operatorcan ban Discontinuous Transmission on the downlink for all calls that areestablished on the BCCH TRX, without hopping, for all types of BTS. This isachieved using the FORBID_DTXD_NH_BCCH parameter. The parameter canbe set to one of two values:
0. This is the default value, and allows Discontinuous Transmission on thedownlink for all calls that are established on the BCCH TRX
1. This bans Discontinuous Transmission on the downlink for all calls thatare established on the BCCH TRX.
4.4.3 Voice Activity Detection
Voice Activity Detection (VAD) is used to detect when there is speech, silenceor just background noise. The VAD device is located in the Transcoder. Oncethe VAD detects speech, it starts transmitting speech bursts. After four burstsof detected silence, the VAD goes back into silent mode, and SID informationframes are transmitted (i.e., the comfort noise generation is activated).
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4.4.4 BSS Discontinuous Transmission Towards Mobile Station
Downlink Discontinuous Transmission is activated on a per call basis bycombining information from the MSC and the OMC-R.
The MSC informs the BSC about its downlink Discontinuous Transmissionpreference. It does this via the Downlink Discontinuous Transmission flag in theAssignment_Request or Handover_Request messages on a per call basis.
The OMC-R can enable or disable the possibility of downlinkDiscontinuous Transmission per BSC via the Discontinuous
Transmission_DOWNLINK_ENABLE parameter. This is a static parameter whichcan be set via the CMISE command M_ LOGICAL_PARAM_MODIFY. The overallsystem reaction is shown in the following table.
OMC-R DiscontinuousTransmission_ DOWNLINK_ENABLE (per BSC basis)
MSC Downlink_DiscontinuousTransmission Flag(per call basis)
ResultDiscontinuousTransmissionFlag
True Allowed ON
True Unavailable/notallowed
OFF
False Allowed OFF
False Unavailable/notallowed
OFF
Table 5: Downlink Discontinuous Transmission Status in Channel Activation
The MSC requests no downlink Discontinuous Transmission during mobilestation-to-mobile station calls, where double clipping can occur if both endsperform Discontinuous Transmission. This can have a staccato-like effecton speech.
The BTS tells the Transcoder to perform Discontinuous Transmission by settingthe Discontinuous Transmission bit in the speech frame.
In the BSS, the Transcoder is responsible for Discontinuous Transmissionoperation.
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In the BTS, the information is processed in the FU in the following way:
1. When the Transcoder detects voice activity it informs the FU, using in-bandsignaling. The speech signaling flag is set in the speech frame.
2. Every 20 ms the FU receives either speech frames or SID frames containingbackground noise characteristics.
3. At the end of the speech period (four bursts of detected silence) the FUsends a SID frame over the Air Interface.
4. During speech inactivity, the last received SID frame is sent at regular 480ms intervals rather than at 20 ms. Otherwise dummy bursts are sent.These dummy bursts are:
Transmitted for traffic channels on the BCCH frequency, due to the needfor constant transmission on the BCCH frequency
Not transmitted for traffic channels on other frequencies.
Note: The BTS uses the measurement_result message to inform the BSCthat Discontinuous Transmission is operating. The BSC compensates forDiscontinuous Transmission when calculating power control and handover.
4.4.5 Mobile Station Discontinuous Transmission Towards BSS
The OMC-R operator controls whether a mobile station can performDiscontinuous Transmission towards the BSS per cell. This information is sentin cell options information (sys_info 3 , and sys_info 6 on the Air Interface).The following table shows the available operator options.
Option Description
Will performDiscontinuousTransmission
This forces the mobile station to use DiscontinuousTransmission. It reduces the call quality but alsoreduces interference in the cell and saves mobilestation battery power. During silent phases only1 in 24 bursts are sent, which greatly reducesinterference.
Can performDiscontinuousTransmission
This allows the mobile station to choose either qualityby not using uplink Discontinuous Transmission,or power-saving by using uplink DiscontinuousTransmission.
Cannot performDiscontinuousTransmission
The OMC-R operator has decided, due to lowinterference, to have improved speech andmeasurement control on the uplink side.
Table 6: Operator Discontinuous Transmission Options
The Transcoder detects that the mobile station is in Discontinuous Transmissionmode by the reception of SIDs.
Note: There is a small quality reduction due to the fact that VAD only starts sendingspeech when a user starts to talk. This can cut the start of each speech activity.Power control and handover are also affected, as the BTS has fewer incomingmessages with which to calculate power and interference.
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The following figure shows the different forms of transmission.
DTX during ’Silence’ in uplinkSound continuously encoded
DTX during ’Silence’ in downlink DTX during ’Silence’ in up and downlink
Continuous Transmission
Discontinuous Transmission
DTX : Discontinuous Transmission
Figure 20: Different Forms of Discontinuous Transmission
4.5 Radio Power ControlRadio Power Control operates independently, but in a co-ordinated manner withthe handover to provide reliable service to the user.
Both directions of the radio link between the mobile station and the BTSare subject to continuous power adjustments. The power adjustment of theBTS and the mobile station are under the control of the BSC (see RadioMeasurements (Section 4.6.2)). RPC improves spectrum efficiency by limitingintra-system interference. It also increases the autonomy of the mobile stationby saving battery power.
The reasons for changing the mobile station power level are:
Uplink power level too high or too low
Uplink link quality too low, or using power resources beyond qualityrequirements of the call.
Similarly, the reasons for changing the BTS power control are:
Downlink power level too high or too low
Downlink link quality too low, or using power resources beyond qualityrequirements of the call.
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4.5.1 BTS Radio Power Control
The mobile station performs power measurements of radio signals beingtransmitted by the BTS. The mobile station, via the SACCH, regularly sends ameasurement_report message to the BTS indicating the quality and strengthof the downlink plus measurements of neighboring cells. This information iscombined with uplink measurements taken by the BTS and sent to the BSC inthe measurement_result message.
The BSC then alters the BTS power, based on the measurement information itreceives from the mobile station. The maximum power level is limited by themaximum power of the BTS, and also by the maximum power allowed in the cell.
The BTS power can be adjusted further than Unbalanced Output Power orCell Shared.
The BTS power can be reduced by the operator due to the following parameters:
BS_TXPWR_MAX
T3106-D
T3106-F
PWR_ADJUSTMENT.
The first 3 parameters on one side and the last one on other side are computedseparately. If one or the other is changed by the operator, the left one ischanged by the OMC.
4.5.2 Mobile Station Radio Power Control
The BTS measures the signal power transmitted by the mobile station. Theresulting measurements are combined with the measurement_report messagefrom the mobile station and are sent to the BSC in the measurement_result
message. The BSC sends commands to change the power level of the mobilestation as needed. The maximum power level is limited by the maximum powerof the mobile station, and also by the maximum power allowed in the cell.
Power control can be applied to traffic channels and Stand-Alone DedicatedControl Channels.
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4.5.3 Radio Link Measurements
Due to interference and signal quality problems on the Air Interface, the uplinkand the downlink transmissions are constantly measured to maintain maximumefficiency of the air waves. A balance is maintained between the transmissionpower, which can interfere with other cells using the same frequency, andthe quality of the actual link.
The following table shows the measurements used to achieve this balance.
Measurement Description
Signal strength Signal strength is calculated on both active andinactive channels.
On active channels, this measurement is used toprovide the actual strength of the signal receivedfrom the transmitter.
Inactive channel strength provides measurement ofinterference levels.
Signal quality The signal quality of a channel is calculated onthe average Bit Error Rate on a particular channel.BER is a standard quality calculation in radiotransmission.
Absolute mobilestation-BS distance
This is estimated by measuring the Time OfArrival (TOA) of the received burst at the BTS foreach allocated timeslot. The TOA is based ontransmission distance and not the actual grounddistance travelled. The calculation of one bit period(3.69 µs) corresponds to 550m.
The statistical parameters of signal level and quality are obtained over ameasurement period. This period is called the ’Reporting Period’. The reportingperiod for a traffic channel is 104 TDMA frames (480 ms). The information istransmitted in the SACCH frames.
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4.5.4 Power Control Decision and Handover
At every measurement interval, the BSC receives:
Pre-processed power measurement information (uplink and downlink)
Timing advance (distance information)
Power level information about neighboring cells (only the best six aretransmitted).
The BSC uses this information to perform power control by:
Lowering the power level in the uplink or downlink, as this has little effect
on the quality of the link
Increasing the power on the uplink or downlink if the link quality/level is low
Producing a handover alarm (refer to Handover Detection (Section 4.6.3) for
more information)
Taking no action, if the quality/level balance is acceptable.
The following figure illustrates the measurements described previously, aswell as power-control flow. Figure 21 shows how power control maintainsoptimum quality and power levels.
MS BTS BSC MSC
Interruption of SACCH frames
start counter connection failure indicationcause value
RF channel release clear request
MIE including cause valueclear command
MS : Mobile Station
TX : Transmitter
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Note: The signal and quality levels are converted into the ranges Received SignalLevel and Received Signal Quality respectively. Each range is classed from0-63 (Received Signal Level where 63 is high) and 7-0 (Received SignalQuality where 7 is poor).
High Quality
Low QualityLow Signal Level
High Signal Level
RXQUAL
RXLEV
Quality badIncrease power output
Signal level too highDecrease power output
Signal level too highQuality badHandover desired
Signal level lowIncrease power output
Desired balance
no change
RXQUAL : Received Signal Quality
RXLEV : Received Signal Level
Figure 21: Power Output Balancing Based on Received Quality and SignalLevels
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4.5.5 Change Power Levels
The BSC controls the power levels of the BTS and the mobile station.
The BTS power level can be altered down from its maximum power. This is donein 2 dBm steps to a minimum of -30 dBm from the maximum level. The BSCinforms the BTS of the new power level via a BS_power_control message.
The mobile station power level can be altered in steps of 2 dBm. The followingtable shows the maximum and minimum power ranges of mobile stations.
Mobile Station Phase GSM850/900/1800/1900 Max Power Min Power
Mobile station phase 1, GSM 900 43 dBm (20 W) 13 dBm
Mobile station phase 1, GSM 1800 30 dBm (1 W) 10 dBm
Mobile station GSM 850 39 dBm (8 W) 13 dBm
Mobile station phase 2, GSM 900 39 dBm (8 W) 13 dBm
Mobile station phase 2, GSM 1800 30 dBm (1 W) 4 dBm
Mobile station GSM 1900 33 dBm (2 W) 0 dBm
Table 7: Mobile Station Maximum and Minimum Power Ranges
The maximum power setting of a mobile station is based on two factors: itsclassmark (its physical maximum power rating), and the maximum mobilestation power setting for the cell.
Each cell can limit the maximum power level for all mobile stations in the cell.For example, a 20 W mobile station can be limited to 5 W maximum power ifthat is the maximum mobile station power level allowed in the cell. However, a 1W mobile station can never exceed 1 W, and can therefore never reach the5 W maximum allowed in the cell.
The BSC informs the BTS of the new power levels via the BS_power_control
message. The BTS in turn transmits a power_command to the mobile stationover the SACCH.
Changing power from one power level to another happens gradually. The powerlevel changes by 2 dB every 60 ms, until the desired level is reached.
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4.6 HandoverA handover changes an active call from one channel to another channel. Thenew channel can be in the same cell or another cell.
The types of handover are:
Internal
External
Directed retry
Incoming emergency
Fast traffic
UMTS to GSM.
Handovers ensure a high level of call quality. They are performed when theBSS detects that the call quality has dropped below a defined level, and thecall can be better supported by a different channel.
The call quality can drop due to problems in the cell, such as an interface oran equipment problem. Call quality can also be affected simply because themobile station has moved to an area where the radio coverage from anothercell is better.
The BSS detects the need for a handover by:
Measuring the Air Interface channel quality, mobile station and BTS power
outputs and the timing advance
Using an algorithm to see if the received information conforms to the criteriafor handover
Selecting a more suitable channel from a list of target cells and their
available channels.
If the BSS decides that a handover is required, the exact sequence of eventsdepends on the type of handover to be performed.
In all cases:
A new channel is assigned, ready to support the call
The mobile station moves over to the new channel
On successful completion of the handover, the system clears the resources
for the old channel.
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4.6.1 Principal Handover Types
The following sections describe the principal types of handover.
4.6.1.1 Internal HandoverInternal handovers take place between cells controlled by the same BSC. Thiscan include channel changes within the same cell. For more information aboutthese handover cases, refer to Target Cell Evaluation (Section 4.6.4).
4.6.1.2 External HandoverExternal handovers take place between cells controlled by different BSCs.These can be under the control of the same MSC or of different MSCs. Formore information about these handover cases, refer to Target Cell Evaluation(Section 4.6.4).
4.6.1.3 Directed Retry HandoverHandovers can also be performed when there is congestion in a cell. Ifcongestion exists, the traffic channel assignment can be queued. For moreinformation about congestion management, refer to Congestion (Section 3.5).
If there is no available traffic channel for the normal assignment procedure, aDirected Retry can be performed. A Directed Retry is an attempt to assign amobile station to a traffic channel in a cell other than the serving cell.
There are two types of Directed Retry:
An Internal Directed Retry without queueing attempts to hand over the call
to a traffic channel of a neighbor cell controlled by the same BSC.
An External Directed Retry attempts to hand over the queued call to a trafficchannel of a neighbor cell which is controlled by a different BSC.
4.6.1.4 Secured Incoming HandoverThe ability to keep free resources in a cell for incoming emergency and powerbudget handovers is provided on a cell basis. When the resource threshold isreached, assignments and other handover types are handled as if the cell wascompletely congested. Once such a request is queued, a directed retry can beperformed as usual. The free resources can also be accessed in the case of afull-rate to half-rate handover for AMR calls, because it allows half a resource(full-rate to half-rate) to be freed from the cell point of view. The featureimproves the quality of service, as it helps to limit the number of lost calls.
4.6.1.5 Fast Traffic HandoverThe fast traffic handover searches in the whole cell for a mobile which canperform a handover to a not-loaded neighbor cell if the received signal level ofthe BCCH is good enough. It is much more efficient than the forced directedretry when the overlap of adjacent cells is reduced, e.g., in the case of singlelayer networks, or for deep indoor coverage (if the umbrella cell does nottotally overlap the microcells).
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4.6.1.6 UMTS-to-GSM HandoverFor circuit-switched services, the BSS supports handover from UMTS to GSM.The handover from GSM to UMTS is not supported in this release of the BSS.A hard handover is performed from the UTRAN to the GSM BSS between aUMTS core network and a 2G MSC. This handover is regarded by the BSS asa GSM inter-BSS handover. The signaling procedures, from the BSS point ofview, rely almost on the normal GSM procedures.
For packet-switched services, the current 3GPP standard does not allowhandover with channel preparation. Therefore, the UMTS mobile stationreceives the 2G radio resource cell change order Information Element from theUTRAN in the Inter System handover message. The UMTS mobile station thenperforms an access request in the GPRS cell. From a BSS point of view, theUMTS mobile station is regarded as a 2G mobile station when it indicates that ithas selected a GSM cell.
4.6.1.7 Load-Based 3G Handover FilteringLoad-Based 3G Handover Filtering lets the BSS reject an incoming 3Ghandover when the G2 target cell is loaded and the MS is still within UTRANcoverage. The feature can be activated and de-activated. Load-basedhandover filtering only applies to service or traffic handovers. That is, handoverrequests with the cause "better cell", "traffic" or "directed retry". A handovercause indicating a problem in uplink or downlink signal quality or signal strengthis considered an emergency handover request and is accepted.
When load-based handover filtering is enabled, the BSC regularly calculatesthe cell load of the 2G cells to assess their 3G_HOReject_Load_State. TheBSC compares the last averages of the traffic load with an O&M threshold todetermine cell load state. The BSC uses the THR_CELL_LOAD_3G_REJECT
parameter to set the load threshold determining whether a 3G-to-2G handoverrequest is rejected or accepted. If THR_CELL_LOAD_3G_REJECT is set to 100 %,the feature is de-activated. Note that even if this feature is not activated, theBSC still calculates cell load, which is used for other handover procedures aswell.
Upon receipt of a 3G to 2G handover request:
1. The BSC checks the target cell traffic load by comparing the current loadto the threshold in THR_CELL_LOAD_3G_REJECT.
2. If the target cell is in 3G_HOReject_Load High State , the BSC checks thehandover cause IE given in the BSSAP handover request message.
3. If the handover cause IE does not indicate an emergency handover, the BSCrejects the HO request. Otherwise the request is accepted.
4. After rejecting the HO request, the BSC send a Handover_Failure
message with the cause indicating "no Radio resource available" andthe Cell Load Information.
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4.6.2 Radio Measurements
The BTS constantly monitors the radio link by:
Measuring the received signal strength for active channels
Measuring the received signal quality for active and inactive channels
Measuring the received signal timing for active channels
Collecting signal strength and quality measurements from the mobile
station for the active channel
Collecting adjacent cell BCCH signal strength measurements from themobile station (adjacent cell BCCH frequencies are sent to the mobile
station in the sys_info 5 message on the SACCH).
The mobile station sends its measurements to the BTS in a Layer 3 RadioResource measurement_report message on the SACCH. The mobilestation and BTS measurements are passed to the BSC in a Layer 3 RRmeasurement_result message. These messages are sent once permultiframe and are processed by the BSC.
The BSC uses this information to:
Perform power control for the BTS and mobile station
Calculate whether a handover is needed
Make traffic channel quality tables
Make the target cell list
Make a handover decision.
4.6.2.1 Power ControlFor more information about BTS and mobile station power control, refer toPower Control Decision and Handover (Section 4.5.4).
From a handover point of view, no handover decision is made due to signalquality until the power levels have been set to maximum.
4.6.2.2 Need for HandoverThe BSC calculates the need for a handover using an algorithm, the use ofwhich is described in Handover Detection (Section 4.6.3).
4.6.2.3 Target Cell ListA target cell list can be made by the BSC using the neighbor cell BCCHmeasurements sent by the mobile station. This is used to evaluate whether aneighbor cell can provide a better channel than the existing one.
4.6.2.4 Handover DecisionHandover decision is based on averaged measurements and the results areaveraged over a period of time. For example, the BSC detects the need fora handover, based on one measurement that may have been caused byfreak conditions changing the signal propagation for a short period. Thismeasurement is averaged with other measurements and a handover decisionmay or may not result, depending on the other measurements.
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4.6.2.5 Traffic Channel Quality TablesThe BSC uses the uplink idle channel measurements made by the BTS to makea table of traffic channels, classified by interference levels. This table is usedto select a channel for assignment.
4.6.3 Handover Detection
Each time the BSC processes a set of Air Interface measurements, it checkswhether a handover is needed. If the need for a handover is detected, ittriggers the target cell evaluation process. See Target Cell Evaluation (Section4.6.4) for more information.
If the handover algorithm in the BSC detects the need for a handover, itproduces a handover alarm. As the target cell evaluation is handled by theBSC, this alarm is also handled internally by the BSC. The alarm includes acause value used by the BSC to evaluate which type of handover is required.
The basic types of handover are:
Quality and level
Better zone
Better cell (power budget)
Distance
Mobile velocity dependent
Preferred band.
4.6.3.1 Quality and Level HandoverThese handovers are used to keep an active call connected when the signalquality falls below a defined threshold. If a handover is not performed, a radiolink failure may be detected and the call cleared.
This type of handover can be caused by the following events:
Quality level too low on the uplink or downlink
Signal level too low on the uplink or downlink
Interference level too high on the uplink or downlink
Signal level too low on the uplink or downlink compared to low threshold(microcells only)
Signal level too low on the uplink or downlink compared to high threshold(microcells only)
Several consecutive bad SACCH frames received (microcells only)
Signal level too low on the uplink or downlink inner cell (concentric cells
only).
For more information about microcell handovers, refer to Microcell (Section7.5.2). For more information about concentric cells, refer to Concentric Cell(Section 7.2).
If the received signal level or the received signal quality is too low, the BSCperforms BTS and mobile station power control to try and achieve the optimumlevel/quality ratio; seePower Control Decision and Handover (Section 4.5.4).
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The figure below shows a graph of received signal level and received signalquality. The hatched areas show where power control is successful. The solidgray shaded areas show where power control fails to achieve the desiredlevel/quality ratio. These areas are where the BSC detects the need for ahandover.
123456123456123456123456123456123456123456123456123456123456123456123456123456123456123456123456
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Power Increase to improve quality
Quality IntercellHandover
Quality IntracellHandover
High Quality
Level Intercell
HandoverReceived Signal Quality
Low Quality
Received Signal Level
High Level
Desired Quality
and Level Balance
(no action needed)
Power Decrease to
Conserve Resources
and Minimize Interference
PowerIncrease
to Improve
Level
Low Level
4.6.3.2 Level Intercell HandoverThe Level Intercell Handover area represents the range of measurementswhere the received signal quality is acceptable, but the received signal level istoo low. If the power output levels are already set to the maximum allowed inthe cell, the BSC generates a handover alarm with a cause value indicatingthe reason for handover. Although the quality of the signal is acceptable (andmay be very good), the call is in danger of being lost if the signal level dropsrapidly, causing a radio link failure.
The handover is an intercell handover, as the serving cell cannot support thecall at the required power level. The call is handed over to a channel in a cellwhich can support the call at the required level and quality.
4.6.3.3 Quality Intercell HandoverThe Quality Intercell Handover area represents the range of measurementswhere both the receive signal quality and the received signal level are toolow. If the power output levels are already set to the maximum allowed inthe cell, the BSC generates a handover alarm with a cause value indicatingthe reason for the handover.
The handover is an intercell handover, as the serving cell cannot support thecall at the required quality and power level. The call is handed over to a channelin a cell which can support the call at the required quality and level.
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4.6.3.4 Quality Intracell HandoverThe Quality Intracell Handover area represents the range of measurementswhere the received signal quality is too low, but the received signal level isacceptable. This situation is caused by interference on the channel, so the callis handed over to another channel in the same cell.
4.6.3.5 Better Zone HandoverThis is used in concentric cell configurations when the mobile station movesinto the inner zone. If the inner zone has a free channel, an interzonehandover is triggered. This enables the mobile station to be supported on achannel requiring a lower power level, therefore creating less interference inthe cell. The detection of this type of handover is performed on signal levelmeasurements only (SACCH of serving cell, BCCH of adjacent cells), as shownin the following figure. This type of handover can be caused by the signal levelbeing too high on the uplink and downlink outer zone (concentric cells only).
High PowerOuter Zone
MS HandedOver toLow PowerZone
Low PowerInner Zone
MS : Mobile Station
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4.6.3.6 Better Cell HandoverThis feature is used to handover the mobile station to a cell that can support thecall using lower BTS and mobile station power levels. The algorithm in the BSCcalculates the power levels for the current cell, and the power levels required byadjacent cells from the adjacent cell information sent by the mobile station.This is shown in the figure below.
This type of handover is often referred to as a power budget handover, as ituses the Power Budget parameter to detect whether an adjacent cell can beused (see also Multiband Power Budget Handover in Multiband Handover(Section 4.6.3.9)). If the power budget for an adjacent cell gives a ’better’reading for a certain amount of time (a defined number of SACCH frames),then a handover alarm is produced.
This type of handover can be caused by the following events:
Power budget is greater than handover margin threshold
High signal level in neighbor microcell (macrocell to microcell handover).
BSS 1 = Best Cell BSS 2 = Best Cell
Target CellBSS 2
Serving CellBSS 1
Zone for Power Budget Handoverfrom BSS 1 to BSS 2
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4.6.3.7 Distance HandoverThis handover occurs when the propagation delay between the BTS and themobile station is considered excessive. The mobile station is considered tobe too far from the BTS and needs to be served by a closer BTS. This isshown in the figure below.
Under normal circumstances, as the mobile station moves away from a BTS, aQuality and Level or Better Cell handover takes place. However, under certainconditions which change the propagation qualities of a signal, a cell canprovide a very high quality signal outside of the normal operating range of theserving cell. These propagation qualities are often due to climactic conditionswhich can change suddenly. If the high quality signal ’disappears’ due to achange in the weather, the call would be lost. The distance handover ensuresthat this does not happen by handing the mobile station over to a ’closer’ cellonce a distance limit is exceeded. This type of handover is caused by too greata distance between the mobile station and the Base Station.
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Area of NormalCell Boundaries
Distance HandoverArea from BSS1 to BSS2
BSS 1 BSS 2
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4.6.3.8 Mobile Velocity Dependent HandoverIn a hierarchical cell structure, where mini or microcells are overlaid byan umbrella cell (macrocell), fast moving mobile stations are handled bythe upper layer cell.
Discrimination of the speed of a mobile station is based on the dwell time ofthat mobile station in a lower layer cell. Depending on the time elapsed in theserving cell, the call is transferred to the lower layer cell or the umbrella cell.
If the dwell time in the serving cell is above the threshold, the mobile stationis considered slow moving and is sent to the lower layer cell that triggeredthe handover.
If the dwell time is below the threshold, the mobile station is considered fastmoving. To prevent a high number of handovers between the smaller lowerlayer cells, the call is sent to the umbrella cell.
Dwell time is only calculated if there is a power budget handover from anotherlower layer cell.
This is to avoid sending a call to the umbrella cell in the following cases:
A call initiated at the limit of the lower layer cell
A call transferred from the umbrella cell to the lower layer cell, just before
reaching the limit of that cell
After an external handover, when there is no information on the preceding
cell and handover cause.
Whatever the dwell time, any emergency handover sends the call to theumbrella cell, which acts as the rescue cell.
The load on the umbrella cell is taken into consideration when determiningthe threshold at which handovers are performed. Saturation of the umbrellacell can cause the loss of calls, when a handover is required from anotherumbrella cell or a lower layer cell.
As the load on the umbrella cell increases, the dwell time threshold isincreased, keeping some mobile stations in the lower layer cells. When theload on the umbrella cell is very high, speed discrimination is disabled, andpriority is given to the load in the umbrella cell. The following figure shows agraph of umbrella cell load and minimum dwell time.
Load in Umbrella Cell
MinimumDwell Time
Macrocell with little traffic
Macrocell saturated
Traffic regulation
High load
Low minimum dwell time
High minimum dwell time
Speed discrimination
disabled
Max speed discrimination
in force
Low load
Figure 22: Umbrella Cell Load in Mobile Velocity Dependent Handover
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4.6.3.9 Multiband HandoverThere are two types of multiband handover: Preferred-band handover andMultiband Power Budget handover. They are described below.
Preferred-Band HandoverNetwork capacity can be expanded by introducing multiband operation. Thismeans that an existing network (for example, GSM 900) is expanded byadding cells in a different band (for example, GSM 1800). In such a network,the original band (GSM 900) is referred to as the first band. The new band(GSM 1800) is referred to as the preferred band.The existing monoband mobile stations, which use the first band, continue todo so. However, multiband mobile stations are handed over to the preferredband, where possible. This is done to free resources in the first band for useby monoband mobile stations. Normal handovers (for example, better cellhandover), hand over multiband mobile stations to the preferred band.A new handover type, called preferred-band handover, hands over multibandmobile stations immediately when a first-band cell reaches a specifiedcongestion threshold. This frees up resources for the monoband mobilestations in the cell.
For a preferred-band handover to occur, the following conditions must bemet:
The first band cell’s traffic load reaches a high threshold
Suitable neighboring cells in the preferred band are available
The preferred band handover facility is enabled.
Multiband Power Budget Handover
In certain networks, two different frequency bands can exist. For example,one frequency band uses the GSM 900 frequencies, the other frequencyband uses the GSM 1800 frequencies. In this case, multiband power budgethandovers can be enabled between the two frequency bands using theEN_MULTIBAND_PBGT_HO parameter:
Setting the EN_MULTIBAND_PBGT_HO parameter to ’True’ enables
multiband power budget handovers between two frequency bands
Setting the EN_MULTIBAND_PBGT_HO parameter to ’False’ disables
multiband power budget handovers between two frequency bands.
This parameter must be defined for each cell where multiband powerbudget handovers are required.
4.6.4 Target Cell Evaluation
Cell evaluation is performed by the BSC. Once a handover alarm is detectedwithin the BSC, it evaluates the neighbor cells and compiles a list of possibletarget cells. The serving cell can be on the target cell list.
The cells are evaluated and ranked by preference, calculated by one of thetwo algorithms, ORDER or GRADE. The Network Operator chooses whichalgorithm is to be used on a cell-by-cell basis.
The BSC tries to hand over to the most suitable cell. If this cell is controlledby the BSC, the BSC handles the handover procedure. If the target cell iscontrolled by another BSC, the serving BSC sends a Handover_Request
message to the MSC.
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4.6.4.1 Target CellThe exact calculation performed to choose the target cell depends on thealgorithm used and the cause of the handover alarm.
The target cell is selected, taking into account the following criteria:
Received signal level
Power budget
Number of free channels
Relative load on the traffic channel of the cell
Maximum power allowed in cell
HO_MARGIN parameter
Mobile station distance from target BTS
Handover cause.
The HO_MARGIN parameter is an O&M parameter set by the Network Operator.It is used to prevent a call being continually handed over between two cells. Forexample, following a power budget handover, the new cell immediately startspower budget calculations for its neighbor cells. It may find that the original cellis giving a better power budget reading and try to hand back immediately. Thiseffect can be caused by slight climactic changes which affect the propagation ofsignals. It is known as the ’ping-pong’ effect. The HO_MARGIN parameter stops acall being handed back to a cell from which it has just been handed over.
There is also an O&M parameter, W_PBGT_HO which can be set by the OMC-Roperator, to add a weighting for the power budget parameters of cells controlledby another BSC. Refer to the 9153 OMC-R Configuration Handbook for moreinformation.
The target cell chosen also depends on the mobile station classmark (seeClassmark Handling (Section 3.6)) and its compatibility with the BTS’s cipheringcapabilities (see Ciphering (Section 3.8)).
The procedures initiated to hand over a call depend on which cell is chosen asthe target cell.
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4.6.4.2 Target Cell HandoversDepending on which cell is chosen as the target cell, one of the followinghandovers takes place.
This handover occurs... If the target and serving cell are...
Internal: Intracell The same, the call is handed over to a channel in the same cell. Thisis an intracell handover. This type of handover is most commonly dueto interference in the cell. It is controlled by the BSC
Internal (IntraBSS): Intercell Not the same but are controlled by the same BSC, this is called anintercell intraBSS handover. This handover is normally controlled bythe BSC. However, the Network Operator can specify that this type ofhandover be controlled by the MSC
External (InterBSS): IntraMSC Not controlled by the same BSC, but the two BSC are controlled bythe same MSC, this is called an interBSS intraMSC handover. Thishandover is controlled by the MSC.
External (InterBSS): InterMSC Controlled by different BSCs and the two BSCs are controlled bydifferent MSCs, this is called an interBSS interMSC handover. Thecontrol of this handover is shared between the MSCs.
Handovers controlled by the BSC are called internal handovers.Handovers controlled by the MSC are called external handovers.
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4.6.5 Synchronous and Asynchronous Handover
The handover to the target cell can be synchronous or asynchronous. Asynchronous handover can be performed if the master clocks of the serving celland the target cell are synchronized.
This is the case when:
The serving cell and the target cell are the same cell
The BTS of the serving cell and the target cell are in a collocatedconfiguration.
BTS in a collocated configuration take the clock pulse from one BTS in theconfiguration.
For a synchronous handover, the mobile station does not have to resynchronizewith the target BTS. Therefore, the physical context procedure for power levelsand timing advance does not have to be performed after the mobile stationaccesses the target cell.
For an asynchronous handover, the mobile station has to synchronize withthe target cell before transmitting any user traffic.
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4.6.5.1 Asynchronous External Handover - Message FlowThis section describes the message flow for an asynchronous externalhandover. The example in the figure below is for a handover of a traffic channelbetween two separate cells controlled by two different BSCs.
MS BTSTarget
BTSServing
BSCTarget
BSCServing
MSC
release withserving BTS
HO detectHO alarm
set up switching path between Abis
& A interfaces
handover detect
measurement reports (SACCH)
handover command
ch+cell+HOref+cipher
measurement results
handover required
channel activation
SACCH/FACCH
channel activation ackhanover request ack
+ handover command
handover command
handover command
Synchronization(FCCH + SCH)
access burst (SACCH)handover detect
HO ref + TAhandover detect
physical info
establish indication
physical info (FACCH)
ack
handover complete
(FACCH)
handover performed
clear command
handover request
channel type+cipher+cell IDs+DTX+cause+cm
1
2
3
4
5
6
DTX : Discontinuous Transmission
FACCH : Fast Associated Control Channel
HO : Handover
MS : Mobile Station
SABM : Set Asynchronous Balanced Mode
SACCH : Slow Associated Control Channel
TA : Timing advance
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4.6.5.2 Asynchronous External Handover ProcessFor Asynchronous External Handovers, the following process applies:
1. The mobile station and BTS take measurements on the Air Interfaceas described in the previous procedure. The mobile station sendsmeasurement information to the BTS in a measurement_report message.The BTS sends mobile station and BTS measurements to the BSC in ameasurement_results message.
2. The BSC detects the need for a handover and creates a handover alarmindicating the reason for the handover. The BSC evaluates possible targetcells and creates a candidate cell list.
To initiate the external handover procedure, the BSC sends aHandover_Required message to the MSC including the candidate celllist. It also starts a timer to prevent it sending the same cell list. It canonly re-send the cell list when the timer times out, or if it receives aHandover_Request_Reject message from the MSC.
The MSC chooses the target cell from the cell list. It sends aHandover_Request to the target BSC to inform it that a mobile station isgoing to be handed over. This message contains:
Channel type required
Cipher mode information
Mobile station classmark information
Serving cell identification
Target cell identification
Downlink Discontinuous Transmission flag
Handover cause.
3. The target BSC initiates the channel activation for the new channel with theChannel_Activation message.
The target BTS sets its resources to support the new channel, starts sendingthe SACCH/FACCH and sends a Channel_Activation_Acknowledgment
message to the target BSC.
4. The target BSC builds a handover command. This command is sent to theMSC in the Handover_Request_Acknowledgment message. The handovercommand contains:
The new channel and its associated control channel
The target cell description
A handover reference
Any cipher mode information (phase 2 mobile stations can change cipher
mode during a handover procedure).
The MSC forwards the Handover_Command message to the serving BSC.
The serving BSC sends the Handover_Command message to the mobilestation.
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5. The mobile station releases its connection to the serving BTS. Itsynchronizes with the target BTS using the FCCH and SCH information.Once synchronized, the mobile station continually sends access burst onthe uplink SACCH until it receives the Physical_Information message onthe FACCH from the target BSC.
When the target BTS receives an access burst, it checks the handoverreference and calculates the timing advance. This is sent to the target BSCin the Handover_Detect message.
The target BSC informs the MSC of the handover detection and establishesa switching path between the allocated Abis and A Interface resources.
6. When the mobile station receives the Physical_Information message, itsends its first frame on the new channel using the timing advance sent in thePhysical_Information message.
The target BTS acknowledges the mobile station’s first frame andsends an Establish_Indication message to the target BSC, and anacknowledgment to the mobile station. On receipt of the acknowledgment,the mobile station sends a Handover_Complete message on the uplinkFACCH to the target BSC.
The target BSC informs the MSC that the handover is performed.
The MSC initiates the call clearing procedure towards the serving BSC.
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4.6.6 Circuit-Switched Telecom Handovers
In order to optimize the regulation of circuit-switched traffic load, specifichandovers may be triggered, as described below.
Specific Handover Description
Capture A capture handover refers to a handover triggered only on the signal levelreceived from the neighbor cell, independently of the signal received fromthe serving cell.
Power Budget A power budget handover refers to a handover triggered on a power budgetcriterion.
The power budget is a measure of the difference between the signal levelreceived from a neighbor cell and the signal level received from the servingcell. The higher is the power budget, the more likely a power budget handoveris triggered.
Cause 14 Handover Cause 14 is used in hierarchical networks to unload the umbrellacells by directing slow mobile station towards a lower or indoor layer cell.Mobile station speed is estimated by measuring the residence time of themobile station in the indoor and lower layer cells. If this residence time isbelow a certain threshold, the mobile station is deemed to move rapidly. If theresidence time is above another threshold, the mobile station is deemed tomove slowly.
Cause 21 In multiband networks, the operator defines a preferred band where multibandmobile station are directed. Handover Cause 21 is triggered when a mobilestation in the non-preferred band receives a good signal level from a neighborcell where the traffic load is not high and which belongs to the preferred band.
Cause 23 Handover Cause 23 reduces the serving cell size when it is high loadedrelative to a low loaded neighbor cell. The traffic handover enables betterdistribution of traffic in the serving cell neighborhood. When the mobile stationmoves away from the BTS, as the path loss increases, the power budgetincreases and a traffic handover is triggered sooner. The power budget isused to evaluate the difference between the signal levels received from theneighbor cell and from the serving cell.
Cause 24 In hierarchical networks where cells use different frequency bands, a generalcapture handover Cause 24 is required to manage, on a per cell adjacencybasis, the ability of the mobile station to be captured by a neighbor cell. Thisallows capture from a macrocell to a microcell or from the same macrocell toanother cell in the preferred band. This general capture handover takes intoaccount the load in the serving cell and in the target cell.
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4.6.6.1 Traffic Handovers in Multiband Mono-layer NetworksIn some multiband networks, the radio coverage is ensured by GSM 1800 cellsin one geographical area and by GSM 900 cells in another geographical area.As these cells form a multiband mono-layer network, the capture handoversbetween cells of different bands are inefficient in regulating circuit-switchedtraffic load in the serving cell neighborhood. The solution consists of allowingintra-layer traffic handovers (Cause 23) based on a power budget evaluationbetween cells of different bands.
4.6.6.2 Inhibition of Capture Handovers for "Single Layer" Serving CellTo avoid the ping-pong effect in multilayer or multiband networks, capturehandovers are inhibited. The T_INHIBIT_CPT timer controls the time duringwhich the capture handover Causes 14, 21, and 24 are inhibited. This timerstarts when an emergency handover is performed towards the serving cell, andthe preceding cell does not belong to the same layer or to the same frequencyband as the serving cell. The timer T_INHIBIT_CPT starts if the serving cell isin the upper or lower layer, but not if the serving cell is in the single layer. Thisimprovement extends the capture handover inhibition mechanism.
4.7 Overload ControlA lot of telecommunications signaling is required for the BSS to supportcommunication between mobile stations in the cells under its control andthe MSC. Telecommunication processors in the BTS or BSC can becomeoverloaded.
To avoid a sudden loss of communication when a processor becomessaturated, the BSS controls the load on these processors as follows:
1. Taking local action to reduce the load.
2. Taking global BSS action to further reduce the load.
Note: The telecommunications processors of the MSC can also become overloaded.However, MSC overload control is not the domain of the BSS.
4.7.1 BTS Overload
The BTS Frame Unit (TRE for a BTS 9100 or BTS 9110) handles all thetelecommunications signaling on the Air Interface. If the FU or TRE becomessaturated, this can result in the loss of calls. Therefore, the BTS monitors theload and takes action where appropriate. On initial detection of the overloadcondition, the BTS takes local action to reduce the load. If the BTS local actiondoes not reduce the load, the BTS sends overload messages to the BSC,which can decide to take global action.
The different stages of BTS overload, from detection to resolution, aredescribed below.
The BTS monitors the load on the FU or TRE by measuring the free time onthe FU or TRE’s Signaling Control Processor and the free message space onthe associated buffers. If either of these passes a set threshold, a counter isincremented. If a threshold is not passed again within a given time, the counteris decremented. The counter has two thresholds. If the first of these is passed,the BTS takes local overload action. If the second of these is passed, the BTSsends overload messages to the BSC.
When local action is triggered in the BTS, it discards low priority messagessuch as the Establish_Indication message to reduce the load on the SCP.
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4.7.2 BSC Overload
The BSC provides two entities for handling telecommunications signaling:
The TCU handles telecommunications signaling for the Abis Interface
The DTC handles telecommunications signaling for the A Interface.
The following sections describe the different stages of BSC overload, fromdetection to resolution.
4.7.2.1 BSC Overload DetectionFor the BTS, overload is calculated on the processor free time and the freemessage space of the associated buffers. As the BSC handles more signalingtraffic than the BTS, the detection of an overload, and whether to trigger local orglobal defense actions, is more complicated. The BSC uses an algorithm thattakes into account which processors are affected, the level of overload, andwhich buffers are affected. Each processor has a local overload controller.The BSC’s centralized overload controller is responsible for global overloaddefense actions.
4.7.2.2 BSC Local Overload ActionLocal action in the BSC is taken by the local overload controller on eachprocessor. Local actions reduce the load on an individual board.
The local actions are:
TCU ActionThe TCU discards a percentage of the measurement_result messagesreceived from the BTS. The percentage of discarded messages is increasedand decreased in steps, under the control of the local overload control. Thisonly affects the handover and power control algorithms, which still functionbut with less information.
DTC ActionWhen the DTC detects an overload, its state is set to congested on theBSC database. This means that it cannot be selected by the resourcemanagement software to provide a new SCCP connection. Also, the DTCcannot send connectionless messages to the MSC.
BSC Global Overload ActionThe BSC controls global actions for the whole BSS. Global action reducesthe amount of telecommunications signaling traffic in the BSS by inhibitingnew calls. The BSC bars mobile station access classes either in one cellif the global action is requested by a BTS or TCU, or in several cells ifa DTC or MSC are overloaded.
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4.7.2.3 Mobile Station Access Class BarringWhen the BSC receives a request for global overload action from a BTS,from the MSC, or from one of its local overload control processors, it checksthe message for errors. If it can accept the request, it builds new systeminformation messages (1 to 4). These messages are sent on the BCCH. Theybar certain mobile station classes from sending Channel_Request messageson the RACH.
If the overload condition persists, the BSC can change the system informationmessages to bar more mobile station access classes from using the RACH.
When the BTS is barring access classes, its behavior can be modified fromthe OMC-R by modifying the following parameters:
AUTO_BAR_CELL enables/disables the automatic barring of cells after all
access classes have been barred. This forces the mobile station to campon another cell
AUTO_BAR_EC enables/disables the automatic barring of emergency calls
EN_BSS_OVRL_CLASS_BARR enables/disables the ability of the BSC to
perform global action for BTS-to-BSC overload conditions.
It is also possible to configure the number of access classes that can be barredand unbarred in one step from the OMC-R.
4.7.2.4 Mobile Station Access Class UnbarringWhen an overload message is received from the BTS or when an overload isdetected in the BSC, a timer is set. If no overload message is received from theBTS, or no overload detected in the BSC during the period of the timer, thetimer expires. When the timer expires, the BSC unbars some access classesaccording to a defined algorithm.
4.8 Call Re-establishment by the Mobile StationThe mobile station initiates call re-establishment when there is already aspeech or data call in a stable state (traffic channel path connected) andthe mobile station detects a radio link failure. The mobile station waits apredetermined time for a response from the network. If there is no response,the mobile station performs a cell reselection procedure.
If the new cell allows the re-establishment procedure to be performed, themobile station initiates the channel request procedure RACH and awaits theImmediate_Assignment message. The mobile station then performs thecontention resolution procedure using the cm re-establishment request
message.
The radio and link establishment procedure continues as described inMobile-Originated Call (Section 3.2).
The network can block the mobile station from performing the channel requestprocedure, due to inhibition of the mobile station access class broadcast inthe sys_info 1 to 4 messages. If this is the case, the mobile station radioresource entity reports the failure of the radio and link establishment procedureto the higher layer entities in the mobile station.
When the MSC receives the cm re-establishment request message, itinitiates the procedures necessary to establish a new radio resource connectionand continue the call management connection.
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5 Call Release
This section provides an overview of the Call Release process and describesthe procedures which ensure resource allocation to a call.
It also describes Remote Transcoder Alarms, and the processes used tobreak a connection and disconnect the resources, depending on the nature ofradio transmission.
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5.1 OverviewThe Call Release procedures ensure that resources allocated to a call are freefor reuse when they are no longer required by the current call.
Call Release procedures are required when:
A call is finished and either the called or calling party hang up
A mobile station is turned off
A call is handed over and the resources for the original call are released
A call is modified and the resources for the original channel are released
There is operator intervention, such as a channel being blocked
There is a failure
There is a radio link failure
The system detects an LAPDm failure.
If a call is terminated normally, the Call Release procedures are triggeredautomatically. If the call is terminated abnormally, the system has to detect thatthe resources are no longer required and release them.
For a complete Call Release, the following resources must be released:
A Interface resources
Abis Interface resources
Air Interface resources
MSC resources:
Layer 3 for the A Interface
SS7 signaling for the A Interface
Layer 1 physical resources for the A Interface.
BSC resources:
Layer 3 for the A, Abis and Air Interface
Layer 2 SS7 for the A Interface and LAPD for the Abis Interface
Layer 1 physical resource for the A and Abis Interface.
BTS resources:
Layer 3 for the A, Abis and Air Interface
Layer 2 LAPD for the Abis Interface and LAPDm for the Air Interface
Layer 1 physical resources for the Abis and Air Interface.
Mobile station resources:
Layer 3 for the Air Interface
Layer 2 LAPDm for the Air Interface
Layer 1 for the Air Interface.
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5.2 Call Release Procedures in Normal ServiceThe Call Release procedures, and the order in which they are triggered,depend on the reason for the release.
This section describes the following Call Release scenarios, which occurduring normal service:
Normal Release (calls terminated by Call Management)
Calls terminated following a channel change.
Note: A VGCS call uses the same general call release procedures as a standard call;any exceptions are described in the relevant procedure descriptions below.
For more information about special cases, including detailed behavior of theMSC, BSC, BTS and mobile station, refer to Call Release - Special Cases(Section 5.3).
5.2.1 Normal Release
Call termination initiated by Call Management is considered to be a normalreason for Call Release. In this type of Call Release, the MSC initiates therelease. Before this can happen, the mobile station must inform the MSC thatit has disconnected the call. This is done with Layer 3 messages passedtransparently through the BSS between the mobile station and MSC, as shownin the following figure.
MS BSS MSC
disconnect (layer 3 CC)
release complete (layer 3 CC)
release request (layer 3 CC)
MS : Mobile Station
Figure 23: Mobile Station Disconnecting a Call
When a mobile station disconnects a call:
1. Once the MSC has confirmation that the mobile station wants to disconnectand no longer requires the connection, it initiates the release proceduretowards the BSC. This procedure:
Releases the circuit (if applicable)
Releases the SCCP connection.
2. The BSC responds to the MSC to clear the connection on the A Interface,and initiates the Call Release procedure toward the BTS and mobile station.This procedure releases the radio resources.
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3. This action triggers the mobile station to release the LAPDm connection(disc message) and the BSC to release physical resources allocated tothe call.
This is shown in the following figure.
MS BTS BSC MSC
release of A interface resources
Timer start (SCCP release)
Timer start (release indication)
Timer
Timer
disable remote TC alarm detect
disc
channel release
deactivate SACCH
clear command
MIE including cause value
(to release LAPDm)
UArelease indication
physical context request
physical context confirm
RF channel release
RF channel release ack
clear complete
SCCP release complete
SCCP released
LAPDm : Link Access Protocol on the Dm Channel
MIE : Mandatory Information Element
MS : Mobile Station
SACCH : Slow Associated Control Channel
SCCP : Signal Connection Control Part
TC : Transcoder
UA : Unnumbered Acknowledgment
Figure 24: Normal Call Release
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5.2.1.1 MSC ActionsThe MSC initiates Call Release at the end of the mobile station transaction.The MSC can be informed of the end of the mobile station transaction:
By a level 3 disconnection message from the mobile station (Figure 23)
By a disconnection message from the Network Operator if thecorrespondent terminates the call
At the end of a service call (i.e., SMS or location updating).
The normal release procedure of the MSC releases both the A Interfaceresources used for the call, if any, and the SCCP connection used for thesignaling which controls the connection.
MS BTS BSC MSC
release of A interface resources
Timer start (SCCP release)
Timer start (release indication)
channel release
deactivate SACCH
clear command
MIE including cause value
clear complete
SCCP release complete
SCCP released
1
2
3
4
MIE : Mandatory Information Element
MS : Mobile Station
SACCH : Slow Associated Control Channel
SCCP : Signal Connection Control Part
Figure 25: Initiation of Normal Release by MSC
When the MSC initiates a normal release procedure:
1. The MSC initiates the release procedure by sending a Clear_Command
message to the BSC. This command can include a cause value in theMandatory Information Element.
2. The BSC accepts the command even if no cause value is included. Itimmediately releases the A Interface resources for the call and replies to theMSC with a Clear_Complete message.
3. The BSC initiates the release of the Abis and Air Interface resources. Italso sets a timer to ensure that the MSC releases the SCCP signalingresources. On receipt of the Clear_Complete message from the BSC, theMSC releases the resources associated with the A Interface and initiates therelease of the SCCP signaling resources by sending the SCCP_released
message to the BSC.
4. The BSC stops its timer and sends the SCCP_release_complete message.The SCCP resources are now released and can be used for another call. Ifthe BSC timer expires before the SCCP_released message is received, thenthe BSC force releases the SCCP connection.
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The MSC also initiates two types of call release for VGCS calls:
Uplink release requested by the BSSWhen the BSS detects that the mobile station is no longer connected, itsends the MSC an Uplink_Release_Indication message containingthe Radio_Interface_Failure message. When the MSC receives thismessage, it initiates the release of the radio and terrestrial resourcesassociated with the call.
Uplink release requested by the MSCThe MSC initiates the release of the radio and terrestrial resourcesassociated with the call when it detects that the previous talking servicesubscriber is no longer talking, or that the talker has left the group call area.
When a mobile station belonging to another BSC area has successfully sizedthe VGCH, the MSC informs the BSC. The BSS then notifies the other mobilestations that the channel is busy.
5.2.1.2 BSC/BTS/Mobile Station InteractionsThe normal Call Release procedure towards the mobile station/BTS releasesthe:
Radio resources associated with the call
Radio Frequency channel.
The call release procedure is as follows:
1. The BSC initiates the release of the radio resource by sending:
A Channel_Release message to the mobile station via the BTS
A Deactivate_SACCH message to the BTS.
2. The Channel_Release message prompts the mobile station to senda disc message to the BTS to release the LAPDm resource. Whenthis is received, the BTS acknowledges this with a ua message tothe mobile station and sends a Release_Indication messageto the BSC. This procedure is supervised by a timer in the BSC.The BSC considers the mobile station to be disconnected and starts theRF channel release when:
The timer expires
The BSC receives the Release_Indication message and stops the
timer.
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3. When the BTS receives the Deactivate_SACCH message, it stopssending SACCH information and disables the remote Transcoder alarmdetection. This stops the sending of Transcoder alarms to the BSC whenthe Transcoder detects inactivity on the channel. This is shown in thefigure below. If the mobile station does not receive the Channel_Release
message, it considers the stopping of SACCH information as a radio linkfailure and performs a local release.
MS BTS BSC MSC
release of A interface resources
Timer start (SCCP release)
Timer start (release indication)disable remote TC alarm detectdisc
channel release
deactivate SACCH
clear command
MIE including cause value
(to release LAPDm)
UArelease indication
clear complete
SCCP release complete
SCCP released
1
2
3
LAPDm : Link Access Protocol on the Dm Channel
MIE : Mandatory Information Element
MS : Mobile Station
SACCH : Slow Associated Control Channel
SCCP : Signal Connection Control Part
TC : Transcoder
UA : Unnumbered Acknowledgment
Figure 26: BSC/BTS/Mobile Station Interactions in Normal Call Release
Once the BSC considers the mobile station disconnected, it initiates releaseof the RF channel from the BTS. In a normal Call Release procedure, thisoccurs following the release of the mobile station from the Air Interface (asdescribed earlier in this section).
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4. Before releasing the RF channel, the BSC sends a physical_context
message to the BTS and starts a timer to supervise the response. Theresponse from the BTS is a physical_context_confirm message whichcontains the last LAPDm performance measurements for the RF channel.
5. On receipt of the physical_context_confirm message, or after thetimer has timed out, the BSC sends an RF_Channel_Release messageto the BTS and starts a timer to supervise the release. The BTSreleases the level 1 and 2 resources for the channel and replies with anRF_Channel_Release_ack message.
On receipt of the acknowledgment, the BSC releases all resources for theRF channel. This is shown in the following figure.
MS BTS BSC MSC
Timer
Timer
physical context request
UA
release indication
physical context confirm
RF channel release
RF channel release ack
4
3
5
MS : Mobile Station
UA : Unnumbered Acknowledgment
Figure 27: Normal Release Final Steps
If the timer supervising the release times out, the BSC sends theRF_Channel_Release message again and restarts the timer. If the timertimes out again, the BSC releases all resources locally. It also sends anO&M error report to the OMC-R with a cause value indicating that the RFchannel release procedure has failed.
Note: The RF channel can be released locally by the BTS and still be active. If theRF channel is still active, it is released when the BSC attempts to assign it toanother call with a Channel_Activation message. The BTS replies with aChannel_Activation_Nack and the BSC releases the channel (refer to CallSet Up (Section 3) for more information).
For VGCS calls, when the mobile station terminates the call, the VGCH isreleased and other mobile stations can attempt to seize the VGCH in order tobecome the subsequent talking mobile station in the VGCS call.
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5.2.2 Calls Terminated Following a Channel Change
This section describes the Call Release procedure following a successfulchannel change procedure. The case presented is an external intercellhandover. For an internal channel change, the serving and target BSCs are thesame, and in some cases, the serving and target BTS are the same.
For calls terminated following a channel change:
1. The target BSC receives confirmation of the successful handover from themobile station when the mobile station sends the Handover_Complete
message. This message is passed transparently through the target BTS.See Call Handling (Section 4) for more information about handovers.
2. The target BSC informs the MSC of the handover and initiates the CallRelease procedure towards the serving BSC, by issuing a Clear_Command
message.
3. The serving BSC issues a Channel_Release message to the mobile stationand a Deactivate_SACCH message to the serving BTS.
The normal Call Release procedure described in Normal Release (Section5.2.1) continues between the serving BSC, the serving BTS, the MSC and themobile station. This is shown in the following figure.
MS BTSTarget
BTSServing
BSCTarget
BSCServing
MSC
handover complete
channel release
handover performed
MIE including
cause value
deactivate SACCH
clear command
(FACCH)
FACCH : Fast Associated Control Channel
MIE : Mandatory Information Element
MS : Mobile Station
SACCH : Slow Associated Control Channel
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5.3 Call Release - Special CasesCall Release can occur for reasons outside normal service.
This section treats the following special cases in which Call Release happens:
Call Release following Reset
BSC-initiated Call Release
BTS-initiated Call Release
Mobile station-initiated Call Release
Remote Transcoder alarms.
5.3.1 Call Release Following Reset
Resets are used in software/hardware failure situations, or when the databaseis corrupted and recovery procedures have failed. The MSC can reset all callswithin a BSC or an individual circuit. For example, if the MSC loses dynamicinformation regarding calls (i.e., preventing it from providing such services asaccounting), it can send a reset or a reset_circuit message to the BSC.
5.3.1.1 ResetThe MSC initiates Call Release when it has to release all calls associatedwith the BSS (Reset).
The MSC sends a reset message containing a cause value to the BSC.The BSC then:
Sends an alarm to the OMC-R
Sends a block message to the MSC to block circuits
Starts to clear all calls in the BSS. For each call, the procedure in NormalRelease (Section 5.2.1) is repeated.
For each SCCP connection on the A Interface, the BSC can send anSCCP_release message and release any A Interface resources associatedwith the SCCP.
A timer allocates a certain amount of time for the calls to clear. When the timerexpires, the BSC sends a reset_ack message to the MSC. Figure 28 showsthe Call Release process after a reset is initiated.
5.3.1.2 Reset CircuitThe reset circuit procedure is initiated from the MSC. The procedure informsthe BSC that an individual circuit is no longer active in the MSC. This triggersthe call clearing procedure if the circuit has an active SCCP connection.
The MSC sends a reset_circuit message to the BSC for each circuit to bereset. Depending on the resources allocated, this can trigger the BSC to:
Release the A Interface resources
Initiate the release of the SCCP
Initiate Call Release towards the BTS and mobile station.
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MS BTS BSC MSC
circuits blocked
timer
reset
channel release
send alarm to OMC−R block
SCCP release
SCCP release complete
SCCP release
SCCP release complete
reset ack
channel release
release indication
discto release LAPDm
discto release LAPDm
physical context request
physical context confirmindication RF channel
release
release
RF channel release ack
context requestphysical
physical context confirm
RF channel release
RF channel release ack
LAPDm : Link Access Protocol on the Dm Channel
MS : Mobile Station
SCCP : Signal Connection Control Part
Figure 28: Call Release Following Reset
Note: If this procedure is invoked due to SCCP problems, then messages on the AInterface may not be passed. The MSC and BSC locally release resourcesfor the A Interface connections. Refer to BSC-Initiated Release (Section5.3.2) for more details.
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5.3.2 BSC-Initiated Release
The BSC is involved in Call Release for both the A Interface and Abis/Airinterfaces.
The BSC initiates Call Release on the A Interface when events internal to theBSS terminate communication with the mobile station.
The Call Release towards the mobile station can already be in progress orhave finished when the BSC initiates a release on the A Interface. If themobile station is still connected when the BSC initiates a release on the AInterface, the release towards the MSC is triggered by the Clear messagefrom the MSC to the BSC.
5.3.2.1 Towards the MSCThe BSC initiates the release towards the MSC by sending a Clear_Request
message. It also starts a timer to supervise the procedure. The MSC releasesresources for the A channel and sends the Clear_Command message to theBSC. This command contains a cause value indicating that the BSC initiatedthe release.
From this point, the Call Release follows the procedure described for normalCall Release (refer to Normal Release (Section 5.2.1)). The procedure startswith the BSC releasing A channel resources. It initiates the release proceduretowards the mobile station (if still attached), and returns a Clear_Complete
message to the MSC. This sequence is shown in the following figure.
MS BTS BSC MSC
clear request
MIE including cause valueclear command
MIE : Mandatory Information Element
MS : Mobile Station
Figure 29: BSC-initiated Call Release Toward the MSC
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5.3.2.2 Towards the Mobile Station/BTSThe Call Release procedure towards the mobile station/BTS releases:
The radio resources associated with the call
The RF channel.
The BSC initiates the release of the radio resource by sending:
A Channel_Release message to the mobile station via the BTS
A Deactivate_SACCH message to the BTS.
This is the Normal Release procedure described in Normal Release (Section5.2.1).
Note: In this process, once the BSC considers the mobile station disconnected, itinitiates release of the RF channel from the BTS.
This can occur following:
The release of the mobile station from the Air Interface (as in the NormalRelease procedure)
A handover, when the BSC is sure that the mobile station has successfullychanged to the new channel. Refer to Calls Terminated Following a Channel
Change (Section 5.2.2).
An immediate assign procedure failure. This ensures that the SDCCH isavailable for reuse as quickly as possible
A normal assignment failure or handover failure. This ensures that the traffic
channel is available for reuse as quickly as possible.
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5.3.3 BSC-Initiated SCCP Release
The BSC initiates an SCCP release when a release procedure has failed orinactivity is detected in the BSC SCCP entity.
Failed Release Procedure
If there are no resources allocated to a call and the normal release of theSCCP connection has failed, the BSC forces the release of the SCCPconnection:
Internally by sending a level 3 command to its SCCP entity
Externally by sending an SCCP_released message to the MSC.
The BSC does not wait for a reply from the MSC before releasing theSCCP connection.If the original failure is due to a problem on the SCCP connection or inthe BSC SCCP entity, the SCCP_released message may not be sent. Ifthe message is sent, the MSC replies with an SCCP_release_complete
message and releases any allocated resources.
Inactivity Procedure
The BSC performs an inactivity procedure for each SCCP connection. Ifthe BSC detects inactivity, it assumes that the associated transactionis no longer active and therefore:
Performs Call Release on the Air and Abis interfaces
Initiates a reset circuit procedure if an A channel is active
Initiates the release of the SCCP connection.
5.3.4 BTS-Initiated Call Release
The BTS initiates a Call Release only if it detects a LAPD failure or whenO&M requests a restart of the BTS.
Otherwise the role of the BTS in Call Release is to:
Relay channel release messages to the mobile station
Deactivate the SACCH under control of the BSC
Send a release_indication message to the BSC when the mobile stationreleases the LAPDm connection.
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5.3.4.1 LAPD FailureWhen the BTS detects a LAPD failure on a link between one of its frame unitsand the BSC, it forces the release of all mobile stations on active channelsassociated with that Frame Unit (TRE for a BTS 9100 or BTS 9110).
The BTS stops SACCH frames and sends a Layer 2 disconnect message toeach affected mobile station. It also starts a timer to supervise each LAPDmdisconnection. The LAPD connection cannot be re-established until the BTSreceives an acknowledgment, or the timer expires for each LAPDm connection.
If a mobile station sends an acknowledgment, the BTS releases the RFresources.
If a mobile station does not respond, the BTS continues to send Layer 2disconnect messages up to a predefined number. It then waits for the timer toexpire and the BTS releases the RF resources.
Note: If the maximum number of disconnect retries is reached, the BTS LAPDm entitysends an error report to the BSC. This does not stop the timer supervisingthe disconnection.
When all mobile stations are disconnected, the BTS attempts to re-establishthe LAPD connection. The BTS then sends an error report to the BSC witha cause value indicating O&M intervention. This cause value indicates thatthe FU or TRE has cleared all calls.
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The BSC re-initializes the link with the frame unit and starts Call Release for theaffected calls with the MSC. This sequence is shown in the following figure.
MS BTS BSC MSC
Detection of LAPD failure. BTS stops
sending SACCH frames.
timer
timer
timer
release RF resources
release RF resources
release RF resources
Re−establish LAPD connection
Re−initialize FU or TRE link
disc
disc
disc
UA
UA
UA
error reportcause value
clear request
MIE including cause valueclear command
clear complete
FU : Frame Unit
LAPD : Link Access Protocol on the D Channel
MIE : Mandatory Information Element
MS : Mobile Station
SACCH : Slow Associated Control Channel
TRE : Transmitter/Receiver Equipment
UA : Unnumbered Acknowledgment
Figure 30: BTS-initiated Call Release following LAPD Failure
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5.3.4.2 O&M InterventionThe BTS initiates a Call Release if its O&M entity requests a restart of a FrameUnit (TRE for a BTS 9100 or BTS 9110).
The FU or TRE’s response to a restart request is to stop sending frameson the Air Interface. The BTS starts a timer to supervise the disconnectionof the mobile stations. The timer allows enough time for the mobile stationsto detect a radio link failure due to the lack of SACCH frames. The BTS RFperforms a local release.
The BTS resets the FU or TRE and waits for the timer to expire. When thetimer expires, the FU or TRE attempts to re-establish the LAPD link with theBSC. The BTS sends an error report to the BSC with a cause value indicatingO&M intervention.
The BSC releases the RF resources and initiates a Call Release with the MSC.
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5.3.5 Mobile Station-Initiated Call Release
The mobile station can initiate a Call Release by:
Initiating a radio link failure
Disconnecting the LAPDm connection.
5.3.5.1 Mobile Station-Initiated Radio Link FailureIf SACCH frames are no longer received from the mobile station, the BTS startsto count the number of missing frames. When the BTS has counted a certainnumber of missing SACCH frames, it considers that the radio link has failed.
This happens when the mobile station ’disappears’ from the Air Interface(caused by adverse radio conditions, the mobile station is switched off, fatalerror, etc.).
Note: There is an optional feature where, after a number of missing SACCH frames,the BSC sets both mobile station and BTS power to maximum in an attempt toregain the Air Interface. If the BTS continues to register missing frames, theradio link fails as described below.
The BTS sends a connection_failure_indication message to the BSC witha cause value indicating that the radio link has failed. The BSC initiates NormalCall Release procedures to the BTS by sending an RF_Channel_Release
message to the BTS and a Clear_Request message to the MSC. This isshown in the following figure.
MS BTS BSC MSC
Interruption of SACCH frames
start counterconnection failure indication
cause value
RF channel releaseclear request
MIE including cause valueclear command
MIE : Mandatory Information Element
MS : Mobile Station
SACCH : Slow Associated Control Channel
Figure 31: Call Release due to Mobile Station-Initiated Radio Link Failure
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5.3.5.2 Mobile Station-Initiated LAPDm DisconnectionIf the mobile station has an error which unexpectedly terminates the call,it sends a disconnect message to the BTS. The system reaction to thedisconnect message in this instance is the same as when the disconnect
message from the mobile station is prompted by a Channel_Release messagefrom the BSC (as explained in BSC-Initiated Release (Section 5.3.2)).
5.3.6 Remote Transcoder Alarms
If the Transcoder detects a break in communication with the BTS, it sets atimer. This timer is defined by GSM standards. On expiration of this timer, theTranscoder sends an alarm to the BTS. If the BTS remote Transcoder alarmdetection is active, a connection_failure_indication message is sent tothe BSC with a cause value indicating a remote Transcoder alarm.
If the BTS detects a break in communication with the Transcoder, it sends aconnection_failure_indication message to the BSC with a cause valueindicating a remote Transcoder alarm. See the figure below.
During an internal handover, this can cause remote Transcoder alarms toarrive at the BSC, as the connection is still active but the call is handed over.The BSC ignores these alarms for a guard period on new and old channelsduring handover.
connection failure indicationcause value
RF channel releaseclear request
clear command
MS BTS BSC MSC
TC detects a communication break and times out
Alarm
MIE including cause value
MIE : Mandatory Information Element
MS : Mobile Station
TC : Transcoder
Figure 32: Call Release Due to Communication Failure Detected by Transcoder
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5.4 Preserve Call FeatureThe Preserve Call feature avoids locking the cell before modifying its logicalconfiguration. The OMC-R marks the TRXs that are impacted by themodification and the BSC shuts down traffic only on those TRXs, preservingthe ongoing calls on other TRXs.
The OMC-R provides the WTC in the Cell-Frequencies-Type group. This WTCis the one which applies by default to cell shutdown.
Modifying a TRX means changing its baseband definition and/or its radiodefinition. The radio definition of a TRX is the allocation of a frequency or of anFHS/MAIO. If the definition of an FHS is changed, the TRXs which use thisFHS must also be considered as modified.
5.4.1 Normal Release
In Normal Release, Preserve Call is set to ’False’ if one of the followingparameters is modified:
attached-sector (PC=False on modified TRX)
ARFN (TRX-TS) (PC=False on modified TRX)
ARFN-Set (FHS) (PC=False on TRX using the concerned FHS)
MAIO (PC=False on modified TRX)
HSN (PC=False on modified TRX)
Channel-Type (PC=False on modified TRX)
Zone_Type (PC=False on modified TRX)The OMC-R considers that the Zone_Type value for a single cell is NotRelevant.When the transition from Not Relevant to another value is not triggered onthe concerned TRX, it remains set to ’False’.
If the TS0 of the TRX which is carrying the BCCH frequency is impacted,all calls must be shut down on the cell. In this case, the OMC-R marks all
TRXs as impacted.
This is the case when there is a modification of the:
BCCH frequency
CBCH channel : combined <-> non-combined.
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5.4.2 Abnormal Release
In the following cases, even if the Preserve Call flag is not set to ’False’ by theOMC-R, calls are released at TRX or at cell level:
Add TRX in a cell and the BSC TCH-RM Entity managing this cell (TrafficChannel Resource Manager) is fullInside the BSC software, the TCH-RM entities manage the radio timeslotallocation on a cell basis. A cell, mapped on a sector, is mapped on aTCH-RM entity. A TCH-RM entity can manage several cells with a maximumcapacity based on the total number of TRX that is limited to 90.If a cell is extended with one or several TRX, the TCH-RM entity managingthe cell takes into account the new TRX. If, adding the TRX, the limit of 90 isexceeded, the concerned cell can no longer be managed by this entity.This cell is mapped automatically by the BSC on another TCH-RM. In thisspecific case, all calls are released on this cell
Due to the "adjust" algorithm, TRX(s) with Preserve Call set to true aredisturbed in remapping
Once the BSC has unmapped and remapped all TRX(s) with Preserve Call
set to ’False’ , the BSC can be in one of the following situations:
There are more TRX than TRE configured
There are enough TRE configured but some are not available
In both cases, the BSC checks whether a recovery is performed to ensurethe availability of the TRX with the highest priority. The application of therecovery also leads to the release of some TRE.
The OMC-R facility "Check Telecom Impact" related to PRCs is based on the"preserve calls" parameter value. Consequently, in the three cases mentionedabove, the result of the check is not accurate.
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6 Handling User Traffic Across the BSS
This section describes the flow of speech and data traffic across the BSS.
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6.1 OverviewThe BSS performs traffic handling in the uplink and downlink directionsfor speech and data.
The BSS uses the BSC and BTS to perform the required radio transmission,control and baseband functions of a cell and to control the BTS in its domain.
Transmission provides the efficient use of the terrestrial links between theBSS components.
Together, these components perform the required encoding and rate adaptationprocedures.
6.2 SpeechSpeech is passed from the mobile station to the PSTN and from the PSTN tothe mobile station. This section describes how speech is encoded from themobile station to the PSTN, as shown in the following figure. Speech in theopposite direction follows the reverse process and so is not described.
BTS BIE BIE SMBSC MSCSM
A 13 kbit/s 64 kbit/s A/D13 kbit/sCIM
TC
MobileStation
Full Rate Speech TCH
Half Rate Speech TCH
A 6.5 kbit/s 64 kbit/s13 kbit/sCIM A/D6.5 kbit/s
PSTN
A : Analog
A/D : Analog/Digital
BIE : Base Station Interface Equipment
CIM : Channel Encoded, Interleaved, and Modulated
PSTN : Public Switched Telephone Network
SM : Submultiplexer
TC : Transcoder
TCH : Traffic Channel
Figure 33: Encoded Speech Transmission Across the BSS with 9120 BSC
The scheme is similar in the BSS with an 9130 BSC, excepting the BIE andSM 9120 BSC transmission components, which are supported by virtualprocessors.
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6.2.1 Analog
The microphone converts speech to an analog signal.
The analog signal is encoded into a digital signal depending on the type oftraffic channel used:
13 kbit/s for a full-rate traffic channel (or enhanced full-rate)
6.5 kbit/s for a half-rate traffic channel.
It is then transmitted on a 16 kbit/s (8 kbit/s for half-rate) radio timeslot. 3kbit/s and 1.5 kbit/s are used for signaling on full-rate and half-rate channelsrespectively.
6.2.2 Interleaving and Forward Error Correction
To pass speech over the Air Interface, error checking and redundancy areincluded to make sure speech information is correctly transmitted. This ensuresthat valid continuous speech is passed through the BSS.
Error correction is based on high redundancy with complicated parity and cyclicredundancy methods. This is done to ensure that many types of parasitic andsporadic errors are detected and to some degree, corrected. In the case ofspeech, there is cyclic coding, convolutional and parity error encoding of thedata. The speech data starts as 260 bits (112 bits) and, after forward errorchecking, is encoded as a 456 bit block (228 bit block).
These blocks are then split into eight (four for half-rate), and interleaved withadjacent blocks into TDMA frames to be transmitted as radio wave bursts.This means that if some of the blocks are lost during transmission, there isa high chance that the other blocks hold enough redundancy to still have avalid speech block.
6.2.3 Speech Data Bursts
The interleaved blocks are transmitted over the Air Interface and are thenreassembled in the BTS. As described above, when the interleaved blocks arereassembled and checked for parity errors, there is a high chance that the datacan be recovered. In speech data the most significant bits are heavily protectedand are always transmitted at the start of a TDMA frame. This ensures thateven if the speech block cannot be reassembled, at least the most significantspeech data can be used to provide a close approximation.
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6.2.4 Digital Speech
Speech bursts are returned to digital speech blocks in the BTS. They are sentto the Transcoder as 13 kbit/s digital speech, plus 3 kbit/s for in-band signalingif they are full-rate speech. The channels on the Abis and Ater interfaces are64 kbit/s. The speech blocks have to be multiplexed on to these links. This isshown in the figure below.
Half-rate speech is sent to the BSC on the Abis Interface as 6.5 kbit/s, plus1.5 kbit/s signaling. Two half-rate 8 kbit/s channels are associated togetherinto a 16 kbit/s channel. On the Ater Interface a 16 kbit/s submultiplexingscheme is used for all types of traffic. The two paired 8 kbit/s Abis channels areindependently switched by the BSC onto two 16 kbit/s Ater channels.
SMSM
Ater Interface Ater−mux Interface
BSC
30 x 16 kbit/s user traffic channelsper link
90 x 16 kbit/s user traffic channelsper link
30 x 16 kbit/s user traffic channels per link
MSC
A Interface
30 x 64 kbit/s user traffic channels per link
Ater Interface
TC
SM : Submultiplexer
TC : Transcoder
Figure 34: Multiplexed Ater Interface
This scheme corresponds to the 9120 BSC. For 9130 BSC, there is no SMor Ater interface beside the BSC.
6.2.5 Digital 64 kbit/s A-law Encoded Speech
The Transcoder converts the 13 kbit/s digital speech to the 64 kbit/s A-lawencoding. This is a standard digital speech interface for ISDN and PSTNexchanges. The information passes through the MSC and is sent to the PSTN.
The Transcoder performs rate adaptation in both directions.
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6.2.6 Enhanced Full-Rate
Enhanced full-rate provides advanced speech encoding on a full-rate trafficchannel, for improved voice quality and user comfort. The feature uses acodec with ACELP coding.
Enhanced full-rate is enabled in the BSC, on a cell-by-cell basis, by the O&Mparameter EFR_ENABLED. When an enhanced full-rate call is set up, thefollowing process occurs:
1. The mobile station makes a call requiring speech, in which it announces itscodec preferences to the MSC in the Set_Up message.
2. The MSC passes appropriate Assignment_Request and Handover_Request
messages to the BSC.
3. The BSC uses the codec list supplied by the MSC to choose the correctcodec, based on the support for the codec in the BTS and A InterfaceTRAU equipment.
4. The BSC activates the selected channel in the BTS, giving the indicationof codec type.
5. The BTS configures itself to handle the correct channel coding, and startssending TRAU frames to the TRAU, in order to configure the TRAU.
6. The BSC builds either an Assignment_Command message or aHandover_Command message, indicating to the mobile station which codec itshould use when accessing the new channel.
7. Once the mobile station is attached, the BSC reports the selected codectype to the MSC.
8. In case of subsequent handover, if the BSC has had to change the codec,the BSC informs the MSC of the change.
For more information concerning enhanced full-rate, refer to the 9153 OMC-RConfiguration Handbook.
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6.2.7 Half-Rate
Half-rate speech channels allow the operator to save timeslots on the AirInterface when the number of available frequencies is very limited. Half-rateuses a different encoding algorithm than full-rate, in order to minimize anyperceived loss of comfort by the subscriber. Use of the half-rate feature doescreate extra overhead on the A Interface.
Half-rate is activated on a per-cell basis. In effect, the cell is capable ofoperating in Dual Rate mode, permitting either half-rate or full-rate trafficchannels to be allocated. VGCS calls can be use either standard full-rate orhalf-rate channels.
Half-rate can be applied to BSSs with the following equipment:
BSC 9120
BSC 9130
G2 Transcoder
9125 Transcoder
One of the following BTS:
G1 BTS equipped with Dual Rate Frame Unit
G2 BTS equipped with DRFU
Alcatel-Lucent BTS.
6.2.8 Adaptive Multiple Rate
Adaptive Multiple Rate (AMR) increases the quality of speech duringconversations and also increases the offered capacity due to the provision ofhalf-rate channels.
When looking at current GSM codecs (full-rate, half-rate, and enhancedfull-rate), each of them answers only one facet of capacity and qualityrequirements:
Enhanced full-rate brings a higher speech quality than full-rate but with
no noticeable impact on capacity
Half-rate provides an answer to capacity requirement, but suffers from poorspeech quality in bad radio conditions, or mobile station-to-mobile station
calls when TFO (see Tandem Free Operation (Section 3.9)) cannot be used
AMR is a new technology defined by 3GPP which relies on two extensive setsof codec modes. One is defined for full-rate and one for half-rate.
When used in combined full-rate and half-rate mode, AMR brings new answersto the trade-off between capacity and quality:
Speech quality is improved, both in full-rate and half-rate
Offered capacity is increased due to the provision of half-rate channels.
This allows the density of calls in the network to be increased, with only
a low impact on speech quality.
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The AMR technology also provides the advantage of a consistent set of codecs,instead of the one-by-one introduction of new codecs.
Alcatel-Lucent offers two versions of AMR:
Full-rate mode only, for operators who do not face capacity issues and wantto benefit from the optimized quality of speech
Combined full-rate/half-rate mode, for operators who want to benefit from
the above defined trade-off between quality of speech and capacity.
Through these codec mode adaptations, AMR is able to adapt the sharing ofspeech information and speech protection to current radio conditions, whichcan vary greatly, depending on location, speed, and interference. Therefore, forany radio conditions, the Alcatel-Lucent BSS is able to offer the best existingcodec, thus the best existing voice quality.
AMR functionality can be activated by configuration of the cells and the BTSradio resources in all the network elements (OMC-R, BSC, BTS). The relevantalgorithms are activated on a call-by-call basis. On the radio interface, the AMRcan only be used with AMR mobiles. On the A Interface , the AMR can onlybe used if the NSS implements it.
The AMR capability is available on a cell-by-cell basis.
This feature is compatible with VGCS.
The AMR Wideband (AMR-WB) codec is developed as a multi-rate codec withseveral codec modes like the AMR codec. Like in AMR, the codec mode ischosen based on the radio conditions. This feature is not compatible with TFO.
The following table refers to supported software versions versus hardwareboards and features.
HW Board/Feature AMR NB withoutTFO NB
TFO NB TFO FR, HR,EFR
AMR WB inclTFO WB
Legacy MT120 yes no yes no
MT120-NB yes no yes no
MT120-WB yes no yes yes
Table 8: Software Version versus Hardware Board/Feature
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6.2.8.1 AMR Normal AssignmentAMR is controlled on a per call basis by the MSC.
1. The MSC sends an Assignment_Request message to the BSC.In the Assignment_Request message, the MSC gives the Channel typeIE, which indicates:
In octet 4, if full-rate or half-rate is to be used and if the BSS is allowed to
change
In octet 5 and above, octets indicate that AMR is allowed in half-rate orfull-rate.
2. The BSC activates the channel in the BTS by sending aChannel_Activation message, containing the IE Multirate configuration. Itindicates the subset of codecs used for full-rate (or half-rate, respectively)link adaptation, the threshold and hysteresis sent to the mobile station forfull-rate (or half-rate, respectively) link adaptation and, optionally, the startmode (i.e., the initial codec mode).
3. If the initial codec mode is not given, the BTS chooses the default start modedepending on the number of codec modes contained in the subset.
4. Once the channel is activated within the BTS, the BSC sends all AMRrelevant parameters to the mobile station in the Assignment_Command
message.
5. When the speech path is established and synchronization is performedbetween the Transcoder and the BTS, the BTS checks if the Requestor Indication Flag (RIF) given in the TRAU frame is coherent with thetype of codec mode (Indication or Command) that should be sent on theradio interface. If necessary, a CMI_CMR alignment command is sentto the Transcoder.
6. Once the BTS detects that downlink CMI/CMR is synchronized between theTRAU frames and the radio interface, it starts codec mode adaptation.
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6.2.8.2 AMR O&M ManagementThe table below summarizes the main O&M configuration parameters that canbe changed by the operator from the OMC-R.
Parameter Description
AMR_SUBSET_FR Bitmap of 8 bits defining the codec subset for AMR full-rate(1 to 4 codecs out of 8), on a per BSS basis.
AMR_SUBSET_HR Bitmap of 6 bits defining the codec subset for AMR half-rate(1 to 4 codecs out of 6), on a per BSS basis.
EN_AMR_CHANNEL_ADAPTATION Flag on a per cell basis, used only for AMR calls, to enableor disable intracell handovers for channel adaptation.
EN_AMR_HR Flag on a per cell basis to enable or disable AMR. This flagis used for AMR half-rate.
EN_AMR_FR Flag on a per cell basis to enable or disable AMR. This flagis used for AMR full-rate.
OFFSET_CA_NORMAL Offset for the channel mode adaptation hysteresis undernormal load. It can take a value from 0.0 to 7.0 (step = 0.1)on a per cell basis.
OFFSET_CA_HIGH Offset for the channel mode adaptation hysteresis underhigh load. It can take a value from 0.0 to 7.0 (step = 0.1) ona per cell basis.
RXQUAL_CA_NORMAL Threshold for channel mode adaptation under normal load.It can take a value 0.0 to 7.0 (step = 0.1) on a per cell basis.
RXQUAL_CA_HIGH Threshold for channel mode adaptation under high load. Itcan take a value from 0.0 to 7.0 (step = 0.1) on a per cellbasis.
AMR_THR_3,
AMR_THR_2,
AMR_THR_1
Definition of thresholds on a per BSS basis.
AMR_HYST_3,
AMR_HYST_2,
AMR_HYST_1
Definition of thresholds and hysteresis, on a per BSS basis
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6.2.9 Channel Mode Adaptation
Channel mode adaptation is the change from one full-rate channel to anhalf-rate channel and vice-versa. This adaptation is independent from thecodec mode currently used.
This feature is available when the AMR half-rate option is installed.The operator has direct operational control of it through the parameterEN_AMR_CHANNEL_ADAPTATION used for both changes from full-rate to half-rateand from half-rate to full-rate.
Full-Rate Channel Adaptation Due to High Radio QualityThis channel adaptation involves ongoing AMR full-rate communicationswithin cells where half-rate is enabled. During any AMR call, the downlinkradio quality is reported by the mobile station through the RX_QUAL. Atthe same time, the uplink radio quality is evaluated by the BTS through theRX_QUAL, and both are compared to a load-dependent threshold. Indeed,in a cell heavily loaded, a half-rate channel will be preferred, even if thequality is not optimal. Whenever both uplink and downlink radio quality arehigher than this threshold, then an intracell handover takes place from afull-rate to a half-rate channel. To take into account the load, two differentthreshold values are used. The change will also only be performed if thecurrent channel type is dual rate and it authorizes changes.
Half-Rate Channel Adaptation Due to Low Radio QualityThis channel adaptation involves ongoing AMR half-rate communications,using a dual-rate channel type authorizing changes. During any suchAMR call, the downlink and uplink radio quality are evaluated with thesame metrics as stated for the full-rate channel adaptation, and the samethreshold comparison is performed. If either uplink or downlink radio qualityare lower than this threshold, then an intracell handover takes place from ahalf-rate to a full-rate channel. To take into account the load, two differentthresholds are also used but they differ from the ones used in full-rateadaptation by an offset value which is also cell load dependent. This offsetallows a hysteresis to be introduced between full-rate and half-rate channels.
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6.2.10 VGCS
Voice Group Call Service (VGCS) is a BSS feature that allows speechconversation for a predefined group of up to 6 mobile stations in half duplexmode on the Air Interface.
VGCS enables a calling mobile station to establish a voice group call todestination mobile stations belonging to a predefined group call area andgroup ID. VGCS typically involves multiple group members in a small groupcall area, which is comprised of one cell or a cluster of cells. Group call areasare predefined in the network by the service provider, and co-ordinated bythe network operator.
The calling and destination mobile stations are any mobile stations that havesubscribed to the related group ID or any dispatcher whose ID is pre-registeredwith the network.
Destination mobile stations are all mobile stations or groups of mobile stationsidentified by the group ID which are currently located in the group call area, andpre-registered dispatchers.
When a mobile station initiates a VGCS call, the group call area is uniquelyidentified by the actual cell in which the mobile station resides at the momentof VGCS call initialization, and by the group ID it sends. When a dispatcherinitiates a VGCS call, the dispatcher is connected to a related predefined groupcall area. The entitlement of the dispatcher is checked by the MSC to verify thecalling identity. Since a dispatcher may be registered to more than one groupcall area and group ID, an indication of the wanted group call area and group IDis given in form of a dedicated address called by the dispatcher.
The service permits only one calling mobile station to talk at any moment, whileup to five dispatchers can be talking simultaneously at one time. Dispatcherswill hear all combinations of voices other than their own. Listening mobilestations will hear the combination of all voices.
For more information about VGCS call set up, call management and callrelease, refer to:
Call Set Up (Section 3)
Call Handling (Section 4)
Call Release Procedures in Normal Service (Section 5.2).
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6.3 Circuit-Switched Data ModesThere are two types of circuit-switched data modes:
Transparent
Non-transparent.
For more information, refer to:
Transparent Mode (Section 6.3.1)
Non-Transparent Mode (Section 6.3.2).
The following figure illustrates data transmission across the BSS.
BTS BIE BIE SMBSC MSCSM
A 13 kbit/s 64 kbit/s A/D13 kbit/sCIM
TC
V.110 data blocks ISDN/Analog
MobileStation
PSTN
A : Analog
A/D : Analog/Digital
BIE : Base Station Interface Equipment
CIM : Channel Encoded, Interleaved, and Modulated
PSTN : Public Switched Telephone Network
SM : Submultiplexer
TC : Transcoder
Figure 35: Data Transmission Across the BSS
6.3.1 Transparent Mode
Transparent data mode is based on the V.110 protocol. V.110 is an ITUrecommendation. It specifies how ISDN supports DTE. It also specifies thetransport of synchronous/asynchronous data over a synchronous link.
Data is packaged and sent to the Transcoder in the same way as speech. It isconverted to the 64 kbit/s ISDN format for data transmission. Error handling isdealt with by the Air Interface.
Transparent mode implies that the following functions are performed by theBSS:
Interleaving and Channel Coding
Rate adaptation.
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6.3.1.1 Interleaving and Channel CodingInterleaving for data is more complicated than for speech. The data block is splitinto 22 parts for interleaving 9.6 kbit/s and 4.8 kbit/s data rates. For 2.4 kbit/s,the interleaving is the same as speech. The lower the data rate, the more spacecan be used for redundancy and error detection. This lowers the error rate.
The Air Interface performs the error handling. The V.110 data packets aregrouped together and transmitted across the Air Interface exactly like speech.The table below shows the data rate and error rate. A low data rate providesmore space for a better forward error correction scheme, in turn reducingthe number of errors.
6.3.1.2 Rate AdaptationData is packaged differently in V.110 for different data rates. The bandwidth isreduced and therefore the rate is lower. See the table below for the rateconversions. The Transcoder plays the final role in the rate adaptation whenthe data stream is adapted to 64 kbit/s packets.
There is a difference between data and speech rate adaptation. Speech isencoded to A-law, while data is transposed to the first bit and, if required, thesecond bit of a Pulse Code Modulation (PCM) byte. PCM transmission is at 8000 bytes (64 kbit/s). The 8 kbit/s and 16 kbit/s intermediate rates (before theTranscoder) are transposed as 1 or 2 bits per byte respectively.
User Rate Intermediate Rate Radio InterfaceError Rate (atFull-Rate)
9600 16 kbit/s 12 kbit/s 0.3%
4800 8 kbit/s 6 kbit/s 0.01%
<=2400 8 kbit/s 3.6 kbit/s 0.001%
Table 9: Circuit-Switched Data Rate Conversions Across the Air Interface
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6.3.2 Non-Transparent Mode
Non-transparent data mode is similar to transparent data mode, although datais transmitted as packets from the modem on the mobile station to the modemin the PSTN. Error handling is handled end-to-end.
Non-transparent data mode is a data transmission protocol. It is based onsending RLP packets as four V.110 frames. This is the same process usedin transparent mode. Interleaving and channel coding are still used, as theyare in the transparent mode. The RLP adds extra protection and also allowsthe retransmission. Packing RLPs in four V.110 frames ensures transparencyover the network. RLP packet size is the same as a radio block size, so itis transmitted as one radio block.
Non-transparent data mode uses a 12 kbit/s radio interface rate. Interleavingand channel coding are at 9.6 kbit/s (the same as in transparent mode). Theonly difference between transparent and non-transparent modes for the BSS isthe processing of the four V.110 frames of an RLP packet.
Error handling and rate adaptation are handled as follows:
Error HandlingNon-transparent data mode has a better error rate as there is no forwarderror checking or interleaving. Therefore, the size of packets remains smalland less prone to errors. There are however, some cyclic redundancy bytesand the protocol is very similar in principle to LAPD.
Rate AdaptationThere is no rate adaptation in non-transparent mode. The rate can only beadapted by physically transmitting less than the full bandwidth available.The data rate is also limited by the number of errors, as packets have to beretransmitted. The difference between transparent and non-transparentmode data links is transparent to the Transcoder, but not to the BTS.The Transcoder, as described in transparent mode, puts the data in thefirst bits of a PCM byte.The BTS must ensure that an RLP packet maps into four V.110 framesnumbered 0, 1, 2, 3. These must be sent in one block on the Air Interface.
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6.4 Short Message Service - Cell BroadcastThere are two types of SMS:
Point-to-point SMS allows a short message to be sent to, or received
from, a mobile station
SMS-CB allows messages to be broadcast to the mobile stations (i.e.,one way).
SMS-CB can be used for a number of reasons, for example, to transmitemergency information, road traffic information, etc. An SMS-CB messagecan be transmitted to all the cells connected to the BSC, or to selected cellsonly, as required.
The following figure shows the SMS-CB components.
OMC−R
BSCBTS
Broadcast Message set up by OMC−R Operator
Broadcast Message to
Selected Cell(s)
Messagebroadcast to allMobile Stations
HMI
Transmission Request
SMS−CB commands
and signaling
CBC
SMS−CB commands
and signaling
Broadcast Message set up by CBC Operator
CBC : Cell Broadcast Center
HMI : Human Machine Interface
SMS-CB : Short Message Service - Cell Broadcast
6.4.1 SMS-CB Operation
The SMS-CB is managed and operated from a separate CBC. The CBC isconnected to the BSC and the data needed to connect the BSC to the CBC issent from the OMC-R.
The operator at the CBC inputs the cell broadcast message identifying thebroadcast text and the selected cell identities. Only one broadcast messageper cell, or cells, is allowed. Any subsequent message simply replaces themessage being broadcast.
The message is sent from the CBC to the BSCs handling the selected cells.The BSCs then send the message to the individual BTS of the selected cells.
On receipt of the transmission request message from the BSC, the BTSbroadcasts the message to the mobile stations in the cell over the CellBroadcast Channel of the Air Interface.
For SMS-CB, the BSC supports only the connection to an external CBCplatform. The SMS-CB implements all of the improvements of the phase 2+recommendations.
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6.4.2 Phase 2+ Enhancements
An external CBC can be connected directly to the BSC. This allows the BSC tosend information to the CBC, e.g., billing information.
Two types of connection can be used to connect the CBC to the BSC:
CBC-to-BSC via PSDNThis is the default connection. A BSC can be connected to one CBC.
CBC-to-BSC via MSCThe CBC and OMC-R must be connected to the same MSC.
In addition to the SMS-CB feature managed from CBC, the phase 2+ GSMrecommendation defines the following enhancements:
Greater throughput with a second CBCH channel (extended CBCH)
Better responsiveness when urgent data is to be broadcast due to the use
of high priority messages. Messages can be allocated a priority of high,normal, or background.
Better service availability through the restart with recovery indication feature.
The feature also offers greater convenience with the support of multipagemessages.
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6.5 Support of Localized Service AreaThe aim of Support of Localized Service Area (SoLSA) is to link radio resources(cells) with services such as specific billing or differentiated access rights.These services are associated with LSAs (Localized Service Area). An LSAcan be defined over several cells, and a cell can belong to several LSAs. Onepossible use of this feature is to enable the efficient deployment of dedicatedcorporate applications. The following description uses this example.
In order to efficiently manage corporate LSAs, the Alcatel-Lucent BSS SoLSAimplementation:
Favors the camping of SoLSA mobiles on cells belonging to an LSA where
they have a subscription. These mobile stations will likely camp on thecorporate cells, even if they are not the best ones.
Informs the end user that he is camping on a cell belonging to a subscribedLSA and thus that he can benefit from the LSA services. This is achieved
through the Localized Service Area Indication SoLSA service.
The localized service area concept gives the operator the basis to offersubscribers or groups of subscribers different service features, different tariffsand different access rights depending on the location of the subscriber.It is up to the operator to decide which services features are required fora specific service.
The LSA can be considered as a logical subnetwork of the operator‘s PLMN.This subnetwork can be configured by the operator. A subscriber can haveLSAs at several PLMNs.
The following list shows examples of different types of localized service area:
Office indoors. The office cells are those that are provided by indoor base
stations.
Home or office and its neighborhood. The localized service area can bebroadened outdoors. The neighborhood cells outdoors can be included
in the local service area.
Industry area. A company with several office buildings may want to have alocalized service area that covers all its buildings and outdoor environments.
A part of a city or several locations.
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6.6 PLMN InterworkingA foreign PLMN is a PLMN different from the own PLMN to which the cellsinternal to the OMC-R belong. Only cells external to the OMC-R can belong toa foreign PLMN. All internal cells belong to the own PLMN.
Both OMC-R own cells and cells external to the OMC-R can belong to anown PLMN.
The Alcatel-Lucent BSS supports:
Incoming inter-PLMN 2G-to-2G handovers
Outgoing inter-PLMN 2G-to-2G handovers (optional feature).The operators are allowed to define handover adjacency links towardsexternal cells belonging to a foreign PLMN, i.e., handovers from a servingcell belonging to the own PLMN towards a target cell belonging to aforeign PLMN.
Inter-PLMN 2G-to-2G cell reselectionThe Alcatel-Lucent BSS allows the operator to define cell reselectionadjacency between two cells belonging to different own PLMN (which musttherefore be owned by two different BSCs).
Multi-PLMN (optional feature).The Multi-PLMN feature allows operators to define several own PLMNin order to support network sharing (Tool Chain, OMC-R, MFS, Abistransmissions - and also BTS, via rack sharing). Inter-PLMN handovers andcell reselection between two different own PLMN are supported. The BSCitself cannot be shared and thus remains mono-PLMN (i.e., all BSC owncells belong to the same own PLMN).The Alcatel-Lucent BSS supports several own PLMN (up to four, at leastone). An OMC-R thus manage at least one (own) PLMN and up to eightPLMN (four own + four foreign). Both cell reselection and handover areallowed between two cells belonging to different own PLMN.The operator is allowed to define handover adjacency between two cellsbelonging to different own PLMN (which must thus be owned by twodifferent BSCs).
The OMC-R (and the Tool Chain) is by definition of the feature itself alwaysshared between the different own PLMN. On the other hand:
The MFS can be shared
The BSC cannot be shared
The BTS can be shared up to the rack sharing level (no radio partsharing)
The Abis transmission can be shared
The transcoder can be shared.
The outgoing inter-PLMN handover feature is a prerequisite for themulti-PLMN feature.
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7 Cell Environments
This section describes the cell environments available in the Alcatel-Lucent900/1800 BSS.
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7.1 OverviewThe Alcatel-Lucent BSS provides coverage suited to the needs of urban, ruraland coastal areas by offering a variety of possible cell environments. The BSSsupports a set of cell configurations to optimize the reuse of frequencies.The operator may choose to deploy a network using both GSM 900 andGSM 1800 bands.
The parameters to define cells are grouped into five types:
Cell dimension
This consists of:
Macro up to 35 km (can be up to 70 km with extended cell), and
Micro up to 300 meters.
Cell Coverage
There are four types of coverage:
Single
Lower
Upper, and
Indoor.
Cell Partition
There are two types of frequency partition:
Normal
Concentric.
Cell Range
The cell range can be:
Normal
Extended.
Cell Band Type. A cell belongs to either the GSM 900 or GSM 1800 bands,
or both in case of a multiband cell.
For the cell name, it is possible to use any combination of the followingcharacters in the ’Name’ and ’Location Name’ fields: a-z, A-Z, 0 - 9, -, _(hyphen, underscore).
Blank spaces are permitted. Use the rules fromO&M Parameters Dictionary.
The ’LAC’ and ’CI’ fields accept up to five numeric characters.
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The following figure shows various configurations of the normal GSM 900 orGSM 1800 cell type. Each of the following sections explains the functionaldifferences between the cell described and the single cell configuration.
Single Cell ConcentricCell
Umbrella Cell
Umbrella & Concentric
Cell
Microcell
Inner Zone
Outer Zone
Microcell
Microcell
MicrocellMicrocell
Microcell
Extended Cell
Inner Cell
Outer Cell
Inner Cell Outer Limit
Outer Cell Inner Limit
Overlap Zone
Sectored Site
Figure 36: Example: Cell Configurations
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7.1.1 Rural and Coastal Coverage
In a rural and coastal environment, coverage is principally a function of cellplanning. Standard cell layouts provide coverage of up to 35 km. Extendedcells, which have two collocated antennae, provide options covering trafficdensity and ranges up to 70 km.
7.1.2 Urban Coverage
In an urban environment the coverage is determined by the location of theBTS antennae.
Two types of cells are normally used:
Macrocells, where the antenna is located above the roof tops andpropagation occurs in all directions. These cells can be sectored by using
specific antenna patterns.
Microcells, where the antenna is located below roof top level, on buildingfacades or street lights. Propagation occurs mainly as line of sight along the
street, with strong attenuation at street corners.
Indoor cells.
These three cell types can be used in a hierarchical cell environment wherecontinuous coverage is provided by the macrocell (umbrella cell) and locationsof increased traffic density are covered by dedicated microcells and indoorcells. See Umbrella Cell (Section 7.5) for more information.
7.2 Concentric CellThe goal of concentric cells is to increase the frequency economy of thenetwork. This is done by reducing the interference levels of some BTS carriers.These carrier frequencies can be reused for smaller distances.
The inner zone serves a high concentration of mobile station calls in a smallarea, with a reduced maximum power output limit. The outer zone performs callhandling for a greater radius with a normal maximum power output limit.
The BCCH, CCCH and SDCCH in concentric cells are put on the outerzone frequencies. Traffic channel assignment during call connection can beallocated to either the outer or inner zones. It depends on the location of themobile station at that time.
The inner and outer zones are part of the same cell, and a frequency carrier isassigned either to the inner or outer zone. This is signalled by the zone_type
flag of 1 or 0, (1=inner, 0=outer).
The outer zone maximum power limit is the same as normal zones. Theinner zone is controlled by two maximum power limit values: one maximumpower limit value for the mobile station and one maximum power limit value forthe BTS.
The micro concentric, mini concentric, indoor concentric cells must bemultiband (the allowed FREQUENCY_RANGE is PGSM-DCS1800 orEGSM-DCS1800). This restriction does not apply to the external cells.
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7.3 Sectored SiteA sectored site consists of one or more BTS. Each BTS hosts up to sixantennae illuminating up to six sectors, each sector covering a separate singlemacrocell. The figure below shows a three-sector arrangement.
The BTS in a sectored site contains up to three transceivers which are eachallocated to different given sectors. Each sector and its associated cell aremanaged independently and are seen functionally, by the OMC-R and BSC, asseparate BTS connected in chain mode.
Within the physical BTS site, there is a master BTS and up to two slave BTS(for G2 BTS and Alcatel-Lucent 9100 BTS, each BTS can have three slavesusing the Shared Cell feature; see Cell Shared by Two BTS (Section 7.6) formore information). Each BTS generates its own clock locally, but the slave BTSare synchronized to the master BTS.
Cell 1
Cell 2
Cell 3
BTS
Antenna
Sector 1
Sector 3
Sector 2
Figure 37: Sectored Site Configuration
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7.4 Extended CellAn extended cell is made up of two cells, an inner and an outer, as shown inthe figure below. The inner cell handles calls up to a distance of 35 km (thesame as a normal cell), while the outer cell handles traffic from 33 km up to amaximum range of 70 km.
There are 3 extended cells allowed on BTS.
Inner Cell
Outer Cell
Highway
Urban Area
35 km max
70 km max
Figure 38: Example of Extended Cell Topology
There are two types of extended cell:
Standard Extended Cell (Section 7.4.1)
Enlarged Extended Cell (Section 7.4.2).
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7.4.1 Standard Extended Cell
The inner and outer cells are covered by two synchronized, collocated G2 BTSor by only one Alcatel-Lucent BTS.
The reception (uplink) of the outer cell is delayed to correspond to a 33 km shiftin range. Radio continuity between the two cells is ensured by the overlap zone.
The inner cell uses two carrier units:
Carrier Unit BCCH Inner: at the inner cell BCCH frequency
Carrier Unit RACH Catcher: at the outer cell BCCH frequency, but withtransmission switched off.
Because the outer cell can have areas of strong signal within the inner cell’scoverage area, it is necessary to prevent a mobile station in such a regionfrom camping on the outer cell frequency. This could lead to sudden signaldegradation as conditions change, and eventual loss of the call.
The RACH Catcher receives Channel_Request messages from mobile stationswhich are synchronized on the outer cell BCCH frequency, but are within 33km of the BTS. The BTS knows, from the timing advance sent by the mobilestation, that it is actually in the inner cell, and assigns the mobile stationto an inner cell SDCCH frequency.
The outer cell uses one Carrier Unit with reception delayed by 60 bits. Thiseffectively shifts the logical position of a mobile station 33 km nearer thanits actual position and allows it to be handled in the standard GSM 0-63 bittiming advance range.
The handover procedure is controlled normally, with the settings ensuring thatthe necessary distance is reached before handing a call over to the outer orinner cell.
Different types of coverage are possible depending on the type of antennaused for the inner and outer cells. The example in the figure above shows anextended cell with an omnidirectional inner cell and directional outer cell.
7.4.2 Enlarged Extended Cell
The enlarged extended cell is an extended cell designed to provide enlargedcapacity for areas where sustained traffic is high. It is especially well-suited forrural areas and dense highways where more than one TRX is necessary tohandle traffic.
The enlarged extended cell relies on the general principles of the extendedcell: it is made up of two sub-cells to handle calls up to a distance of 70 km.However, with the enlarged extended cell, the two sub-cells are covered byone BTS, assuring a higher synchronization rate.
The following telecom features are supported:
The TDMA frame timeslots can be used independently, providing any
TRX with full capacity
Inner cell mobile station access requests use the outer cell BCCH frequency
Handover between the two sub-cells
BCCH TRX recovery.
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7.4.3 PS in Extended Cell
(E)GPRS is supported in extended cell:
NC2 mode is not offered in the extended cell
The Network Assisted Cell Change is not allowed in the extended cell
The (Packet) PSI status procedure is not allowed in the extended cell.
7.5 Umbrella CellIn much denser traffic areas, depending on the required traffic capacity, ahierarchical network is used, where continuous coverage is provided by anumbrella cell (macrocell), and traffic hotspots are covered with dedicated lowerlayer cells of limited range. Fast moving mobiles are kept in the upper layer cellto avoid a high rate of handovers.
For medium density areas small macrocells (called mini cells) are overlaid withone umbrella macrocell. See Mini Cell (Section 7.5.1) for more information.
For higher traffic densities microcells are installed in all the streets where verydense traffic occurs. Umbrella macrocells provide continuous coverage for leveland quality handovers, and saturated overlaid cells.
Refer to Microcell (Section 7.5.2) for more information about the relationshipbetween umbrella cells and microcells.
7.5.1 Mini Cell
Mini cells are used for dense urban areas where traffic hotspots are coveredby very small macrocells (500 m to 1 km radius) and continuous coverage isprovided by an overlaid macrocell (5 to 10 km radius). The lower layer minicells handle pedestrian traffic while the umbrella cell handles the faster movingmobiles. As only macrocells are used there is no street corner effect.
The following figure shows the application of the two-layer hierarchical network,with macrocells for both layers, in a small town.
Umbrella Cell
Mini Cells
Urban area
Pedestrian area
Figure 39: Umbrella Cell with Mini Cells
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7.5.2 Microcell
Microcells have a small coverage area (less than 300 m radius). These cellsare usually situated indoors or along streets in built-up areas. Microcellshave an umbrella cell (1 to 2 km radius) to minimize the risk of losing callsby providing maximum coverage.
The microcell’s small radius is created by limiting the maximum power outputstrategically to cover a pre-defined microcell area.
Handover occurs more frequently in a microcell environment due to thesmall radius sizes.
Microcell handovers occur:
To handle stationary mobile stations (especially mobile stations usedindoors)
When a mobile station moves in a street covered by microcells
To avoid losing calls. Whenever there is a risk of losing a call, a handover
is triggered to the umbrella cell.
Fast moving mobiles are handled by the umbrella cell. A mobile handled by amicrocell is sent to the umbrella cell if the delay between handovers becomestoo small. Conversely a mobile is sent to a microcell if it receives a highlevel of signal for a sufficient time.
Call quality/control is achieved by providing four thresholds for microcellhandover and one handover threshold for macrocell handover.
7.5.2.1 Micro-to-Micro HandoverMicrocell to microcell handover occurs due to the proximity of the two cells.When the power budget is better in another cell, the mobile station is handedover to the cell which will serve the call more efficiently. This normally occurs inmicrocells serving in the same street.
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7.5.2.2 Micro-to-Macro HandoverThe following table describes the three types of micro-to-macro thresholdhandovers.
This Handover Type... Occurs when...
High Threshold Handover The signal strength has dropped below the theoretical signal level at theradius of the cell. This would normally mean that the mobile station hasturned a street corner.
Low Threshold Handover The mobile station level is under the high threshold and the signal level hasdropped below the low threshold. The handover is to the umbrella/macrocell,which supports the call until the mobile station moves into another cell.When the macro to micro threshold is exceeded in the umbrella/macrocell,the mobile station is passed to a new microcell.
Rescue Handover The mobile station is forced to handover to the umbrella cell when nomeasurement reports are transmitted. This occurs after a number ofconsecutive SACCH reporting periods.
7.5.2.3 Macro-to-Micro HandoverThis occurs when the mobile station signal level in a microcell is above theM_to_m threshold for a certain period. This threshold value must alwaysbe higher than the low threshold value of the cell. Otherwise, a handoverping-pong effect can occur between the umbrella and the microcell.
Note: If the low threshold is not used, the M_to_m Threshold value must be above thehigh threshold value.
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7.5.2.4 Threshold Handover ExampleThe example in the figure below shows two typical cases of handover inmicrocells:
Micro-micro handover along a street (Case 1 in the figure below)
Signal levels rising and dropping, causing macro-micro handover (Case2 in the figure below). This example shows the use of the two levels
of macro-micro handover (strong to weak signal, and weak to weakersignal). This is represented by the high and low threshold handovers. This
example also shows the macrocell handing back to a microcell once astronger signal level is received.
Low Signal Level
High Signal Level
dBm
Low Threshold
M_to_m Threshold
High Threshold
4
5
1
2
3 6
Micro−MicroHandover
Micro-Micro Handover (Case 1)
A mobile station is moving along a street.
As it moves along a street, the mobile station is handed over from microcell tomicrocell (1).
Macro-Micro Handover (Case 2)
A mobile station turns a corner then moves indoors.
1. Call starts at (2). The signal level is normal.
2. The mobile station signal level drops below the high threshold level (3), e.g.,when turning a corner. To protect the call, it is handed over to the macrocelluntil a better microcell is found. The call remains with the macrocell until astrong signal from another microcell is received (normal case).
3. If a strong signal from a microcell cannot be found, a weaker signal from amicrocell with enough strength to be above M_to_m threshold level, but thatremains below the high threshold is found (4).
In this case, as long as the signal strength remains above the low thresholdand there is not a better microcell, the call remains with that microcell(e.g., the mobile station is indoors).
4. The signal level drops below the low threshold (5). The mobile station isagain passed to the macrocell (e.g., the mobile station moves further insidea building). The macrocell is used to ensure call quality.
5. The mobile station moves into a position where the mobile station reports amicrocell signal level above the M_to_m threshold (6). The call is handedover to that microcell, e.g., the mobile station is still indoors, but has astronger signal from a microcell.
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7.5.3 Indoor Cell
The aim of indoor layer support is twofold:
Firstly, to enable a better radio coverage inside large buildings (hotels,
shopping malls, corporate centers) by the public network
Secondly, to unloaded the cells provided for outdoor coverage but which are
accessible from these buildings.
Indoor cells can be deployed in all types of network, even in very densenetworks which already have two layers (upper and lower). The feature easesthe optimization of multilayer networks which include cells dedicated to indoorcoverage. Indoor coverage is performed mostly from outdoor BTS. Althoughalready satisfactory in many cases, the indoor quality of service can beimproved by using dedicated in-building equipment. Together with this improvedquality, an increase in the indoor capacity can be achieved, particularly in highdensity public areas such as airports, train stations, shopping malls, businessparks, etc. A three layer per band management is introduced and a new typeof cell is defined (the indoor cell) that maximizes traffic in these indoor cellswhile preserving quality. In idle mode, classical criteria (C2) allows mobiles tobe forced to camp on indoor cells.
For example, when entering a building covered by an indoor cell, calls areautomatically transferred from outdoor cells, whatever their type. When movinginside the building, calls are transferred from one indoor cell to another one,even if the received power from outdoor cells is higher. It is only when themobile leaves the indoor coverage that it is transferred to an outdoor cell.
It is important for the Operator to minimize interference from indoor tooutdoor. Therefore, indoor cells will often be used with very low radiatedpower (picocells). In this context, the feature also provides enhanced PowerControl algorithms.
The cells added to the network for indoor coverage are referred to as indoorcells and form a new layer referred to as the indoor layer. The following figuregives an example of network structure with three layers and two bands.
Umbrella cell 900
Umbrella cell 1800 Upper layer
Lower layer
Indoor layerIndoor cell 1800
Micro−cell 900
Micro−cell 1800
Micro−cell 900Micro−cell 1800
Micro−cell 900
Micro−cell 1800
Indoor cell 900
Figure 40: Indoor Cell Example Network Hierarchy with Three Layers and Two Bands
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The already deployed network hierarchy has to be adapted as follows:
If there were already two layers, cells belonging to the upper layer will
remain unchanged. Outdoor cells belonging to the lower layer will alsoremain in the lower layer. New cells introduced for the indoor layer will
belong to the indoor layer
If there was only one layer, cells having the cell_layer_type "single" willbecome upper. New cells introduced for the indoor layer will belong to the
indoor layer. There is no lower layer.
7.6 Cell Shared by Two BTSThe system is able to handle cells whose TRXs are located in two different BTS.
This feature brings important flexibility by allowing:
An existing site to be extended by only adding TRXs in a new BTS, notchanging the arrangement of the existing BTS
Existing cells to be combined into one, e.g., combine one 900 cell and one
1800 cell in order to create a multiband cell
The support of 3x8 TRX configurations in two racks (instead of three)
The support of 16 TRX per cell.
Note: This feature only applies to BTS 9100.
Each set of TRX in a certain BTS must have its own coupling. It is possible tocombine the coupling output towards the same antenna through an additionalduplexer, although this is a special installation. The fact that part of the sector isin another BTS does not increase the number of necessary antennae. For BTS9100, each BTS can have one slave, but each slave can in turn have anotherslave, up to a maximum of three linked slaves for one master BTS. If linked BTSsupport part of the same cell, the linked BTS must be clock synchronized witheach other (master/slave).
With this feature, the operator can associate two physical sectors from differentBTS into one shared sector. This shared sector can be mono or dual-bandand it can support one cell as a normal sector. It takes the identity of one ofthe physical sectors, called the primary sector. The other physical sector isthe secondary sector.
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7.7 Unbalancing TRX Output Power per BTS SectorThe feature allows unbalanced configurations on the same antenna network.This configuration behaves as a concentric cell, where the output powerbalancing is performed on a zone basis instead of on the sector basis.Furthermore, for 3 TRXs per ANc configuration, 2 TRXs are used in combiningmode on the first antenna path and 1 TRX is connected in by-pass modeon the second antenna path. This leads to the same sort of concentric cellconfiguration as in the case TREs with different output power are used.
When the feature is activated, the BSC maps, on the HP TRE, the TRXconfigured by the operator on the outer zone and maps the TRX of the innerzone on the others. A new mapping algorithm takes the place of the adjustwhen the feature is activated on a concentric cell.
The BTS informs the BSC, for each TRE, about the GMSK and 8PSK outputpower (after coupling). The BTS informs the OMC-R through a hardware auditabout the output power of each TRE for GMSK and 8PSK modulation.
The feature can be activated at the OMC-R through one of the Power Controlparameters (EN-Unbalanced-Output-Power). It is not an optional feature.
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8 Operations & Maintenance
This section provides an overview of O&M and describes O&M functions in thecontext of an operational network.
For more information about O&M, refer to the Operations & MaintenancePrinciples.
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8.1 OverviewTo ensure that the BSS operates correctly, O&M actions are implemented atall levels within the BSS.
The O&M functions in the BSS are grouped into three categories:
Configuration ManagementThe main benefit of configuration management is the reduced time neededto perform operations and reduce telecom outages. This is achieved byhaving fewer operator commands and providing smooth migration andequipment configuration. The main functions of configuration managementinclude radio configuration management and equipment management.
Fault ManagementFault Management is used to supervise and to repair the network whenanomalies occur. This is done through a sequence of steps from detection toreport and recovery. These are carried out by all the BSS/MFS subsystems,and are reported to the operator at the OMC-R.
Performance Management.Performance Management is used to monitor the efficiency of the systemand the telecom services. It is controlled entirely from the OMC-R andprovides measurements and statistics about various traffic events andresource use in the BSS.
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8.1.1 Subsystem O&M Functions
The table below provides a brief description of the O&M functions at thesubsystem level.
This O&M function... Is used...
ConfigurationManagement
To view and control network resources. Configuration Management allows theoperator to:
Configure the BSS/MFS hardware and software when it is first installed
Change the network by adding, deleting, or moving network entities
Upgrade to new hardware or software
Change equipment and telecom parameters to improve system performance.
For more information, see Configuration Management (Section 8.4).
Fault Management By the BTS to monitor the condition of the hardware modules it manages, andreport any change in status to the BSC.
By the BSC to supervise its own hardware modules and report changes in statusto the OMC-R.
By the BSC and Transcoder together to provide a set of transmission O&Mfunctions to ensure a high level of fault tolerance and reliability. The functions alsoprovides efficient use of the terrestrial links between the equipment of the BSS.
By the MFS to supervise its own hardware modules and report changes in statusto the OMC-R.
For more information, see Fault Management - Alarms (Section 8.5).
PerformanceManagement
By the BSC and the MFS to:
Collect raw measurement data from network elements
Transfer the raw measurement data to the OMC-R, where the results are
processed and displayed.
For more information, see Performance Management (Section 8.6).
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8.1.2 System O&M Functions
The OMC-R is responsible for O&M functions at the system level.
Its principal operations are:
Network configuration
It provides the operator with an interface to the system to:
Perform software configuration management (files, version downloading)
Perform hardware configuration management (e.g., update the
configuration according to extension/reduction operations, configurecertain BSS parameters such as Abis link characteristics and some
BTS characteristics)
Provide configuration functions for logical parameters.
Network supervision
It provides the operator with an interface to the system to:
Display alarm status and history
Display equipment and resource states
Monitor and display performance measurement results
Provide Usage State on Demand observations
Define and supervise counter thresholds (Quality of Service alarms).
Network maintenance
It provides the operator with an interface to the system to:
Access equipment management functions (test)
Access resource equipment state management.
Lock and unlock equipment and resources
Keep track of hardware and software configurations in the system and
managing software versions
Provide mediation between the BSS and one or more NMCs. This uses theQ3 interface.
Provide an interface to the electronic documentation collection.
For more information about the OMC-R and its functions, refer to the Operations& Maintenance Principles and the Getting Started document.
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8.2 O&M Control - SubsystemsO&M functions are controlled either at subsystem level using the LMTs and theIMT (for the MFS) or by the OMC-R at BSS/MFS level. This section provides abrief overview of subsystem control.
8.2.1 LMTs and IMT
Local Maintenance Terminals are used when performing maintenance tasks atthe BSC, BTS, and Transcoder. LMTs are connected directly to the equipment.The operations available at the LMTs act only on the local hardware, noton logical resources.
The IMT performs maintenance tasks at the MFS, using a Mozilla browser.All these tasks (except for three tasks associated with alarms, enable/disablesound, view history file, and enable/disable external alarm management) canalso be accessed from the OMC-R terminal. The IMT alarm tasks are notprovided when the IMT is accessed from the OMC-R because the OMC-Ralready has its own alarm management tasks.
The IMT software can be accessed from either the IMT or the OMC-R. It hasthree different user profiles: administrator, operational, basic.
If the IMT software is accessed from the IMT, two administrator sessions at atime can be run. Two instances of the IMT can be in use at the same time.
The IMT is integrated into the OMC-R and, as a result, provides:
Multiple entry points to the IMT (from MFSUSM, RNUSM and DCN)
Centralized user management: at the OMC-R (the OMC-R operator nolonger has to log on to the IMT)
Parallel access to a given MFS, with up to eight users per session
A separate time out is used for every administrative user. The time out delayproposed is 15 minutes.
N basic users and (8-N) GPU users at most (8 > = N always) are supported
Better performance on the OMC-R, due to IMT Fast Start.
With the exception of multiple entry points to the IMT, the above features areonly available when both the OMC-R and the IMT are in B10.
For more information about LMTs, refer to one of the following:
BSC Terminal User Guide
Transmission Terminal User Guide
BTS Terminal User Guide
Alcatel-Lucent 9125 Compact TC Terminal User Guide
Alcatel-Lucent 9135 MFS IMT User Guide
9130 MFS Evolution IMT User Guide.
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8.2.2 OML Auto-Detection
An OML auto-detection feature exists to take full advantage of the transmissionconfiguration via OML feature (which is more reliable and more robust thanconfiguration via the Qmux channel). The OML auto-detection feature providesthe following benefits:
Transmission configuration via OML on all Alcatel-Lucent BTS
No LMT configuration necessary during Move BTS
Secure recovery after OML breakdown
Simplification of BTS installation (for Plug and Play BTS).
See OML Auto-Detection (Section 8.4.6) for more information.
8.2.3 Managed Objects
Managed Objects are used to represent elements of the TelecommunicationTMN environment on the Q3 Interface in terms of system resources. Thisconcept is also used to represent the activities of management function blocksperformed on these resources.
In Alcatel-Lucent’s network management model, Managed Objects can bephysical entities, such as a BSS, BTS, BSC, or a hardware module within one ofthese entities. They can also be a logical entity, such as programs or programroutines which implement communication protocols.
8.2.4 Security Blocks
Alcatel-Lucent has an internal object model structure, based on objects calledSecurity Blocks. Security Blocks are only used for the BSC, the BTS, and theTranscoder. Security Blocks are only visible to an operator performing localmaintenance using certain LMTs, such as the BSC terminal, BTS terminal,or Transmission terminal. The SBL model is not used by the OMC-R or theIMT. The OMC-R can display SBLs in certain circumstances, for example, inBSSUSM.
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8.3 O&M Control via OMC-RThe OMC-R is the primary control station for the BSS/MFS and manages themajority of O&M functions. The OMC-R provides the operator interface usedto perform Configuration Management, Fault Management and PerformanceManagement actions. The following features help the OMC-R to manageO&M activities.
8.3.1 Multiple Human-Machine Interface
This feature permits one OMC-R operator to perform actions normally done byseveral OMC-Rs, typically during off-duty hours. The connection between themultiple access workstation and the other OMC-R hosts is via an X.25 network.The following figure illustrates the operation principles.
Central Site
Additional Workstation
Printer
HMI Server
Multiple Access Workstation
OMC−R Host 1
OMC−R Host 2
OMC−R Host n
X.25 Network
HMI : Human Machine Interface
Figure 41: Multiple HMI Access to OMC-Rs
The implementation of this feature takes advantage of the distributedconfiguration of the OMC-R which usually consists of a host machine anddistinct local or remote HMI servers.
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The site used for multiple access contains the following:
Printing facilities
Additional workstations which connect to the multiple access workstation,
but only connect to the same OMC-R
Configuration of each OMC-R is specific to the multiple access workstation
and its peripherals.
8.3.2 ACO
Alarm Call Out (ACO) is a process within the HMI server used to perform alarmmanagement tasks for a complete network. Alarms from the BSSs controlledby other OMC-Rs are directed to one OMC-R. These links are used to transferalarm notifications from the controlled OMC-Rs to the ACO OMC-R, as shownin the figure below.
The ACO OMC-R:
Collects alarms from these OMC-Rs
Applies filters defined by the on-duty operator
Sends the filtered results to a dedicated printer
Sends e-mail to support technicians.
It is possible to start and stop ACO from any OMC-R.
OMC−R 1
OMC−R 3
OMC−R 2
Area 1
Area 3
Area 2
ACO OMC−R
Workstation
ACO : Alarm Call Out
Figure 42: ACO Links
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8.3.3 Connection from BSC to OMC-R
8.3.3.1 Secured X.25 Connection From 9120 BSC to OMC-RThe Secured X.25 Connection feature provides redundant links in the event of alink failure on either the OMC-R or BSC side. When a link failure occurs, theinitiator system involved must process the changeover.
The configuration for the X.25 links consists of two physical links, one forCMISE, and one for FTAM. The following figure illustrates the configurationwithout redundancy.
OMC−RX.25 Network
CMISE BSC A
FTAM BSC A
CMISE
FTAM
BSC A
OSI CPRA 1
OSI CPRA 2
HSI BOARD
012
3
CMISE : Common Management Information Service Element
CPRA : Common Processor Type A
FTAM : File Transfer Access and Management
HSI : High Speed Interface
OSI : Open System Interconnection
Figure 43: X.25 Without Redundancy
Definition of the primary and the secondary links based on their hardwareconfiguration can achieve various types of redundancy, such as:
OMC-R-side redundancy
BSC-side redundancy
Complete redundancy.
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The following figure illustrates these redundancy types.
OMC−RX.25
NetworkBSC
OSI CPRA 1
OSI CPRA 2
HSI Board
0
1
2
3
Primary Link
1
2
3
Secondary Link Configurations
1. OMC−R side redundancy2. BSC side redundancy3. Complete redundancy
Secondary Link
CPRA : Common Processor Type A
HSI : High Speed Interface
OSI : Open System Interconnection
Figure 44: X.25 With Redundancy
When the OMC-R or the BSC sets up a CMISE or FTAM association, thesubsystem chooses the active link. The active link is the primary link if it is intraffic, otherwise it is the secondary link.
The following events occur:
The transfer is performed on the primary link if the association is successful.
The association is attempted three times.
The primary link is set out of service if the association is unsuccessfulafter the third try
If the secondary link is in traffic, it becomes the active link and the
association is tried on this link.
If the secondary link is out of service, the application is impossible.
Links are periodically tested for availability. When the primary link is recovered,it becomes active and in traffic. Loss of one link (i.e., primary or secondary)triggers an alarm and the recovery triggers the end of alarm.
8.3.3.2 Secured IP Connection From 9130 BSC to OMC-R
Note: For the 9130 BSC, the X25 links are replaced by IP. As with the 9120 BSC, the9130 BSC can support both routes to connect to the OMC-R, namely over adirect IP network or over an Ater and IP network.
In order to maintain stable ISO services and decrease development costsand risks, TS is used on the TCP which is specified by RFC1006 for the IPinterface between the 9130 BSC and OMC-R. TSAP and TS are maintained,and original NS primitives are replaced with TCP primitives. FTAM is replacedwith FTP for file transfers.
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8.3.4 Electronic Documentation
Installation and use of the electronic documentation collection depends on theconfiguration.
Small ConfigurationsThe documentation collection is installed on each OMC-R. To search thedocumentation collection, install the documentation collection CD-ROM on asingle PC, and use the search function provided on the CD-ROM.
Standard, Large, and XLarge Configurations.The license for the documentation collection is installed on one OMC-R. Allother OMC-Rs on the same site are connected to this OMC-R. The maximumnumber of users that can be managed for each search engine license is 75.This corresponds to a site with five Large configuration OMC-Rs.
Refer to 9153 OMC-R Capacity per BSS Category for more information aboutthe various OMC-R configurations.
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8.4 Configuration ManagementConfiguration Management is the process of putting in place the essentialhardware and software components of the network, and determining theiroperating capabilities. The table below shows the configuration managementfunctions of each network element.
NetworkElement
Configuration Management Functions
BSC Software and database replacement
Reading and modifying logical parameters.
BTS Supervision of the BTS equipment. This includes initializing and configuring the BTS.
Transfer of software and data files to the FUs (G1/G2 BTS) or TREs (BTS 9100/9110)
Software and database replacement
Auto Identification (BTS 9100/9110 only). See Auto-Identification (Section 8.4.5) for
more information.
Application of the logical configuration of the BTS.
Transcoder Communication through the Q1 Interface with the Transcoder, SM and BIE modules
Permission for configuration and reconfiguration of the Transcoder, SM and BIE modules.
TSC Communication through the LAPD link with the BSC
MFS Reading and modifying parameters
Control station and GPU configuration
Framer configuration for Gb Interface messages
GPU switch configuration for circuit-switched connections.
For detailed information about configuration management, refer to ConfigurationManagement in the Operations & Maintenance Principles or the descriptivedocumentation.
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8.4.1 Hardware Configuration
Hardware Configuration enables the operator to:
Control the placement in service of both BSS and MFS hardware
Control the manner in which deployed hardware elements will act andinteract within the BSS and MFS
Modify the parameters that control these elements.
It also permits the operator to view the current hardware configuration statusof the network.
8.4.2 Logical Configuration
There are three types of Logical Configuration:
Radio Logical Configuration allows the operator to change the parameters
that control the Air Interface. This includes channel definitions, manipulatingand reconfiguring the Carrier Units or TREs and defining the Frequency
Hopping System.
Cell Logical Configuration displays and modifies BSS logical parametersand threshold values which influence a cell’s operational behavior. These
are divided into several classes which simplify searches.
GPRS Logical Configuration allows the management of the following:
The telecommunications application, including bearer channels, GbInterface, Ater Mux Interface towards the BSC, and cell management
domains
Synchronization of the logical GPU resource states after a server
changeover
Configuration of a logical GPU when requested by the GPU (after astart, reset or changeover)
Network service configuration and the supervision of the Gb Interfacedomain.
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8.4.3 Default Parameter Customization
Customers receive a standard set of default telecom parameters. It is notpossible for these default parameters to fit each customer’s specific networkconfiguration. Until recently, customers had to manually modify certain defaultparameters for their network. The default parameter customization featuremakes it easier to perform this task.
This feature allows access to the list of customizable parameters via adedicated menu, Default Values Customization. This menu display a windowwith a parameter list containing all relevant information about each modifiableparameter. From this window, the user can edit the default values for eachlisted parameters as necessary. A filter mechanism allows users to search forspecific parameters by name and/or by object type.
The allowed parameter object types are:
BSC parameters
CELL parameters
ADJACENCY parameters
TRX parameters.
For detailed information about this feature, refer to the 9153 OMC-RAdministration Handbook.
8.4.4 Software Configuration
Software Configuration enables new versions of the BSS software to beinstalled in the BSS. This feature also allows the operator to display currentsoftware versions of the BSS. BSC and BTS software is managed from theOMC-R, while MFS software is managed from the IMT.
8.4.5 Auto-Identification
Auto-Identification provides the BTS 9100 and the BTS 9110 with the capacityto recognize their own hardware configuration, and to provide this informationto the OMU and the BTS Terminal.
The auto-identification procedure is triggered by the OMU in the followingsituations:
BTS/SUM power up
BTS reset
OMU reset/auto reset
Module initialization (on maintenance operator command, or during a Local
Recovery Action or Hardware Extension; the auto identification takes placeonly for the module(s) concerned by the operation).
The BTS 9100 and the BTS 9110 capabilities received by the OMU atauto-identification are stored and can be used internally by the OMU softwareor sent to the BSC at Hardware audit.
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8.4.5.1 Auto-Identification ComponentsAuto-identification has the following two components:
Remote Inventory
Remote inventory identifies the following:
RIT type of each managed module
Hardware capabilities of each RIT.
RF Cable Identification
RF Cable Identification provides the following information:
Location of each RIT (subrack and slot)
Sector to antenna network x mapping
TRE to antenna network x mapping.
For more information, refer to the BTS Functional Description and the BTSTerminal User Guide.
8.4.5.2 Consistency ChecksWhen a new Configuration Data Message is received from the BSC, the BTS9100 and/or the BTS 9110 perform a consistency check of capabilities againstthe Configuration Data Message. They also do this at module initialization dueto maintenance operator command or to a Hardware Extension operation. TheBTS 9100 and/or BTS 9110 also check that the received OMU ConfigurationParameter Data File is valid for this generation of BTS. Consistency checks arealso performed by G1 and G2 BTS.
For more information, refer to the following:
Alcatel-Lucent BTS 9100/9110 Functional Description
Alcatel-Lucent BTS 9100 Hardware Description
Alcatel-Lucent BTS 9110 Hardware Description
BTS Terminal User Guide.
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8.4.6 OML Auto-Detection
The OML auto-detection feature was introduced in order to take full advantageof the transmission configuration via OML feature (which is more reliable andmore robust than configuration via the Qmux channel).
The OML auto-detection feature provides the following benefits:
The feature allows one extra timeslot to be used for signaling (if no G1/G2
BTS are present on the Abis Interface). This provides an increase of telecomtraffic on one Abis (because there are no timeslots dedicated to the Qmux).
There is no need for onsite BTS reconfiguration during a move BTS scenario
(using the LMT to reconfigure the BTS). Also, the Qmux address for theAlcatel-Lucent BTS can be modified remotely from the OMC-R.
There is no need for onsite BTS reconfiguration during an OML multiplexingchange (from 16k to 64k)
Secure recovery after OML breakdown
Simplification of the commissioning procedure: Synchronization between
OMC-R and commissioning personnel is no longer required. The BTS canbe installed before or after the BTS is created at the OMC-R.
The OMC-R operator no longer needs to know on which timeslot the OML is
located, and no longer needs to configure it manually
Transmission configuration via OML for all Alcatel-Lucent BTS.
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8.4.7 Network Element Provisioning
Network element provisioning allows equipment that is not yet in commercialuse to be distinguished from equipment that is under maintenance. Thisis not important for network monitoring. The feature introduces the status"commercial use" that is associated with the BTS. This status is changeableonline from the OMC-R. It is also available at the radio configurationexport/import interface of the OMC-R for co-ordination with the operators’information systems. For the BTS marked as "not in commercial use", potentialalarms are raised with a "warning" severity and the performance measurementresults are not taken into account. BTS marked as "not in commercial use"are not reported in the topology files sent to the 9159 NPO. They can also befiltered from the supervision view.
Previously, as soon as a BTS was declared, it was supervised, but this raisedpermanent alarms when the BTS was not physically connected. If cells werecreated on this BTS and PM cell measurements ran on it, this led to very poorPM results as the BTS was not in commercial service.
An attribute (commercialUse = On or Off) is associated with each BTS. Theattribute can be changed at both the SC and the PRC radio network level tomark the BTS as out of commercial use, or in commercial use. When thisattribute is set (i.e., the BTS is out of commercial use), all alarms related to theBTS have a maximum severity equal to a warning (except for the alarms fromthe MFS). At the OMC-R, the operator still sees all of the alarms and alarmstates, and is able to trigger all O&M commands. This allows the operator to beaware of the fault situation of the BTS, but does not give a false status of thenetwork. There is no PM handling and storage for BTS that are marked outof commercial use (except for the PM counters that are relative to RSL/OMLtraffic which are not filtered).
To avoid any impact of cells not in commercial use on 9159 NPO indicators, theoperator follows the sequence below:
1. Create the BTS.
2. Set it in ’no commercial use’.
3. Map the cell onto the BTS.
In the scenario above, none of the PM observed by the BSC on this cell aretaken into account by MPM/9159 NPO. If the operator maps the cell beforeputting the BTS in commercial use, the BSC starts reporting PM on it. As soonas PM results are collected by MPM/9159 NPO, indicators are computed. Dueto the extrapolation function of 9159 NPO, these indicators are computedfor a long period. At this point, it is essential to prevent any reporting soas to avoid misleading indicators.
8.5 Fault Management - AlarmsThe BSS generates alarms to signal a change in the behavior of a particularfunction within the system, such as a potential problem or a confirmed failurein the system.
This section describes the alarm generation process. It describes the alarmsand their effects on the system.
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The following table shows the fault management functions of each networkelement.
NetworkElement
Fault Management Functions
BSC BSC
Fault detection, fault correlation and fault localization on all devices controlled bythe processor
BSC reconfiguration in case of loss of the BCCH, Terminal Control Unit/FU or aCarrier Unit (G1 or G2 BTS)
BSC reconfiguration in case of loss of the BCCH, TCU/TRE (BTS 9100/9110).
Through the TSC, the BSC also performs the following functions:
Monitors the status of the Transcoder, SM and BIE modules
Provides local access to configure the Transcoder, SM and BIE modules via anRS-232 connection to the BSC terminal
Gives access to the fault localizing features of the TSC (for example, the ability to
set up loop-back tests).
BTS BTS
Testing the equipment. This includes collecting alarms and reporting to the BSC.
Fault detection, fault correlation and fault localization for the BTS
Management of equipment states. This includes triggering BTS channel configuration
in case of a failure.
Provides access for local diagnostics and configuration of the BTS
BTS power supply control
Event report management. See Alarm Generation (Section 8.5.1) for further
information concerning events.
MFS MFS
Collects all fault information for telecom and external alarms, the telecommunicationshardware and the active server
Records the fault information in a table
Allows the IMT and the OMC-R access to the fault information
Generates the ending alarm for pending alarms
Manages the communications with the IMT.
For additional information about fault management, refer to the descriptivedocumentation and Fault Management in the Operations & MaintenancePrinciples document.
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8.5.1 Alarm Generation
When an Alarm is generated, it is indicated as either:
Fault (begin or end)If a fault arises, the related alarm is stored in the relevant BSS unit, and alsoin the OMC-R. The alarm begin message signals that a particular systemactivity has stopped due to an error. When the error is corrected, an alarm
end message is sent to indicate that the condition no longer exists, and thealarm is taken out of the Alarms-in-Force list.
EventAn Event occurs when an unexpected situation arises during systemoperation.
Alarms can be generated as a result of previous alarms or events whichinfluence other parts of the system. For example, when the Carrier Unitproduces an alarm to signal an internal fault, the FU and the Radio SignalingLink produce alarms to signal that no information is being received from theCarrier Unit. Fault correlation and filtering actions are performed by the O&Mmodules in each unit, so that a single fault is sent as an alarm. In the case ofthe faulty Carrier Unit, an alarm is sent signaling a Carrier Unit fault. In thisexample, the loss of the RSL link is signalled from the BSC but is not correlated.
For more information, refer to Alarm Handling in the Operations & MaintenancePrinciples document.
8.5.2 Alarm Functions
The following alarm functions help the operators monitor and correct faultconditions in the system.
8.5.2.1 CorrelationCorrelation refers to the collection and analysis of all available fault indicationsfor a particular problem. Fault correlation is performed to define where and whythe fault occurred.
An example of correlation is when:
1. Several boards in the BTS report clock problems, and these reports arecorrelated by the OMU.
2. The ’clock generator is faulty’ alarm is sent to the OMC-R via the BSC.
8.5.2.2 FilteringAlarms are filtered to minimize the number of fault alarms reported anddisplayed to the operator and are displayed in order of severity.
To reduce the number of alarms in the OMC-R, short end alarms are filtered.For these alarms a BEGIN is raised soon after the previous END.
These END /BEGINs are not considered significant and are filtered. Theoperator sees fewer alarms and is informed that alarms are filtered, becausethe number of filtered alarms, if any, is indicated in AS.
For more information, refer to Alarm Handling in the Operations & MaintenancePrinciples document.
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8.5.2.3 PersistencyA fault is signaled only if there is no recovery after the timer expires. Forexample, for a LAPD failure of an RSL link, an alarm is only sent if the LAPDlink has not recovered before the persistency timer has expired.
8.5.2.4 Alarm SurveillanceAS is an OMC-R application that supports fault management integration inTMN functions. It collects alarms issued by applications residing in the variousManagement Layers and processes them.
To improve operator action visibility on alarms in RNUSM, the displayedinformation is reshuffled, as RNUSM was not designed to support supervision.The operator can see whether unacknowledged alarms are still present.
Use of alarm acknowledge status, alarm status, and alarm synthesis arecomputed on all active alarms. The operator is, as yet, unaware of new alarms.
It is presumed that an operator is aware of each alarm he acknowledges andunaware of alarms that he has not acknowledged.
8.5.2.5 Alarms-in-Force ListEach BSS component keeps an Alarms-in-Force list, so that the systemknows that an alarm has begun. This list ensures synchronization of alarmsthroughout the BSS components. This makes the alarm situation visibleat all times. The OMC-R also keeps track of all the Alarms-in-Force listsfor each BSS component.
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8.5.3 BSC Alarms
The BSC detects alarms on the Abis and A trunk via the TCU and the DTC. Italso detects alarms from each functional unit of the BSC.
For more information, refer to Alarm Handling in Operations & MaintenancePrinciples.
8.5.3.1 Processor FailureThe active S-CPRA creates a daisy-chain map of all the processors in theBSC. Every ten seconds, the S-CPRA sends the map to the next processor.This processor sends the information to the next processor in line, until theS-CPRA receives the daisy-chain map.
The daisy-chain map can be modified by an intermediary processor when thatprocessor cannot send the map to the next processor in line. In this case, theintermediary processor skips the processor and removes that processorfrom the daisy-chain map. When the S-CPRA receives the map with thesame processor missing twice in a row, it tries to recover the processor. Ifthe processor cannot be recovered, the S-CPRA places the processor inthe FLT state.
The S-CPRA signals the processor failure to the OMC-R as follows:
If the processor failure is in the TCU, recovery only takes place to ensure
BCCH functionality
If a DTC processor fails, the BSC tries to inform the MSC, so that the MSCis aware the SS7 link is out of service. This implies:
The loss and, if possible, the changeover of the SS7
The blocking of circuits.
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8.5.3.2 Telecom Link or Trunk FailureThe TSC supervises its trunks between the Transcoder, BTS, and MSC.
Failure of the Abis Interface is signaled to the BSC by all of the RSLs of theassociated BTS. A single RSL failure reflects the status of the correspondingLAPD and FU.
All A Interface faults are controlled by the Transcoder and the MSC. Howeverthey are also monitored by the BSC, in order to define the status of each"end-to-end" A-trunk. The following figure shows RSL fault correlation onthe Abis Interface.
Note: The BTS_TEL SBL describes the status of the GSM-defined BTS telecomfunctions. Its state is defined by operator commands, and correlation of theLAPD RSL states or of the different Carrier Units.
RSL−1
RSL−2
RSL−N (last RSL)
Fault Start CPR Informed RSL State Change
Persistency Correlation
Alarm begin BTS_TEL
Fault Start
Fault Start
INACTIVE
ACTIVE
CPR : Common Processor
RSL : Radio Signaling Link
Figure 45: RSL Correlation on the Abis Interface
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8.5.3.3 Abis Interface Fault MonitoringThe BSC monitors the Abis Interface faults as follows:
1. The BSC detects the first LAPD RSL link failureof the BTS. The BSC starts a persistency timer.It puts the SBL of the RSL into a Maintenance Seized-Auto state while thefollowing actions occur:
The RITs are now in the SOS state. This is because the RIT belonging to
the RSL still functions, but cannot communicate with the BSC
Telecoms resources are blocked to prevent new activity at the BSC
end of this link
The RSL SBL is put into the FLT state, reflecting the loss of the RSL.
2. The persistency timer expires and the CPR is informed of the fault. If thelink recovers during the persistency period, nothing is reported. Otherwisea correlation timer starts and waits for further RSL link failures belongingto the same BTS.
3. Once the correlation timer expires, the BSC sends a state-change-report
message to the OMC-R. The message contains a list of all RSL that are inthe FLT state.
4. The OMC-R is then informed about the state of the BTS_TEL. If all the RSLsbelonging to the BTS have failed, then an alarm is sent to the OMC-Rsignaling the loss of the cell. When an SBL is put in to the FLT state, it isshown in the Alarms-In-Force list.
8.5.3.4 A Interface Fault MonitoringWhen the BSC detects a DTC failure, the BSC puts the DTC SBL in theMSD-Auto state, then into the FLT state. Through TS0 signaling, the MSC isinformed that the trunk is no longer operational and prevents all transactionsrequiring the A channel (including new mobile-originated calls) from using thefailed link of the DTC. The failure is also signalled to the OMC-R. The TSC alsodetects a failure of the Ater link and signals the failure to the OMC-R.
Note: The A channel is allocated only by the MSC.
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8.5.3.5 Failures Detected by SoftwareSoftware throughout the BSC detects error and alarm conditions. It reportsthese conditions to the alarm handling software. The alarm handling softwareperforms persistency, filtering and correlation actions on the received alarmindicators, and determines the required action (e.g., to isolate a faulty SBL).
The figure below shows an example alarm report.
If one or more RSL links remain for the failed BTS, an event change is sent. TheBTS_TEL is put in a FIT state, as some channels for that cell are in operation.The AIFL shows the new alarm. The BSC marks the cell as degraded inservice and reconfigures the BTS.
Figure 46: Example Alarm Report
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8.5.4 BTS Alarms
Alarms in the BTS are tracked by the OMU. The following sections describe theOMU hardware and alarm functions, and also BTS alarm collection.
8.5.4.1 BTS Alarm Hardware
Alarm Hardware OMU Function
G1/G2 Alarm Buses The OMU has a Q1 Interface to the Carrier Units, MCLU, EACB, and FHU modulesin the system, as well as a Token Bus Interface with all of the FU modules.
BTS 9100/9110Alarm Buses
The BSII provides the OMU with an interface to the TRE functional unit, and to theantenna network x and TRANS & CLOCK functional entities, which have their ownon-board controllers. The BCB provides an interface to all the functional entities inthe BTS.
8.5.4.2 BTS Alarm Functions
Alarm OMU Function
Q1 Interface (G1/G2BTS)
On the Q1 Interface, a system of double polling takes place. The OMU polls eachsubsystem individually to find out if there is an error. If there is an error, the OMUdemands an error report from that board. Normally, the information from the errorreport is used as an alarm or an event notification.
Token Bus Interface(G1/G2 BTS)
The OMU is informed by the FU about the type of error that has occurred. The OMUsends the alarm information to the BSC.
BSSI (BTS9100/9110)
Each module spontaneously reports errors to the OMU, which processes the reportas an alarm or an event notification.
BCB (BTS9100/9110)
The Base Station Control Bus operates in a master/slave configuration where theSUM functions as Pilot (master) and the functional entities function as Terminals(slaves) in normal conditions. The OMU collects alarm information on the BCBand sends it to the BSC.
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8.5.4.3 Alarm CollectionThe mechanism for BTS alarm collection on all buses is as follows:
1. The alarm is added to the AIFL.
2. The OMU enters alarm information in a queued buffer. In this way, alarms arequeued even if the link between the BTS and the BSC is temporarily unusable.If the buffer becomes full (over 100 messages):
All fault/state change messages are deleted
No more messages are sent until a state and alarm audit takes place
to synchronize the BSC and the OMC-R. An audit BTS request istransmitted on a regular basis until an audit occurs.
3. The alarm messages containing the alarm information are transmitted to theBSC. For specific information about the alarm messages, refer to the BTSAlarm Dictionary and the BSC/TC Alarm Dictionary.
4. The message is sent to the CPRA, where it is date and time stamped.
5. The BSC performs one of two activities:
If possible, it converts the alarm into a CMISE message, performs
an action and sends a different alarm/event to the OMC-R, via thealarm queue
Otherwise, it retransmits the message to the OMC-R, via the alarmqueue.
6. The message is put in the alarm queue for BTS alarms. If the queueoverflows, the BSC performs an Alarms-in-Force audit on all the modulesin the BTS. This signals that information was received and lost when thequeue overflowed, and that resynchronization is required.
7. The OMC-R receives the alarm over the CMISE link. The alarm is put intothe AS component where it is logged.
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8.5.5 Alarms Detected by the TSC
TSC O&M activities are similar to those performed by the BTS. The TSC hasa Q1 Interface to the transmission equipment. A system of double pollingoccurs on the Q1 Interface:
The first poll checks if there is a change in states.
The second poll occurs only if the state has changed, in order to obtain
more information about the changes.
The Transcoder supervises PCM links. The loss of a link between the BSC andTranscoder is reported by the Transcoder to the TSC.
8.5.6 MFS Alarms
The MFS generates alarms to signal a change in the behavior of a particularfunction within the system, such as a potential problem or a confirmed failure inthe system. The Global Alarm Manager manages the MFS alarms.
It processes all hardware and telecom alarms and is responsible for:
Collecting all fault information relating to GPUs, the active server, andtelecom and external alarms
Recording alarms in a table
Allowing the IMT and the OMC-R to access the alarms
Generating ending alarms when a fault is cleared (for example, when aGPU is replaced)
Managing a communication session with the IMT.
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8.5.7 Recovery Example: Carrier Unit Failures with BCCH
This recovery example is based on a BTS with two Carrier Units. One CarrierUnit is used for BCCH channel handling, the other is used for normal traffic.If the Carrier Unit holding the BCCH fails, it is switched out and the secondCarrier Unit takes the place of the first.
As an example, this section describes the system’s reactions when a CarrierUnit (TRE for a BTS 9100 or a BTS 9110) which has the BCCH channel fails.
Note: In the BTS 9100 or the BTS 9110, the SBLs FU and Carrier Unit have beenmerged into one indivisible SBL, called the TRE. At the BSC, however, all BTS9100 and BTS 9110 TRE faults are mapped to the Carrier Unit to providecompatibility with G1 and G2 BTS. Therefore, at the BSC, all such errors aredisplayed as Carrier Unit faults. That is how they are presented in this example.
FU faults in G1 and G2 BTS continue to be reported as such.
8.5.7.1 Fault Recovery MechanismThe recovery mechanism in the BSS allows a failed unit to switch to areplacement unit, such as:
Redundant hardware
A similar unit which had lower priority active use than the failed unit. Forexample, the BCCH has to exist for the cell to function, so another Carrier
Unit/FU pair (TRE for a BTS 9100 or a BTS 9110) is expendable to replacethe failed Carrier Unit.
The recovery mechanism of the BSS recognizes that the Carrier Unit canchange to its twin Carrier Unit.
Refer to Carrier Unit Recovery Scenario (Section 8.5.7.2) for a step-by-stepscenario of Carrier Unit recovery.
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8.5.7.2 Carrier Unit Recovery ScenarioThe Carrier Unit recovery process is as follows:
1. The Carrier Unit holding the BCCH fails.
2. The BTS sends the BSC a recovery request, reporting that the Carrier Unitis faulty and is out of service, and that a recovery is required.
The BTS also suggests a new Carrier Unit to the BSC, to be used to carrythe BCCH. When the recovery request is received, the BSC temporarilyblocks the resources while it checks if reconfiguration is available. Ifreconfiguration is available, the BTS_TEL SBL becomes FIT, all calls on theCarrier Unit are immediately released, and the RSL is blocked.
3. The BSC sends an alarm to the OMC-R, signaling the loss of BCCH.
4. The BSC attempts a recovery. The recovery command isBTS-CONF-DATA(2).
5. The BTS receives and acknowledges the recovery message. It thenswitches off the faulty Carrier Unit and switches on the second Carrier Unit.The second Carrier Unit adjusts its frequency to the BCCH frequency.
6. If the configuration was successful, the BTS sends a confirmation to theBSC. The BSC then sends the new sys_info (1-6).
7. The BCCH is now broadcasting on the same frequency as before, viathe newly configured Carrier Unit.
8. The BSC sets the BTS_TEL SBL to FIT and informs the OMC-R by sendingan end of alarm. The BTS_TEL remains FIT due to the loss of a channel.
9. If the new Carrier Unit was previously IT, its previously attached resourcesare lost. An alarm is sent to the OMC-R to update the information onlost channels.
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The following figure shows the redundancy process for a failed Carrier Unitwith BCCH.
OMC BSC BTS
Resourcesblocked, BCCHreconfiguration possible
BTS_TEL=FIT
BTS_TEL=IT
BTS_TEL=FIT
CU Fault
BTS_TEL=FIT
1
2
3
4
6
8
9
BTS performs the reconfiguration5
Alarm (cell, loss of BCCH begin)
Alarm (cell, loss of BCCH end)
Alarm (cell, loss of TCH begin)
Reco_req (CU, FOS)
BTS_CONF_DATA (2)
BTS_CONF_COMPL
SYS_INFO (1..6)
BCCH : Broadcast Control Channel
CU : Carrier Unit
TCH : Traffic Channel
Figure 47: Example: Loss of Carrier Unit Holding BCCH.
Note: The BTS_TEL SBL describes the status of the GSM-defined BTS telecomfunctions. Its state is driven by operator commands, or by correlation of theLAPD RSL states or of the different Carrier Units.
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8.5.8 Automatic Power-Down
This feature is available only on the BTS 9100. It is used typically in an outdoorinstallation where the BTS has a backup battery power supply.
In the case of a main power-supply failure, the BTS 9100 is automaticallyswitched to battery power. This situation continues until the main power isrestored or the battery is drained, whichever happens first.
To extend the time during which the BTS 9100 can function under battery power,the BTS is reduced to a minimum configuration to reduce power consumption.
Once a power-supply failure alarm arrives, the OMU starts a timer. If, once thetimer expires, the alarm is still active, the OMU switches off all TREs exceptthe BCCH TRE (one per sector for a sectored site), by placing the TREs tobe powered down in the FOS state.
If, in a given sector of a sectored site, the BCCH TRE is configured without atraffic channel, another TRE (which carries the SDCCH) is kept powered on, sothat calls are still possible in this sector, though limited to one TRE.
When the power-supply failure alarm disappears, the OMU starts a timer. If thealarm re-occurs before the timer expires, the OMU takes no further action. Thisis to guard against a possible unstable restoration of power.
If the BTS power-supply remains stable until the timer expires, the OMUperforms an autonomous auto reset with BTS activation. This re-initializesall available TREs.
For more information about this feature, refer to the following:
Alcatel-Lucent BTS 9100/9110 Functional Description
Alcatel-Lucent BTS 9100 Hardware Description
Alcatel-Lucent BTS 9110 Hardware Description.
8.5.9 BSC Alerter
The BSC Alerter is a telecom supervision function which generates an alarmevent when the system suspects abnormal behavior of a resource. This issystem defined and not dependent on site configuration or traffic conditionsin a particular cell.
An Alerter functions by monitoring and computing the levels of specificPerformance Management counters. If the count exceeds the operator-definedparameters, the Alerter generates an alarm for the BSC resource. This alarm issent to the OMC-R operator.
Note: For performance reasons, each alerter type has a maximum limit of 16 alarms.
For more information about BSC Alerters, refer to BSC Alerters in theOperations & Maintenance Principles document.
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8.6 Performance ManagementThe following provides a brief overview of performance management facilities inthe BSS.
For detailed information about performance management, refer to PerformanceManagement in the Operations & Maintenance Principles document.
For a description of individual counters, refer to PM Counters and Indicators.
The following table shows the performance management functions of theBSC and the MFS.
NetworkElement
Performance Management Functions
BSC BSC
Result collection and collation
X.25-related counters
Traffic measurements on radio channels
Performance Measurement result reporting
Trace invocation result reporting.
MFS MFS
Collects the performance management counters
associated with each logical GPU
Creates a file of counter values.
8.6.1 Traces
Trace management coordinates and triggers trace activities within the BSS.Tracing is originated from the MSC. There are two types of tracing:
Call tracing
IMSI tracing.
Call tracing follows a specified transaction (subscriber call, location update,short message, etc.) inside the BSC. When the specified transaction ends, orthe transaction changes to another BSC, the trace activity ends.
IMSI tracing is not restricted to speech. It includes information about the radioresources set up for the mobile. This includes, for example, location updating,supplementary services, short messages, etc.
For more information about trace management, refer to Trace Management inthe Operations & Maintenance Principles document.
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8.6.2 Performance Monitoring
Monitoring system performance provides information that can be used toimprove the system performance, optimize traffic levels, perform network radioplanning and optimization, and plan network reconfiguration. The OMC-Rmanages the gathering of data collected from all the network elements bymeans of PM counters. PM counter values are collected into results files inthe BSC.
In the BSS, there are two types of raw counters: standard and detailed. Thesetwo counter types are gathered in the following counter groups:
Cumulative counters
Status inspection counters
DER counters
RMS counters.
8.6.3 Radio Measurements Statistics
Radio Measurements Statistics (RMS) provides counters and indicators tomeasure the performance of the Mobile Assisted Frequency Allocation (MAFA)feature and the Adaptive MultiRate (AMR) feature. Other improvements toTiming Advance statistics have also been added.
Radio Measurement Statistics for MAFA is available on G1 BTS Mk2, G2 BTSequipped with DRFU and Alcatel-Lucent BTS. AMR Radio MeasurementStatistics are only available on Alcatel-Lucent BTS.
8.6.3.1 MAFA Radio Measurement StatisticsIn order to help the operator find "clean" frequencies for better frequencyplanning, RMS counters provide information based on the Mobile AssistedFrequency Allocation (MAFA) feature. MAFA is a standardized GSM featurethat provides a way for the system to ask each mobile station to measure extrafrequencies (frequencies of non-neighbor cells). MAFA can also be used tocheck interferences from non-neighbor cells. RMS is a BSC/BTS feature thatrecords measurements from the BTS and mobile stations. For MAFA, specificmobiles supporting this standardized GSM feature are required. Every mobilestation supporting MAFA acts as a potential spectrum analyzer and providesexcellent information about the radio conditions for each single cell.
Using this feature, the operator can:
Detect interfered frequencies
Assess the quality of the cell coverage
Detect and quantify cell unexpected propagation
Assess the traffic distribution in the cell from statistics on reported neighbor
cells
Evaluate the voice quality in the cell.
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During the observation period, the BTS/FU keeps track of all the RMSstatistics derived from the measurements reported by the mobile stationsor measured by the BTS/FU itself on the TCH (SDCCH are not used withRMS). At the end of the observation period when the RMS data is collectedfrom the concerned BTS/FUs, the BSC builds a report (called the RMSresult file). The transfer towards the OMC-R occurs via FTAM. In addition,it is possible during the observation period to apply MAFA (also calledExtended Measurement Reporting). This procedure consists of sending anExtended Measurement Order (EMO) to the mobile stations. On receipt ofthe command, the mobile stations take one SACCH multiframe to performmeasurements on specific frequencies. The measurements are reported viathe EXTENDED_MEASUREMENT_REPORT message. The EMO is sent only once percall. The statistics related to MAFA are collected in the BTS and integrated inthe RMS results. The statistics are based on the measurements performed atthe BTS and the mobile station, on the TCH only.
The statistics can be classified as follows:
Radio related statistics. These can be classified as follows:
Statistics related to the whole serving cell
Statistics related to the TRXs.
Voice quality statistics. Nine counters and indicators provide an overview of
the communications quality (TCH only) for each TRX.
8.6.3.2 Detailed Radio Measurement StatisticsSeveral new improvements have been added to RMS, including the introductionof Radio Measurement Statistics counters and indicators for AMR. Newcounters reporting timing advance statistics were also added. These are allreported within existing RMS jobs.
AMR codecs (both FR and HR) are monitored to find which codecs are usedthe most often. Because FR and HR use different parameters and differentcodecs are used in UL and DL, results are provided for:
AMR FR uplink
AMR FR downlink
AMR HR uplink
AMR HR downlink
Matrixes are used to show the total number of good speech frames per codecgathered in RXLEV intervals. These results make it possible to deduce theaverage frame erasure rate per AMR codec in the uplink. Results are providedat TRX level.
Knowing the codec use and comparing it with the link level in the cell enablesthe operator to monitor proper operation of AMR and the quality of radiocoverage in a cell. Statistics on the frame erasure rate in the uplink andcomparisons between codec distribution and RXLEV allows an assessment ofthe voice quality and to adapt AMR thresholds to specific cell conditions.
Timing advance is a good indicator of the position of an MS relative to a cell.The RMS counters provide statistics on timing advance in order to understandthe geographical distribution in a cell. These statistics can be used to identifyresurgences and hot spots.
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To allow operators to obtain information about BTS output power on a TRXbasis, a new counter is implemented. This counter retrieves the GMSK TRXpower level applied at the BTS antenna output connector in dBm. This counterreports on the BTS_MAX_OUTPUT_POWER variable, used for power controland path balance statistics.
These RMS improvements help the operator to:
Optimize speech quality using AMR
Optimize network planning, through identification of resurgences andhot spots.
8.6.4 Results Analysis
Using the OMC-R, an operator can view alarms from the OMC-R databasesand analyze the PM measurements.
Counter and indicator information is processed by an OMC-R tool. The resultscan be used to generate QoS alarms to notify the operator of possible networkproblems. The results, also can be sent to the 9159 NPO to produce reports.
9159 NPO is usually a standalone tool that runs on a separate Sun machine.
It can also run on the OMC-R machine:
As 9159 NPO embeded, if the number of managed cells is up to 200. In this
case the full 9159 NPO functionality is available.
A s MPM, if the OMC-R manages more than 200 cells. In this case only
QoS feature is available.
For more information about results analysis and the tools available to processcounter and indicators information, refer to the Results Analysis section of theOperations & Maintenance Principles document.
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8.7 AuditsAudits can be automatic or initiated by an operator. They can be performed atseveral levels:
From the OMC-R to the Transcoder, the BSC, or the MFS
From the BSC to the BTS.
For more information about Audits, refer to:
Configuration Management Audits in Configuration Management
Audits/Resynchronization
Fault Management Audits in Fault Management Audits.
Using the IMT, it is possible to perform a radio re-initialization, or a radioresynchronization of the MFS.
8.7.1 Audit Types
The following table describes the various types of audits.
Type Description
Logical Audit A logical audit is performed on logical parameters. The logical parameters includedynamic cell information, its power ratings, information about adjacent cells, theradio configuration of the cell, and hopping and paging groups. No logical auditis provided for the MFS side.
Software VersionAudit
The software version audit controls the versions of software that exist on thesubsystem.
Hardware Audit Hardware audits control the hardware on the subsystem. This audit provides aphysical list of all components in the subsystem, their SBLs, and their associatedRITs. The OMC-R updates the database with this information.
Alarm Audit The OMC-R requests the AIFL from a unit of the BSS. The OMC-R then comparesthis with its own list and updates its database if there are any differences.
State Audit A state audit checks the state of SBLs on a particular subsystem, to ensure that SBLdatabases are synchronized. All the SBLs and their states are compared with thedata in the OMC-R. If the SBL does not exist in the database, it is created and itsstate is registered.
The BSC/BTS SBL audit does not line up BSC and BTS databases when the BTSreceives a state-update-request with different SBLs states. So in this case the BSClines-up completely itself on BTS view, without useless audits.
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Two types of action are possible for the MFS:
Re-initialize GPRS configurationAllows the OMC-R to force the logical configuration of the MFS, by deletingthe current one, and then recreating one from scratch, using the currentOMC-R configuration. This is roughly the equivalent of a Force configurationat the BSS side. However, it always induces some outages.
Resynchronize GPRS configuration.Allows the OMC-R to force the logical configuration of the MFS, bycomputing the differences with the current OMC-R configuration. It isthe preferred synchronization action at the MFS side, as it minimizes theMFS outage.
A suite of audits is automatically invoked by the OMC-R or the BSC toresynchronize the system. This is done:
To perform a RESET/RESTART
When there is a loss of links between subsystems. This ensures that the
system databases are synchronized after autonomous operation while the
link was down (i.e., the BTS_O&M was disabled).
To make changes in the databases, without the possibility of aligning
both subsystems
To start a BSC Alarms-in-Force audit if the BSC alarm queue overflows
To perform software database replacement.
Audit information for the whole system is stored in the OMC-R.
8.7.2 Audit Flow
Audit flow is based on an action request from the OMC-R, or on an automaticrequest.
The subsystem receiving the audit request performs an audit of its functionalunits.
The reply can have one or several report messages to pass the information backto the request originator. The request originator can generate more actionsbased on the information received. For example, when the state of the CarrierUnit and its pair FU do not match, the BSC disables the FU/Carrier Unit pairs.
The OMC-R, on reception of the audit report, updates its database. Duringdownload the results of the software audit are used to provide the list ofmodules the OMC-R needs to update the BSS subsystem. This is done bycomparing the OMC-R lists of modules to transfer, and their version numbers,to see if they already exist in the subsystem. Only the newer versions aretransferred to the subsystem.
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8.8 Remote InventoryThe Remote Inventory feature allows an operator to get hardware and firmwareinformation from the OMC-R. This information is used for retrofit, deployment ormaintenance. The main benefit is that the amount of site visits can be reducedconsiderably. The Remote Inventory data is reported to the OMC-R by theMFS, by Alcatel-Lucent BTS (9100/ 9110) which are numerous and spread outin the field and by the 9125 STM-1 TC. The operator can get this data in twoways, automatically or on-demand. The on-demand mode remains availableeven when the automatic mode is selected. Among the reported data isinformation that is very useful for retrofit or maintenance actions, e.g., the sitename, the exact location of the board, the serial number, the part number andthe variant. Sending the data to external tools is possible because the inventorydata files on the OMC-R can be consolidated into a single (tabular format)csv file per BTS, per MFS and per 9125 STM-1 TC. Existing external toolscan therefore be re-used.
The Remote Inventory feature brings the following benefits:
ReliabilityInventory data is reported directly (periodically if requested) by the BTSto the OMC-R (through the BSC, which is transparent), so the operatoralways has the correct information. To keep the OMC-R at a high levelof performance, Alcatel-Lucent recommends using the automatic modewith a seven-day acquisition period.
Cost cuttingIt is no longer necessary to go onsite to get hardware and firmwareinformation before performing a retrofit or a maintenance action.
Remote Inventory can be performed at the MFS. Information can be displayedfor the selected subrack. For a BSC and MFS which share the same rack, eachnetwork element will provide its own inventory files, which are managed by theOMC-R. A remote inventory can be built and collected either automatically,according to a defined schedule, or on demand, via IMT or OMC-R request.
For more information about the IMT, and the tasks that can be performed,refer to the:
Online help provided for the 9130 MFS IMT
Alcatel-Lucent 9130 MFS IMT User Guide.
Online help provided for the 9135 MFS IMT
Alcatel-Lucent 9135 MFS IMT User Guide.
For more information about Remote Inventory, see Remote Inventory in theOperations & Maintenance Principles document.
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