Voice over LTE

Voice over LTEEPS and IMS Networks

André Perez

First published 2013 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.

Apart from any fair dealing for the purposes of research or private study, or criticism or review, aspermitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced,stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers,or in the case of reprographic reproduction in accordance with the terms and licenses issued by theCLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at theundermentioned address:

ISTE Ltd John Wiley & Sons, Inc.27-37 St George’s Road 111 River StreetLondon SW19 4EU Hoboken, NJ 07030UK USA

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© ISTE Ltd 2013The rights of André Perez to be identified as the author of this work have been asserted by him inaccordance with the Copyright, Designs and Patents Act 1988.

Library of Congress Control Number: 2013942893

British Library Cataloguing-in-Publication DataA CIP record for this book is available from the British LibraryISBN: 978-1-84821-534-4

Printed and bound in Great Britain by CPI Group (UK) Ltd., Croydon, Surrey CR0 4YY

Table of Contents

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix

Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii

Chapter 1. The EPS Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1. Architecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1.1. Access network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.1.2. Core network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.1.3. Protocol architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1.2. Signaling protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111.2.1. NAS protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111.2.2. RRC protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161.2.3. S1-AP protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211.2.4. X2-AP protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241.2.5. GTPv2-C protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

1.3. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301.3.1. Attachment procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . 301.3.2. Location update . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341.3.3. Bearer activation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361.3.4. Handover procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Chapter 2. The LTE Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

2.1. Structure of the radioelectric interface . . . . . . . . . . . . . . . . . . . . 472.2. Data link layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482.2.1. PDCP protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482.2.2. RLC protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502.2.3. MAC protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

2.3. Physical layer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

vi Voice over LTE

2.3.1. Frequency range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 602.3.2. Spatial multiplexing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 622.3.3. Time multiplexing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 632.3.4. Physical signals and channels. . . . . . . . . . . . . . . . . . . . . . . 68

2.4. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 802.4.1. Cell searching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 802.4.2. System information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 802.4.3. Random access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 802.4.4. Data scheduling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 822.4.5. Re-transmission in the case of error . . . . . . . . . . . . . . . . . . . 84

Chapter 3. The CSFB Function. . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

3.1. Reminder about NGN. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 893.1.1. Architecture of NGN. . . . . . . . . . . . . . . . . . . . . . . . . . . . 893.1.2. Signaling transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 913.1.3. Transport of voice data . . . . . . . . . . . . . . . . . . . . . . . . . . 93

3.2. The CSFB function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 943.3. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 953.3.1. Attachment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 953.3.2. Tracking area update . . . . . . . . . . . . . . . . . . . . . . . . . . . . 963.3.3. Outgoing call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 983.3.4. Incoming call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Chapter 4. SIP and SDP Protocols . . . . . . . . . . . . . . . . . . . . . . . . . . 103

4.1. Entities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1034.2. Identities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1044.3. Structure of SIP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1054.3.1. Requests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1054.3.2. Responses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1094.3.3. Headers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

4.4. Description of the media . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1164.5. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1184.5.1. Registration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1184.5.2. The session. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120

Chapter 5. The IMS Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

5.1. Architecture of IMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1375.1.1. Session control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1395.1.2. Application servers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1415.1.3. Databases. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1425.1.4. Interconnection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142

Table of Contents vii

5.1.5. Media processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1435.1.6. Charging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

5.2. Registration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1465.2.1. First phase of registration . . . . . . . . . . . . . . . . . . . . . . . . . 1465.2.2. Second phase of registration . . . . . . . . . . . . . . . . . . . . . . . 1505.2.3. Subscription . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1535.2.4. Notification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

5.3. The session between IMSs . . . . . . . . . . . . . . . . . . . . . . . . . . . 1585.3.1. Establishment of the session . . . . . . . . . . . . . . . . . . . . . . . 1585.3.2. Termination of the session . . . . . . . . . . . . . . . . . . . . . . . . 164

5.4. DIAMETER messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1655.4.1. The messages related to registration and routing . . . . . . . . . . . 1665.4.2. Messages relating to control of the media . . . . . . . . . . . . . . . 166

5.5. Interoperation with the CS network . . . . . . . . . . . . . . . . . . . . . 1675.5.1. Call initiated by the IMS network . . . . . . . . . . . . . . . . . . . . 1675.5.2. Call generated by the CS network . . . . . . . . . . . . . . . . . . . . 1695.5.3. Release of the communication . . . . . . . . . . . . . . . . . . . . . . 170

Chapter 6. Telephone Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173

6.1. Service profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1736.2. Communication Diversion . . . . . . . . . . . . . . . . . . . . . . . . . . . 1756.2.1. CFU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1756.2.2. CFB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1766.2.3. CFNR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1776.2.4. CD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1796.2.5. CFNL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180

6.3. Identification presentation . . . . . . . . . . . . . . . . . . . . . . . . . . . 1806.3.1. OIP and OIR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1806.3.2. TIP and TIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181

6.4. Message Waiting Indication . . . . . . . . . . . . . . . . . . . . . . . . . . 1816.5. Call parking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1846.6. Conferencing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1856.7. Communication transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1876.8. Communication Waiting . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1896.9. Malicious Communication Identification . . . . . . . . . . . . . . . . . . 1926.10. Automatic callback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1936.10.1. CCBS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1936.10.2. CCNR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1966.10.3. CCNL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197

6.11. Communication rejection . . . . . . . . . . . . . . . . . . . . . . . . . . . 1986.11.1. ACR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198

viii Voice over LTE

6.11.2. ICB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1986.11.3. OCB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198

6.12. Announcements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198

Chapter 7. The SRVCC Function . . . . . . . . . . . . . . . . . . . . . . . . . . 203

7.1. Impact on architectures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2037.1.1. Impact on mobile networks . . . . . . . . . . . . . . . . . . . . . . . . 2037.1.2. Impact on the IMS network . . . . . . . . . . . . . . . . . . . . . . . . 205

7.2. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2077.2.1. Registration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2077.2.2. Session establishment . . . . . . . . . . . . . . . . . . . . . . . . . . . 2117.2.3. PS-CS handover. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2147.2.4. Transfer of the communication . . . . . . . . . . . . . . . . . . . . . . 216

Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225

Preface

This book discusses the mechanisms used in the 4G EPS (Evolved PacketSystem) mobile network for telephone service support, and in the IMS network(IP (Internet Protocol) Multimedia Sub-system) to provide a telephone service.

The 4G network does not provide a telephone service because it does not processtelephone signaling. It operates in PS (Packet Service) mode, and only transports IPpackets. Therefore, it only transfers IP packets containing voice data or telephonesignaling.

The IP packet containing voice data has the following structure:

– AMR (Adaptative Multi-Rate) codec;

– RTP (Real-Time Transport Protocol) header;

– UDP (User Datagram Protocol) header;

– IP header.

The IP packet containing telephone signaling has the following structure:

– SIP (Session Information Protocol) message;

– UDP header;

– IP header.

Chapter 1 introduces the different entities of the 4G network. It describes the 4Gsignaling protocol exchanged between the different entities, enabling a mobile toattach, update its location, establish sessions for the transport of IP packets andchange cells (known as handover). For the purposes of the transport of IP packets,

x Voice over LTE

the 4G network has supports in place that are known as bearers. A bearer is similarto a virtual circuit.

Each bearer has a QCI (QoS Class Identifier) associated with it. Thus, for eachmobile, two bearers are created: one for the transport of the telephone signaling(QCI = 5) and the other for the transport of the voice data (QCI = 1).

Chapter 2 presents the LTE (Long Term Evolution) radioelectric interfacebetween the mobile and the 4G networks. The radioelectric interface serves totransport the mobile traffic (IP packets containing voice data or telephone signaling)and the 4G signaling exchanged with the 4G network.

The procedures specific to the radioelectric interface relate to connection of themobile to the 4G network, scheduling of the IP packets and re-transmission in thecase of error.

To begin with, the establishment of a telephone communication will not be doneover a 4G network, because of the difficulty in handover from PS mode to CS(Circuit Service) mode, when the mobile is transferred from a 4G cell to a 2G or 3Gcell.

Chapter 3 discusses the mechanism of CSFB (CS FallBack), which is an interimsolution. It enables a mobile connected to the 4G network to receive an alert sent bya 2G/3G network (this is known as paging). This page is sent when a call comes inon the 2G/3G network. On receiving the page, the mobile is transferred to the 2G/3Gnetwork, over which the telephone communication can then be established.

Similarly, a mobile connected to the 4G network and wishing to make anoutgoing call must first be transferred to the 2G/3G network.

Chapter 4 presents the SIP protocol, upon which the telephone signalingtransferred by the 4G network is based. SIP defines two fundamental procedures:registration of the mobile and establishment of the session (i.e. the telephonecommunication).

Chapter 5 introduces the IMS network which provides a telephone service, usingthe 4G network for the transport of the voice data and telephone signaling. Thetelephone signaling again uses SIP, enriching it.

The IMS network defines the routing of the telephone signaling, access todatabases containing the profile and secret data of the subscriber, and the specificprocessing of voice data to provide particular services, such as conference calling,for instance.

Preface xi

Telephone communication can be established between two 4G mobiles. Thetelephone signaling is processed by the IMS entities of the home operator of eachmobile. The voice data is directly transferred between the 4G networks (seeFigure 1).

Figure 1. Telephone communication between two 4G mobiles

Telephone communication can also be established between a mobile and aterminal connected to the fixed network PSTN (Public Switched TelephoneNetwork) or the mobile network PLMN (Public Land Mobile Network). TheIMS network provides the entities which perform conversion of the protocols andinterconnection with these networks (Figure 2).

Figure 2. Telephone communication betweena 4G mobile and a terminal connected to the PLMN or PSTN network

Chapter 6 presents the telephone services offered by a particular entity within theIMS network – the TAS (Telephone Application Server). These services relate tocommunication forwarding, identification presentation or restriction, messagewaiting indication, communication hold, conference, communication transfer, callwaiting, malicious communication identification, completion of communication, callrejection and announcements.

xii Voice over LTE

The telephone communication established over the 4G network in PS modeneeds to be maintained when the mobile is transferred to the 2G/3G network in CSmode.

Chapter 7 finally discusses the mechanism of SRVCC (Single Radio Voice CallContinuity), which takes care of this call maintaining in the case of a PS–CS inter-system handover. SRVCC is a particular function of the IMS network. It anchors theflows of telephone signaling and voice data (Figure 3).

Figure 3. The SRVCC mechanism

Acronyms

A

AAA Authorization-Authentication-AnswerAAL2 ATM Adaptation Layer 2AAR Authorization-Authentication-RequestACM Address Complete MessageACR Anonymous Communication RejectionAM Acknowledged ModeAMR Adaptive Multi-RateANM Answer MessageAPN Access Point NameARQ Automatic Repeat reQuestAS Application ServerASA Abort-Session-AnswerASR Abort-Session-RequestATCF Access Transfer Control FunctionATGW Access Transfer GatewayATM Asynchronous Transfer Mode

B

B2BUA Back-to-Back User AgentBCCH Broadcast Control ChannelBCH Broadcast ChannelBGCF Breakout Gateway Control Function

xiv Voice over LTE

BICC Bearer Independent Call ControlBSS Base Station Sub-systemBSSMAP BSS Management Application Part

C

CCBS Completion of Communications to Busy SubscriberCCCH Common Control ChannelCCNL Completion of Communications on Not Logged-inCCNR Completion of Communications on No ReplyCD Communication DeflectionCDF Charging Data FunctionCDIV Communication DiversionCDR Charging Data RecordCFB Communication Forwarding on Busy userCFI Control Format IndicatorCFNL Communication Forwarding on Not Logged-inCFNR Communication Forwarding on No ReplyCFU Communication Forwarding UnconditionalCGF Charging Gateway FunctionCM Call ManagementCQI Channel Quality IndicatorC-RNTI Cell Radio Network Temporary IdentityCS Circuit ServiceCSCF Call Session Control FunctionCSFB Circuit Service FallBackCTF Charging Trigger FunctionCW Communication Waiting

D

DCCH Dedicated Control ChannelDCI Downlink Control InformationDFTS Discrete Fourier Transform SpreadDL-SCH Downlink Shared ChannelDNS Domain Name SystemDRB Data Radio Bearer

Acronyms xv

DRS Demodulation Reference SignalDSCP DiffServ Code PointDTCH Dedicated Traffic ChannelDTM Dual Transfer ModeDwPTS Downlink Pilot Time Slot

E

E-CSCF Emergency-CSCFECT Explicit Communication TransferEMM EPS Mobility ManagementeNB evolved Node BEPC Evolved Packet CoreEPS Evolved Packet SystemE-RAB EPS Radio Access BearerESM EPS Session ManagementETWS Earthquarke and Tsunami Warning SystemE-UTRAN Evolved Universal Terrestrial Radio Access Network

F

FDD Frequency Division Duplex

G

GMSC Gateway MSCGP Gap PeriodGPRS General Packet Radio ServiceGSM Global System for MobileGTP-C GPRS Tunnel Protocol ControlGTP-U GPRS Tunnel Protocol UserGUTI Globally Unique Temporary Identity

H

HARQ Hybrid ARQHDB3 High Density Binary 3

xvi Voice over LTE

HI HARQ IndicatorHSS Home Subscriber ServerHTTP Hypertext Transfer Protocol

I

IAM Initial Address MessageICB Incoming Communication BarringICIC Inter-Cell Interference CoordinationI-CSCF Interrogating-CSCFiFC initial Filter CriteriaIFFT Inverse Fast Fourier TransformIMS IP Multimedia Sub-systemIMS-GWF IMS Gateway FunctionIMSI International Mobile Subscriber IdentityIP Internet ProtocolIPSec IP SecurityISIM IMS Services Identity ModuleISUP ISDN User Part

L

LAI Location Area IdentifierLIA Location-Info-AnswerLIR Location-Info-RequestLTE Long Term Evolution

M

M3UA MTP 3 User AdaptationMAA Multimedia-Auth-AnswerMAC Media Access ControlMAR Multimedia-Auth-RequestMCC Mobile Country CodeMCCH Multicast Control ChannelMCH Multicast Channel

Acronyms xvii

MCID Malicious Communication IdentificationMeGaCo Media Gateway ControllerMGCF Media Gateway Control FunctionMGW Multimedia GatewayMIB Master Information BlockMIMO Multiple Input Multiple OutputMISO Multiple Input Single OutputMM Mobility ManagementMME Mobility Management EntityMMEC MME CodeMMEGI MME Group IdentityMMEI MME IdentityMNC Mobile Network CodeMRF Multimedia Resource FunctionMRFC MRF ControllerMFRP MRF ProcessorMSC Mobile-services Switching CentreMTCH Multicast Traffic ChannelM-TMSI MME - Temporary Mobile Subscriber IdentityMTP Message Transfer PartMU-MIMO Multi User-MIMOMWI Message Waiting Indication

N

NAS Non Access StratumNGN Next Generation Network

O

OCB Outgoing Communication BarringOCS Online Charging SystemOFDM Orthogonal Frequency-Division MultiplexingOIP Originating Identification PresentationOIR Originating Identification Restriction

xviii Voice over LTE

P

PBCH Physical Broadcast ChannelPCCH Paging Control ChannelPCEF Policy and Charging Enforcement FunctionPCFICH Physical Control Format Indicator ChannelPCH Paging ChannelPCRF Policy Charging and Rules FunctionP-CSCF Proxy-CSCFPDCCH Physical Downlink Control ChannelPDCP Packet Data Convergence ProtocolPDN Packet Data NetworkPDSCH Physical Downlink Shared ChannelPGW PDN GatewayPHICH Physical HARQ Indicator ChannelPLMN Public Land Mobile NetworkPMCH Physical Multicast ChannelPMI Precoding Matrix IndicatorPPA Push-Profile-AnswerPPR Push-Profile-RequestPRACH Physical Random Access ChannelPS Packet ServicePSS Primary Synchronization SignalPSTN Public Switched Telephone NetworkPUCCH Physical Uplink Control ChannelPUSCH Physical Uplink Shared Channel

Q

QAM Quadrature Amplitude ModulationQCI QoS Class IdentifierQoS Quality of ServiceQPSK Quadrature Phase-Shift Keying

R

RACH Random Access Channel

Acronyms xix

RANAP Radio Access Network Application Part)RAR Random Access ResponseRB Resource BlockRE Resource ElementREG Resource Element GroupREL ReleaseRI Rank IndicatorRLC Radio Link ControlRLC Release CompleteROHC Robust Header CompressionRRC Radio Resource ControlRS Reference SignalRSRP Reference Signal Received PowerRSRQ Reference Signal Received QualityRTA Registration-Termination-AnswerRTP Real-Time Transport ProtocolRTR Registration-Termination-Request

S

SAA Server-Assignment-AnswerSAE System Architecture EvolutionSAR Server-Assignment-RequestSCC AS Service Centralization and Continuity Application ServerSCCP Signaling Connection Control PartS-CSCF Serving-CSCFSCTP Stream Control Transmission ProtocolSDH Synchronous Digital HierarchySDP Session Description ProtocolSGSN Service GPRS Support NodeSFBC Space Frequency Block CodeSFN System Frame NumberSGW Serving GatewaySGW Signaling GatewaySIB System Information BlockSIGTRAN Signaling Transport over IPSIMO Single Input Multiple Output

xx Voice over LTE

SIP Session Information ProtocolSISO Single Input Single OutputSLF Subscription Locator FunctionalSRB Signaling Radio BearerSRS Sounding Reference SignalSRVCC Single Radio Voice Call ContinuitySS7 Signaling System 7SSS Secondary Synchronization SignalSTA Session-Termination-AnswerS-TMSI Shortened-TMSISTN-SR Session Transfer Number for SRVCCSTR Session-Termination-RequestSU-MIMO Single User MIMO

T

TAC Tracking Area CodeTAI Tracking Area IdentityTAS Telephony Application ServerTCP Transmission Control ProtocolTDD Time Division DuplexTDM Time Division MultiplexingTEID Tunnel Endpoint IdentifierTIP Terminating Identification PresentationTIR Terminating Identification RestrictionTLS Transport Layer SecurityTM Transparent ModeTMSI Temporary Mobile Subscriber IdentityTTI Transmission Time Interval

U

UA User AgentUAA User-Authorization-AnswerUAC User Agent ClientUAR User-Authorization-RequestUAS User Agent Server

Acronyms xxi

UCI Uplink Control InformationUDP User Datagram ProtocolUE User EquipmentUL-SCH Uplink Shared ChannelUM Unacknowledged ModeUMTS Universal Mobile Telecommunications SystemUpPTS Uplink Pilot Time SlotURI Uniform Resource IdentifierUTRAN Universal Terrestrial Radio Access Network

X

XML eXtensible Markup Language

Chapter 1

The EPS Network

1.1. Architecture

The 4th-generation mobile network EPS (Evolved Packet System) comprises acore network EPC (Evolved Packet Core) and an access network E-UTRAN(Evolved Universal Terrestrial Radio Access Network) (Figure 1.1).

Figure 1.1. Architecture of the EPS network

2 Voice over LTE

The access network E-UTRAN takes care of connection of mobiles. The EPCcore network interconnects the access network and provides the interface for thePDN (Packet Data Network). It ensures the attachment of mobiles to the networkand the establishment of the bearers.

The term SAE (System Architecture Evolution) is used for the study of theevolution of the core network EPC.

The term LTE (Long Term Evolution) is attributed to the study of the evolutionof the radioelectric interface Uu between the EPS and the mobile UE (UserEquipment).

1.1.1. Access network

The access network E-UTRAN includes only one type of entity, the radioelectricstation eNB (evolved Node B) to which the UE connects (Figure 1.1).

The eNB is responsible for managing radioelectric resources, the allocation ofbearers to the mobile and the mobility of the UE.

The eNB transfers the traffic data from the mobile (or respectively theSGW (Serving Gateway) of the EPC) to the SGW (or respectively the mobile).When the eNB receives data from the UE or from the SGW, it examines the QCI(QoS Class Identifier) to implement the packet scheduling mechanism.

For outgoing data destined for the SGW, the eNB performs DSCP (DiffServCode Point) marking of the IP (Internet Protocol) packets in relation with the QCIassigned to each packet.

The eNB compresses and encrypts the data traffic on the radioelectric interface.

The eNB encrypts and controls the integrity of the signaling data exchanged withthe mobile.

The eNB selects the MME (Mobility Management Entity) in the EPC to whichthe mobile will be attached.

The eNB processes the paging request sent by the MME for broadcast into thecell. The cell is the area of the eNB’s radioelectric coverage.

The eNB also broadcasts the data relating to the characteristics of theradioelectric interface into the cell, which the mobile uses to connect.