Download ppt - Chapter 3

2001/10/192001/10/19 Prof. Huei-Wen FerngProf. Huei-Wen Ferng 11

Chapter 3Chapter 3

General Packet Radio Service General Packet Radio Service (GPRS)(GPRS)


GSMGSM

A Brief IntroductionA Brief Introduction


ArchitectureArchitecture


Components/ ElementsComponents/ Elements

Mobile Station (MS)Mobile Station (MS) Base Station Subsystem (BSS)Base Station Subsystem (BSS)

• Base Transceiver Station (BTS)Base Transceiver Station (BTS)• Base Station Controller (BSC)Base Station Controller (BSC)

Mobile Switching Center (MSC)Mobile Switching Center (MSC) Four databasesFour databases

• Home Location Register (HLR)Home Location Register (HLR)• Visitor Location Register (VLR)Visitor Location Register (VLR)• Equipment Identity Register (EIR)Equipment Identity Register (EIR)• Authentication Center (AUC)Authentication Center (AUC)


Standard InterfacesStandard Interfaces

UUmm:MS-BTS:MS-BTS Abis: BTS-BSCAbis: BTS-BSC A-interface: BSA-interface: BS

C-MSCC-MSC

SIM:SIM: Subscriber IdentiSubscriber Identi

ty Modulety Module


Physical ChannelPhysical Channel


Physical Channel (Cont’d)Physical Channel (Cont’d)


Logical ChannelLogical Channel


Logical Channel (Cont’d)Logical Channel (Cont’d)

TCH (Traffic Channel)TCH (Traffic Channel)• TCH/FTCH/F• TCH/HTCH/H

Signaling channelsSignaling channels• BCH (Broadcast CH)->3 CHsBCH (Broadcast CH)->3 CHs• CCCH (Common Control CH)->3 CHsCCCH (Common Control CH)->3 CHs• DCCH (Dedicated Control CH)->3 CHsDCCH (Dedicated Control CH)->3 CHs


GSM DataGSM Data


EvolutionEvolution

CSD:Circuit-Switched DataCSD:Circuit-Switched Data SMS: Short Message ServiceSMS: Short Message Service HSCSD: High-Speed CSDHSCSD: High-Speed CSD EDGE: Enhanced Data rate for GSM EvolutionEDGE: Enhanced Data rate for GSM Evolution


Pre-GPRS SystemsPre-GPRS Systems


SMS in GSMSMS in GSM Two-way non-blocking packet-mode messaging servicTwo-way non-blocking packet-mode messaging servic

ee• Allowing non-real-time (NRT) dialog between mobile terminalAllowing non-real-time (NRT) dialog between mobile terminal

ss Transmission on GSM’s signaling channel (e.g., SDCCTransmission on GSM’s signaling channel (e.g., SDCC

H)H)• Up to 160 bytes (PTP/broadcast)Up to 160 bytes (PTP/broadcast)

Offered message categoriesOffered message categories• SMS-mobile-terminated PTP (stored intermediately in the SMSMS-mobile-terminated PTP (stored intermediately in the SM

S service center (SMS-SC))S service center (SMS-SC))• SMS-mobile-originated PTPSMS-mobile-originated PTP• Cell broadcast SMSCell broadcast SMS


HSCSDHSCSD

Aggregation of multiple slots in a GSM Aggregation of multiple slots in a GSM frameframe• Speed ranges from 14.4 kbps to 64 KbpsSpeed ranges from 14.4 kbps to 64 Kbps

Using the existing GSM infrastructureUsing the existing GSM infrastructure Affects to GSMAffects to GSM

• Channel allocationChannel allocation• Connection setupConnection setup• Handoff proceduresHandoff procedures• Access to the fixed networkAccess to the fixed network


GPRSGPRS


About GPRSAbout GPRS

Initiated in 1994 by ETSIInitiated in 1994 by ETSI Services offered: PTP and PTMServices offered: PTP and PTM Systems adopted: GSM and IS-136Systems adopted: GSM and IS-136 SpeedSpeed

• Single slot->14.4 kbpsSingle slot->14.4 kbps• Multiple slot->115.2 kbpsMultiple slot->115.2 kbps

Web page browsing and Internet surfingWeb page browsing and Internet surfing Channel allocationChannel allocation

• Fixed/Static or dynamicFixed/Static or dynamic


GPRS Network ArchitectureGPRS Network Architecture


Elements-SGSNElements-SGSN

Serving GPRS Support Node (SGSN)Serving GPRS Support Node (SGSN)• Functions similar to MSC/VLRFunctions similar to MSC/VLR• Monitors user locationMonitors user location• Handles charging dataHandles charging data• Provides security via A5 ciphering algorithmProvides security via A5 ciphering algorithm• Manages sessions, mobility, and logical channelsManages sessions, mobility, and logical channels• QoS management: policing and schedulingQoS management: policing and scheduling• Network access control Network access control


Elements-GGSNElements-GGSN

Gateway GSN (GGSN)Gateway GSN (GGSN)• Inter-works GPRS network with external Inter-works GPRS network with external

packet-switched networkspacket-switched networks• Data formattingData formatting• Address translationAddress translation• Protocol conversionProtocol conversion• Routing of packetsRouting of packets• Firewall, billing, and packet filtering Firewall, billing, and packet filtering


GSNGSN

GSN includes SGSN and GGSNGSN includes SGSN and GGSN A GPRS network consists of multiple SGSA GPRS network consists of multiple SGS

Ns but only one GGSN for internetworkinNs but only one GGSN for internetworkingg

GTP (GPRS Tunnel Protocol)GTP (GPRS Tunnel Protocol)• Communication protocol between two GSNCommunication protocol between two GSN

ss• User data is encapsulated and tunneled thrUser data is encapsulated and tunneled thr

ough the IP backbone networkough the IP backbone network


GPRS Coding SchemesGPRS Coding Schemes

Four schemes: CS-1~CS-4Four schemes: CS-1~CS-4 Convolutional CodeConvolutional Code


GPRS Protocol Stack (Data Trans.)GPRS Protocol Stack (Data Trans.)


Protocol DescriptionProtocol Description

Layer 1/ Physical layerLayer 1/ Physical layer• PLL (Physical Link sub-Layer)PLL (Physical Link sub-Layer)

Data unit framingData unit framing Data codingData coding Error detection and correctionError detection and correction

• RFL (Radio Frequency sub-Layer)RFL (Radio Frequency sub-Layer) Conforms to GSM 05 series recommendationsConforms to GSM 05 series recommendations Performs modulation and demodulationPerforms modulation and demodulation Specifies carrier freq., radio channel structures, raw Specifies carrier freq., radio channel structures, raw

channel data rates, transceiver characteristics, channel data rates, transceiver characteristics, performance requirementsperformance requirements


Protocol Description (Cont’d)Protocol Description (Cont’d)

Layer 2/ Data link layerLayer 2/ Data link layer• LLC (Logical Link Control)LLC (Logical Link Control)

Supports PTM transmissionSupports PTM transmission Provides secure logical pipe between MS and Provides secure logical pipe between MS and

SGSNSGSN

• RLC (Radio Link Control)/ MAC (Medium RLC (Radio Link Control)/ MAC (Medium Access Control)Access Control)

Provides access signalingProvides access signaling Resolves access contentionsResolves access contentions Provides link level ARQProvides link level ARQ



Relay functionRelay function• In the BSS, relays LLC PDUs between the UIn the BSS, relays LLC PDUs between the U

m and Gb interfacesm and Gb interfaces• In the SGSN, it relays packet data protocol In the SGSN, it relays packet data protocol

(PDP) PDUs between the Gb and Gn interfac(PDP) PDUs between the Gb and Gn interfaceses



SNDCP (Sub-Network-Dependent ConveSNDCP (Sub-Network-Dependent Convergence Protocol)rgence Protocol)• Handles TCP/IP headers and data compressHandles TCP/IP headers and data compress

ionion• Deals with multiplexing, encryption, and seDeals with multiplexing, encryption, and se

gmentationgmentation BSSGP (BSS GPRS Protocol)BSSGP (BSS GPRS Protocol)

• QoSQoS• Routing between BSS and SGSNRouting between BSS and SGSN


GPRS QoS IssuesGPRS QoS Issues

Access delay: 4 classes (Um~Gi)Access delay: 4 classes (Um~Gi) Priority: 3 classesPriority: 3 classes Reliability: 5 classesReliability: 5 classes Mean throughput: 31 classesMean throughput: 31 classes Peak throughput: 9 classes (Gi~R)Peak throughput: 9 classes (Gi~R)


Access DelayAccess Delay


The OthersThe Others Priority classes: high, medium, and lowPriority classes: high, medium, and low Reliability classes: relates to prob. Of corruptioReliability classes: relates to prob. Of corruptio

n, loss, mis-sequencing, duplication of packetsn, loss, mis-sequencing, duplication of packets Mean throughput classes: class 1 (0.22bps)~claMean throughput classes: class 1 (0.22bps)~cla

ss 30 (111kbps), class 31 (best effort)ss 30 (111kbps), class 31 (best effort) Peak throughput classes: 8 kbps~2048 kbpsPeak throughput classes: 8 kbps~2048 kbps <Remark>:<Remark>: delay class and mean throughput a delay class and mean throughput a

re used by the SGSN for scheduling and admisre used by the SGSN for scheduling and admission control sion control


MSDRA MAC ProtocolMSDRA MAC Protocol

MSDRA: Master-Slave Dynamic Rate AccMSDRA: Master-Slave Dynamic Rate Accessess

Channel conceptChannel concept• PDCH (Packet Data CHannels)PDCH (Packet Data CHannels)

Channels are dedicated to packet mode transferChannels are dedicated to packet mode transfer Uplinks and downlinks are basically used as indUplinks and downlinks are basically used as ind

ependent channel resourcesependent channel resources Further divided into MPDCH (Master PDCH) and Further divided into MPDCH (Master PDCH) and

SPDCH (Slave PDCH)SPDCH (Slave PDCH)


Channel Concept (Cont’d)Channel Concept (Cont’d)

SPDCHs: the channels on which user data and SPDCHs: the channels on which user data and signaling is transferredsignaling is transferred• Packet Traffic Channels (PTCHs)Packet Traffic Channels (PTCHs)

Dedicated to one MS or a group of MSs used for user data tDedicated to one MS or a group of MSs used for user data transferransfer

• Packet-Associated Control Channels (PACCHs)Packet-Associated Control Channels (PACCHs) Transport signaling info related one MSTransport signaling info related one MS

• Packet Data Broadcast Channels (PDBCHs)Packet Data Broadcast Channels (PDBCHs) Downlink to broadcast user dataDownlink to broadcast user data


Channel Concept (Cont’d)Channel Concept (Cont’d) MPDCHs: accommodate Common Control Channels (CMPDCHs: accommodate Common Control Channels (C

CHs) that carry the signaling information required to iCHs) that carry the signaling information required to initiate packet transfernitiate packet transfer• PRACH (Packet Random Access CH)PRACH (Packet Random Access CH)

Uplink to initiate data transfer of the MSUplink to initiate data transfer of the MS• PPCH (Packet Paging CH)PPCH (Packet Paging CH)

Downlink to inform MSs about incoming packetsDownlink to inform MSs about incoming packets• PPRCH (Packet Paging Response CH)PPRCH (Packet Paging Response CH)

Uplink to respond to pagingUplink to respond to paging• PAGCH (Packet Access Grant CH)PAGCH (Packet Access Grant CH)

Downlink to send CH reservation info to an MSDownlink to send CH reservation info to an MS• PBCCH (Packet Broadcast Control CH)PBCCH (Packet Broadcast Control CH)

Downlink to broadcast all GPRS-specific info.Downlink to broadcast all GPRS-specific info.


Phases of MACPhases of MAC

MAC is based on a slotted ALOHA MAC is based on a slotted ALOHA reservation protocol which has three reservation protocol which has three phases on the uplinkphases on the uplink• Contention phaseContention phase• NotificationNotification• TransmissionTransmission

Two phases on the downlinkTwo phases on the downlink• NotificationNotification• TransferTransfer


PRACH Performance Analysis PRACH Performance Analysis

RACH and PRACH: slotted ALOHA with reRACH and PRACH: slotted ALOHA with retransmission (# of max. retrx.=7)transmission (# of max. retrx.=7)

AssumptionAssumption• Equal new call arrival ratesEqual new call arrival rates• System is memorylessSystem is memoryless• Capture effect is consideredCapture effect is considered


Performance Analysis (Cont’d)Performance Analysis (Cont’d)

For infinite number of users, PDF of interfering For infinite number of users, PDF of interfering packets is Poissonpackets is Poisson

where G is total access attemptswhere G is total access attempts Pc(Su|n): the prob of success of a test packet gPc(Su|n): the prob of success of a test packet g

iven n interfering packetsiven n interfering packets PC(Su|n)=Pr(Pt>zPn), z is the capture ratio PC(Su|n)=Pr(Pt>zPn), z is the capture ratio



Pc(Su|n) is given byPc(Su|n) is given by Pc(Su) is given by Pc(Su) is given by

The access throughpThe access throughput is ut is



The prob that a packThe prob that a packet will be successfullet will be successfully exactly k transmissiy exactly k transmissionsons

Average number of trAverage number of transmissions needed ansmissions needed for a successful recefor a successful receptionption




Channel Allocation for GPRSChannel Allocation for GPRS

Packet Data Traffic Packet Data Traffic CH (PDTCH)CH (PDTCH)

Packet Common Packet Common Control CH Control CH (PCCCH)(PCCCH)

Packet Dedicated Packet Dedicated Control CH Control CH (PDCCH)(PDCCH)


Allocation AlgorithmsAllocation Algorithms

Fixed resource allocation (FRA)Fixed resource allocation (FRA) Fixed resource allocation with queue Fixed resource allocation with queue

capacity (FRAQ)capacity (FRAQ) Dynamic resource allocation (DRA)Dynamic resource allocation (DRA) Dynamic resource allocation with Dynamic resource allocation with

queue capacity (DRAQ)queue capacity (DRAQ)


EGPRS (EDGE)EGPRS (EDGE)

Initiated in 1997Initiated in 1997 Using the GPRS core network but a Using the GPRS core network but a

new air interface with 8 coding new air interface with 8 coding schemesschemes

8-PSK modulation8-PSK modulation Max data rate: 384 kbpsMax data rate: 384 kbps



ReferencesReferences

Book: Wireless Personal Communications SystBook: Wireless Personal Communications Systems by D. J. Goodman ems by D. J. Goodman

Paper: GPRS-features and packet random accePaper: GPRS-features and packet random access channel performance analysis by A. Gyasi-Ass channel performance analysis by A. Gyasi-Agyei et al.gyei et al.

Paper: Concepts, services, and protocols of nePaper: Concepts, services, and protocols of new GSM phase 2+ General Packet Radio Service w GSM phase 2+ General Packet Radio Service by G. Brasche et al.by G. Brasche et al.

Paper: Channel allocation for GPRS by Phone LPaper: Channel allocation for GPRS by Phone Lin et al.in et al.