General Packet Radio Service

王詔丘

GPRS History

Established by ETSI(European Telecommunications Standards Institute)GSM phase 1 --- 1992GSM phase 2 --- 1996GPRS begin in 1994 and published at the end of 1997

General Packet Radio Service

Packet switchingGPRS is evolved from GSM by introducing two new core network nodes SGSN and GGSNExisting GSM nodes(BSS,MSC/VLR and HLR) are upgradedConcept foresees bit rates of nearly 170kb/sQoS Support ： service precedence 、 delay 、 reliability 、 mean throughput 、 peak throughput etc. QoS parameters

General Packet Radio Service

Several users can use the same channel simultaneouslyAlways on lineRadio resource allocationCharging is based on amount of transmitted dataNo need to access HLR for every GPRS packetBurst data transmission

GPRS Objectives

GPRS uses packet switched resource allocation Dynamic channel allocation

1 to 8 time slots Available resources shared by active usersUp and down link channels reserved separatelyGPRS and circuit switched (GSM) services can use same time slots alternatively

Efficient delivery of SMS over the GPRS air interface Connections with data networks

IP network,X.25,GPRS own protocols

GPRS Development

PhasePoint-to-PointPoint-to-Multipoint

ClassSupport GPRS and other GSM simultaneouslySupport GPRS and GSM network parallelOnly GPRS

Multi-slot TypeHalf-DuplexFull-Duplex

Service type of GPRS

GPRS provides two types of services:

PTP (Point-To-Point)Connectionless: IPConnection-oriented: X.25

PTM (Point-To-Multipoint)Multicast Service (PTM-M)Group Call Service (PTM-G)

GPRS Applications

WWWFTPTelnetChatE-mailImageAudioVideoGPS(Global Positioning System)

GSM Architecture

MS(Mobile Station)BSS(Base Station Subsystem)BTS(Base Transceiver Station)BSC(Base Station Controller)MSC(Mobile Switching Center)PSTN(Public Switched Telephone Network)HLR(Home Location Register)VLR(Visitor Location Register)AUC(Authentication Center)

GSM Architecture

GPRS Architecture

Comparison between GPRS & Circuit-switched

GPRS Architecture

GPRS Components

GPRS support node(GSN)Packet routing and transfer within PLMN(Public Land Mobile Network)

Gateway GPRS support node(GGSN)Acts as a logical interface to external PDN(Packet Data Network)Maintains routing information used to tunnel the PDUs(Protocol Data Unit) to the SGSN currently serving the MS(Mobile Station)

Serving GPRS support node(SGSN)Delivery of packets to the MSs within its service area

Mobile Transmission

SGSN(SGSN-S) encapsulates the packets transmitted by the MS and routes them to the appropriate GGSN(GGSN-S)Based on the examination of the destination address, packets are then routed to the GGSN-D through the packet data networkThe GGSN-D checks the routing context associated with the destination address and determines the SGSN-D and relevant tunneling informationEach packet is then encapsulated and forwarded to the SGSN-D, which delivers it to the destination mobile

Simple example of transmission

Packet Data Transmission Scenario

Mobile-originatedMS to some LAN host

Mobile-terminatedReceive packet from some host when MS is in Home Public Land Mobile Network （ PLMN ）

Mobile-terminatedReceive packet from some host when MS is roaming at some Visited Public Land Mobile Network （ PLMN ）

Simple example of routing

GPRS Architecture

MS

BS

BS

BS

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MS

B SC

B SC

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MS

MS

BS

BS

BS

BSC

BSC

MS

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MSC

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Voice

SS7 si gnaling

Voice and data

Air interface

S GSN

GGS N

X.2 5

Intr a-P LMN

Back bone

BG

I nter -P LMNBack bone

Host

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GPRS Coding Scheme

Best reliability : CS-1No reliability : CS-4Maximum data rate : 171.2Kbps(21.4Kbps x 8) with eight time slots

FDMA & TDMA

Mobility Management

Two encapsulation schemes:Between GSNsBetween MS and SGSN

Before MS sends data, MS has to attach to GPRS using an attachment procedureWhen moving to another SGSN(location update), GGSN and GR/HLR are informed about the new routing context

Mobility Management

State Diagram

GPRS Protocols

Sub-Network Dependent Convergence Protocol (SNDCP)maps a network-level protocolprovides compression, segmentation and multiplexing of network-layer messages to a single virtual connection

Logical Link Control (LLC)assures the reliable transfer of user data across a wireless network

Base Station System GPRS Protocol (BSSGP)processes routing and QoS information uses the Frame Relay Q.922 core protocol

GPRS Tunnel Protocol (GTP)tunnels the protocol data units between GSNs

GPRS Protocols

GPRS Mobility Management (GMM)handles roaming, authentication, and selection of encryption algorithms

Network Servicemaps BSSGP's service requests to the Frame Relay Q.922 Core

Radio Link Control(RLC)/MACEnable multiple MSs to share a common transmission medium which consist of several physical channels

Physical Link Sublayer(PLL)Data coding, detection and correction

Physical RF Sublayer(RFL)Perform the modulation and demodulation of the physical waveforms

Protocol Architecture

Air Interface – Physical Layer

GPRS air interface protocol is concerned with communication between MS and BSSPhysical Channel divided into Packet Data Channel （ PDCH ） and Traffic Channel（ TCH ），PDCH --- Dedicated to Packet Data Traffic ，TCH --- GSM Voice or Data Traffic 。Allocation of TCHs and PDCHs is done dynamically according to the 「 Capacity-on-demand 」 principles

GPRS Architecture

GPRS Protocol Stack

GPRS Logical Channels

Packet Broadcast Control Channel(PBCCH)Transmits system information to all GPRS terminals in a cell

Packet Common Control Channel(PCCCH)Initiate packet transfers or respond to paging messages

Packet Traffic Channels(PTCH)Channel resource allocation

GPRS Logical Channels(cont.)

Uplink

Downlink

HSCSD and EDGE

High-Speed Circuit-Switched Data （ HSCSD ）Multi-timeslotUsing V42bis coding scheme can achieve 14.4KbpsMaximum data rate : 115.2Kbps(14.4Kbps * 8) Circuit switching

Enhanced Data for GSM Evolution （ EDGE ）Maximum data rate : 384kbps EDGE use the new Modulation Technique --- eight-phase-shift （ 8PSK ） Support Packet switching and Circuit switching simultaneously

GPRS GlossaryETSI(European Telecommunications Standards Institute)MS(Mobile Station)BSS(Base Station Subsystem)BTS(Base Transceiver Station)BSC(Base Station Controller)MSC(Mobile Switching Center)PSTN(Public Switched Telephone Network)HLR(Home Location Register)VLR(Visitor Location Register)AUC(Authentication Center)GPRS support node(GSN)Gateway GPRS support node(GGSN)Serving GPRS support node(SGSN)packet data network(PDN)Public Land Mobile Network （ PLMN ）Sub-Network Dependent Convergence Protocol (SNDCP)Logical Link Control (LLC)Base Station System GPRS Protocol (BSSGP)GPRS Tunnel Protocol (GTP)GPRS Mobility Management (GMM)Packet Data Channel （ PDCH ）Traffic Channel （ TCH ）Packet Broadcast Control Channel(PBCCH)Packet Common Control Channel(PCCCH)Packet Traffic Channels(PTCH)High-Speed Circuit-Switched Data （ HSCSD ）Enhanced Data for GSM Evolution （ EDGE ）

Reference

J. Cai and DJ Goodman, General Packet Radio Service in GSM, IEEE Communications,vol. 35, no. 10, pp. 122-131, October 1997G. Brasche and B. Walke, Concepts, Services, and Protocols of the New GSM Phase2+ General Packet Radio Service, IEEE Communications, vol. 35, no. 8, pp. 94-104, Aug 1997C. Bettstetter, GSM PHASE 2+ GENERAL PACKET RADIO SERVICE GPRS:ARCHITECTURE, PROTOCOLS AND AIR INTERFACE, IEEE Communications,1997