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
BS
MS
B SC
B SC
MS
MS
MS
BS
BS
BS
BSC
BSC
MS
MS
S GSN
BS
In terne t
PS TN
HL RVLR
S S7
MSC
MSData
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
R
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
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