An Overview of GPRS

Shourya RoyPradeep Bhatt

Gururaja K.

What is GPRS? A new bearer service for GSM that

greatly improves and simplifies wireless access to packet data networks,e.g to the internet.

Motivation Speed Immediacy New and better applications User friendly billing

GSM Architecture

BTSMS

BTS

BTS

MS

BSC

BSC

MSC

GMSC

MS

EIR

VLR

HLR

AUC

PSTNPDN

ISDN

GPRS Architecture

BTS

BTSMS

BSC Gb

SGSN

Gf

GsGr

DEIR

MSC/VLR

HLR

Gc

Gn

GGSNGi

PDN

Gp GGSN

Other GPRSPLMN

Protocol Architechture

Transmission Plane GPRS specifies a tunnel

mechanism to transfer user data packets .

Signalling Plane GTP specifies a tunnel control

management protocol.The signalling is used to create modify and delete tunnels.

Registration of a Mobile Node

A mobile station must register itself with GPRS network.

GPRS attach GPRS detachGPRS detach can be initiated by the

MS or the network.

Session ManagementAfter Successful attach a MS gets one or

more Packet Data Protocol(PDP) address.This address is unique only for a particular session.

It consists of, PDP type PDP address assigned to MS Requested QoS Address of the corresponding GGSN

Session Management(Contd.)

PDP-Address allocation: Static:Assigned by network

operator of User’s home PLMN. Dynamic:Assigned by

Corresponding GGSN.

PDP Context Activation MS SGSN

GGSNActivate PDP Context Request

Security Functions

Activate PDP Context Accept

Create PDP Context Request

Create PDP Context Response

PDP type,PDP AddressQoS Requested,Access Point,…

PDP type,PDP AddressQoS Negotiated,Access Point,…

PDP type,QoS Negotiated,…PDP type,PDP AddressQoS Negotiated,…

Routing

PLMN1 PLMN2

MS

BTS

BSC

SGSNGn

Intra-PLMNGPRS Backbone

Gn

Gn

SGSN

GGSNGi

Packet Data Network(PDN)Eg.Internet,Intranet

Border Gateway

Gp

Inter-PLMNGPRS Backbone

Border Gateway

Intra-PLMNGPRS Backbone

GGSN

RouterLANHost

SGSN

BSCBTS

Location Management MS frequently sends location

update messages to inform the SGSN where it is.

Determining frequency of update messages is non-trivial.

The location update frequency is dependent on the state of the MS.

Location Management(Contd.)

A MS can be in 3 states: IDLE READY STANDBY

Transmission Plane The protocols provide

transmission of user data and its associated signalling

Signalling Plane Comprises protocols for the

control and support of functions of the transmission plane

Protocol Architechture

Transmission PlaneGPRS Backbone:SGSN GGSN

GTP tunnels the user packets and related signalling information between the GPRS support nodes.

Subnetwork dependent convergence protocol

It is used to transfer packets between SGSN and MSData link layer

LLC(MS-SGSN) RLC/MAC(MS-BSS)

Physical layerPLL:channel coding,detection of errors, forward error correction, interleaving, detection of physical link congestionRFL:modulation and demodulation

PLL RFL Phy Layer

MAC Network Service

RelayRLC BSSP

Phy Layer Phy Layer

Network Data Link Service Service

BSSGP IP

LLC TCP/UDP

RelaySNDCP GTP

Phy layer

Data Link Layer

IP

TCP/UDP

Network Layer(IP or X.25)

GTP

RLC :Radio link control BSSGP:BSS GPRS Application protocolPLL :Physical link layer GTP :GPRS tunneling protocolRFL :Physical RF layer TCP :Transmission control protocolMAC:Medium access control UDP :user datagram protocol IP :Internet Protocol

Transmission Plane

BSS SGSN GGSNGm Gb Gi

PLL

RFL

RLC

MAC

LLC

SNDCP

Network Layer

Application

PLL PHY RFL Layer

MAC Network Service

RelayRLC BSSGP

MSBSS

SNDCP:Subnetwork dependent convergence protocolLLC :Logical link controlRLC :Radio link control

Um

Application

Application

LLC

RLC

MAC

GSM/RF

GMM/SM

GSM RF Physical layer

MAC Network service

Relay RLC BSSGP

Phy Layer

Networklayer

BSSGP

LLC

GMM/SM

MS BSS SGSN

GMM/SM:GPRS Mobilty Management and session Management ProtocolGSM/RF:GSM physical layer(radio interface) I.e.PLL and RFL

Signalling Plane:MSSGSN

Um Gb

BSSAP

SCCP

MTP3

MTP2

Phy Layer Phy Layer

MTP2

MTP3

SCCP

BSSAP

Signalling Plane SGSN MSC/VLR

SGSN MSC/VLR

Gs

MAP

TCAP

SCCP

MTP3

MTP2

Phy Layer Phy Layer

MTP2

MTP3

SCCP

TCAP

MAP

MAP :Mobile Application PartTCAP :Transaction capabilities and application partSCCP :Signalling connection control partMTP :Message transfer part

SGSN HLR(and EIR)

Signalling Plane SGSNHLR/SGSNEIR

Gr

GSM TDMA Frame Slots and Bursts

1

123

2

1

124

. . .

. . .

935 MHz

935.2 MHz

960 MHz

959.8 MHz

200 KHz

1

123

2

124

. . .

. . .

890 MHz

890.2 MHz

915 MHz

914.8 MHz

200 KHz

1 2 3 4 5 6 7 8

Data Burst = 156.25 bit periods

11 2 3 4 5 6 7 8

TDMA Frame

TDMA Frame

Uplink

Downlink

Time Slot

GPRS Air Inteface0 1 2 43 5 6 7 0 1 2 3 40 1 2 43 5 6 7 0 1 2 3 4

0 1 2 43 5 6 7 0 1 2 3 40 1 2 43 5 6 7 0 1 2 3 4

Uplink

Downlink

Voice User1

Voice User2

GPRS User1

GPRS User2

GPRS User3

F1

F2

F3

F4

F1F2F3F4

Time Slot Number

CarrierFrequency

GPRS Air Interface Master slave concept

One PDCH acts as Master Master holds all PCCCH channels The rest of channels act as Slaves

Capacity on demand PDCH(s) are increased or decreased

according to demand Load supervision is done in MAC Layer

GPRS Logical ChannelsGroup Channel Function Direction

Packet data Traffic channel

PDTCH Data Traffic MS BSS

Packet broadcast control channel

PBCCH Broadcast Control MS BSS

Packet commonControl Channel(PCCCH)

PRACH

PAGCH

PPCH

PNCH

Random Access

Access Grant

Paging

Notification

MS BSS

MS BSS

MS BSS

MS BSS

Packet DedicatedControl Channels

PACCH

PTCCH

Associated Control

Timing Advance Control

MS BSS

MS BSS

Uplink Data TransferMS BSS

PRACH or RACH

PAGCH or AGCH

Random Access

Transmission

Packet channel Request

PACCH

PACCH

PDTCH

PACCH

PDTCH

PACCH

Packet Immediate assignment

Packet resource Request

Packet resource assignment

Frame Transmission

Negative Acknowledgement

Retransmission of blocks in error

Acknowledgement

Downlink Data Transfer

PRACH or RACH

PAGCH or AGCH

Paging

Transmission

Packet channel Request

PACCH

PACCH or PAGCH

PDTCH

PACCH

PDTCH

PACCH

Packet Immediate assignment

Packet paging response

Packet resource assignment

Frame Transmission

Negative Acknowledgement

Retransmission of blocks in error

Acknowledgement

Packet paging requestPPCH or PCH

MS BSS

Multi Slot Operation GPRS allows a mobile to transmit data

in up to 8 PDCHs (eight-slot operation) 3-bit USF at beginning of each radio

block in downlink points to next uplink radio block

Comparison with single-slot GSM Higher delay at higher load Low blocking rate Improved Throughput

Conclusion GPRS provides efficient access to

Packet Data Networks. Multislot operation in GPRS leads

to efficient channel utilization. GPRS is more effective for long

data packet transmission than short ones.

References “General Packet Radio Service in GSM”, Jian

Cai and David J. Goodman, Rutgers University, IEEE Communications Magazine, Oct 1997

http://www.comsoc.org/pubs/surveys/3q99issue/bettstetter.html

http://www.wsdmag.com/2000/aug2200/38-45.html

“Wireless Internet Access based on GPRS”, IEEE Personal Comm. April 2000.