Gprs 6a1w6u

An Overview of GPRS Shourya Roy Pradeep 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 friendly billing

GSM Architecture PSTN PDN ISDN MS

BTS

GMSC

BSC

MSC BTS

BSC EIR

MS

AUC HLR

BTS MS

VLR

GPRS Architecture Other GPRS PLMN Gp

BSC Gb

MS

Gn

SGSN Gf Gs

BTS BTS

EIR

GGSN

Gr

D MSC/VLR

Gc GGSN Gi HLR

PDN

Protocol Architechture 

Transmission Plane GPRS specifies a tunnel mechanism to transfer 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 itself with GPRS network.  GPRS attach  GPRS detach GPRS detach can be initiated by the MS or the network.

Session Management After 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 ’s home PLMN.  Dynamic:Assigned by Corresponding GGSN.

PDP Context Activation MS GGSN Activate PDP Context

SGSN

PDP type,PDP Address Request QoS Requested,Access Point,… Security Functions Create PDP Context Request PDP type,PDP Address QoS Negotiated,Access Point,… Activate PDP Context Accept PDP type,PDP Address QoS Negotiated,…

Create PDP Context Response PDP type,QoS Negotiated,…

Routing BSC

BTS

BSC BTS

SGSN

MS PLMN1

Intra-PLMN GPRS Backbone

SGSN Gn

Gp Border Gateway

Gn

Inter-PLMN GPRS Backbone

Intra-PLMN GPRS Backbone

Border Gateway

Gn

GGSN

SGSN GGSN

Gi

Packet Data Network(PDN) Eg.Internet,Intranet RouterLANHost

PLMN2

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

Protocol Architechture 



Transmission Plane  The protocols provide transmission of data and its associated signalling Signalling Plane  Comprises protocols for the control and of functions of the transmission plane

Transmission Plane 

GPRS Backbone:SGSN GGSN GTP tunnels the packets and related signalling information between the GPRS nodes. 

Subnetwork dependent convergence protocol 

It is used to transfer packets between SGSN and MS





Data link layer LLC(MS-SGSN)  RLC/MAC(MS-BSS) 



Physical layer PLL:channel coding,detection of errors, forward error correction, interleaving, detection of physical link congestion RFL:modulation and demodulation 

Network Layer (IP or X.25) Relay SND LLC

GTP

GTP

T/UDP

T/UDP

Relay RLC MAC

PLL RFL

BSSP

BSSGP

IP

IP

Network Service

Network Service

Data Link Service

Data Link Layer

Phy Layer

Phy Layer

Phy layer

Phy Layer

Gm BSS RLC :Radio link control PLL :Physical link layer RFL :Physical RF layer MAC:Medium access control

Gb SGSN GGSN BSSGP:BSS GPRS Application protocol GTP :GPRS tunneling protocol T :Transmission control protocol UDP : datagram protocol IP :Internet Protocol

Transmission Plane

Gi

MS

BSS

Application Network Layer SND LLC Relay

RLC

RLC MAC

MAC PLL

BSSGP Network Service

PLL

RFL

RFL

Um

SND:Subnetwork dependent convergence protocol LLC :Logical link control RLC :Radio link control

PHY Layer

SGSN

BSS

MS

GMM/SM

GMM/SM

LLC

Application LLC Application RLC MAC GSM/RF

RLC

MAC GSM RF

Relay BSSGP

BSSGP

Network service

Network layer

Physical layer

Phy Layer

Um

Gb

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

Signalling Plane:MSSGSN

SGSN

MSC/VLR

BSSAP

BSSAP

SC

SC

MTP3

MTP3

MTP2

MTP2

Phy Layer

Phy Layer Gs

Signalling Plane SGSN MSC/VLR

SGSN

HLR(and EIR)

MAP

MAP

TCAP

TCAP

SC

SC

MTP3

MTP3

MTP2

MTP2

Phy Layer

Phy Layer

Gr MAP TCAP SC MTP

:Mobile Application Part :Transaction capabilities and application part :Signalling connection control part :Message transfer part

Signalling Plane SGSNHLR/SGSNEIR

GSM TDMA Frame Slots and Bursts 960 MHz 959.8 MHz

124

Time Slot

123 ... 200 KHz

...

Downlink

1

2

3

4

5

6

7

2 935.2 MHz 935 MHz

TDMA Frame

1

915 MHz 914.8 MHz

1 8

Data Burst = 156.25 bit periods

124 123 ...

200 KHz

...

Uplink

1

2

3

4

5

6

7

1 8

2 890.2 MHz 890 MHz

1

TDMA Frame

GPRS Air Inteface Time Slot Number

0

1

2

3

4

5

6

7

0

1

2

3

4

F1

Uplink

F2 F3

Carrier Frequency

F4 0

1

2

3

4

5

6

7

0

F 1 F 2 F 3 F 4

1

2

3

4

Downlink

Voice 1

GPRS 1

Voice 2

GPRS 2

GPRS 3

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 Channels Group

Channel

Packet data Traffic channel

PDTCH

Packet broadcast control channel

PBCCH

Packet common Control Channel (PCCCH)

Packet Dedicated Control Channels

Function

MS

BSS

Broadcast Control

MS

BSS

PRACH

Random Access

MS

BSS

PAGCH

Access Grant

MS

BSS

PPCH

Paging

MS

BSS

PNCH

Notification

MS

BSS

MS

BSS

Timing Advance Control MS

BSS

PACCH PTCCH

Data Traffic

Direction

Associated Control

Uplink Data Transfer MS PRACH or RACH PAGCH or AGCH PACCH PACCH

PDTCH PACCH PDTCH PACCH

BSS Packet channel Request Packet Immediate assignment Packet resource Request Packet resource assignment Random Access

Frame Transmission Negative Acknowledgement Retransmission of blocks in error Acknowledgement

Transmission

MS BSS Downlink Data Transfer Packet paging request PPCH or PCH PRACH or RACH PAGCH or AGCH PACCH PACCH or PAGCH

PDTCH PACCH PDTCH PACCH

Packet channel Request Packet Immediate assignment Packet paging response Packet resource assignment Paging

Frame Transmission Negative Acknowledgement Retransmission of blocks in error Acknowledgement

Transmission

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/3q99issu e/bettstetter.html http://www.wsdmag.com/2000/aug2200/3845.html “Wireless Internet Access based on GPRS”, IEEE Personal Comm. April 2000.