GPRS

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GENERAL PACKET RADIO GENERAL PACKET RADIO SERVICESSERVICES

(GPRS)(GPRS)

Introduction Course of


GPRS

• WHAT is GPRS?• GPRS Network Architecture• GPRS Protocol• ZXG10-BSS GPRS Introduction


What’s GPRS?• GPRS: General Packet Radio Service

– Providing for subscribers end to end mobile data services based on packet switching and transmission. Especially suitable for long-time, low traffic burst data service.

– GPRS＝Mobile＋ IP， is the combination of GSM wireless access technology and Internet packet switching technology.

– Smooth upgrading. Providing general packet radio service with least modification and least cost.


Wireless Data Transmission• Ordinary CS Data Service

– Max. data transmission rate：9.6kb/s– Supporting transparent and non-transparent data

transmission– Supporting Fax/data service– Supporting PSTN/ISDN/PDN interconnection


• High Speed Circuit-Switched Data（HSCSD）

– Multiple slots bundled, at most 4 time slots.– Max. 14.4kb/s per time slot– Mainly by software upgrading. No new network

entity is needed.

Wireless Data Transmission


• GPRS– Multiple slots bundled, at most 8 time slots. – CS-1(9.05kb/s), CS-2(13.4kb/s), CS-3(15.6kb/s), CS-

4(21.4kb/s)– Channel shared by multiple users.– GPRS terminals can keep connections with network for

long time and can be “always on line”.– Charged on traffic flow, low expense.

Wireless Data Transmission


CS Service vs GPRS

Low speed rate(9.6Kb/s)High expenseLow utilization rate(dedicated)Long delay(>20s)

High rate(171.2Kbps)Low expenseHigh utilization rate (shared)Short delay(<1s)


Evolution of GSM Data Service

9.6K

57.6K

171.2K

384K

2M


GPRS Services• Phase I

– PTP– CS-1, CS-2– SMS over GPRS– Charged on packet traffic

• Phase II– PTM– CS-3, CS-4– Other supplementary services– Network applied services.


GPRS Services

• Vehicle tracing• Dynamic traffic

managing• Police dispatching• Bank information

service

• Ordering status and alarm monitoring

• Fixed and mobile point of selling

• Remote measuring (highway traffic), weather forecasting

• Remote meters reading• Distributing operation: taxi

managing


GPRS System Structure

• SGSN：Serving GPRS Supporting Node• GGSN：Gateway GPRS Supporting Node• PCU：Packet Control Unit• GPRS Mobile Station• CG：Charging Gateway


GPRS Network

GMSC

ZXG10 GPRS System Structure

BSS

InternetX.25

ISDNGPRS MS

TE

MSC

PCU

SGSN GGSN

GSNBackbone

Voice

Packet Data

CS service line

PS service line


GPRS OPERATION GPRS OPERATION –– Main NodesMain Nodes


SGSN AND GGSN SGSN AND GGSN SERVING GPRS SUPPORT NODESERVING GPRS SUPPORT NODE

GATEWAY GPRS SUPPORT NODEGATEWAY GPRS SUPPORT NODE

SGSN2

SGSN1

PLMN GSS

IP network 5

IP network 4

IP network 3

IP network 2

IP network 1GGSN1

GGSN3

GGSN2

IP backbone


CHARGING GATEWAY (CG)CHARGING GATEWAY (CG)

• Receives CDRs from GSNs via the Ga interface

•Saves the CDRs as CDR files after preprocessing including filtering and consolidation

•Sends the CDR files to the billing center


HOME LOCATION REGISTER (HLR)HOME LOCATION REGISTER (HLR)

• Save GPRS subscription data

• Provide location/route information for MM and route selection, such as:

– Save and update user SGSN number and address

– GPRS user location deletion indicator

– MS reachable tag


PACKET CONTROL UNIT (PCU)PACKET CONTROL UNIT (PCU)

CCU

CCU

CCU

CCUBSC

PCU

PCU

BSC

BTS

BTS

SGSN

Um Abis

Gb

CCU = Channel Control UnitPCU = Packet Control Unit

SGSN

SGSN

PCU

BSCCCU

CCU

Gb


GPRS MSGPRS MS

Class AThe MS is attached to both GPRS and other GSM

services, and the MS supports simultaneous operation of GPRS and other GSM services.

Class BThe MS is attached to both GPRS and other GSM

services, but the MS can only operate one set of services at a time.

Class CThe MS is exclusively attached to GPRS services.


GPRS OPERATION GPRS OPERATION –– Main InterfacesMain Interfaces

GPRS network

SGSN

GGSNSGSN IP networkGiGn

Gb

Sig. + data

Pure Sig.

Mobile GPRS

BSS MSC SMS-GMSCHLRAUm

GsGr

Gd

Gc


GPRS OPERATIONGPRS OPERATION


GPRS OPERATION GPRS OPERATION –– Mobile StatesMobile States

"Idle" Attachment to network

Detachment

Out of Time

Packet Tx or Rx

Detach

mentor

Out of

Time

"Ready""Stand-by"


GPRS PROTOCOLSGPRS PROTOCOLSand RADIO Interfaceand RADIO Interface


GPRS PROTOCOL STACK STRUCTUREGPRS PROTOCOL STACK STRUCTURE

relay

relaySNDCP GTP

Um Gb Gn Gi

Application Application

IP/X25 IP/X25 IP/X25

SNDCP GTP

LLC LLC UDP/TCP UDP/TCP

RLC RLC (BSSGP) (BSSGP) IP IP

MAC MAC Network service

Networkservice L2 L2

L2 (MAC)

PhysicalLayer

PhysicalLayer

PhysicalLayer

PhysicalLayer

PhysicalLayer

PhysicalLayer

PhysicalLayer

MS BSS SGSN GGSN


TRANSMISSION PROTOCOL PLATFORMTRANSMISSION PROTOCOL PLATFORM

• SNDCP （ Sub Network Dependent Convergence Protocol):Network layer protocol. The main functions include: PDPsmultiplexing；Compressing and decompressing user data and control information; divide network PDU（N-PDU）into logic link PDU（LL-PDU, or vice versa.

• LLC (Logic Link Control):A very reliable, independent and scrambled logic link, so as to modify the network with the least when another GPRS solution is introduced.



• RLC/MAC：Provides transfer service for layers over physical layer. RLC is the radio link control protocol between MS and BTS. The main functions include: Um interface data block error detection; error data block selecting and retransmission. MAC controls the access signaling processing ,makes judgment when a lot of MSs access the network. Maps the LLC frames onto GSM physical channels.

• GSM RF


RADIO BLOCK STRUCTURERADIO BLOCK STRUCTURE

User data

Segment Segment

InfoFH FCS

PH

Segment Segment Segment

InfoBH BCS Tail

Coding and interleaving

Burst Burst Burst Burst

...

...

Network layer

SNDCP layer

SNDCP layer

LLC layerLLC layer

RLC / MAC layer

RLC / MAC layer

Physical layer

Packet(PDU)

LLC frame

RLC block

Normal Burst

PH : Packet Header BH : Block Header FCS : Frame Check SequenceFH : Frame Header BCS : Block Check Sequence

456 bits

114 bits 114 bits 114 bits 114 bits


TRANSMISSION PROTOCOL PLATFORMTRANSMISSION PROTOCOL PLATFORM• Relay：

To relay LLC PDU between Um and Gb interfaces in BSS and relay PDP PDU between Gb and Gn in SGSN.

• BSSGP（BSS GPRS Protocol):This layer transfers route-related and QoS related information between BSS and SGSN. No error correction is implemented.

• NS (Network Service):This layer transfers BSSGP PDU.

• L1bis、L1、L2:Not regulated in GPRS regulations.



• GTP（GPRS Tunnel Protocol):This protocol supports data and signaling transmission among nodes of GPRS backbone network. All PTP PDU PDP are packed with GTP.

• UDP/TCP：TCP carries GTP PDU that needs reliable data link, X.25 for example, in GPRS backbone.UDP carries GTP PDU that does not need reliable data link, IP for example, in GPRS backbone. TCP provides traffic control and protects GTP PDU from losing and damaging.UDP protects GTP PDU from damaging.

• IP：GPRS backbone protocol used for routing user data and control signaling. Currently based on IPv4, finally IPv6.


RADIO BLOCKSRADIO BLOCKS

fi

1 TDMA frame TDMA1 TDMA51

1 2 3 4 5 760

multiframe (52)

TS0Block0

0 to 3

PDCH0

51Block11

47 to 50

PDCH7

8 physical channels


PACKET PHYSICAL CHANNELSPACKET PHYSICAL CHANNELS

PACKET DATA CHANNELS (PDCH) – physical channels that are assigned for use by GPRS System

2 TYPES OF PDCH

1. Dedicated PDCHs – allocated and released by operator command and are considered a permanent GPRS resource in the cell. No GSM traffic can use these channels.

2. On-demand PDCHs – serve as temporary dynamic GPRS resources and are allocated and released depending on GPRS (and GSM) traffic demand

BCH TCH TCH TCH PDCH PDCH PDCH PDCH

Dedicated On-demand

PSET


PACKET LOGICAL CHANNELSPACKET LOGICAL CHANNELS

GPRS logical channels

Packet control channels Packet traffic channels

PCCH PBCCH

DL

PDTCH

UL/ DL

PACCH

UL/ DL

PTCCH

UL/ DL

PRACH

UL

PPCH

DL

PAGCH

DL

PNCH

DL


PACKET TRAFFIC CHANNELS PACKET TRAFFIC CHANNELS –– (PTCH)(PTCH)

• PDTCH – Packet Data Traffic Channel

- logical channel allocated for user data transfer.

• PTCCH/ U – Packet Timing Advance Control Channel/ Uplink

- used to transmit random access burst to allow estimation of the timing advance for one MS in packet transfer mode.

• PTCCH/ D – Packet Timing Advance Control Channel/ Downlink

- used to transmit timing advance information updates to MS.


PACKET TRAFFIC CHANNELS PACKET TRAFFIC CHANNELS –– (PTCH)(PTCH)

• PACCH – Packet Associated Control Channel

- conveys signaling information related to a given MS on both the uplink and the downlink.eg:power control and confirm


PACKET BROADCAST CHANNEL PACKET BROADCAST CHANNEL –– (PBCH)(PBCH)

• PBCCH – Packet Broadcast Control Channel

- broadcasts packet data specific System information.

- If there is no PBCCH allocation, packet-data-specific system information is broadcasted via BCCH


PACKET COMMON CONTROL CHANNELS PACKET COMMON CONTROL CHANNELS ––(PPCH)(PPCH)

• PPCH – Packet Paging Channel

- is used to page an MS prior to downlink packet transfer.

- can be used also for circuit-switched data services

• PRACH – Packet Random Access Channel- is used by MS to initiate uplink transfer for sending data or signaling information.

• PAGCH – Packet Access Grant Channel- is used in the packet transfer establishment phase to resource assignment to an MS prior to packet transfer.


CHANNEL COMBINATIONCHANNEL COMBINATION

i. PBCCH + PCCCH + PDTCH + PACCH + PTCCH

ii. PCCCH + PDTCH + PACCH + PTCCH

iii. PDTCH + PACCH +PTCCH


GPRS MULTIFRAME STRUCTUREGPRS MULTIFRAME STRUCTURE


MAPPING OF PTCCH/ UMAPPING OF PTCCH/ U

• While MS is assigned a PDTCH, it will be assigned a PTCCH/U on the same PDTCH.

• PTCCH/U’s period is 8*52 multiple frames and include 16 PTCCH/U sub-channels(0…15).

• Each MS’s PTCCH/U sub-channel is determined by TAI(Timing Advance Index).


MAPPING OF PTCCH/ UMAPPING OF PTCCH/ U


DATA TRANSMISSION AND RECEPTIONDATA TRANSMISSION AND RECEPTION


AbisAbis Allocation for CS1 and CS2Allocation for CS1 and CS2

BTS

Support CS－1and CS－2

BSC（PCU）

E1

CS－1 and CS－2 occupy 16kb/s of link


AbisAbis Allocation for CS3 and CS4Allocation for CS3 and CS4

BTSSupport CS-3

and CS-4 BSC

（PCU）E1

CS-3 and CS-4 occupy 2*16kb/s links


GPRS

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