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					GPRS INTRODUCTION

2008年11月25日

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GPRS
WHY GPRS? GPRS Network Architecture GPRS Protocol ZXG10-BSS GPRS Introduction

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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.
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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

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Wireless Data Transmission
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.

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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.

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CS Service vs GPRS
Low speed rate
(9.6Kb/s)

High expense Low utilization rate
(dedicated)

Long delay(>20s)

High rate(115.2Kbps) Low expense High utilization rate(shared) Short delay(<1s)

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Evolution of GSM Data Service
2M

384K

171.2K

57.6K 9.6K
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GPRS Services
Phase I
PTP-CLNS, PTP-CONS CS-1, CS-2 SMS over GPRS Charged on packet traffic

Phase II
PTM CS-3, CS-4 Other supplementary services Network applied services.

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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

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Vehicle Location And Intelligent Dispatching System

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Tele-sensing, telemetering and telecontrol

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Mobile VPN Service

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Internet access via WAP

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Multimedia messaging service

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

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GPRS Network
MSC GMSC

ISDN
GPRS MS
BSS

Voice CS service line PS service line
PCU GSN Backbone

TE

Packet Data

Internet X.25

SGSN

GGSN

ZXG10 GPRS System Structure

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Position of PCU
Um BTS CCU PC U CCU A bis BTS CCU PC U CCU B SC site G SN site B SC site Gb G SN site

A

B

BTS CCU

B SC site

G SN site PC U

C

CCU

k ey:

circu it switching fu nction (1 6 or 6 4 Kbps) pack et switching fu nction

Gb

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GPRS Network

(Um)

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GPRS System Upgrading
SW BTS MS BSC SW + HW

MSC/VLR SW

SMS-G/IW MSC AUC SW

HLR

SGSN
Backbone Network External IP Network

New design

Traffic & Signalling Signalling SGSN - Serving GPRS Support Node GGSN - Gateway GPRS Support Node BTS - Base Transceiver Station BSC - Base Station Controller MSC - Mobile Switching Centre HLR - Home Location Register

GGSN

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GPRS Protocol Platform

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Interfaces between BSS and GPRS
Um: Adopts RLC/MAC protocol to interconnect with MS,
paging, assignment and release, for example

. Gb:Adopts BSSGP protocol to transport radio-related information, QoS and routing, for example. Paging request and traffic flow control are also processed.

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Transmission Protocol Platform
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
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Transmission Protocol Platform
SNDCP(Subnet Dependent Convergence Protocol): Network layer protocol. The main functions include: PDPs multiplexing;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. Relay:To relay LLC PDU between Um and Gb interfaces in BSS and relay PDP PDU between Gb and Gn in SGSN.
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Transmission Protocol Platform
BSSGP(BSS GPRS Protocol):This layer transfers route-related and QoS related information between BSS and SGSN. No error correction is implemented. It acts as the interface between LLC and RLC/MAC within BSS. NS:Network Service. This layer transfers BSSGP PDU. L1bis、L1、L2 :Not regulated in GPRS regulations.

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Transmission Protocol Platform
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

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GPRS Coding Procedure

Payload 有效负 载

Add BCS 加块检查序列

Add precoded USF 加预编码的上行状态标识符

Add tail bits 加结尾码

Coding 编码

Puncture 穿孔减码

456 bits

• BCS : Block Check Sequence • USF : Uplink State Flag

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Packet transformation data flow
Packet (PDU) PH Segment FH Segment BH Info Segment Info User data
Network layer SNDCP layer

...
FCS

Segment
SNDCP layer

LLC frame

LLC layer LLC layer RLC / MAC layer

...
BCS Tail

Segment RLC block

456 bits

RLC / MAC layer Physical layer bits

Convolutional encoding
114 bits 114 bits 114 bits 114

Burst
PH : Packet Header FH : Frame Header
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Burst

Burst

Burst

Normal Burst

BH : Block Header FCS : Frame Check Sequence BCS : Block Check Sequence

GPRS PDCHs
 Packet Broadcasting Control Channel
PBCCH: Carries parameters determining the mapping of channels to multiple frames

 Packet Common Control Channel(PCCCH)
PRACH: Used for MS transmitting data or responding paging PAGCH: Assigns one or more PDTCH to transport packet data PPCH: MS’s paging PTCCH: Packet Time Common Control Channel PNCH: To notify MS the call of PTM-M. DRX is needed

 Traffic Channel
PDTCH/U/D: Packet Data Transmission Channel, carries user’s data, assigned to one MS or more MSs( PTM-M). Under multiple time slot mode, more PDTCH can be used by one MS at the rate from 0-21.4kb/s. A single direction channel. PACCH: Packet Associated Control Channel, carries signaling such as channel confirmation and power control. A bi-directional channel
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GPRS Channel Configuration
PBCCH+PCCCH+PDTCH+PACCH+PTCCH PCCCH+PDTCH+PACCH+PTCCH PDTCH+PACCH+PTCCH Shares BCCH and CCCH with CS.

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GPRS Radio Frame Structure

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Mapping of PTCCH/U

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Mapping of PTCCH/U
While MS is assigned a PDTCH, it will be assigned a PTCCH/U on the same PDCH. 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)

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Logical layer of GPRS Um interface

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Data transmission and reception flow

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Radio block structure
Be consisted of MAC Header, RLC data block or RLC/MAC control block. Be always carried by 4 Normal Burst(NB).

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Channel encoding(1)
PDTCH defines 4 coding modes: CS-1 to CS-4
Radio Block USF rate 1/2 convolutional coding BCS

puncturing

456 bits

*Interleaving 52 TDMA Frames
B0 B1 B2 T B3 B4 B5 X B6 B7 B8 T B9 B10 B11 X

12 Radio Block Periods = 240 ms

Coding mode of CS-1 to CS-3
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Channel encoding(2)

*Interleaving 52 TDMA Frames
B0 B1 B2 T B3 B4 B5 X B6 B7 B8 T B9 B10 B11 X

12 Radio Block Periods = 240 ms

Coding mode of CS-4
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Comparison of 4 coding modes

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The end

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Realization of GPRS in BSS-Abis

CS-1 and CS-2 occupy 16kb/s of link

BTS
Support CS-1 and CS-2 E1 BSC (PCU)

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Realization of GPRS in BSS-Abis

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

Support CS-3 and CS-4

E1

BSC ( PCU )

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Realization of GPRS -NS

Position of NS in Gb protocol stack
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Realization of GPRS -NS
Functions of NS: transport NS SDU data between BSS and SGSN, receiving and transmitting upper layer PDU(Protocol Data Unit). Two layer structure NS Control Layer(NSCL)

NS Drive Layer(NSDL)

NSDL provides communication services for peers of NSCL. NSCL utilizes NSDL to realize peer-peer entity communication. Transports NS SDU through NS-VC
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Realization of GPRS -NS
Definitions: 1. FR: Frame Relay. Performs physical and data link functions of OSI. Adopting virtual circuit (VC) technology, therefore efficiently utilize network resources and has high throughput, low time delay. Suitable for burst data service 2. PVC: permanent virtual circuit. It refers to setting up fixed virtual circuit connection between FR terminal users and providing data transmission service. It’s a logic link. 3. NS-VC: An end to end VC between BSS and SGSN. It’s a PVC in FR.
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Realization of GPRS -NS
4. NS-VL:A physical link support one or more NS-VL. One NS-VL is supported by only one physical link. Generally, NS-VL is used to visit frame relay network. In point to point configuration of Gb interface, NS-VL can also be end to end connection between BSS and SGSN. One NS-VL is identified by NS-VLI. In FR, physical link is frame relay bearer channel. NS-VL is the local link of UNI interface of PVC in FR. NS-VLI is the combination of DLCI(Data Link Connection Identity) and bearer channel identity(BRCH) in FR.

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Relationship of NS-VC and NS-VL

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Relationship of NS-VC and NS-VL
 One NS-VC is identified by NS-VCI and has end to end effectiveness in Gb.  The setting-up of NS-VC includes setting-up of physical link and NS-VL.  NS-VL and NS-VC are established permanently by managing method. NS-VCI is also assigned through managing method. The mapping table between NS-VCI, NS-VLI and physical link identity is stored in power-off protection memory .

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5. BVC: BSSGP Virtual Connection, used to transport NS SDU between network entity(NSE), which is identified by NSEI. A NSE is the combination of a group of NSVC. A BSC may have one or more NSE. One NSE provides one or more BVCs for NS user entities. One BVC is supported by one NS-VC group. One NS-VC group supports one or more BVCs. NS performs the mapping of BVC to NS-VC group. One BVC is identified by BVCI and has end to end effectiveness at Gb interface. In SGSN, BVCI and NSEI, which are used to realize layer to layer communication at NS-SAP, altogether identify one BVC.
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Connection of Gb interface

Gb

BSS (user)

SGSN (network)

Gb interface connection
Gb Gb

BSS (user)

FR

SGSN (user)

FR PVC connection

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Addressing of Gb interface
1.Physical link is the bearer channel of FR 2.NS-VL is the local link of FR PVC(at UNI) 3.NS-VLI is the identity of FR DLCI and bearer channel (BRCH). One BRCH can carry multiple PVC which is identified by DLCI. A PVC, whose DLCI=0, is used to carry FR signaling 4.NS-VC is FR PVC 5.NS drive entity is FR entity

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Addressing at Gb interface
LSP1 LSPn LSP1 LSPn

BVC1 BVCn

BVC1 BVCn

NSE

NSE

NSVC1 NSVCn PVC1 PVCn

NSVC1 NSVCn PVC1 PVCn

FR Net

BSC

SGSN

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Dynamic Adjustment of TSs

TS7 Ê Ï 7 ±¶ TS6 Ê Ï 6 ±¶ ±¶ TS5 Ê Ï 5 TS4 TS3 TS2 TS1
±¶ ÊÏ4 ±¶ ÊÏ3 ±¶ ÊÏ2 ±¶ ÊÏ1

±¶ TS0 Ê Ï 0

P2 P2 P1 P1 C4 C3 C2 C1
1

P1 P1 P1 P1 P1 C3 C2 C1
2
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P3 P3 P1 P1 P1 C3 C2 C5
3

P3 P4 P4 P1 P1 C3 C6 C5
4

P3 P4 P4 P5 P1 C3 C6 C5
5

P3 P5 P5 P5 P1 C3 C6 P5
6

P3 C8 C9 P5 P1 C3 C6 C7
7

P3 C8 C9 P5 C10 C3 C6 C7
8

P3 C8 C9 P5 C10 C3 P1 C7
9 ±ä ʼ

2008年11月25日


				
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