GPRS Basics

GPRS BasicsGPRS Basics

Zhang ChunpingZhang Chunping

AgendaAgenda

GPRS Network Structure

GPRS Interface and Protocol

GPRS Address ， Identity

GPRS Radio Interface Technology

GPRS Mobility Management

GPRS Session Management


GPRS Interface and Protocol





What’s GPRS

GPRS － General Packet Radio Service

High spectrum efficiency for data application

provide data service based on existing GSM

GPRS can keep long connection with network ， charge based on data flow

internetLow Speed Circuit Switching Data Service

Low Spectrum efficiency Long Time for Call Setup Narrow Bandwidth & Low Data Rate High Cost

Disadvantages for Circuit Switching Data Service

IWFIWF

Support connecting with PSTN/ISDN/PDN

Provide Data & Fax Service

Most Data rate is just 9600bps

Support transparent & non-transparent Data

Service

Demands increase IWF Function Module in MSC

9.6K

57.6K

171.2K

384K

2M

GSM Revolution

GPRS Network StructureGPRS Network Structure

BTS SGSN GGSNBSC

MSC/VLR

Gi

Gn

GrGs

Gb

Gn

A

Abis

HLR

IPNetwork

GPRSBackbone

BGBG

Other PLMN

Gp

PCU

SGSN

GGSN

Gn

GnBGBG

SS7

GPRS CompositionGPRS Composition

SGSN-Serving GPRS support Node

GGSN-Gateway GPRS Support Node

BG- Border Gateway

PCU- Packet Control Unit

GPRS Mobile Station

Network access control

Authentication

Charging information collection

SGSN FunctionSGSN Function

Routing and tunnel transmission

Encryption and decryption

Subscriber data storage and forwarding

Route selection

Encapsulation and tunnel transmission

MM and SM

Network access control (external PDN side)

Message filtering

Charging information collection

SM

Route selection and forwarding

Storage and forwarding

Route selection

Address translation and mapping

Encapsulation and tunnel transmission

Dynamical IP address allocation( optional)

GGSN FunctionGGSN Function

BG realize the interworking between operators

Based on router

Safety protocol and route protocol Embedded

BG function, GPRS Backbone NetworkBG function, GPRS Backbone Network

GPRS backbone network based on IP protocol

Consist of backbone router

Interworking with each NE, SGSN, GGSN…

Every NE occupy unique IP address

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

HLR FunctionHLR Function

HLR GPRS user informationHLR GPRS user information

Domain Description

IMSI User identifier

MSISDN User basic MSISDN

SGSN Number Registered SS7 number of SGSN

SGSN Address Registered SGSN IP addressSMS Parameters 短消息有关的用户签约数据MS Purged for GPRS 用户 GPRS 清除标志MNRG 用户 GPRS不可及标志GGSN-list 列表，每一项包含某一 GGSN的 SS7号码和 IP地址

PDP Context Identifier PDP上下文索引PDP Type PDP类型PDP Address PDP地址

Qos Profile Subscribed 用户登记的 Qos过滤VPLMN Address Allowed 是否允许用户使用 VPLMN的 APNAccess Point Name 外部分组数据网接入点

MSC/VLR Additional FunctionMSC/VLR Additional Function

SGSN connect with MSC via Gs interface( optional)

Combined IMSI/GPRS attach/detach

Combined location area/routing area updating

Improve radio resource

GPRS support SMSGPRS support SMS

SGSN connect with SMSC via Gd interface

capable of sending SM by GPRS, thus decrease the influence to voice service

Share the existing short message information source

Transfer SMS by MSC or SGSN upon decision of operator

AgendaAgenda


GPRS Network interface and protocol

GPRS address and identity

GPRS radio interface technology





GPRS address and identity

GPRS radio interface technology



GPRS Network StructureGPRS Network Structure

BTS SGSN GGSNBSC

MSC/VLR

Gi

Gn

GrGs

Gb

Gn

A

Abis

HLR

IPNetwork

GPRSBackbone

BGBG

Other PLMN

Gp

PCU

SGSN

GGSN

Gn

GnBGBG

SS7

Data Transmission PlatformData Transmission Platform

GSM RF

MAC

RLC

LLC

SNDCP

L1

NetworkService

BSSGP

LLC

SNDCP

MS BSS SGSNGbUm

IP

L2

IP

UDP/TCP

IP

UDP/TCP

GTP

L1bi s

NetworkService

BSSGP

GSM RF

MAC

RLC

Relay

IP IP

Gn Gi

RelayIP

Relay

Appli-cation

Appli-cation

GGSN ISP

L1

L2 L2

L1

L2

GTP

MS-BSS-SGSN Signaling PlatformMS-BSS-SGSN Signaling Platform

GMM: GPRS Mobility Management

SM: Session Management

MS BSS SGSN

BSSGP

GMM/SM

LLC

RLC

MAC

GSM RF

GMM/SM

LLC

BSSGP

L1bis

Um Gb

NetworkService

RLC

MAC

GSM RF L1bis

NetworkService

relay

Gb InterfaceGb Interface

BTS SGSNBSCGbAbis

PCU

L1bis ： physical transmission layer, based on E1or T1

NS ： transmit BSSGP PDU based on frame

BSSGP ： provide link without connection for data transmission without acknowledgement ；

For signaling platform, transmit radio related information ， such as QoS 、 routing ；

Process paging request ， flow control to data transmission

L1/L2 ： lower layer transmission networks :ATM,Ethernet,DDN

IP ： backbone protocol, routing selection for data and control ；

UDP/TCP ： UDP bear PDU no requiring reliable transmission;

TCP provide flow control and loss, error protection to bear PDU requiring reliable transmission

GTP ： data and protocol transmission between GSN

Gn/GP interfaceGn/GP interfaceBTS SGSN GGSNBSC

Gn

Gb

Gn

Abis

GPRSBackbone

BGBGOther PLMN

Gp

PCU

SGSN

Gn

BGBG

SCCP

MTP2

MTP3

MTP2

MTP3

SCCP

GrGd

SGSN

TCAP

MAP

TCAP

MAP

L1 L1

No.7 Signaing InterfaceNo.7 Signaing Interface

Gr : Authentication, MM

Gd: transmit SM via GPRS network

HLRSMC

Submit SMS Submit SMS

SMSC check destination address of SMS,request location

information of relevant HLR

HLR return information include the current SGSN or MSC

number ,or both to SMS.

if no SGSN number ,means MS not reachable via SGSN;

SGSN is given priority to be chosen for SMS delivery

AgendaAgenda


GPRS Network Interface and Protocol

GPRS Address and Identity

GPRS Radio interface technology





GPRS Address and Identity

GPRS Radio interface technology



SGSN GGSN

GPRS BackboneGPRS Backbone

PDP addressP-TMSIIMSI

TLLI/ NSAPI

IP address

No.7 signaling address

TID=IMSI+NSAPI

Address, IdentityAddress, Identity

TLLI/NSAPI used to uniquely identify PDP PDU of MS between

MS and SGSN ; TID used to uniquely identify PDP PDU of MS between GSNs;

used to forward user data with tunnel transmission mechanism, is

composed of IMSI/NSAPI, existed in head of GTP

IPNetwork

IP address

No.7 signaling address

P-TMSI ： assigned by SGSN for attached GPRS user used in

PS, correspond to TMSI in CS;

TLLI ： Identify logical link between MS and SGSN, deduct

from P-TMSI

NSAPI ： used to specify specific PDP Context for MS

IMSI/NSAPI or NSAPI/TLLI in routing cell can be used

to uniquely identify specific PDP context for specific user.

TID ： IMSI+NSAPI, used to uniquely identify a PDP context

between SGSN and GGSN, or new SGSN and old SGSN

Address, IdentityAddress, Identity

GSN address ： every GSN has one or more IP address , internal

address , each one has one or more domain name for communication

GSN Number ： Each SGSN has a SS7 numbering to communicate with HLR and MSC.

GGSN shall have a SS7 numbering as well if GGSN connect with HLR via Gc interface

PDP Address ： IP address （ IP4 or IP6 ） or X.121 address

（ for X.25 service ）

Address ,IdentityAddress ,Identity

IP Address AllocationIP Address Allocation

In GPRS network, SGSN, GGSN,CG,DNS is communicated with each other by IP address, each NE shall be allocated one IP.

The IP address of SGSN,GGSN,DNS is private or public, which

need to be planned in whole GPRS network.

CG usually use private IP for safety purpose. MS shall be allocated IP address, IP address allocation :

Static address assigned to MS when subscription; or

dynamic address allocated to MS when PDP context activation;

IP address can be private or public;

If MS use private address, address mapping and conversion need to

be implemented by network when MS visit external IP network.

BSSInternetGPRS Backbone

DNS

SGSN GGSN

FireWare

10.2.1.1

10.2.1.2

202.1.1.1202.1.1.2 202.100.1.1

202.1.1.4

10.2.1.1 <-> 202.100.1.1:100110.2.1.2 <-> 202.100.1.1:1002

IP for NE interface （ Gn ， Gi ） is public address ；

Mobile Terminal is allocated as private address （ dynamic ）

IP Address AllocationIP Address Allocation

AgendaAgenda













Radio Channel Allocation Radio Channel Allocation

GPRS share the physical channel of radio

interface with GSM

Radio resource allocation ：

Dynamic allocation

Fixed allocation

PS/CS Channel Dynamic AllocationPS/CS Channel Dynamic Allocation

P2 P1 P3 P3 P3 P3 P3 P3 P3P2 P1 P3 P4 P4 P5 C8 C8 C8P1 P1 P1 P4 P4 P5 C9 C9 C9P1 P1 P1 P1 P5 P5 P5 P5 P5C4 P1 P1 P1 P1 P1 P1 C10 C10C3 C3 C3 C3 C3 C3 C3 C3 C3C2 C2 C2 C6 C6 C6 C6 C6 P1C1 C1 C5 C5 C5 P5 C7 C7 C7

7时隙

时间21

0时隙1时隙2时隙3时隙4时隙5时隙6时隙

83 75 64 9

P: Packet channel ， C ： voice channel

Coding Scheme For Radio ChannelCoding Scheme For Radio Channel

Higher data transmission rate of each timeslot is compensated by lower error-tolerance.

Scheme CodeRate

USFbits

Pre-codedUSFbits

RadioBlock(excl. USF

and BCS)

BCS Tailbits

Codedbits

Puncturedbits

DataRate

(kbps)

CS-1 1/2 3 3 181 40 4 456 0 9.05

CS-2 ~2/3 3 6 268 16 4 588 132 13.4

CS-3 ~3/4 3 6 312 16 4 676 220 15.6

CS-4 1 3 12 428 16 0 456 0 21.4

Add BCS(

Add precoded USF

Add tail bits Coding Puncture 456bits

Effective load

• BCS : Block Check Sequence

• USF : Uplink State Flag

Steps for GPRS codingSteps for GPRS coding

rate 1/2 convolutional coding

puncturing

456 bits

USF BCS

Radio Block

B0 B1 B2 T B3 B4 B5 X B6 B7 B8 T B9 B10 B11 X

52 TDMA Frames

12 Radio Block Periods = 240 ms

*Interleaving

Radio block structure from CS1 to CS3Radio block structure from CS1 to CS3

Radio Block Structure for CS4Radio Block Structure for CS4

blockcode

no coding

456 bits

USF BCS

Radio Block

*Interleaving

B0 B1 B2 T B3 B4 B5 X B6 B7 B8 T B9 B10 B11 X

52 TDMA Frames

12 Radio Block Periods = 240 ms

Channel Data Flow RateChannel Data Flow Rate

C/I 载干比 (dB)•CS1 and CS2 least influenced by carrier-to-interference radio

•CS3 and CS4 has low efficiency for low C/I, used when C/I >10 DB

0

5

10

15

20

25

0 4 8 12 16 20 24

CS1CS2CS3CS4

Typical city area, moving speed at 3km/h

User data

Segment Segment

Info FH FCS

PH

Segment Segment Segment

InfoBH BCS Tail

Convolutional encoding

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 LLC:Logic Link Control, RLC:Radio Link Control

456 bits

114 bits 114 bits 114 bits 114 bits

Data flow for Packet TransmissionData flow for Packet Transmission

AgendaAgenda



GPRS Address, Identity










MS AttachMS Attach

Attach Type ：When MS turn-on, initiate attach procedure, Attach Type included in Attach Request indicates the type

Log on GPRS onlyLog on GPRS/ Non-GPRS, SGSN initiate location update procedure to MSC/VLR MM Context ：PMM has three states , can be converted under the trigger of different event , each state corresponds to certain functionality and a series of relevant information, which constitute MM context; one user corresponds to a unique MM context, which existed in MS and SGSN.

Idle GPRS connection

Or PDP activation

GPRS detach

Timer Timeout

Send or receive PDU

Timer

timeo

ut o

r loc

ation

canc

ellat

ion

MS State ModelMS State Model

Ready

CI is known

Standby

RAI is known

In GPRS, location management is based on RA. RA is a subset Of location area, a location area can be viewed as a RA, can also be defined as several RA. Every RA is served by one SGSN, location update includes:

Cell update; CI changes, RA unchanged;RA update: RAI changes, Intra-SGSN RA update Inter-SGSN RA updateCombined RA/LA update Intra-SGSN Combined RA/LA update Inter-SGSN Combined RA/LA updatePeriodical Location Update

Location ManagementLocation Management

Mobility Management enable the system acquire the user state info and location info.Includes:

GPRS Attachment: establish MM context, MM state changed to Standby state.GPRS Detachment: Delete MM context, MM state changed to IdleCan be initiated by MS or Network sideSafety function: authentication, encryption,identification check, etc.Location Management: RA update, periodical update, Cell update

Mobility Management FunctionMobility Management Function

MS BSS new SGSN HLRGGSNold SGSN

2. SGSN Context Response

3. Security Functions

1. Routeing Area Update Request

2. SGSN Context Request

6. Update PDP Context Request

6. Update PDP Context Response

7. Update Location

10. Update Location Ack

11. Routeing Area Update Accept

8. Cancel Location

8. Cancel Location Ack

9. Insert Subscriber Data Ack

9. Insert Subscriber Data

12. Routeing Area Update Complete

5. Forward Packets

4. SGSN Context Acknowledge

C1

C3

C2

Inter-SGSN Update

MS SGSN HLR

Insert Subscriber Data

Attach Request

. Update Location

Update Location AckInsert Subscriber Data Ack

Attach Accept

Triplet request

Authentication

GPRS MS Attachment ProcedureGPRS MS Attachment Procedure

AgendaAgenda













If GPRS service applied by a user involved in one or more than one external PDN( e.g. Internet,X.25), GPRS subscribed data shall include 如果一个用户所申请的 GPRS 业务涉及一个或多个外部PDN（如等），则在其 GPRS 签约数据中就将包括一个或多个与这些 PDN 对应的 PDP 地址。每个 PDP 地址对应有一个PDP 上下文。每个 PDP 上下文由 PDP 状态及相关信息来描述，存在于 MS 、 SGSN 、 GGSN 中。一个用户的所有PDP 上下文都与该用户唯一的一个 MM 上下文相关联。

Session Management-PDP Context Session Management-PDP Context

MS send “PDP activation request” to SGSNAPNPDP type (IP)PDP address requestQoS and others

SGSN check user dataAPNDynamic or static IP address

BTS BSC

SGSN

GGSN

Intranet

GPRS Core

Network

SS7

HLR

DNS

Internet

1.

AccessPoint

PDP Activation - 1PDP Activation - 1

Definition of APN Structure Definition of APN Structure

APN Network Identification define the external network GGSN connected (mandatory ) APN Operator Identification define the GPRS Network where GGSN located (optional)APN correspond to a GGSN domain name

www.zte.com.cn.mnc<MNC>.mcc<MCC>.gprs

APN Network Identification

APN Operator

Identification

BTS BSC

SGSN

GGSN

GPRS Core

Network

DNS

Intranet

Internet

1.

2.

AccessPoint

(1) SGSN obtain GGSN IP address from DNS

APN mapping GGSN IP address

(2) SGSN send “ create PDP context” request to GGSN

PDP type （ e.g.IP ） PDP address （ dynamic or

static ） APN QoS and other parameters


BTS BSC

SGSN

GGSN

GPRS Core

Network

Intranet

Internet

1.

2.

APN identify external data network the user want to use Dynamic address allocation: allocated by GGSN address pool or external DHCP server GGSN return “create PDP context response” to SGSN SGSN return “PDP context activated”to MS SGSN can establish routing between MS and GGSN


PDP Activation on Network side (1)

MS SGSN GGSN

3. PDU Notification Request

HLR

1. PDP PDU

2. Send Routeing Info for GPRS

2. Send Routeing Info for GPRS Ack

4. Request PDP Context Activation

5. PDP Context Activation procedure

3. PDU Notification Response

PDP Activation on Network side(2)

MS SGSN GGSN

PDU Notification Request

HLR

PDP PDU

Send Routeing Info for GPRS

Send Routeing Info for GPRS Ack

Request PDP Context Activation

PDP Context Activation procedure

PDU Notification Response

PLMN Backbone Network

Visiting Network Home Network

GPRS MS ClassificationGPRS MS Classification

Class ACan Attache GPRS and non-GPRS network, and implement the CS and PS service simultaneously.

Class BCan Attache to GPRS and GSM network, but can’t implement CS and PS service simultaneously.

Class CCan’t attach to GPRS and GSM network simultaneously, only one of them can be selected, unselected service state is in off state, which can be connected.

Procedure for MS Access to InternetProcedure for MS Access to Internet

Procedure: 3 steps Attach PDP activation Access to Internet

Attach_request (IMSI)

Triplet request

Authentication

Update_location

GPRS MS AttachGPRS MS Attach

SGSN HLR

Insert_subscriber_data

Update_location_ack

GPRS MS AttachGPRS MS Attach

Attach_accept (TLLI)

MS TLLI

SGSN HLR

Activate_PDP_context_req(NSAPI1,type [+ @ of PDP] , APN, QoS)

DNS_query (APN)

DNS_response (IP of GGSN)

DNS

PDP ActivationPDP Activation

SGSN

Create_PDP_context response (IP )

Activate_PDP_context_accept (IP )

Create_PDP_context_req(type, APN, QoS)

TID1 Create_PDP_ctxt GGSN IP

PDP ActivationPDP Activation

GGSNSGSN

GPRS MS Data TransmissionGPRS MS Data Transmission

TLLI IMSI

NSAPI + IMSI TID

NSAPI TLLI

NSAPITLLI User packet

User packet

User packetTIDGGSN

PDP network (IP/X.25)

GGSNSGSN

Roaming － Connected to Home GGSN

Roaming － Connected to Home GGSN

Home PLMN

GGSN

GGSN

BG

ISP Network

ISP Network

BG

MS SGSN

HLR

Visiting PLMN

RoamingMS

Re-attach

Subscriptiondata GTP addres-

sing

IPSectunnelhop-by-hop

SGSNMS

Home PLMN

GGSN

GGSN

BG

Home ISP Network

Home ISP Network

BG

MS SGSN

HLR

Visiting PLMN

RoamingMS

Re-attach Visiting ISP

Network Visiting ISP

Network

SGSN

RADIUS

RADIUS

Roaming agreement between ISP’s

MS

Roaming-Connected to Visiting GGSN

Roaming-Connected to Visiting GGSN

Th

ank

You

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GPRS Basics