1

Chapter 1

The GPRS NetworkContents:

1.1 GPRS and GSM1. GPRS and GSM

1.2 Network elements and functions1. The GSM PLMN2. GPRS Network Architecture3. Functions of GGSN4. Functions of SGSN5. Additional PS core entities 6. Modifications for GPRS in the BSS7. GPRS MS

1.3 Services and Network evolution1. GPRS Network Services2. Network evolution into GERAN3. GERAN reference architecture (Rel 5)

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Chapter 1.1

The GPRS Network1.1 GPRS and GSM

1. GPRS and GSM

3

GPRS and GSM

higher flexibility on radio interface!

higher efficiency

higher throughput

GSMPhase 2+

High Speed Circuit Switched Data (HSCSD)

channel bundling

new coding schemes:up to 14.4 kbps/TS

General Packet Radio Service (GPRS)

channel bundling

new coding schemes:up to 21.4 kbps/TS

171.2kbps

115.2kbps

+ capacity on demand+ multiplexing of subscribers on one phy. channel

EnhancedData rates for GSMEvolution(EDGE)

newmodulation

andcoding

schemes

EnhancedCircuitSwitchedData(ECSD)

up to

up to

348kbps

up to

476kbps

up to

EnhancedGeneralPacketRadioService(EGPRS)

5

The GSM PLMN

MSC/VLR GMSC

HLREIR AuC

NSS

BSS

BSCPSTN

TC

BTS

BTS

MS

A E

(H)

F DC

Ater

Abis

Ext

Main element in the NSS is the Mobile Switching Center (MSC) which contains the Visitor Location Register (VLR). The MSC represents the edge towards the BSS and on the other side the Gateway MSC (GMSC), the connection point to all external networks, like the Public Switched Telephone Network or ISDN. GSM is a circuit switched network, there are physical links to transport control information (signalling) and user data. The signalling links are SS7 based and circuits (voice channels) are switched through the MSC (or GMSC).HLR Home Location Register, a main database that contains data for each subscriber like IMSI, MSISDN,

subscribed services, access rights etc. EIR Equipment Identity Register, if supported, may be integrated in the HLR. AuC Authentication Center, provides Authentication Triplets for every subscriber to perform authentication

and ciphering (performed by MSC/VLR).SCP Service Control Point, a database for Intelligent Network services.CSE CAMEL Service Entity, a database for PLMN specific Intelligent Services, e.g. charging of roaming

subscribers.SMSC Short Message Service Center, used for transfer of short messages.

The GSM Public Land Mobile Networks (PLMN) consists out of a Network Switching Subsystem (NSS) and a Base Station System (BSS).  

CSESCP SMSC

SS7

6

GPRS Network Architecture

GGSNSGSN Gn

MSC/VLR GMSC

HLREIR AuCGs

Gr GcGf

Gi

NSSGERAN

BSS

PSTN

ISP IPvXbackbone

TC

BSS

BTS

Gb

TCBTS

BTS

BTS

BTS

BTS

MS

A

Abis

E

(H)

F D C

Ater

Abis

Ext

Home SubscriberServer (HSS)

Rel 5

GPRS PS Core Network

BSCPCU

BSCPCU

7

Functions of GGSN

GMSCGatewayMobile servicesSwitching Centre

GGSN Gateway GPRS Support Node

• signalling evaluation (SS7)

• switching (cs traffic)

• operational tasks incl.- collection of traffic statistics- alarms- generation of charging records

• interrogation of HLR

• often interfacing external networks, such as PSTN, ISDN

• signalling evaluation (IP header)

• routing and tunneling of packet data (ps traffic)

• operational tasks incl.- collection of traffic statistics - alarms- generation of charging records

• interrogation of HLR

• interfaces external IP networks

• Interfaces internal IP network (IP BB)

• Allocates dynamic or static IP addresses to mobiles either by itself or with the help of a DHCP or a RADIUS server

Gateway GPRS Support Node is an IP router that provides access to various PDP networks,

e.g. the Internet

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(V)MSC/VLRVisited MSC/Visitor Location Register

SGSN ServingGPRS Support Node

• signalling evaluation (SS7)

• switching (cs traffic)

• operational tasks incl.- collection of traffic statistics- alarms- generation of charging records

• Mobility Management, incl. authentication, authorisation, location area updates

• Connection Management, incl. call control, SMS, supplementary services

• Paging (CS)

• signalling evaluation (IP header)

• routing (ps traffic)

• operational tasks incl.- collection of traffic statistics - alarms- generation of charging records

• GMM (GPRS Mobility Management), incl. authentication, authorisation, routing area updates        

• SM (Session Management), incl. PDP (Packet Data Protocol) context management and SMS

• Paging (PS –and CS as option)

• Protocol conversion between IP backbone and BSS protocols e.g. data compression for IP-Header and IP payload (V.42 bis, RFC 1144).

Functions of SGSN

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Additional PS core entities

GGSNSGSN IPvXbackbone

GPRS PS Core Network

CG

BillingCentre

BG

Inter-PLMNNetwork

LIG

LEA

DNSCharging Gateway:

GPRS charging data records (CDR) are generated by

SGSNs and GGSNs, and sent to the CG via interface

Ga.

The Charging Gateway •collects all this data together•processes it •passes it to the Billing System

Border Gateways: BGs are to interconnect operators' GPRS backbone networks via a secure

connection to support roaming

Lawful Interception Gateway:

•Lawful interception is an action based on the law, which is performed by the GPRS network

•It provides information for a Law Enforcement Agency (LEA) about some pre-defined target subscriber

•Information could include •data sent and received by the interception target•location information•subscriber information•etc.

Domain Name Server:used to convert IP names into IP

addresses or vice versa.DNS

BG

LIG

CG

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Modifications for GPRS in the BSS

SGSN siteBSC siteBTS

CCU

CCU

PCUAbis

Channel Codec Unit:BTS SW upgrade for new Coding Scheme (CS 1-4 or CS 1+2).

Gb

Ater

CCU

The PCU (Packet Control Unit):Performs radio specific functions (Radio Resource Management)

       Manages sub-multiplexing of multiple MS on one physical channel       Decides which radio resources are dynamically allocated to packet switched or circuit switched use       Is responsible for packet segmentation and re-assembly       Guarantees reliable link to MS       Terminates Gb interface In most vendors implementation the PCU is a part of the BSC, in principle it could be as well a standalone module or integrated in the BTS.

PCU

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GPRS MS

Simultaneous CS and PS • attach• activation• monitorno simultaneous traffic

simultaneous• attach• activation• monitor• invocation• trafficof GSM and GPRS pure GPRS or

alternative use of GSM and GPRS only

classB class

C

classA

A class A MS may be attached to the CS and PS core simultaneously. While the MS is in packet transfer mode and there is an incoming call the MS can continue its packet session while making the call and enters the Dual Transfer Mode (DTM). DTM requires additionally support by networks (BSS).

A class B MS may be attached to the CS and PS core simultaneously. While the MS is in packet transfer mode and there is an incoming call the MS can take the call, the packet transfer has to be suspended and resumed after the call is finished.

A class C MS may be attached to the CS or PS core. While the MS is in packet transfer mode there can be no incoming call. Usually these MSs are PCMCIA cards.

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GPRS Network Services

ISPInter-net

GPRSISP

RouterRouter

ApplicationServer

MS

IPbackbone

ISPBSS

NSS

GGSN

GGSNSGSNPCU

user's point of view

The objective of this training are the (E)GPRS signalling protocols, and to show, how a user data packet is transmitted through the GPRS network. The user data transmission can be seen from two points of view:

• end user's point of view:The subscriber wants to exchange user data packets between the mobile terminal (MT) attached to his MS (or internal) and an application server, located in a PDN.

• operator's point of view:The operator is especially responsible to transmit the user data from one access point of the PLMN to another. The access points to and from the PLMN are the MS and the GGSN.

 The operator is required to offer a certain Quality of Service (QoS) in order to enable new services. Services are categorized into (Rel 99)

Interactive classBackground classStreaming classConversational class

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Network evolutions into GERAN

2G Network

GERAN (GSM/EDGE Radio Access Network)

GSM

HSCSD

GPRS

ECSD

EGPRSclassic

TDMA/136

TDMA/136 +

TDMA/136HS Outdoor

TDMA/136HSindoor

EGPRScompact

Support of Interactive and Background PS Services (Rel 99)

Support of streaming (Rel 4) and conversational PS Services (Rel 5)

In order to deliver the required QoS for a certain service the existing networks are enhanced. ETSI standardized the GSM radio interface and defined GSM, GPRS, EDGE access to PS Core Network (Rel 97, 98 ,99). Due to aspects of harmonization and interworking with 3G the specifications has been moved to 3GPP. Rel 99 has been adopted by 3GPP. Since then the GSM access network is referred to as GERAN. The evolution of GERAN is done in Rel 4, 5, 6,... (along with the evolution of CN entities).Currently Rel 4, 5 and 6 features are adopted in order to fullfil the requirements for new services

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GERAN Reference architecture (Rel 5)

GSM/UMTSCore Network

GERAN

Gb

A

IuCS

MSUm

Iur-g

BSC

BTS

BTS

BSS

BSS

MS

Iur-g

UTRAN

RNC

A MS may operate in Gb mode (class A, B or C MS) or Iu mode. For Iu mode the MS may operate

• CS/PS mode: correspondends to Class A in A/Gb mode• PS mode: MS can only operate packet switched services• CS mode: MS can only operate circuit switched services

IuPSTo 3G CN (Iu mode)

To 2G CN (A/Gb mode) required for Rel 4 or older MSs

Enhancedcompared to Rel 99 (Support of Realtime

Packet services)

-Interactive,-Background,-Streaming

PS Services

-Interactive,-Background,-Streaming-Conversational

PS Services

Iur-g (cancelled)-Interface carries only control signalling-no user data-improved interworking GERAN-UTRAN-Radio specific procedures handled completely inside RAN

IuCS

IuPS

To 3G CN