LZT 123 5374 r3a GPRS system survey

OBJECTIVES: Upon completion of this chapter the student will be able to: • Briefly describe the evolution of cellular data services • Describe the principles of data communication • Lis

GPRS System Survey

STUDENT BOOK LZT 123 5374 R3A

DISCLAIMER

This book is a training document and contains simplifications Therefore, it must not be considered as a specification of the system

The contents of this document are subject to revision without notice due to ongoing progress in methodology, design and manufacturing

Ericsson assumes no legal responsibility for any error or damage resulting from the usage of this document

This document is not intended to replace the technical documentation that was shipped with your system Always refer to that technical documentation during operation and maintenance

Copyright © 2003 by Ericsson AB

This document was produced by Ericsson AB

• It is used for training purposes only and may not be copied or reproduced in any manner without the express written consent

of Ericsson

This Student Book, LZT 123 5374, R3A supports course number

LZU 108 876

Table of Contents

INTRODUCTION 18

BACKGROUND 18

DATA EVOLUTION IN CELLULAR NETWORKS 18

WCDMA/GSM GPRS SYSTEM 22

CHARACTERISTICS OF DATA COMMUNICATION 22

CIRCUIT-SWITCHED COMMUNICATION 24

PACKET-SWITCHED COMMUNICATION 26

PACKET DATA APPLICATIONS 26

THE ROLE OF THE WCDMA/GSM GPRS NETWORK 27

FEATURES OF THE WCDMA/GSM GPRS SYSTEM 29

THE GPRS SUPPORT NODES (GSN) 31

THE ROLE OF THE SGSN 32

ROLE OF THE GGSN 33

WCDMA/GSM GPRS SYSTEM ARCHTIECTURE 34

OTHER WCDMA/GSM GPRS SYSTEM COMPONENTS 35

WCDMA UE DEFINITIONS 35

TERMINAL EQUIPMENT (TE) 35

MOBILE TERMINAL (MT) 35

USER EQUIPMENT (UE) 35

GSM MS DEFINITIONS 36

TERMINAL EQUIPMENT (TE) 36

MOBILE TERMINAL (MT) 36

MOBILE STATION (MS) 36

GPRS MS FEATURES 37

BASE STATION SYSTEM (BSS) 39

HOME LOCATION REGISTER (HLR) 40

VISITOR LOCATION REGISTER (VLR) 41

EQUIPMENT IDENTITY REGISTER (EIR) 42

AUTHENTICATION CENTER (AUC) 42

SHORT MESSAGE SERVICE-INTERWORKING MSC (SMS-IW-MSC) 43

SHORT MESSAGE SERVICE GATEWAY MSC (SMS-GMSC) 43

SERVING GPRS SUPPORT NODE (SGSN) 43

GATEWAY GPRS SUPPORT NODE (GGSN) 44

PACKET EXCHANGE MANAGER (PXM) 44

DNS SERVER 45

BILLING GATEWAY (BGW) 45

OPERATION SUPPORT-SYSTEM (OSS) 45

GSM GPRS AIR INTERFACE 53

DEDICATED OR ON-DEMAND GPRS PHYSICAL CHANNEL 53

DEDICATED PDCHS 53

ON-DEMAND PDCH 54

UPLINK/DOWNLINK RADIO RESOURCES FEATURES 56

DOWNLINK RADIO RESOURCES ALLOCATION 56

DOWNLINK TRANSFER 58

UPLINK RADIO RESOURCES ALLOCATION 59

UPLINK TRANSFER 60

WHAT IMPACTS GPRS THROUGHPUT 62

EDGE TECHNOLOGY 64

EDGE MODULATION TECHNIQUE 65

EDGE CODING SCHEMES 66

PACKET HANDLING IN EDGE 68

ADDRESSING WINDOW 69

LINK ADAPTATION 70

INCREMENTAL REDUNDANCY 71

CELL CHANGE IN GSM AND GPRS 72

CELL CHANGE IN GSM 72

CELL CHANGE IN GPRS 72

CELL RESELECTION, A DOWNLINK TRAFFIC CASE 74

CELL RESELECTION, AN UPLINK TRAFFIC CASE 75

WCDMA AIR INTERFACE 83

QUALITY OF SERVICE 83

CONVERSATIONAL 84

STREAMING 84

INTERACTIVE 85

BACKGROUND 85

CHANNELS 86

CHANNEL TYPES 87

PHYSICAL CHANNELS 87

TRANSPORT CHANNELS 89

LOGICAL CHANNELS 90

RADIO RESOURCE CONTROL STATES 91

IDLE STATE 92

CELL-DCH STATE 93

CELL-FACH STATE 93

CELL-PCH & URA-PCH STATES 94

SIGNALING CONNECTIONS 95

USER PLANE BEARERS 96

RADIO BEARERS 97

RADIO ACCESS BEARERS 97

DYNAMIC BANDWIDTH ACROSS THE AIR INTERFACE 97

IN CELL-DCH 98

IN CELL-FACH 98

IN CELL-PCH OR URA-PCH 98

INTRODUCTION 105

DATA TRANSPORT IN GPRS ARCHITECTURE 105

GPRS TERMINOLOGY 105

PDP CONTEXTS 105

PDP ADDRESS 106

ACCESS POINT NAME 106

MULTIPLE PDP CONTEXTS 107

NSAPI 107

PDP CONTEXT STORAGE 108

TRAFFIC FLOW TEMPLATES 108

GTP TUNNELS IN GENERAL 109

GTP-U TUNNELS 109

TUNNEL ENDPOINT IDENTIFIERS (TEID) 110

IU TRANSPORT IN WCDMA 111

GB TRANSPORT IN GSM 111

GN TRANSPORT 111

FUNCTIONS OF TRAFFIC MANAGEMENT 111

MOBILITY MANAGEMENT 113

INTRODUCTION 113

MM STATES IN WCDMA 114

PMM-DETACHED STATE 114

PMM-IDLE STATE 115

PMM-CONNECTED STATE 116

NETWORK MODES IN WCDMA 116

MM STATES IN GSM 118

IDLE STATE 118

STANDBY STATE 118

READY STATE 118

NETWORK MODES IN GSM 119

MOBILITY MANAGEMENT PROCEDURES 120

SESSION MANAGEMENT 120

SESSION MANAGEMENT PROCEDURES 121

TRAFFIC CASES FOR WCDMA 122

GPRS ATTACH 122

PDP CONTEXT ACTIVATION 124

SECONDARY PDP CONTEXT ACTIVATION 126

INTER SGSN RA UPDATE 127

TRAFFIC CASES FOR GSM 129

GPRS ATTACH 129

PDP CONTEXT ACTIVATION 130

INTER SGSN RA UPDATE 131

GSN ROADMAP 139

SGSN 140

SGSN INTRODUCTION 140

SGSN HARDWARE TYPES 142

HARDWARE CHARACTERISTICS 142

CABINET – BYB 501 143

SGSN MAGAZINES 143

PLUG-IN UNITS 148

PUBLIC AND PRIVATE IP ADDRESSES 150

DYNAMIC AND STATIC IP ADDRESSES FOR UE 150

PARTITIONING OF THE GPRS IP CONNECTIVITY 150

THE ISP NETWORK OR CORPORATE NETWORK 151

GPRS INTERNAL BACKBONE 152

SGSN SS7 COMMUNICATION 153

IP INTERFACE 155

GGSN INTRODUCTION 157

FUNCTIONALITY 159

GTP SERVICES 159

CONTROL AND USER PLANES 159

SESSIONS 160

ADDRESSING 160

LOGICAL INTERFACES 162

J20 GGSN HARDWARE ARCHITECTURE 163

ROUTING ENGINE 164

PACKET FORWARDING ENGINE 165

PICS 166

NETWORK INTERFACE PICS 167

SERVICES PICS 167

ROUTING 168

FORWARDING 168

IPSEC 168

TUNNELING AND VPNS 168

RADIUS 169

AUTHENTICATION 170

ACCOUNTING 170

MSISDN AND IMSI TRANSFER BY RADIUS MESSAGE 170

DHCP 170

QUALITY OF SERVICE AND ACCESS CONTROL 170

DOWNLINK PACKETS 171

QOS SETTINGS BASED ON PDP CONTEXT 171

PER-TRUNK QOS 171

UPLINK PACKETS 172

CHARGING 172

INTERNET PROTOCOL VERSION 6 (IPV6) 173

OPERATION AND MAINTENANCE 173

BSS ARCHITECTURE FOR GPRS 183

GPRS FUNCTIONALITIES 183

SOFTWARE AND HARDWARE IMPLEMENTATION 184

BSC AND PCU 184

RAN ARCHITECTURE FOR GPRS 193

GPRS FUNCTIONALITIES 193

RAN ARCHITECTURE 193

RAN INTERFACE ARCHITECTURE 194

APPENDIX A 200

PACKET SWITCHED SERVICES (CONTROL PLANE)-WCDMA 200

PACKET SWITCHED SERVICES (USER PLANE) - WCDMA 201

PACKET SWITCHED SERVICES (USER PLANE) - GSM 202

APPENDIX B 204

REFERENCES AND ACRONYMS 204

APPENDIX C 206

TABLE OF FIGURES 206

Intentionally Blank

1 Introduction

Intentionally Blank

This chapter is designed to provide the student with an introduction

to data communication and an overview of the GSM GPRS System and WCDMA GPRS system

OBJECTIVES:

Upon completion of this chapter the student will be able to:

• Briefly describe the evolution of cellular data services

• Describe the principles of data communication

• List and describe the function of the units and network architecture of the WCDMA/GSM Systems GPRS architecture

• Understand what are the advantages and the principle of GPRS

Figure 1-1: Objectives

Intentionally Blank

Table of Contents

INTRODUCTION 18

BACKGROUND 18

DATA EVOLUTION IN CELLULAR NETWORKS 18

WCDMA/GSM GPRS SYSTEM 22

CHARACTERISTICS OF DATA COMMUNICATION 22

CIRCUIT-SWITCHED COMMUNICATION 24

PACKET-SWITCHED COMMUNICATION 26

PACKET DATA APPLICATIONS 26

THE ROLE OF THE WCDMA/GSM GPRS NETWORK 27

FEATURES OF THE WCDMA/GSM GPRS SYSTEM 29

THE GPRS SUPPORT NODES (GSN) 31

THE ROLE OF THE SGSN 32

ROLE OF THE GGSN 33

WCDMA/GSM GPRS SYSTEM ARCHTIECTURE 34

OTHER WCDMA/GSM GPRS SYSTEM COMPONENTS 35

WCDMA UE DEFINITIONS 35

TERMINAL EQUIPMENT (TE) 35

MOBILE TERMINAL (MT) 35

USER EQUIPMENT (UE) 35

GSM MS DEFINITIONS 36

TERMINAL EQUIPMENT (TE) 36

MOBILE TERMINAL (MT) 36

MOBILE STATION (MS) 36

GPRS MS FEATURES 37

BASE STATION SYSTEM (BSS) 39

MOBILE SERVICES SWITCHING CENTER (MSC) 40

HOME LOCATION REGISTER (HLR) 40

VISITOR LOCATION REGISTER (VLR) 41

EQUIPMENT IDENTITY REGISTER (EIR) 42

AUTHENTICATION CENTER (AUC) 42

SHORT MESSAGE SERVICE-INTERWORKING MSC (SMS-IW-MSC) 43

SHORT MESSAGE SERVICE GATEWAY MSC (SMS-GMSC) 43

SERVING GPRS SUPPORT NODE (SGSN) 43

GATEWAY GPRS SUPPORT NODE (GGSN) 44

PACKET EXCHANGE MANAGER (PXM) 44

DNS SERVER 45

BILLING GATEWAY (BGW) 45

OPERATION SUPPORT-SYSTEM (OSS) 45

Intentionally Blank

INTRODUCTION

BACKGROUND

The purpose of this course is to provide a comprehensive overview

of Ericsson’s General Packet Radio Services for both GSM Systems and WCDMA Systems system architecture, hereafter referred to as the WCDMA/GSM GPRS system It is assumed that the reader is already familiar with cellular circuit-switched

communication concepts

DATA EVOLUTION IN CELLULAR NETWORKS

Digital wireless standards continue to evolve, increasing capacity, coverage, quality and user data-rates The technology roadmap is illustrated in Figure 1-2

2G 2.5G 3G phase 1 Evolved 3G

<64 Kb/s 64 – 144 Kb/s 384Kb/s – 2Mb/s 384Kb/s – 8Mb/s

cdmaOne IS-95A PDC

TDMA GSM

<64 Kb/s 64 – 144 Kb/s 384Kb/s – 2Mb/s 384Kb/s – 8Mb/s

cdmaOne IS-95A PDC

TDMA GSM

Figure 1-2: Cellular packet data evolution

Second-generation (2G) digital cellular networks offer data services at rates of between 9.6kbps, 14.4kbps and 76.8kbps depending on the network technology used (GSM, TDMA or CDMA) Data is sent over dedicated voice channels in much the same way that dial-up modems use the standard telephony network for inter-machine communication

Because data transmission over 2G technologies uses dedicated resources (circuit switching), time based charging is used; that is, the user pays for the time that they are connected to the network (refer to Figure 1-3) This affects usage patterns and user

perception Transactions are always user-initiated and typically involve short-duration data transfer such as email downloads and fax transmissions

=

Dedicated Resource

=

Dedicated Resource

Figure 1-3: 2G Data Technologies

Some 2G cellular technologies are enhanced with multi-channel circuit switched data capabilities, allowing n x (base data rate) data transfer This improves download speed, but the circuit switched usage limitations remain the same Ericsson implements the HSCSD (High Speed Circuit Switched Data)

The next step in the evolution of cellular data networking involves the introduction of packet-switched services These enhancements

to the predominantly voice oriented 2G technologies are called GPRS and IS-95B (for GSM and CDMA networks respectively) and are often referred to as 2.5G technologies

Introduction of these technologies mandates the establishment of packet data network infrastructure (refer to Figure 1-4) and the introduction of several new nodes into the network The main limitation of 2.5G technologies is the narrowband air interface

This restricts the types of service that can reasonably be supported

GSM RAN

GSM RAN CS NetworkCS NetworkGSMGSM

PS Core Network

To ISDN/PSTN

To Internet & Corporate LANs

CDMA RAN

CDMA RAN CS NetworkCS NetworkCDMACDMA

PS Core Network

To ISDN/PSTN

To Internet & Corporate LANs

GSM RAN

GSM RAN CS NetworkCS NetworkGSMGSM

PS Core Network

To ISDN/PSTN

To Internet & Corporate LANs

CDMA RAN

CDMA RAN CS NetworkCS NetworkCDMACDMA

PS Core Network

To ISDN/PSTN

To Internet & Corporate LANs

Figure 1-4: GPRS & IS-95B Packet Switching Core Networks

Because GPRS uses packet switching across the air interface (refer

to Figure 1-5), charging can be volume-based; this allows users to

be “always on” Note: this is not the case for IS-95B, which does not use a packet switching air interface

=

Shared PS Resource

=

Shared PS Resource

Figure 1-5: GPRS’ packet switched air interface & volume based charging

Beyond 2.5G is a range of technologies that provide true broadband capabilities across the air interface Collectively, these technologies are referred to as 3rd Generation (3G) mobile

networks

The path to 3G may involve technologies such as Enhanced Data rates for Global Evolution (EDGE) or CDMA2000 1X The former is an evolution of the GSM/GPRS network that uses enhanced modulation and related techniques The latter is an evolution of cdmaOne technology Both have the characteristic that they achieve significantly better data rates whilst utilizing the same bandwidth allocation as their respective 2/2.5G technologies

(this implied in the name of CDMA2000 1X—the 1X refers to 1 times the bandwidth requirement of cdmaOne)

The first phase of true 3G technologies includes Wideband Code Division Multiplexing (WCDMA) and CDMA2000 1XEV (where

EV stands for evolution) WCDMA uses the same control logical architecture as GSM/GPRS, while CDMA 2000 1XEV uses an enhanced cdmaOne logical architecture Either case provides a clear migration path

Note: CDMA2000 1XEV will first be available as a data only

overlay technology (CDMA2000 1XEV-DO) Later it will be available as a combined data/voice technology (CDMA2000 1XEV-DV)

The remainder of this course will be concerned only with the WCDMA/GSM implementation of the GPRS architecture

• Efficient use of radio resources

• A flexible service, with volume-based (or session based) billing

duration-• Fast set-up/access time

• Efficient transport of packets in the Radio Access Network

• Simultaneous circuit-mode and packet-mode services; existence without disturbance

co-• Connectivity to other external packet data networks, using IP The solution for IP communication between a UE and an ISP permits services beyond those that a voice-only network can provide, allowing customer segments beyond those using 2G solutions today Machine-to-machine communication is one example of possible services

The broadband air interface improves on service perception over 2.5G solutions for services such as multi-media messaging

The Ericsson WCDMA/GSM GPRS System supports open interfaces, for maximum flexibility

CHARACTERISTICS OF DATA COMMUNICATION

Before looking further into the WCDMA/GSM GPRS solution, it is worthwhile characterizing the data traffic that the system is

designed to carry

The term, data, is fairly ambiguous in telecommunications at

present In the 1970’s and 1980’s, there were relatively clear distinctions between the traffic that we called voice, and that which

we called data The term, data, was used to refer to the transport of services such as bank transaction information over circuit switched infrastructure

Data services may be transported over either Circuit-Switched (CS) networks or Packet-Switched (PS) networks (also called packet data networks) Each technology has its advantages and

disadvantages and may be more or less appropriate in a given situation, depending on the characteristics of the data source and the level of service required from the network

Data sources may be characterized by many parameters Two of

the more important characteristics are bandwidth requirement and

burstiness

Bandwidth requirement relates to the size of the resource

allocation required to carry the service; that is, the size of the data

pipe

Burstiness relates to how the data source changes its bandwidth requirement over time Data sources that change their bandwidth requirement over short time frames are said to be bursty

Non-bursty services are suitable for transmission over switched networks Bursty services are better suited to packet-switched networks

circuit-Figure 1-6 roughly characterizes common services in terms of burstiness and bandwidth consumption Burstiness and bandwidth requirements affect the type of communication chosen - circuit-switched or packet-switched

Email File Transfer

Note: pricing is an important factor when choosing the manner of communication for an application

Figure 1-7 shows the main difference between circuit switching and packet switching from a resource-utilization perspective While circuit switching has a connection open all-way full-time, packet switching includes connection partway i.e part-time

Fixed, dedicated, end-to-end resource allocation

On-demand, shared, point-to-point resource utilization

Connectionless Packet Switching

Circuit Switching

Fixed, dedicated, end-to-end resource allocation

On-demand, shared, point-to-point resource utilization

Connectionless Packet Switching Circuit Switching

Figure 1-7: Resource allocation for Circuit Switched and Connectionless Packet Switched networks

is very good

Circuit-switched communication is suitable for data traffic when one or more of the following cases apply:

• Constant bandwidth data flow

• Data is sensitive to even small connection delays

For example circuit-switched communication could be chosen for videoconferences because of its sensitivity to connection delays

The video conferencing in the implementation of 3G will be done using Circuit switched Data services

PACKET-SWITCHED COMMUNICATION

For packet-switched communication, the network delivers data packets as the need arises On the air interface, radio channels are shared as an access resource, between several UEs/MS’s

simultaneously For WCDMA Systems, if the data rate for a given user connection exceeds a certain threshold, the UE may

temporarily be assigned a dedicated resource on the air interface The UE will drop back to a shared resource when the source data rate is reduced

Address information is included with each packet to enable the packet to find its addressee Packet-switched communication is suitable for data traffic when one or more of the following cases apply:

• Data is sent in bursts

• Data is sensitive to errors

For example packet-switched communication should be chosen for telemetry applications and e-mail, the former because of its

sensitivity to errors and the latter because the data is sent in bursts (refer to Figure 1-6)

PACKET DATA APPLICATIONS

The WCDMA/GSM GPRS system supports end-users wishing to access the Internet and Intranets using a UMTS UE or GPRS MS

as the connecting device Some examples of user applications enabled by 3G are given below:

• Video Telephony and Video Conferencing

• Broadband Web Browsing and Multimedia Streaming; for example, video clips, news on demand and music

• Multimedia Messaging (voice mail with pictures)

• Location-based Services Additionally, all data services enabled by 2.5G technologies will also be available For example, some horizontal applications enabled by 2.5G are:

• E-mail

• Internet chats

• File transfer using the File Transfer Protocol (FTP)

• Point of sale (credit card readers)

• Database searches

• Two-way messaging Note: horizontal applications are defined as generic applications meeting broad communication needs In contrast, vertical applications are applications adapted to solve a specific company’s data communication requirements Examples of vertical

applications enable by cellular data services are:

• Field sales

• Bank applications

• Telemetry applications (vendor machines, power meter readers)

• Distribution system optimization (supply services, invoices)

• Dispatch services (police, courier, taxi, etc)

THE ROLE OF THE WCDMA/GSM GPRS NETWORK

Before studying the WCDMA/GSM GPRS network further, it is important to understand the role of the GPRS network in providing user connectivity

Unlike the Circuit Mode (CM) component of the WCDMA/GSM Systems network, which is capable of providing user-to-user connectivity, the Packet Mode component of the network is used to

provide access to:

• an Internet Service Provider (ISP)

• a private network such as a corporate intranet

• Other external Packet networks

At this point in time there is no such thing as a user-to-user data call… more on this later

It is instructive to compare GPRS with the more familiar scenario

of a dial-up modem access to the Internet (refer to Figure 1-8)

WCDMA RAN WCDMA RAN

ISP PSTN

Transmission Network

RADIUS MAIL

To Internet Modem

Home Computer

Twisted

(channelized)

ISP PSTN

Transmission Network

RADIUS MAIL

To Internet Modem

Home Computer

IP Backbone Network

RADIUS MAIL

To Gi

ISP GPRS

IP Backbone Network

RADIUS MAIL

To Gi

WCDMA RAN GSM BSS A-interface

The ISP’s Remote Access Server (RAS) answers the call and begins communication with the user’s modem to negotiate a data transfer speed and other parameters of the session Once

negotiation is complete, there exists a transparent communication

pipe directly between the user’s computer and the ISP’s network

Typically, the RAS will be configured to demand authentication and logon using a RADIUS server (Remote Authentication Dial In User Server) before a user is granted access to the Internet or their email At this stage, the user may also be given an IP address for use for the duration of the session (This is called dynamic IP address allocation and occurs when a user has not been allocated its

own static IP address; that is, the user borrows rather than owns an

IP address.)

The details of the above scenario are not really important for this course (although arguably should be known by anyone studying GPRS) What is important is the concept of two separate networks;

the ISDN/PSTN provides access to the ISP; the ISP provides access to the Internet and other IP-based services

So too it is with GPRS The GPRS network provides access to ISPs and corporate networks; the ISPs and corporate networks provide access to the Internet and other IP-based services The task

is inherently more complex with GPRS, due to the issue of Mobility Management, but the role is the same

It should also be noted that the above architecture does not preclude the possibility of the GPRS provider and the ISP being the same corporate entity… in fact, this scenario is much more likely than not, in which case the ISP function is often referred to as the

Service Network For horizontally integrated networks in 3G these

types of services are what form the Application layer of the Core Network

FEATURES OF THE WCDMA/GSM GPRS SYSTEM

Ericsson’s WCDMA/GSM GPRS system is an additional service to the WCDMA/GSM Circuit Switched System, and supports end-users who wish to access the Internet or a corporate LAN using a packet data UE/MS as the connecting device The UE/MS can consist of one Mobile Terminal (MT), which is a WCDMA/GSM access device (telephone), and one Terminal Equipment (TE), which is a computer that is connected to the MT Perhaps more typically, the UE/MS will be an MT and a TE integrated in one piece of equipment; for example, a mobile Personal Digital Assistant (PDA) When 2.5G was introduced the Mobile Station (MS) consisted of a MT and TE

GPRS data transfer is based on the Internet Protocol (IP) The packet data transmission is thus carried out on an end-to-end basis, including the air interface The WCDMA GPRS system uses packet switching air interface, according to the 3GPP UMTS standards Whereas GSM GPRS System uses packet switching air interface, according to ETSI GSM standards

Note: While the PM architecture supports the transfer of many

TCP/IP (Transmission Control Protocol / Internet Protocol)

user-services Additionally, it is worth noting the terminologies Packet

Mode and Circuit Mode are used throughout this chapter rather

than the more conventional Packet Switched and Circuit Switched

This is because, in the WCDMA Systems architecture, traditional circuit switched traffic is delivered over the top of a packet (or cell) switched architecture… it is no longer truly circuit switched The

GSM System would still be referred to as conventional Packet

Switched and Circuit Switched

A GPRS network can be seen as an integrated component of a WCDMA/GSM System network By introducing the GPRS system architecture, it is possible to attach, authenticate and handle subscriber and terminal data for both circuit-switched and packet-switched communication

When a message consisting of large data quantities is to be transferred, it is divided into several packets When these packets reach the addressee, they are reassembled to form the original message All the received packets are stored in data buffers

Data packets from the UEs/MS’s can use different radio channels for different packets during transmission

The UE/MS in the GPRS system can be used for packet-switched communication only, or used for both circuit-switched and packet-switched communication A dedicated packet data UE/MS can be used for packet-switched communication or as a stand-by for packet-switched communication attach A UE/MS for both circuit-switched and packet-switched communication can be used for either circuit-switched or packet-switched communication, or as a stand-by for incoming circuit-switched communication or for packet communication attach

THE GPRS SUPPORT NODES (GSN)

In order to provide the required functionality in GPRS, two types

of GPRS Support Node are required:

• The Serving GPRS Support Node (SGSN)

• The Gateway GPRS Support Node (GGSN) The Serving GSN (SGSN) acts as a user access point to the GPRS network implementing the principles of Connection Management (CM) and Mobility Management (MM) The GGSN acts as a gateway to the required external Packet networks such as ISP’s or Corporate Intranet’s (refer to Figure 1-9)

RNS 2

RNS 3

RNS 1 RNC 1 RNC 2 RNC 3

RNS 5

RNS 6

RNS 4 RNC 4 RNC 5 RNC 6

SGSN A

SGSN B

GGSN X

GGSN Y

ISP A

Corporate Intranet 1 Corporate Intranet 2

ISP B

ISP C

Corporate Intranet 3

WCDMA RAN

RNS 2

RNS 3

GSM 1 BSC 1 RNC 2 RNC 3

RNS 5

GSM 6

GSM 4 BSC 4 RNC 5 BSC 6

SGSN A

SGSN B

GGSN X

GGSN Y

ISP A

Corporate Intranet 1 Corporate Intranet 2

ISP B

ISP C

Corporate Intranet 3

Figure 1-9: GPRS Support Nodes

The involvement of a particular SGSN in a PS call for any given user is determined only on the basis of the user’s location within the WCDMA/GSM radio networks and the network’s topology (SGSN Service Area or SGSN Routing Area) For example, (with reference to Figure 1-9), if a user were located in the part of the

(BSC) number 1(that is, within Radio Network System 5 – RNS 5), then the user’s traffic would be channeled through SGSN B

For WCDMA Systems, if the same user were to move from RNS 5

to RNS 4 whilst in an active transfer, an inter-RNS handover would take place from Serving RNS (SRNS (5)) to Drift RNS (DRNS (4)) The user’s traffic would still be routed through SGSN B

If, however, the user were to move from RNS 4 to RNS 3, an SGSN handover would be initiated and the user’s traffic would be redirected through SGSN A from the reallocation of the already established GTP-C and GTP-U tunnel ( GTP is the tunneling protocol established at PDP Context activate.)

inter-For a PM Service, the user-selected ISP or Corporate LAN determines the participating GGSN If a user wanted to “surf the Web” using ISP A, then GGSN X would be involved in the PM Service provision If the same user wanted to access their work email on Corporate LAN 3, then GGSN Y acts as the gateway

Each of these external entities are identified with a unique Access Point Name (APN), which also provides a Quality Of Service (QoS) class to negotiate network resources

From the discussion so far, it should be evident that both an SGSN and a GGSN are required for each GPRS call It should also be evident that these nodes must relay user traffic from the RAN to the Core Network (SGSN) and from the Core Network to an external provider (GGSN)

Beyond their relaying functionality, the roles of the GSNs are described below

THE ROLE OF THE SGSN

The SGSN is the node responsible for Mobility Management in the WCDMA/GSM GPRS architecture Like its Circuit Mode

equivalent, the control layer for PM services must be aware of a user’s location within the WCDMA/GSM Radio network and must

deal with Location Updating as the user moves from one area to

another; the Home Location Register (HLR) must be informed of the user’s current location

The SGSN communicates with the HLR during location updating

as well as with the User Equipment (UE) for general Mobility Management tasks

The SGSN is also responsible for connection / session management In Ericsson’s implementation, only the UE/MS may

initiate a PM connection and does so by sending a Setup message

to the SGSN In the GSM system implementation the BSC is ordered to allocate GPRS resources to be used by the MS For WCDMA systems the SGSN is then responsible for requesting a

Radio Access Bearer from the Radio Access Network (specifically,

the RNC), as well as locating and establishing a connection to the appropriate GGSN Part of this procedure involves authenticating users, participating in encryption parameter exchange and checking requested services against subscription data

The SGSN is also responsible for creation of Charging Data Records relating to the usage of the air interface This now incorporates volume based charging not the traditional time based charging As we are not tying up a dedicated resource for the duration of a “ Packet switched call”

ROLE OF THE GGSN

Like the SGSN, the Gateway GPRS Support Node (GGSN) is a primary component in GPRS network provisioning The GGSN provides:

• The interface toward the external IP packet networks The GGSN therefore contains access functionality that interfaces with external ISP (Internet Service Provider) functions like routers and RADIUS (Remote Access Dial-In User Service) servers, which are used for security purposes From the external

IP network’s point of view, the GGSN acts as a router for the

IP addresses of all subscribers served by the GPRS network The GGSN thus exchanges routing information with the external network

• GPRS session management, communications setup toward external network

• Functionality for associating the subscribers with the right SGSN

• The GGSN provides support of routing protocols such as RIP and OSPF to dynamically adjust routing in their network (internal and external) in abnormal circumstances

the GGSN and the SGSN collect billing information on usage

of the GPRS network resources

WCDMA/GSM GPRS SYSTEM ARCHTIECTURE

The Figure below covers the various Network elements of both the GSM System and the WCDMA System

Network architecture

BSC

GMSC MSC/VLR

Gp

HLR AUC SMS-IWMSC

Iu

Iur

Abis

PCU

BTS - Base Transceiver Station

BSC - Base Station Controller

PCU - Packet Control Unit

MSC - Mobile Switching Centre

HLR - Home Location Register

SGSN - Serving GPRS Support Node GGSN - Gateway GPRS Support Node OSS - Operating Sub System PXM - Packet eXchange Manager NTP - Network Time Protocol BGw - Billing Gateway RNC - Radio Network Controller

Traffic & Signalling

Signalling

Uu

Figure 1- 10: WCDMA/GSM Network architecture

The following explanations are to explain the roles of some Network elements mentioned above

OTHER WCDMA/GSM GPRS SYSTEM COMPONENTS

WCDMA UE DEFINITIONS

TERMINAL EQUIPMENT (TE)

The Terminal Equipment is the data terminal on which the end-user works The TE acts as the sender and receiver of end-user packet data For example, the TE could be a laptop computer or a PDA

The WCDMA GPRS system provides IP connectivity between the

TE and an Internet Service Provider or Corporate LAN (Local Area Network) connected to the GPRS system

From the TE point of view, you could compare the Mobile Terminal to a modem, connecting the TE to the GPRS system

MOBILE TERMINAL (MT)

The Mobile Terminal is a WCDMA interface device that communicates locally with a TE and over the air interface with a Node B (RBS 3000) The MT must be equipped with software for GPRS functionality when used in conjunction with the GPRS system The MT is associated with a WCDMA subscriber The MT establishes a link to an SGSN and interacts with the Radio Network Controller to negotiate radio resource allocation The IP connection

is static from the TE point of view; that is, the TE does not know it

is mobile and retains its assigned IP address until the MT performs

a PDP Context deactivation

USER EQUIPMENT (UE)

As described previously in the “Features” section in chapter one, the combination of a TE and an MT is a UE Depending on the UE and the network capabilities, GPRS UEs can operate in three different modes:

• PS/CS mode of operation: The UE is attached to both the PS domain and CS domain, and the UE is capable of simultaneously operating PS services and CS services

However, this does not prevent CS-like services to be offered over the PS domain (for example, Voice over IP—VoIP)

• CS mode of operation: The UE is attached to the CS domain only and may only operate services of the CS domain However, this does not prevent PS-like service to be offered over the CS domain (for example, circuit switched video conferencing) The CS mode of operation is outside the scope

of this course

GSM MS DEFINITIONS

TERMINAL EQUIPMENT (TE)

TE is the computer terminal on which the end-user works This is the component used for the GPRS system to transmit and receive end-user packet data For example, the TE can be a laptop

computer or a palm device or a specific equipment as Ericsson MC218 MC218 is equipped with WAP-browser and it works with all Ericsson MSs via Infrared

MOBILE TERMINAL (MT)

The MT performs GPRS functionalities The MT establishes a logical link to an SGSN, it performs location updating and user data transfer on the air interface

The GPRS network provides IP connectivity between the TE and the Internet or Corporate network From the TE point of view, you can compare the Mobile Terminal to a modem, connecting the TE

GPRS MSs can operate in three different modes:

• Class A, it supports simultaneous circuit-switched and switched traffic

packet-• Class B, it supports circuit-switched or packet-switched traffic, but does not maintain both kinds of traffic simultaneously

• Class C, it works either as a packet-switched or circuit-switched terminal

In addition, « MS Classmark » specifies MS capabilities such as:

• RF power capability (max power in transmission)

• SMS MT capability (yes or no)

• Frequency capability (900/1800 or/and 1900)

• Multislot downlink+uplink capability (for instance, an MS 3+1

it works either as a packet-switched or circuit-switched terminal.

Figure 1- 12: GPRS Mobile Terminal (1)

In addition, « MS Classmark » specifies mobile capabilities such as:

- RF power capability (max power in transmission)

- SMS MT capability (yes or no)

- Frequency capability (900/1800 or/and 1900)

- Multislot downlink+uplink capability (3+1, 2+1 …etc)

Figure 1- 13: GPRS Mobile Terminal (2)

The GSM GPRS System has three modes of operation These are explained below:

• PS/CS mode of operation: The MS is attached to both the PS domain and CS domain, and the MS is capable of simultaneously operating PS services and CS services

• PS mode of operation: The MS is attached to the PS domain only and may only operate services of the PS domain However, this does not prevent CS-like services to be offered over the PS domain

• CS mode of operation: The MS is attached to the CS domain only and may only operate services of the CS domain However, this does not prevent PS-like service to be offered over the CS domain like Circuit switched data calls

BASE STATION SYSTEM (BSS)

The Base Station System (BSS) consists of a Base Station Controller (BSC) and a Base Transceiver Station (BTS) relating to the implementation of GSM Systems

The BTS is the radio equipment that transmits and receives information over the air to let the BSC communicate with MSs in the BSC’s service area A group of BTSs is controlled by a BSC

The BTS must contain GPRS-specific software

The BSC provides all radio-related functions The BSC can set up, supervise, and disconnect circuit-switched and packet-switched calls It is a high capacity switch that provides functions, including handover, cell configuration data, and channel assignment The BSC must be equipped with GPRS hardware and software when used for GPRS One or several BSCs are served by an MSC, and a number of BSCs is served by an SGSN

The BTS separates the MS-originated circuit-switched calls from packet data communication, before the BSC forwards CS calls to the MSC/VLR, and PS data to the SGSN

Standard GSM protocols are used with the BSC to achieve the desired compatibility

RADIO NETWORK SYSTEM (RNS)

A Radio Network System (RNS) is a subset of the WCDMA Radio Access Network (WCDMA RAN) that consists of a Radio

Network Controller (RNC) and many Node Bs

The RNS that a UE is attached through is referred to as the Serving RNS (SRNS)

A Node B is the radio equipment that transmits and receives information over the air interface allowing the RNC (and SGSN) to communicate with UEs A group of Node Bs is controlled by an RNC The Ericsson Node B product is referred to as an RBS3000 and is based upon the Cello Packet Platform (CPP)

The RNC controls all radio-related functions The RNC can set up, supervise and disconnect circuit-switched and packet-switched calls It is a high capacity switch that provides functions including handover, cell configuration data, interface configuration data, and channel assignment The Ericsson RNC product is also based upon the Cello Packet Platform One or more RNCs are served by an SGSN (and MSC for circuit mode calls)

The RNC separates the UE-originated circuit-mode calls from packet-mode communication, before forwarding CM calls to the MSC/VLR (combined architecture) or MGW (split architecture), and PM data to the SGSN

MOBILE SERVICES SWITCHING CENTER (MSC)

The Mobile services Switching Center (MSC) performs the telephony control functions for circuit-mode traffic It is reused in both the GSM System and WCDMA System implementation It controls calls to and from other telephony and data systems, such

as the Public Switched Telephone Network (PSTN), Integrated Services Digital Network (ISDN), Public Land Mobile Network (PLMN), Public Data Networks, and possibly some private networks

HOME LOCATION REGISTER (HLR)

The Home Location Register (HLR) is the database that holds subscription information for every person who has bought a