Gprs

GPRS Overview Manual GSM Network Release 9.0

401–380–061 Issue RFA Version May 2000

Copyright © 2000 Lucent Technologies. All Rights Reserved.

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Issue RFA Version

May 2000

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Contents

About this information product

Reason for reissue

xi

Safety labels

xi

Conventions used

xi

Related documentation

xi

.....................................................................................................................................................................................................................................

1

Introduction

Overview

1-1

What is General Packet Radio Service (GPRS) ?

1-2

Development/History

1-5

The Services GPRS Provides

1-7

The Benefits GPRS Provides (Compared to Circuit Switched Data)

1-8

.....................................................................................................................................................................................................................................

2

System Overview

Overview

2-1

GPRS Network Architecture

2-2

Mobile Station

2-4

The GPRS Backbone System (GBS)

2-16

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C O N T E N T S i i i

New Network Area

2-18

New Network Elements - Functional Entities

2-19

Frame Relay

2-24

New Network Interfaces

2-28

GSM Elements Affected by GPRS

2-30

Base Station Subsystem

2-32

GPRS introduction to the Base Transceiver Station (BTS)

2-33

GPRS Introduction to the BCF-2000

2-34

GPRS Input for the OMC-2000 part

2-38

Network Switching Subsystem (NSS) and GPRS

2-47

The TCP/IP Suite

2-51

IP addressing

2-54

Address Resolution

2-57

Internet Protocol (IP)

2-59

Transmission Control Protocol (TCP)

2-62

User Datagram Protocol (UDP)

2-64

TCP/IP Example

2-65

.....................................................................................................................................................................................................................................

3

Interfaces

Overview

3-1

GSM System Interfaces

3-2

GPRS System Interfaces

3-4

.....................................................................................................................................................................................................................................

4

GPRS Signalling and Transmission Protocols

Overview

4-1

....................................................................................................................................................................................................................................

C O N T E N T S i v

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The GPRS Signalling Plane

4-2

The GPRS Transmission Plane

4-4

GGSN Protocols

4-6

SGSN Protocols

4-9

BSS Protocols

4-18

GPRS MS Protocols

4-24

The GPRS Air Interface

4-25

GPRS Logical Channels

4-26

Mapping of packet data logical channels onto physical channels

4-28

GPRS MS

4-34

.....................................................................................................................................................................................................................................

5

GPRS Procedures

Overview

5-1

Mobility Management

5-2

GPRS Attach Procedure

5-5

Detach Procedures

5-10

Routing Area Update

5-15

Combined RA / LA Update Procedure

5-21

PDP Context Activation Procedure

5-29

.....................................................................................................................................................................................................................................

6

Call Management

Overview

6-1

GPRS - BSS Mobile Originated Packet Transfer

6-2

GPRS - BSS Mobile Terminated Packet Transfer

6-4

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7

Radio Resource Management

Overview

7-1

PCU Functionality

7-2

Multislotting Operation Effects

7-3

Channel Coding Schemes

7-5

.....................................................................................................................................................................................................................................

8

Future Enhancements

Overview

8-1

Enhanced Data rates for GSM Evolution (EDGE)

8-2

.....................................................................................................................................................................................................................................

GL

Glossary

GL-1

.....................................................................................................................................................................................................................................

IN

Index

IN-1

....................................................................................................................................................................................................................................

C O N T E N T S v i

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List of Figures

1

Introduction

1-1

GSM System Architecture

1-2

1-2

GPRS System Architecture

1-3

.....................................................................................................................................................................................................................................

2

System Overview

2-1

GSM System Architecture

2-3

2-2

The Principal GPRS Network Architecture

2-16

2-3

Architecture Overview

2-17

2-4

Location and Routing Areas

2-18

2-5

Placement of PCU within the Lucent BSS

2-21

2-6

Frame Relay Network

2-24

2-7

Frame Relay Structure

2-26

2-8

Frame Relay Network

2-27

2-9

New GPRS Interfaces

2-28

2-10

Shared Network Resources

2-30

2-11

rPCU Integration into the BCF-2000

2-34

2-12

Distribution of functionality

2-35

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F I G U R E S v i i

2-13

GPRS - OMC solutions

2-37

2-14

GPRS Impact on NSS

2-47

2-15

TCP/IP suite

2-51

2-16

IP Addressing Scheme

2-54

2-17

Router Address

2-55

2-18

Message Exchange Process

2-58

2-19

IP Header Format

2-59

2-20

TCP Header

2-62

2-21

UDP Header Format

2-64

2-22

Message Flow

2-65

.....................................................................................................................................................................................................................................

3

Interfaces

3-1

GSM Interfaces

3-2

3-2

Gb Interface Protocol Stack

3-4

.....................................................................................................................................................................................................................................

4

GPRS Signalling and Transmission Protocols

4-1

Map Signalling

4-2

4-2

BSSAP Signalling

4-3

4-3

Transmission Plane

4-4

4-4

LLC Frame Numberf

4-6

4-5

GGSN Activity

4-8

4-6

Multiplexing different protocols

4-9

4-7

SNDCP Service Model

4-11

4-8

SNDCP Header

4-12

4-9

LLC FrameFormat

4-13

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F I G U R E S v i i i

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4-10

llc_address_field

4-13

4-11

Control Field

4-14

4-12

BSSGP Service Model

4-16

4-13

SGSN Activity

4-17

4-14

RLC/MAC Control Block

4-18

4-15

Uplink RLC Data Block

4-19

4-16

Downlink RLC Data Block

4-19

4-17

Uplink Mac Header Format

4-20

4-18

Downlink Mac Header Format

4-21

4-19

Air Interface

4-22

4-20

BSS Activity

4-23

4-21

MS Activity

4-24

4-22

Logical channels for GPRS

4-25

4-23

52 Multiframe

4-28

4-24

Time-Slot Configuration

4-29

.....................................................................................................................................................................................................................................

5

GPRS Procedures

5-1

GPRS Attach/Detach States

5-3

5-2

GPRS GMM/SM Control Plane

5-4

.....................................................................................................................................................................................................................................

6

Call Management

6-1

GPRS Mobile Originated Packet Transfer

6-3

6-2

GPRS Mobile Terminated Packet Transfer

6-4

.....................................................................................................................................................................................................................................

7

Radio Resource Management

7-1

Operation Effects

7-4

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F I G U R E S i x

7-2

Segmentation

7-4

7-3

Channel Coding Schemes

7-5

....................................................................................................................................................................................................................................

F I G U R E S x

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About this information product

...............................................................................................................................................................................................................................................................

Purpose

General Packet Radio Services (GPRS) has been specified to optimise the way data is carried over GSM networks with new requirements for features, network capacity and bearer services. The technology allows GSM license holders to share physical resources on a dynamic, flexable basis between packet data services and other GSM services. This GPRS Overview manual presents a detailed description of the GPRS system.

Reason for reissue

Safety labels Conventions used Related documentation

This document has been updated to increase the overall level of information provided to users. There are no safety labels associated with this information product There are no special conventions used in this information product The following documents can provide additional useful information: •

GPRS Introduction Procedure (401–380–060)

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1

Introduction

Overview .................................................................................................................................................................................................................................... Purpose

General Packet Radio Services (GPRS) has been specified to optimise the way data is carried over GSM networks with new requirements for features, network capacity and bearer services. This chapter gives an overview of a General Packet Radio Services (GPRS) network and other Data Networks in Europe and throughout the world. This section also lists the history of GPRS, the services provided & the main benefits.

Contents

This chapter contains the following information. What is General Packet Radio Service (GPRS) ?

1-2

Development/History

1-5

The Services GPRS Provides

1-7

The Benefits GPRS Provides (Compared to Circuit Switched Data)

1-8

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1-1

Introduction

What is General Packet Radio Service (GPRS) ? .................................................................................................................................................................................................................................... Introduction

GPRS is a data service for GSM, the European standard digital cellular service. GPRS is a packet-switched mobile data service, it is a wireless packet based network. GPRS, further enhancing GSM networks to carry data, is also an important component in the GSM evolution entitled GSM+. GPRS enables high-speed mobile data usage. GPRS provides a packet data service for GSM where Time-Slots (TS) on the air interface can be assigned to GPRS over which the packet data from several mobile stations (MS) is multiplexed. GPRS, further enhancing GSM networks to carry data. Figure 1-1 GSM System Architecture

The GSM system architecture includes, the air interface (Um), the Abis and the A Interface and others mentioned later in this document. The GSM functionality is between the Mobile station (MS), the Base Station Subsystem (BSS) and the Mobile Switching Centre (MSC). The BSS includes two types of elements: the Base Transceiver Station (BTS) which handles the radio interfaces towards the MS and the Base Station Controller (BSC) which manages the radio resource and controls handovers. A BSC can manage several BTSs. Through the MSC, the GSM system communicates to other networks such as the Public Switched Telephone Network (PSTN), Integrated Services Digital Network (ISDN), Circuit Switched Public Data Network (CSPDN) and Packet Switched Public Data Network (PSPDN). GSM specifies 4 databases, the Home Location Register (HLR), the Visitor

....................................................................................................................................................................................................................................

1-2

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What is General Packet Radio Service (GPRS) ?

Introduction

Location Register (VLR) and the Authentication Centre (AUC) and Equipment Identity Register (EIR). The ETSI Standard introduces two new elements, the Serving GPRS Support Node (SGSN) and the Gateway GPRS Support Node (GGSN) (Shown in the diagram below as shadowed objects) are introduced to create an end-to-end packet transfer mode. Figure 1-2 GPRS System Architecture

The HLR is enhanced with GPRS subscriber data and routing information. Two services are provided; •

Point-To-Point (PTP)

•

Point-To-Multipoint (PTM) (not yet specified by the Standards)

Independent packet routing and transfer within the Public Land Mobile Network (PLMN) is supported by a new logical network node called the GPRS Support Node (GSN). The Gateway GPRS Support Node (GGSN) acts as a logical interface to external packet data networks. The Serving GPRS Support Node (SGSN) is responsible for the delivery of packets to the MSs within its service area. Within the GPRS network, Protocol Data Units (PDUs) are encapsulated at the originating GSN and decapsulated at the destination GSN. In between the GSNs, Internet Protocol (IP) is used as the backbone to transfer PDUs. This whole process is defined as tunnelling in GPRS. The GGSN also maintains routing information used to tunnel the PDUs to the SGSN that is currently serving the MS. All GPRS user related data needed by the SGSN to perform the routing and data transfer functionality is stored within the HLR.

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What is General Packet Radio Service (GPRS) ?

Introduction

The European Telecommunications Standards Institute (ETSI) has specified GPRS as an overlay to the existing GSM network to provide packet data services. In order to operate a GPRS service over a GSM network, new functionality has to be introduced into existing GSM Network Elements and new Networks elements have to be integrated into the existing operators GSM networks. The Base Station Subsystem (BSS) of GSM is upgraded to support GPRS over the air interface. The BSS works with the GPRS Backbone System (GBS) to provide GPRS service in a similar manner to its interaction with the Switching subsystem for the circuit switched services. The GPRS backbone system manages the GPRS sessions set up between the mobile terminal and the network, by providing functions such as admission control, Mobility Management and Session Management. Subscriber and equipment information is shared between GPRS and the switched functions of GSM by the use of a common HLR and the co-ordination of data between the VLR and the GPRS support nodes of the GBS. The GBS is comprised of two new network elements, the Serving GPRS Support Node (SGSN) and the Gateway GPRS Support Node (GGSN). GPRS will be the Industry Standard interface for mobile packet systems. The maximum data rate is 171.2 kbps gross rate.

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1-4

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Introduction

Development/History .................................................................................................................................................................................................................................... Development

Over the last ten years, there have been numerous predictions that Mobile Data is about to explode in the marketplace and indeed, most of the data trends confirm this. With the rapidly advancing technology it does appear that mobile data will become a widespread reality, but perhaps not quite as quickly as first thought. Until now, the only GSM data services available have been the Short Message Service (SMS) and low speed bearer services for fax and data transmission at 9.6kbps. The general take up of these services has been slow and only a very small percentage of mobile users (estimated at 3-5%) are enabled for data services. The current data rate for GSM is 9.6 kbps. To maintain competitive edge, modifications and enhancements will need to be made. The proposed enhancements will mean an increase in the amount of user data to be carried across the network. These have included the High Speed Circuit Switched Data (HSCD) which has data rates up to 57.6 kbps and General Packet Radio Service (GPRS) which has up to 171.2 kbps.

History

The following section lists the main development dates associated with GPRS. •

GPRS has been established at the European Telecommunications Standards Institute (ETSI) in 1994

•

ETSI R97 was the first issue of the GPRS standards

History of GPRS Date

Event

1969

Advanced Research Projects Agency of the U.S. Department of Defense (ARPA) Contract award

1983

APPnet moves to TCIP/IP

1987

National Science Foundation’s TCIP/IP based NETwork (NSFnet) funded to provide regional sites & backbone

1991

Gopher is introduced

1991

Commercial Internet Exchange CCIX7 set up for commercial traffic

1992

First Cellular Digital Packet Data (CDPD) specifications appear

1992

World-wide web is introduced

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Development/History

Introduction

Date

Event

1993

Wireless Data Cellular Digital Packet Data (CDPD) forum started

1994

GPRS introduced to ETSI subcommittees & first commercial CDPP networks

1998

GPRS Phase 1 standards published

....................................................................................................................................................................................................................................

1-6

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Introduction

The Services GPRS Provides .................................................................................................................................................................................................................................... Introduction

The services provided by GPRS are extensive. GPRS is ideal for sending & receiving bursty data via the Mobile Station (MS). This enables the user to send information via e-mail and also have access to Mobile Internet/Intranet Services, like Emerging services, and WWW access. It could also be used for the following: •

E-Commerce, Credit Card checks, Ticketing

•

Vertical Market Applications These include: -

Transportation: vehicle load monitoring

-

Emergency Services: command & control

-

Field Service job dispatch, issue & control

-

Utilities: meter reading

•

Image Transmission - Low resolution, Sketches & Images

•

Telemetry - Logging & Slow Update Tele-control such as Tele-Traffic control, Automatic Vehicle location (AVL)

•

Location Services, LCS (ETSI Specified)

•

Point-To-Point (PTP) and Point-To-Multipoint (PTM) packet services Vertical Market Applications (will be defined later)

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Introduction

The Benefits GPRS Provides (Compared to Circuit Switched Data) .................................................................................................................................................................................................................................... Introduction

The data transferred is encapsulated into short packets with a header containing the origin and destination address. The packets are then sent individually over the transmission network. Packets originating from one user may take different routes through the network to the receiver. Packets originating from many users can be interleaved, so that the transmission capacity is shared. No pre-set time-slots are used. Instead, network capacity is allocated when needed and released when not needed. This is called statistical multiplexing, in contrast to static time division multiplexing. In static time division multiplexing, time-slots are reserved for one user for the length of the connection regardless of whether it is used or not, as with PCM lines and GSM voice and circuit switched data. GPRS upgrades GSM data services to be more compatible with LANs, WANs and the Internet. GPRS uses radio resources only when there is data to be sent or received, and so is well adapted to the very bursty nature of data applications. Furthermore, it provides fast connectivity and high throughput. While the current GSM system was originally designed for voice sessions, the main objective of GPRS is to offer access to standard data networks such as TCP/IP. These networks consider GPRS to be normal sub-network. The current GSM system operates in a circuit-switched ’end-to-end’ transmission mode, in which circuits are reserved. GPRS offers a number of benefits to the operator and end user. The operator benefits of GPRS are: •

Optimal support for packet switched traffic. The operator can join the Internet boom with true IP connectivity

•

The possibility to offer new, innovative services. New user segments such as telemetry of electric meters will become accessible to the operator

•

The ability to profit with idle capacity that would otherwise be used only to cover peak-hour traffic. Many users can use one time-slot simultaneously

•

Using GPRS as a ’radar screen’ to pinpoint where potential EDGE or 3rd generation rollout could be started

•

It is economical to the user as it supports multiple users on the same channel(s)

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The Benefits GPRS Provides (Compared to Circuit Switched Data)

Introduction

•

Profitable to the operator (value added service, efficient use of channels)

•

Packet based applications are given wide mobile support

•

Reuse of existing network infrastructure

The end user benefits are: •

Optimal support for packet switched traffic. The operator can join the Internet boom with true IP connectivity

•

The possibility to offer new, innovative services. New market segments such as telemetry of electric meters will become accessible to the operator

•

The ability to profit with idle capacity that would otherwise be used only to cover peak-hour traffic. Multiple users can use one time-slot simultaneously

•

Using GPRS as a ’radar screen’ to pinpoint where potential EDGE or 3rd generation rollout could be started

•

It is economical to the operator as it supports multiple users on the same channel(s)

•

Profitable to the operator (value added service, efficient use of channels)

•

Packet based applications are given wide mobile support

•

Reuse of existing network infrastructure

•

Due to the wide GSM coverage, GPRS will offer true global mass market wireless access to the Internet and other packet-based networks

•

Applications will be user-friendly with a seamless on-line network connection independent of time and place. All existing TCP/IP-based applications can be used with GPRS as if they were connected to a LAN

•

GPRS offers very fast session set-up and the end user can stay on-line for long periods paying only for the capacity used (depending on the billing model)

•

GPRS makes using existing applications easier and enables new applications

•

High bit rates in peak-hour, and uncompressed data rates of 171.2kbps

•

The existing e-mail subscriber base in the Internet gives even the very first GPRS user a large group of ’B-subscribers’ to communicate with

•

Packet based applications are given wide mobile support

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2

System Overview

Overview .................................................................................................................................................................................................................................... Purpose

Contents

This chapter describes the basic layout of the GPRS system architecture in terms of the major entities involved. This chapter covers the following topics: GPRS Network Architecture

2-2

New Network Area

2-18

New Network Elements - Functional Entities

2-19

Frame Relay

2-24

New Network Interfaces

2-28

GSM Elements Affected by GPRS

2-30

The TCP/IP Suite

2-51

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System Overview

GPRS Network Architecture .................................................................................................................................................................................................................................... Overview

GPRS is an overlay on the existing GSM structure, which means that an existing GSM network is used with added new GPRS network entities. The new GPRS network entities are, the Gateway GPRS Support Node (GGSN), the Serving GPRS Support Node (GGSN) and additional functionality in the BSS. GPRS will require modifications and enhancements to the existing GSM network architecture to enable it to support both packet and switched data.

GSM System Entities

The GSM system entities represent groupings of specific wireless functionality. A Public Land Mobile Network (PLMN) includes the following system entities: •

Mobile Station (MS)

•

Base Station Subsystem (BSS) The BSS consists of the following: -

Base Transceiver Station (BTS)

-

Base Station Controller (BSC)

•

Operation and Maintenance Centre (OMC)

•

Mobile - services Switching Centre (MSC)

•

Home Location Register (HLR)

•

Visitor Location Register (VLR

•

Equipment Identity Register (EIR)

•

Authentication Centre (AUC)

....................................................................................................................................................................................................................................

2-2

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GPRS Network Architecture

System Overview

•

Other Network Elements

Figure 2-1 GSM System Architecture

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System Overview

Mobile Station .................................................................................................................................................................................................................................... Overview

The Mobile Station (MS) represents the terminal equipment used by the wireless subscriber supported by the GSM wireless system. The MS consists of two entities, each with its own identity: •

Subscriber Identity Module (SIM)

•

Mobile Equipment (ME)

The SIM may be a removable module. A subscriber with an appropriate SIM can access the system using various mobile equipment. The equipment identity is not linked to a particular subscriber. Validity checks made on the MS equipment are performed independently of the authentication checks made on the MS subscriber information. Functions of a Mobile Station

Types of Mobile Stations:

The Mobile Station performs the following: •

Radio transmission termination

•

Radio channel management

•

Speech encoding/decoding

•

Radio link error protection

•

Flow control of data

•

Rate adaptation of user data to the radio link

•

Mobility management

•

Performance measurements of radio link

•

Call Control

Mobile stations can come in different power classes, which define the maximum RF power level that the unit can transmit. For GSM 900 there are five power classes, for GSM 1800 there are three power classes. The mobile station output power is specified in the GSM Specifications 05.05. Power Classes Class

Max RF Power (Watts) GSM 900

GSM 1800

I

–

1

II

8

0.25

III

5

4

IV

2

–

....................................................................................................................................................................................................................................

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Mobile Station

System Overview

Class

Max RF Power (Watts)

V

0.8

–

Vehicular and portable units can be either class I or II, while Handheld units can be class III, IV or V. Typical vehicular and portable stations are of power class II or III while the typical handheld is of power class IV. Lucent Base Station Subsystem

Functions of the Base Transceiver Station (BTS)

The Base Station System consists of: •

Base Transceiver Station (BTS-2000)

•

Base Station Controller (BSC) The BSS consists of: -

Base Station Controller Frame (BCF-2000)

-

Speech Transcoding Frame (STF-2000)

Signalling data intended for the mobile station is inserted in the correct signalling channel on the air interface. This signalling and traffic data is protected against transmission errors, interleaved, and encrypted to protect against unauthorised eavesdropping. Signal and protocol processing covers the following areas: •

Channel coding

•

Interleaving

•

Encryption and Decryption

•

Burst Formation

•

Delay Correction

•

Modulation

•

Demodulation

Channel Coding

Channel coding tasks include coding and decoding of voice data, data channels, and signalling data. Since the data to be transmitted can sometimes become partially corrupted by the fading effect, the data must be appropriately protected. Additional check bits are generated for this purpose, which make it possible to detect transmission errors and to reconstruct the original data to a certain degree.

Encryption and Decryption

To prevent unauthorised eavesdropping of the signalling information and user information (voice and data), this data can be encrypted. Correct identification of the mobile station is a prerequisite for transferring encryption parameters. The BTS-2000 possesses two different encryption algorithms. Different parameters are used for each connection. The encryption parameters are determined by the

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Mobile Station

System Overview

Authentication Centre (AUC) and are transmitted via the Mobile-services Switching Centre (MSC) to the BTS-2000. Interleaving

Burst Formation

The sub-blocks of a data block created by channel coding are distributed over several TDMA frames (interleaving). Because of the interleaving, only isolated sub-blocks are affected by interference variables. This increases the overall interference resistivity of the channels, since minor errors can be corrected with the aid of the check bits inserted during channel coding. After they have been received, the interleaved sub-blocks are recomposed into complete data blocks, checked for errors, and corrected, if necessary. The interleaved and encrypted data is packed into bursts. A burst is a time segment of the radio frequency carrier that is the same length as a time slot and therefore constitutes the physical content of a time slot. The burst types are listed below: •

Normal Burst - Transmission of voice and signalling data

•

Dummy Burst - Sent in unoccupied time slots on the BCCH carrier

•

Access Burst - Request for a connection, location update, and responses to a paging cell

•

Synchronisation Burst - Synchronises the mobile station to the frame clock and the bit clock of the BTS-2000

•

Frequency Correction Burst - Corrects the transmit and receive frequencies of the mobile station

Delay Correction

Because of the varying distances between mobile radio stations, the radio signals may have different delay times. For this reason, controls are necessary to equalise these delays. For an existing connection, the group delay is constantly changing because of the movement of the mobile station. For this reason, deviations from the correct time are continuously measured at the BTS-2000, and the correction parameters are automatically inserted and transmitted to the mobile station.

Modulation

The modulator has the task of converting the serial data stream into a GMSK-modulated radio frequency signal.

Demodulation

In the receive direction, the incoming signal is filtered, demodulated, and amplified. A signal proportional to the receive field strength is generated in parallel to this signal recovery.

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Mobile Station

Call Handling Functions

System Overview

Call handling functions include all the functions that are required for setting up, maintaining, and releasing connections. These functions are controlled by the BSC. The BTS-2000 is the executing element in the GSM system, in this case. The following call handling functions are carried out at the BTS-2000: •

Radio channel management

•

Detection of loss of connection

•

Connection control measurements

•

Control and supervision of the STF-2000

Radio Channel Management

The BSC informs the BTS-2000 of all relevant parameters, such channel type, carrier frequency, time slot number, channel coding, and rate adaption. The BSC determines what is to be sent over the signalling channels. The BTS-2000 must send the messages associated to the various channels at the right times in accord with its channel configuration. Only the correction parameters for the delay are inserted automatically by the BTS-2000 itself.

Detection of Loss of Connection

The BTS-2000 is equipped with a counter that automatically detects the loss of a radio connection. In the event that several SACCH messages in sequence cannot be decoded, this situation is reported to the BSC. The BSC sends the command to increase the BTS-2000 and mobile station transmit power. If SACCH messages still cannot be decoded, the connection is considered broken and the BTS-2000 deactivates the radio channel and the BSC releases the connection.

Connection Control Measurements

The BTS-2000 conducts internally different measurements on each voice/data channel for monitoring the transmission quality. These include the following measurements: •

Receive field strength measurement (taken over one SACCH period)

•

Receive field strength measurement (taken over a subset of the TDMA frames)

•

Signal quality measurement (bit error rate; taken over one SACCH period)

•

Signal quality measurement (bit error rate; taken over one subset of the TDMA frames with Discontinuous Transmission) Interference levels are measured for all unused channels and the measurements are forwarded to the BSC. The obtained values are used to determine the channel allocation.

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Mobile Station

Control and Supervision of the STF-2000

Functions for Transmission Quality Improvement

System Overview

The BTS-2000 performs the synchronisation between the STF-2000 and the BTS-2000 and also controls the functions of the STF-2000. This operation is performed by means of the appropriate control bits included in the TRAU-Frames exchanged between the BTS-2000 and the STF-2000. The following BTS-2000 functions improve the quality of transmission to the mobile station: •

Frequency Hopping

•

Antenna Diversity

•

Transmit Power Control

Frequency Hopping

Frequency hopping could equalise the relation of the fading effects to the frequency. Fading effects are dependent on location and frequency. Because the frequency is constantly changing, the fading effects are evened out.

Antenna Diversity

The antenna diversity function serves to improve the reception quality. It is enabled by installing two spatially separated reception antennas for each cell, each of which is connected to its own transmission path in the transmitter.

Transmit Power Control

BTS-2000 transmit power control is optional in the GSM system and can be activated and deactivated by the OMC-2000 (operation and Maintenance Centre). The aim of transmit power control is to use a low transmit power that will enable problem-free high-quality transmission of voice/data.

Functions of the Base Station Controller Frame (BCF-2000)

The BCF-2000 is the central control module in the GSM network. It is connected in the transmission paths between the BTS-2000 and the STF-2000. A BCF-2000 can manage a number of BTSs through the Abis-links. It is connected to the STF-2000 via an M-link. The functions of the BCF-2000 are performed either autonomously or under control of the OMC-2000 and are related to: •

Call handling

•

Operations and Maintenance

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Mobile Station

System Overview

Call handling functions:

•

Management of the BTS-2000 radio terminals and the assigned radio frequencies

•

Establishing and holding supervising calls for all subordinate BTSs

•

Handling of signalling connections to the mobile stations (LAPD à Link Access Procedure on the D-Channel) and RIL3 (Radio Interface Layer-3) and to the MSC (CCS7 à Common Channel Signalling No. 7) and BSSAP (Base Station System Application Part)

•

Switching of speech data between the Abis-links and the M-links

•

RF power control and handover management

•

Configuration Management to control the various BSS elements

•

Fault Management to detect, localise and correct system faults

•

Performance Management to control the measurements initiated by the OMC in order to obtain statistical data (e.g. for planning and analysis). Statistical data can be gathered by recording information in connection with special events, and reading special event counters. Performance Management gathers the requested data and passes it on to the OMC at specified intervals

•

Software Loading used to load the software from the OMC-2000 (or locally from floppy disk) onto the hard disk of the BCF, as well as to the memory of the other network elements

•

Speech transcoding

•

Data transmission between the A- and the M-interface

•

4 : 1 multiplexing

•

Through-switching of any channel

Operations and Maintenance

Functions of the Speech Transcoder Frame (STF-2000)

Speech Transcoding

The STF-2000 supports the Full Rate (FR), Enhanced Full Rate (EFR) and Half Rate (HR) coding algorithms. In the transmission direction from the MSC to the BSC, the STF-2000 transcodes 64kbps A-interface speech channels into 16kbps or 8kbps M-interface speech channels. In the transmission direction from the BSC to the MSC, the STF-2000 transcodes 16kbps or 8kbps M-interface speech channels into 64kbps A-interface speech channels.

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System Overview

Data Transmission

For data signals, the STF-2000 reads the 9.6kbps traffic data out of the 64kbps time slot of the A-interface and forms a 16kbps M-interface time slot (and vice versa). Transmission of data is possible only in Full Rate connections.

4 : 1 Multiplexing

The STF-2000 combines four 16kbps M-interface channels into one 64kbps traffic channel. In total, the STF-2000 multiplexes four A-interfaces into one M-interface.

Through-switching of any Channel Functionality of the Operations and Maintenance Centre (OMC–2000)

The STF-2000 switches any channels, e.g. the CCS7 signalling channel, between the BSC and the MSC through transparently. The OMC-2000 (Operations and Maintenance Centre) manages the BSS-2000 (Base Station Subsystem) and the 5ESS-2000 Switch MSC (Mobile-services Switching Centre) in a GSM network.. It provides operation and maintenance control capabilities from a central (remote) location. To perform daily operational and maintenance routines, the OMC-2000 provides the following functions: Function

Provided for BSS-2000

Configuration Management

X

Fault Management

X

Performance Management

X

System Administration

X

Switchover to redundant ports

X

On-line access via terminal-oriented interface

Provided for 5ESS-2000 Switch MSC

X

X

Configuration Management

•

Network configuration change control (e.g. defining new cells)

•

Centralised storage of BSS network configuration data

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Mobile Station

System Overview

•

Managing object states (e.g. restarting a piece of equipment that has failed)

•

Software administration for BSS loadable units

•

Alarms indicating abnormal conditions for the BSS

•

Alarm management functions (acknowledging and clearing alarms)

•

Alarm correlation

•

Fault tracking records

•

Support for external alarms

•

Gathering Performance Measurements

•

Storing Performance Measurements

•

Analysing Performance Measurements

•

Workstation administration (adding and modifying workstation information)

•

User administration (adding and modifying user accounts)

•

Loading error definition files

•

Maintaining the network clock

Fault Management

Performance Management

System Administration

Switchover to redundant ports

Network Switching Subsystem (NSS)

Switchover to redundant ports provides a means of fast recovery of the possible link failure causes (e.g. a physical link failure between the OMC-2000 and the connected BSSs, etc.). Switchover to redundant ports enables the operator to quickly switch over from a faulty X.25 connection to another X.25 connection. Mobile-services Switching Centre (MSC) performs the switching functions for all mobile stations located in the geographic area covered by its assigned BSSs. Functions performed include interfacing with the Public Switched Telephone Network (PSTN) as well as with the other MSCs and other system entities, such as the HLR, in the PLMN. Functions of the MSC include: •

Call handling that copes with mobile nature of subscribers

•

Management of required logical radio-link channel during calls

•

Management of MSC-BSS signalling protocol

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System Overview

•

Handling location registration and ensuring interworking between Mobile Station and Visitor Location Register

•

Control of inter-BSS and inter-MSC handovers

•

Acting as a gateway MSC to interrogate the HLR

•

Exchange of signalling information with other system entities

•

Standard functions of a local exchange switch in the fixed network (e.g. charging)

Functions of the Home Location Register (HLR):

The Home Location Register (HLR) contains the identities of mobile subscribers (IMSI), their service parameters, and their location information. The HLR contains: •

Identity of mobile subscriber

•

ISDN directory number of MS

•

Subscription information on teleservices and bearer services

•

Service restrictions (if any)

•

Supplementary services

•

Location information for call routing

Functions of the Visitor Location Register (VLR):

The Visitor Location Register (VLR) contains the subscriber parameters and location information for all mobile subscribers currently located in the geographical area (i.e. cells) controlled by the MSC. The VLR contains: •

Identity of mobile subscriber

•

Any temporary mobile subscriber identity

•

ISDN directory number of mobile

•

A directory number to route calls to a roaming station

•

Location area where the MS is registered

•

Copy of (part of) the subscriber data from the HLR

Functions of the Equipment Identity Register (EIR):

The Equipment Identity Register (EIR) is accessed during the equipment validation procedure when a MS accesses the system. It contains the identity of the mobile station equipment (IMEI) which may be valid, suspect, or known to be fraudulent.

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Mobile Station

System Overview

The EIR contains: •

White or Valid list. This is a list of valid MS equipment identities List

•

Grey or Monitored list. of suspected mobiles under observation

•

Black or Prohibited list. List of mobiles for which any service is barred

Functions of the Authentication Centre (AUC):

The functions of the Authentication Centre (AUC) contains: •

Subscriber authentication data called Authentication Key (Ki)

•

To generate the security related parameters needed to authorise service using Ki

•

To generate a unique pattern called the Cipher Key (Kc) needed for the encryption of user speech and data

Mapping of Functions to Logical Architecture Function

MS

BSS

SGSN GGSN HLR

Network Access Control: Registration

X

Authentication and Authorisation

X

Admission Control

X

X X

X

Message Screening Packet Terminal Adaptation

X

X X

Charging Data Collection

X

X

Packet Routing & Transfer: Relay

X

X

X

X

Routing

X

X

X

X

Address Translation and Mapping

X

X

X

Encapsulation

X

X

X

X

X

Tunnelling Compression

X

X

Ciphering

X

X

Mobility Management

X

X

X

X

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System Overview

Function

MS

BSS

SGSN GGSN HLR

Logical Link Management Logical Link Establishment

X

X

Logical Link Maintenance

X

X

Logical Link Release

X

X

Radio Resource Management Um Management

X

X

Cell Selection

X

X

Um-Tranx

X

X

Path Management

X

X

Field descriptions: Field

Description

IMSI

IMSI is the main reference key.

MSISDN

The basic MSISDN of the MS.

SGSN Number

The SS7 number of the SGSN currently serving this MS.

SGSN Address

The IP address of the SGSN currently serving this MS.

SMS Parameters

SMS-related parameters, e.g., operator-determined barring.

MS Purged for GPRS

Indicates that the MM and PDP contexts of the MS are deleted from the SGSN.

MNRG

Indicates that the MS is not reachable through an SGSN, and that the MS is marked as not reachable for GPRS at the SGSN and possibly at the GGSN.

GGSN-list

The GSN number and optional IP address pair related to the GGSN that shall be contacted when activity from the MS is detected and MNRG is set. The GSN number shall be either the number of the GGSN or the protocol-converting GSN as described in the subclauses ″MAP-based GGSN HLR Signalling″ and ″GTP and MAP-based GGSN - HLR Signalling″.

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Mobile Station

System Overview

Field

Description

Each IMSI contains zero or more of the following PDP context subscription records: PDP Context Identifier

Index of the PDP context.

PDP Type

PDP type, e.g., X.25 or IP.

PDP Address

PDP address, e.g., an X.121 address. This field shall be empty if dynamic addressing is allowed.

Access Point Name

A label according to DNS naming conventions describing the access point to the external packet data network.

QoS Profile Subscribed

The quality of service profile subscribed. QoS Profile Subscribed is the default level if a particular QoS profile is not requested.

VPLMN Address Allowed

Specifies whether the MS is allowed to use the APN in the domain of the HPLMN only, or additionally the APN in the domain of the VPLMN.

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System Overview

The GPRS Backbone System (GBS) .................................................................................................................................................................................................................................... Introduction

The GBS represents the packet switching network that provides GPRS connectivity between the BSS and external packet data networks to support GPRS terminals. The GBS comprises several different types of network elements as well as the interconnecting transmission hardware (e.g. routers, repeaters) and the transmission links between them. The ETSI standards introduce new functional network elements: •

Serving GPRS Support Node (SGSN)

•

Gateway GPRS Support Node GGSN)

The SGSN provides subscriber management, mobility management, as well as session management for any mobile GPRS user that has been associated with this SGSN. In order to achieve this task, the SGSN holds interfaces to the GSM subscriber databases: HLR, VLR, AUC and EIR. The SGSNs also hold the interfaces to the BSSs, and provides the authentication and encryption services for secure transmission of user data. The GGSN provides connectivity to external Packet Data Networks (PDNs). The ETSI standards specify the Internet and X.25 networks as external PDNs. The GGSN also provides address translation services. Rate adaptation services between the GBS and external networks may also be included in the GGSN. The Border Gateway provides connectivity to another Operator’s GPRS network. New interfaces will be required to connect the new entities to the existing GSM network elements. These interfaces will be pre-fixed with the character ’G’ and will support both traffic and signal connections. Figure 2-2 The Principal GPRS Network Architecture

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The GPRS Backbone System (GBS)

System Overview

Unlike circuit switched services, packet services allow concurrent usage of the same resources by multiple users. In order to support GPRS in a GSM network, the BSS has to be upgraded to support packet services and a GPRS Backbone System (GBS) has to be added to the basic GSM network to provide packet connection from GPRS capable mobile stations to other packet users, both fixed and mobile. Figure 2-3 Architecture Overview

The GPRS Backbone System (GBS) comprises of the following: •

A GPRS operator managed IP domain and Domain Server to map logical names for each element connected to the GBS domain to IP addresses

•

Multiple Serving GPRS Support Nodes (SGSN) which provide packet service management for GPRS subscribers

•

Multiple Gateway GPRS Support Nodes GGSNs which provide subscribers with access to external packet data networks and Public Land Mobile Networks PLMNs

•

A GBS Management Network Element Manager (NEM) called an Operations and Maintenance Centre for the GBS or OMC-G

•

A Performance Gateway function that collects Measurement Data from the GSNs and forwards to a Performance Monitoring Centre

•

A Charging Gateway function that collects Accounting Data from the GSNs and forwards to a Billing Centre

The IP domain may be entirely operator provisioned or part of a larger IP network operated as a Virtual Private Network domain. The Network supporting the IP domain is called the GPRS Backbone Network (GBN). .................................................................................................................................................................................................................................... 401–380–061 Issue RFA Version , May 2000

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System Overview

New Network Area .................................................................................................................................................................................................................................... Overview Routing Area

Location Area

GPRS introduces a new network area, the Routing Area. A Routing Area (RA) can consist of one or more cells and is always served by only one SGSN. However, one SGSN could serve more than one Routing Area. A Location Area (LA) can contain one or more Routing Areas, but one Routing Area could not span more than one Location Area. Figure 2-4 Location and Routing Areas

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System Overview

New Network Elements - Functional Entities .................................................................................................................................................................................................................................... The SGSN

For GPRS the GSM Base Station Subsystem (BSS) requires upgrading to support packet capabilities. This is done by adding the functionality of a Packet Control Unit which provides true packet access over the GSM radio interface with no changes to the radio interface. New logical radio packet channels provide packet access to the GPRS BSS and the PCU handles these packet channels and forwards packets to the SGSN. The SGSN is a new network element that is the master of packet access to the GPRS system. In a similar way to the MSC for GSM, the SGSN provides service to Mobile Stations for packet transfer. The SGSN is the master of packet transmission through the GPRS system. The SGSN provides Admission Control, Packet Service Management and GPRS Mobility Management. Unlike the MSC, the SGSN additionally provides several access level options in the form of multiple Quality of Service (QoS) options and Session Management. SGSN Connections

The SGSN contains the following connections: •

Connection to the GSM BSS via the Gb - interface

•

Connection to the HLR via the Gr - interface

•

Connection to the EIR via the Gf- interface

•

Connection to the GSM MSC/VLR via the Gs - interface

•

Connection to the SMS - SC via the Gd- interface

•

Connection to other PLMNs via the Gp - interface

SGSN Functions

The SGSN carries out the following functions: •

Network Access Control (CDR Collection, QoS Admin, Authentication)

•

Packet Routing (GBS to other GSNs, GTP Tunnelling, Address Translation, Address Resolution, IP Functions)

•

GPRS Mobility & Session Management (PDP Context, HLR Updates)

•

Logical Link Management (sliding window, cyphering, traffic support, RIL3 support)· Compression

•

GSM Circuit Switched Interactions (Paging, etc)

•

BSS Queue Management (Queuing of data/users)

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New Network Elements - Functional Entities

The GGSN

System Overview

•

Data Packet Counting (Billing)

•

Gb Resource Management (Flow Control of BVCs over Gb, Frame Relay - PVC, NS - VC for support of BVCs, Support of E1 Physical Layer)

The GGSN is a new network element that provides access from the GBS to external packet data networks such as the Internet. The gateway is primarily an IP router. The GGSN provides routing across the GBS on GPRS Tunnelling Protocol (GTP) request from the SGSN and out onto the external network. This entity is therefore responsible for managing both routing of traffic from multiple SGSNs and access to the external network this it is connected. The GGSN provides dynamic IP addresses on request from a SGSN, if a static address is not requested by the MS and manages routing of requests from external Packet Data Networks (PDN) to both PDP active and non-PDP active, GPRS attached MSs. The GGSN and the SGSN functions may be combined in a single physical unit or in different physical nodes. The connection between the GGSN and the SGSN, i.e. the Gn interface, utilises IP routing functionality and as such, standard IP routers may be found on this interface between the two GSNs (GPRS Support Nodes). When the GGSN and the SGSN reside in different locations, the connection is made via the Gp interface. The Gp interface has the same functionality as the Gn interface with additional security such as firewall. GGSN Connections

The GGSN contains the following connections: •

Connection to the SGSN via the Gn - interface

•

Connection to other PDNs via the Gi - interface

•

Connection to other PLMNs via the Gp - interface

GGSN Functions

The GGSN carries out the following functions:

The Packet Control Unit

•

Access Control (Firewall between GBS and PDN / Message screening)

•

Packet Routing and Transfer (GBS to other GSNs, GTP, Relay from GBS to PDN, IP Routing over PDN, APN Addressing)

•

Data/Packet counting The GGSN is the first point of interconnection from a PLMN to a PDN.

The Packet Control Unit (PCU) is a new functional entity of GPRS.

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New Network Elements - Functional Entities

System Overview

The GSM Phase 2+ GPRS Standards introduces the Packet Control Unit (PCU) as the functional entity that handles all packet traffic related tasks within a BSS or a cell. It can be implemented in the Base Transceiver Station (BTS), then called Integrated Packet Control Unit (iPCU), as well as in the Base Station Controller Frame (BCF-2000), then it is called Remote Packet Control Unit (rPCU) (According to the Lucent terminology). The Packet Control Unit (PCU) is the unit that adds the packet functionality to the Base Station System (BSS). It controls the radio interface which allows multiple users to access the same radio resource Additionally it also provides the Gb interface. Figure 2-5 Placement of PCU within the Lucent BSS

In the downlink direction, the Packet Control Unit (PCU) receives data from the Gb interface unit (GBIU) in the form of Logical Link Control (LLC) Protocol Data Units (PDUs). Its task is to segment them into Radio Link Control blocks (RLC) and schedule the transmission at the radio interface per slot and per mobile station. In the uplink direction, the Packet Control Unit (PCU) receives data in form of Radio Link Control blocks (RLC) from the Channel Codec Unit (CCU). Its task is to reassemble the Radio Link Control blocks (RLC) into complete Logical Link Control frames, which then are transferred via the Gb interface to the Serving GPRS Support Node (SGSN).

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New Network Elements - Functional Entities

System Overview

The Packet Control Unit (PCU) needs to do this for each mobile context established at the radio interface. Up to eight subscribers are allowed to share the same radio resource in each direction, i.e. PDCH. To achieve higher data rates for packet transfers, the Packet Control Unit (PCU) is able to assign multiple radio resources to a single user. The Packet Control Unit (PCU) is a logical, not a physical unit implemented in the Base Station System (BSS). The Gb Interface Unit (GBIU)

The GBIU is a term that is used by Lucent Technologies to cover all functions that are provided by the Gb interface. The Gb interface has been introduced by the Standards to provide packet data transport functionality between the BSS area and the GPRS backbone system. The Gb interface is an open standard interface allowing GPRS equipment from different vendors to co-operate. IT comprises Frame Relay (FR), Network Services (NS) and the Base Station Subsystem GPRS Protocol (BSSGP). In the downlink the GBIU receives PDU’s from the SGSN and forwards them to the addressed PCU or the GSE, if it is a signalling PDU. In the uplink the GBIU receives PDU’s from the PCU or the GSE and transfers them to the SGSN. The data link and subnetwork layer of the Gb interface is based on Frame Relay. The Gb interface allows load sharing through the usage of multiple links and provides limited protection against link failures

The GPRS Signalling Entity (GSE)

The GPRS Signalling Entity (GSE) is a Lucent Technologies term to identify a functional entity that summons all signalling functionality related to the BSS Gb protocol. The signalling functionality of the BSS Gb protocol comprises the control of the Gb interface, as well as the handling of paging of GPRS attached mobiles.

The Channel Codec Unit (CCU)

The Channel Codec Unit (CCU) is a unit located in the Base Transceiver Station (BTS). In the downlink direction, the Channel Codec Unit (CCU) receives the RLC block from the PCU. It generates a Frame Check Sequence for each block and appends it to the RLC block before transmission over the radio interface. The Channel Codec Unit (CCU) applies fourfold rectangular interleaving to the Radio Link Control blocks (RLC). They are thereafter transferred to the Mobile Station over the radio interface. In the uplink direction the Channel Codec Unit (CCU) receives the Radio Link Control blocks (RLC) over the radio interface from the

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New Network Elements - Functional Entities

System Overview

Mobile Station. The Channel Codec Unit (CCU) is responsible for de-interleaving and for checking the Frame Check Sequence in order to detect erroneous Radio Link Control blocks (RLC). The Radio Link Control blocks (RLC) are then transferred to the Packet Control Unit (PCU) for further processing. Non erroneous Radio Link Control blocks are transferred. An additional task of the Channel Codec Unit (CCU) is the handling of timing advance. For a newly accessing mobile, the Channel Codec Unit (CCU) is responsible to determine the initial timing advance. The determined timing advance will be forwarded to the Packet Control Unit (PCU), which conveys it to the mobile. After the initial timing advance has been determined, the Channel Codec Unit (CCU) handles the continuous timing advance procedure. The Cell Control Function (CCF)

The Cell Control Function (CCF) is a Lucent Technologies term. It is used to characterise all GSM functionality in the Base Station System (BSS) that is necessary for providing circuit switched services related to one cell. The Cell Control Function (CCF) carries out the following standard GSM function: •

Administration of radio resources associated with the cell

The GSM Phase 2+ GPRS Standards require that it shall be possible to support GPRS in a call even if there is no dedicated control channel for GPRS traffic defined. As a consequence the Cell Control Function (CCF) needs to: •

support broadcast of GPRS System Information on the Broadcast Control Channel (BCCH)

•

paging of GPRS mobiles using the Paging Channel (PCH)

•

recognition and processing of access burst of GPRS mobiles

•

as well as transfer of access grant messages for GPRS mobiles on the Access Grant Channel (AGCH)

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System Overview

Frame Relay .................................................................................................................................................................................................................................... Frame Relay

Frame Relay is a high-speed communications technology that is used in lots of networks throughout the world to connect Local Area Networks (LAN), System Network Architecture (SNA), Internet and even voice application. It is a way of sending information over a wide area network (WAN) that divides the information into frames or packets. Each frame has an address that is used by the network to determine the destination of the frame. The frames travel through a series of switches within the frame relay network and arrive at their destination. Frame relay is a connection oriented packet service protocol that multiplexes many logical data connections over a single physical transmission link. It provides fast packet switching (more efficient than X.25) and is optimized for high throughput and low end-to-end delay. Figure 2-6 Frame Relay Network

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Frame Relay

System Overview

Frame Relay is based on the following three convergent parameters:

No Error Correction by Frame Relay

No Flow Control by Frame Relay

1.

Increasing demand for high throughput

2.

Highly reliable physical network

3.

Intelligent end systems A low protocol overhead is responsible to allow a high throughput. The data link protocol is cut down, there are no sequence numbers, only address field (Data Link Connection Identifier, DLCI) and a cyclic redundancy check (CRC). There is no network layer in Frame Relay .

There is no time consuming error correction in Frame Relay networks. Only error detection is done by the CRC and corrupted frames are discarded. The retransmission is done only by end systems. There is no flow control in Frame Relay networks. Special bits provide a simple congestion notification and the congestion control in the network is done by discarding frames. In case of a link failure there is no explicit rerouting mechanism in a Frame Relay network. Frame Relay Terms: •

User to Network Interface (UNI) Specifies signaling and management functions between a frame relay network device and the end user´s device.

•

Virtual Circuit (VC) The connection between two frame relay ports.

•

Permanent Virtual Circuit (PVC) A predefined Virtual Circuit (VC).

•

Switched Virtual Circuit (SVC) A Virtual Circuit that is established dynamically (not used in GPRS phase 1).

•

Committed Information Rate (CIR) The average bandwidth defined for a Virtual Circuit.

•

Excess Information Rate (EIR) Increment in excess of CIR (CIR + EIR <= Port speed)

•

Frame Relay Structure

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Frame Relay

Frame Relay Structure

System Overview

The structure of Frame Relay contains the following fields: •

Flag Field: Indicates the start/end of a frame. If there are two successive frames, only one flag field is used to indicate the end of the one frame and the start of the next frame.

•

Address Field: This field is the comprise of two octects. It is used to carry the Data Link Connection Identifier (DLCI) which is needed for routing the frame between different nodes. In the address field there is also an Address Field Extension (EA) that indicates the last octet in the address field. There are also some bits to indicate whether a frame has encountered some congested resources, the Forward Explicit Congestion Notification (FECN) and the Backward Explicit Congestion Notification (BECN). Another bit, the Discard Eligibilty bit (DE) is used in case of congestion in a network to indicate a specific frame that can be discarded.

•

Information Field: The purpose of this field is to carry the user information

•

Frame Check Sequence: The purpose of this field is to determine any errors that may have occurred during transmission. In Frame Relay there is only a error detection not a error correction !

Figure 2-7 Frame Relay Structure

Frame Relay Structure Legend: •

EA Address field extension bit

•

C/R Command response bit (not used)

•

FECN Forward explicit congestion notification

•

BECN Backward explicit congestion notification

•

DLCI Data link connection identifier

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System Overview

•

DE Discard eligibility indicator

Figure 2-8 Frame Relay Network

Frame Relay implementation in the BCF

The Frame Relay (FR) module is used on the Gb Interface Unit (GBIU) of the BCF supporting GPRS feature. The FR stack will run in user mode on the GWS.

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System Overview

New Network Interfaces .................................................................................................................................................................................................................................... Overview

New Interfaces will be required to connect the new entities to the existing GSM Network Elements. These Interfaces will be pre-fixed with the character G and will support both traffic and signal connections. The diagram below displays the new interfaces.

Interface Connectivity Figure 2-9 New GPRS Interfaces

Interface Connectivity Interface

Connecting

Gb

Between SGSN and BSS

Gn

Between SGSN and GGSN or between two SGSNs

Gi

From GGSN to an external network

Gs

Between MSC/VLR and SGSN to allow co-ordination of location information and paging

Gc, Gr

MAP interfaces between the HLR and GGSN/SGSN to support authentication

Gf

Interface to EIR to support the check IMEI procedure

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New Network Interfaces

System Overview

Interface

Connecting

Gd

Interface from SMSC to the SGSN to allow SMS traffic to be carried over the GPRS channels

Gp

Equivalent to the Gn, except that the connected GSNs are in different networks

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System Overview

GSM Elements Affected by GPRS .................................................................................................................................................................................................................................... Overview

Shared Network Resources

There are GBS implications on several existing GSM network elements. These are , the BSS, OMC, MSC, VLR, HLR AUC and EIR. Several other new network elements are required by GPRS which the GBS feature has impact upon, these are the SGSN, GGSN, OMC-G, DNS and Data Gateways (CG and Performance Gateway). The figure below shows how network resources will be shared. The HLR & VLR record field size have been extended to accommodate for GPRS. Figure 2-10 Shared Network Resources

GPRS Impact on the Base Station Subsystem (BSS)

GPRS Impact on the Base Station Subsystem (BSS) Element

Description of changes required

BSC

New Interface to new GPRS elements, Gb to the SGSN. New functionality to handle packet data, Remote Packet Control Unit (rPCU). Note: If current link capacity is not sufficient to support GPRS and GSM Circuit Switched (CS) traffic, then additional interface boards (M interface for nailed up connections) would need to be added

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GSM Elements Affected by GPRS

GPRS Impact on the Network Switching Subsystem (NSS)

System Overview

Element

Description of changes required

BTS

Software Modifications to handle packet data for handling the GPRS traffic. Additional processing requirements to support GPRS. The Abis interface has to be adapted to support GPRS

OMC

O & M modifications to cover overlaid packet network.

GPRS Impact on the Network Switching Subsystem (NSS) Element

Description of changes required

MSC/VLR

The Mobile switching Centre / Visitor Location Register (VLR) needs to be updated to allow for the efficient co-ordination of circuit switched calls and GPRS packet data services. Also a new interface (Gs) is needed between the MSC/VLR and the SSGN.

HLR

The Home Location Register (HLR) needs to be updated to store and manage new GPRS subscriber data. To manage the new GPRS subscriber data, two new interfaces are created, (Gc) between the GGSN and the HLR, and (Gr) between the SGSN and HLR.

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System Overview

Base Station Subsystem .................................................................................................................................................................................................................................... Overview

The introduction of GPRS to the Base Station System (BSS) is a smooth introduction (software update). Call processing will still be possible while introducing the GPRS functionality. Preconditions for GPRS Introduction:

BSS GPRS Features (NR 9.0)

1.

All network elements are running at least at NR 8.2

2.

Software release 9.0 available with appropriate ″Customer Specific Database″

3.

All cabling activities for Gb interface completed

4.

Additional hardware for STF in place (if needed)

BSS GPRS features (NR 9.0) include: •

New channel type supporting TCH/F or GPRS

•

Synchronisation of Time Alignment and TDMA Frame Number (FN) between CCU and PCU

•

GPRS Data Channels

•

CS-1 with 184 Bit / TRAU-Frame

•

CS-2 with 271 Bit / TRAU-Frame

•

PRACH with 11 Data Bit

•

Sharing resources between circuit switch and GPRS

•

Maximum of 93 simultaneously active PDCHs

•

Dynamic switching between coding scheme one and coding scheme two is not supported

•

Packet control channels not supported

•

No ″cs″-paging

•

Number of performance measurements in Rel. 1: Two

•

Radio Link Control in acknowledged mode

•

No frequency hopping for PDCHs

•

Maximum of 500 Temporary Block Flows (TBFs): 250 in uplink direction and 250 in downlink direction

•

Maximum of four PDCHs per downlink-TBF and maximum of 2 PDCH per uplink-TBF

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GPRS introduction to the Base Transceiver Station (BTS) .................................................................................................................................................................................................................................... Overview

Abis - PCU Interface

The PCU schedules

The CCU reports to PCU

The GPRS Um Interface

GPRS will be implemented in the BTS-Family through a software solution only. This software upgrade will support coding scheme 1 and coding scheme 2. There is a maximum of one GPRS Transceiver (TRX) per cell and also a maximum of eight GPRS time-slots per TRX. Abis - PCU Interface: •

Interface between CCU and Remote PCU

•

Uses a 16 kbits/s Subslot on Abis interface (modified TRAU interface)

•

20ms Frame Structure like TCH/F

•

Interface not defined by GSM (Proprietary Lucent Solution)

•

Time Alignment and FN Synchronisation Function

•

CCU is Master for this Synchronisation

•

Each Frame contains the FN where the Data have to be sent on the Um Interface

The PCU schedules: •

Which MS receives next Downlink Block

•

Which MS sends next Uplink Block

•

Access or Normal Burst Reception

•

MAC layer

•

RLC layer

•

Flow control (downlink direction only)

The CCU reports to PCU •

Receive Level

•

Receive Quality

•

No further GSM Measurements done in BTS-2000 Frequency Offset Measurements and Timing Advance Measurements handled by BTS.

The GPRS Um Interface •

BTS knows only Channel PDCH

•

Mapping of logical Channels PACCH, PBCCH, PCCCH, PDTCH is done by PCU (Future release)

•

BTS supports Frequency Hopping for GPRS

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System Overview

GPRS Introduction to the BCF-2000 .................................................................................................................................................................................................................................... Overview

The GPRS functionality within the BCF-2000 is assigned to one server. Hence an extra server including an Advanced Communication Card (ACC) card will be required as a GPRS extension unit per BCF-2000.

GPRS workstation (GWS)

One new type of logical workstation will be implemented. The new workstation is called GPRS workstation (GWS). This leads to a reduction of four Cell Workstations per BCF-2000. There will be one GWS instance per BCF. Adding a GWS to a BCF–2000 requires no hardware changes, because every available server can come up as a GPRS workstation.

rPCU Integration into the BCF-2000 Figure 2-11 rPCU Integration into the BCF-2000

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GPRS Introduction to the BCF-2000

System Overview

Distribution of functionality Figure 2-12 Distribution of functionality

All GPRS relevant units in the BCF are placed in the GPRS workstation. The GPRS Signalling Entity (GSE), the Gb Interface Unit (GBIU) and the Packet Control Unit (PCU) are located in the GPRS Workstation. These three new UNIX processes will be combined into the GPRS Virtual Machine (GVM). The ACC card will have a new software and be the holder of the RLC/MAC scheduler. There will be no GPRS specific database and no GPRS specific OA&M. GSE functionality

GSE functionality: •

Interface to OA&M

•

Supervision of data distribution

•

Prepares and broadcasts paging messages, which are received from the SGSN

•

Central fault management for rPCU

•

Synchronisation of rPCU during start-up

•

rPCU common management of performance measurements

It receives all non- connection related messages, which are received from the SGSN. The non-connection related parts of the GPRS Mobility Management (GMM) and of the Network Management (NM) functionality is also handled by the GSE.

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System Overview

The explicit tasks handled by the GSE are: •

Distribution of configuration data to the PCUP

•

Distribution of configuration data to the GBI

•

Maintaining a table of cell specific information

•

Routing of paging messages

•

Co-ordination of the recovery of the rPCU application

•

Filtering and forwarding of rPCU specific fault messages to Fault Management (FM)

By analyzing the BSSGP Virtual Identifier and the primitive type, it is decided by the BSSGP layer whether a received Protocol Data Unit (PDU) must be routed to the GSE or not. As a consequence, the GSE receives only PDU′s which contain the signalling BSSGP Virtual Connection. It also receives all paging messages from the Gb Interface Unit (GBIU). These paging messages are analyzed by the PAGER process and they are forwarded to the Line Transmission Virtual Machines (LTEVMs) via the User Datagram Protocol (UDP) broadcast. For GPRS release 1 no paging messages are forwarded to the PCUP, because no PBCCH (i.e. PPCH) is supported. GBIU functionality

GBIU functionality: •

The GBIU supports the following three layers -

Base Station Subsystem GPRS Protocol (BSSGP)

-

Network Service

-

Frame Relay

•

Interface to BOND available

•

Configuration data provided from OA & M (via the GSE)

•

Load sharing within NS-layer

GBIU connectivity: •

The Gb interface is distributed over four internal E1 links.

•

There is a maximum of 31 time-slots (64kbs each)

•

Distribution over all available M-links is possible

•

There are nail-ups during recovery of Network Service Virtual Connection (NSVC)

•

The Gb interface is not involved in dynamic switching (static switching)

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GWS Recovery procedures

Reliability Parameters

System Overview

The recovery procedures for the GWS are listed below: •

Creation of a GBIU (via database or OMC)

•

BCC recognises that GPRS is enabled Checking the LCA flag

•

SRS-Handler selects suitable server as GWS Selection based on availability of internal E1 slot capacity

•

CCP starts GVM -

Start of GSE, GBIU and PCUP

-

Download of GPRS specific ACC image

•

Synchronisation of GVM (communication paths between all GVM UNIX processes have to be established)

•

Creation of at least one NSVC

•

Configuration of PCU

Reliability Parameters: •

Recovery type: -

Off-line failed GWS

-

Failed GWS replaces existing CEWS

•

The total number of GVM restarts

•

The total number of GWS reboots

•

The total number of servers to try for GWS

Figure 2-13 GPRS - OMC solutions

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System Overview

GPRS Input for the OMC-2000 part .................................................................................................................................................................................................................................... Overview GPRS Support for BSS

The following pages describe the impact of GPRS on the OMC-2000. Before a complete set of new General Packet Radio Service (GPRS)-related objects (GBIU, PCU, and at least one NSVC) can be created, the following conditions must be met: •

The NECONN object associated with the BSS must have its GPRS Supported parameter set to True.

•

The BSS must have its GPRS Supported parameter set to True.

•

The BTS must have its GPRS Supported parameter set to True.

•

At least one Transcoder (TRC) object with a TRC Type of ″GPRS″ must be available before you can create an NSVC object.

Reset of GPRS Support

If the GPRS Supported parameter in the BSS is reset from True to False to stop any support of GPRS traffic, any active GPRS-related measurement groups are not deleted automatically. In addition, the BSS continues to ″collect″ GPRS measurement data even though none of the counters associated with those measurements are incremented. To optimise your data collection activities, delete any GPRS measurement groups before resetting the GPRS Supported parameter on the BSS to False. Important! Before you disable GPRS in the BSS, you must manually change the GPRS Supported parameter in the BTSs to False. When a BSS does not Support GPRS

There are two conditions under which GPRS capability cannot be selected: •

If the OMC-2000 is not configured to support GPRS operations, the GPRS Supported parameter is greyed out, and inaccessible.

•

If the BSS Model Type is not BCF Release 3.0 or later, the GPRS Supported parameter is greyed out, and inaccessible.

How to disable GPRS Support in a BSS

Before you can disable GPRS capability in a BSS (that is, before you set its GPRS Supported parameter to False), you must do the following: •

Under the BTS, delete any contained PCU object

•

Make sure no RTs have CHNs configured with a channel type of TCHFullandPDCH

•

In the BTS, set the GPRS Supported parameter to False

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GPRS Support for BTS

System Overview

•

Manually delete all NSVC objects

•

Under the BSS, ensure that there is no GBIU object Once the above conditions are met, you can set the BSS GPRS Supported parameter to False.

The parent BSS must have its GPRS Supported parameter set to True before you can create a BTS with GPRS capability. How to disable GPRS Support in a BTS-2000

To disable GPRS capability of a BTS-2000, you must do the following:

GPRS Support for RT

•

Delete any contained PCU object.

•

Make sure no contained CHNs are configured with a Channel Type of TCHFullandPDCH.

•

In the BTS, set the GPRS Supported parameter to false.

In order to support GPRS functionality, the BTS must be able to map new logical channels on the RTs. To support GPRS communications, a new channel type, the Traffic Channel Fullrate and Packet Data Channel (TCHFullAndPDCH), is added. At any given time, only one RT within a BTS–2000 can support GPRS channels. Thus, the maximum number of channels that can be configured as PDCHs is 8. To determine which of the RTs within a BTS–2000 has GPRS channels assigned, you can open the RT Browser or RT Detail View and look at the GPRS Active column. The OMC-2000 sets the value of this parameter to Y automatically as soon as a channel on an RT is configured as a PDCH. Before Configuration

When no channels are configured as GPRS channels, such as when you are configuring the first one, all RTs will show ″False″ in the GPRS Active column. Display RT channel usage

The RT channel usage dialog displays information associated with GPRS communications, that is a Channel Status that indicates busy PDCH, only when GPRS capability exists for an RT. GPRS Support for CHN

Before traffic can move across the network, you must first configure the channels (CHNs) on the Radio Terminals (RTs). To support GPRS capabilities, a new channel type TCGFullAndPDCH is added. The Channel object (CHN) is also known as a physical channel. It represents one physical time-slot in the air interface on an RT. There

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System Overview

are up to eight different channels for every RT. Every channel created must be configured, which includes assigning a channel type to designate its function. For GPRS additional channel types are defined: •

Packet Data Traffic Channel (PDTCH) which belongs to the class Packet Data Channel and will be used for Uplink and Downlink direction

•

Packet Associated Control Channel (PACCH) which belongs to the class Packet Data Channel and will be used for Uplink and Downlink direction

•

Packet Timing Advance Control Channel (PTCCH) which belongs to the Class Packet Data Channel and will be used for Uplink direction

GPRS Channel Description •

PDTCH - This corresponds to the resource allocated to a single mobile station on one physical channel for user data transmission. One PDTCH has an instantaneous bit rate of 0 to 22.8 Kbit/s. When a channel is configured as a PDCH, it is a shared resource and can be used either for circuit switched or packet switched operation. The BSS determines how it is used based on the number of requests for each type service, and according to resource availability. Creating a channel of this type does not mean that it will be used for GPRS services, even it is available and required.

•

PACCH - Used to carry signalling information associated with a PDTCH.

•

PTCCH - Used in the uplink to transmit random bursts to allow for the estimation of the timing advance for one mobile station on the packet transfer mode, and in the downlink to transmit timing advance updates for one or several mobile stations. The existing control channels handle all GPRS-specific information and control operations.

The following information will help you to create a CHN object to support GPRS capabilities: •

Only one RT within a BTS can support GPRS at any given time. It is on this RT that you can create a CHN with a Channel Type TCHFullAndPDCH to support GPRS.

•

Shared resources must have a Frequency Hopping Relationship (frequency usage) value of 255, which means they are not allowed to be part of a Frequency Hopping scheme.

•

All shared resources assigned within one BTS must be contained in the same RT.

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GPRS Support for a TRC

The allocation of the bearer channel by the Network Services Virtual Connection (NSVC) object is done by reference to a TRC object, which has been configured to carry GPRS data. This means that the 64Kb/s channel is passed transparently through the transcoder. To do this and avoid confusion with existing CCSS7 signalling channels, a new parameter called TRC Type GPRS is added to the TRC object.

Packet Control Unit (PCU) Object

GPRS channel control, allocation, and operation is performed by the Packet Control Unit (PCU). There is one functional PCU for each BTS supporting GPRS. Since the PCU is a child object of the BTS, you must delete it before you disable GPRS capabilities of the parent BTS object. Prerequisites

Before you can create a PCU object, the following must be true: •

The BTS parameter, GPRS Supported, indicates if GPRS functionality is supported by the BTS. It must be set to True before an operator can create a PCU object.

•

A GBIU object must exist.

•

The BTC object within the BTS must exist.

•

No PCU object currently exists within the BTS-2000.

Attributes of the PCU object

Attributes of the PCU object •

Routing Area Colour Code (RACC) - This service affecting parameter is used to determine if GPRS capability is supported by a BTS-2000. A mobile station to do a cell reselection also uses it. Values can range from 0 through 7.

•

Routing Area Code (RAC) - The value of this service affecting parameter is determined by each network using the structure, which is specified in the GSM standards. Values can range from 1 through 253, and must match the value set at the SGSN.

•

BVCI - The BSSGP Virtual Connection Identifier. The value of this service-affecting attribute identifies the BSSGP Virtual Connection used between the PCU and SGSN. Values can range from 2 through 181, and must be unique within the BTS-2000.

•

Max(imum) Number of PDCHs Allowed - This parameter determines the maximum number of idle TCHFullAndPDCH within a BTS-2000 that the PCU can allocate for GPRS service at any time. Once this number has been reached, no more channels can be assigned for GPRS service even if more idle TCHFullAndPDCH channels are available. Values can range from 1 through 8. Default is 8.

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•

Number of PDCHs Available - This attribute maintains a running count of the number of radio channels available for GPRS. For a channel to be counted it must be configured as TCHFullAndPDCH and Unlocked and Enabled.

•

Priority Access THR - This parameter, sometimes, referred to as the packet access class indicator, indicates whether or not a mobile station of a certain priority class is authorised to do a random access request of a GPRS service. Values can be the following:

•

-

Packet Access not allowed by the BTS-2000.

-

Access allowed for Priority Class 1

-

Access allowed for Priority Class 1 and 2

-

Access allowed for Priority Class 1, 2 and 3

-

Access allowed for Priority Class 1 through 4 (default)

Max(imum) Time For Non-DRX Mode - This parameter indicates the maximum time allowed for a mobile station to request non-discontinuous (non-DRX) reception mode after packet transfer mode. Values can be any of the following: -

No Non-DRX mode after packet transfer mode

-

Maximum of 1 second Non-DRX mode after packet transfer mode

-

Maximum of 2 seconds

-

Maximum of 4 seconds

-

Maximum of 8 seconds

-

Maximum of 16 seconds (default)

-

Maximum of 32 seconds

-

Maximum of 64 seconds

•

RLC Counter PAN_MAX - This counter is related to cell reselection. Values can range from 4 through 32 increments of 4.

•

Power Control Counter N_Avg_I - This parameter defines the interference signal strength filter constant for power control. Values can range from 0 through 15.

•

Power Control Timer T_Avg_W - This parameter defines the signal strength filter period for power control in ″packet idle″ mode. Values can range from 0 through 25.

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Network Services Virtual Connection (NSVC) Object

System Overview

•

Power Control Timer T_Avg_T - This parameter defines the signal strength filter period for power control in packet transfer mode. Value can range from 0 through 25.

•

BTS Receive Signal Strength SSb - This parameter relates to open loop power control. Values can range from 0 (less than -110dBm) through 63 (greater than -48 dBm) in 1 dBm increments. Default=63.

The Network Services Virtual Connection (NSVC) object is a child of the Gb Interface Unit (GBUI) object. This object is available only if the OMC is GPRS enabled, and if its parent BSS object has its GPRS Supported attribute set to True. Prerequisites

Before you create an NSVC, do the following: •

•

Locate a TRC that can be used as a Gb Service Provider for creating an NSVC object. Do this as follows: 1.

Obtain the list of available TRCs under a TCG of type STF-2000

2.

Check the browser to determine if a TRC object exists for the BSS under which you want to create the NSVC

3.

If a TRC exists, ensure that the TRC Type field is set to GPRS

4.

For any GPRS TRCs, ensure that TRC Assigned = FALSE

Ensure that a GBIU object exists.

If these conditions are satisfied, then the TRC can be used as a Gb Service Provider for creating an NSVC object. If a PCU is created and activated, as long as at least one NSVC is unlocked and enabled, GPRS operations can begin. No association needs to be made between the PCU and the NSVC. NSVC Attributes

NSVC Attributes •

NSVC Id is the Network Services Virtual Connection (NSVC) object identifier. Values can range from 0 through 30.

•

NS_VCI is the Network Services Virtual Connection Identifier. It is on of the two Network Services mapping elements. Values can range from 0 through 65535, and must be unique within the BSS.

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Gb Interface Unit (GBUI) Object

System Overview

•

DLCI is the Data Link Connection Identifier for the frame relay. It is one of the two Network Services mapping elements. Values can range from 16 through 991, and must be unique within the BSS.

•

Gb Service Provider displays the distinguished name of the TRC in the BSS that provides the bearer channel for the NSVC.

Each BSS is capable of supporting up to 31 NSVC objects for GPRS data, where one bearer channel represents one 64 Kb/s timeslot on an M-link. The allocation of the bearer channel is accomplished by referencing a Transcoder (TRC) object that has been configured to carry GPRS data. The channel is passed through the TRC transparently. The Network Services (NS) layer sits above Frame Relay, and is responsible for the correct routing of data between the SGSN and the BSS. This is done by setting up Network Services Virtual Connections (NSVCs). These NSVCs are identified by their NS_VCI. This value uniquely identifies the NSVC within the SGSN. The OMC-2000 uses point-to-point connections, so the Network Services Virtual Connection Identifier (NS_VCI)-to-DLCI mapping must be the same at the BSS and the Serving GPRS Service Node (SGSN). The mapping of the NS_VCI-toDLCI to bearer channel relationship is contained in the NSVC objects. There is a limit of one NSVC per bearer channel. Up to 31 NSVC objects are contained by the GBIU object. Once the data has been delivered to the BSS, the GBIU determines the final destination of each data packet within the BSS. This data is contained in the BSSGP layer. The transfer of BSSGP data is accomplished with the setting up of a BSSGP Virtual Connection (BVC). These BVCs exist between the BSSGP layers of the SGSN and the final destination within the BSS. To uniquely identify the destination within a BSS each BVC is given a BSSGP Virtual Connection Identifier (BVCI), which must be unique within a BSS. The BVCI is a parameter with the Packet Control Unit (PCU). It identifies the BSSGP Virtual Connection used between the PCU and SGSN. Types Of Packets

There are two types of BSSGP packets: •

Those that carry data traffic to/from the mobile stations.

•

Those that carry signalling information to be processed in the BSS.

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System Overview

How Packets Are Routed

Data traffic is forwarded to the PCU responsible for the BTS-2000 where the mobile is currently located. Signalling traffic is passed to the GPRS Signalling Entity (GSE) for processing. The GSE is a BSS entity, which is not visible on the OMC-2000. To uniquely identify a PCU or GSE within an SGSN domain, a Network Services Element Identifier (NSEI) is provided at the Network Services layer. The NSEI uniquely identifies a BSS within an SGSN. It is, therefore, the combination of the NSEI plus the BVCI, which uniquely identifies the final destination of each BSSGP packet within an SGSN domain. Prerequisites

The following are prerequisites to create a GBIU object: •

The GPRS Supported parameter in the parent BSS must be set to True

•

No GBUI object currently exists in the BSS

GBIU Attributes

GBIU Attributes: •

NSEI - The Network Service Entity Identifier. The NSEI is a service-affecting attribute that provides the network management functionality required operating the Gb interface. The BSS and the SGSN to determine the NSVC that provides service to a BSSGP Virtual Connection Identifier (BVCI) within the PCU use the NSEI. Values can range from 0 through 65535, and must be unique within the SGSN.

•

BSSGP Timer T1 - This timer is used for blocking and unblocking procedures. Values can range from 1 second to 30 seconds

•

BSSGP Timer T2 - This timer is used for the reset procedure. Values can range from 1 second through 120 seconds

•

BSSGP Timer C - This timer determines the minimum period of time after which the BSS may send a flow control message to the SGSN for a specific BSSGP Virtual Connection (BVC) or mobile station. The valid range is 1 through 10 seconds, and must match the value set at the SGSN. (Default=1)

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GPRS Input for the OMC-2000 part

STF-2000

System Overview

•

BSSGP Timer Th - This timer defines the period of time after which the SGSN will change the flow control settings for a particular mobile to the default values. For the BSS to prevent default values from being assigned by the SGSN, FLOW_CONTROL_MS messages must be sent before expiration of the Th timer. This timer value must be greater than BSSGP Timer C. Values can range from 5 seconds through 6000 seconds, and must match the value set at the SGSN. (Default=32)

•

Network Services Timer Tns Test - This timer determines how often the NSVC test procedure is performed. Values can range 1 second through 60 seconds (Default=10)

•

Frame Relay Timer T391 - This is a link integrity verification polling interval timer. The value of this timer must be less than the value of the SGSN T392 timer. Values can range from 5 seconds through 30 seconds (Default=10)

•

Frame Relay Counter N392 - This counter works with N393 counter to provide a way to detest service affecting conditions by detecting N392 errors in the last N393 events. The value of this counter must be less than or equal to the N393 counter. Values can range from 1 through 10 (Default=3)

•

Frame Relay Counter N391 - This counter triggers a request for a full status of all PVCs every N391 polling cycles. Values can range from 1 through 255 (Default=6)

•

Frame Relay Counter N392 - This counter works with N393 counter to provide a way to detest service affecting conditions by detecting N392 errors in the last N393 events. The value of this counter must be less than or equal to the N393 counter. Values can range from 1 through 10. (Default=3)

•

Frame Relay Counter N393 - This counter works with N392 counter to provide a way to detect service affecting conditions by detecting N393 errors in the last N393 events. The value of this counter must be greater than or equal to the N392 counter. Values can range from 1 through 10 (Default=4)

Lucent is able to support transparent 64 Kbit/s channels for the purposes of providing an entry level physical Gb interface provisioned using STF nailed up 64kbps per time–slot on E1 links.

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System Overview

Network Switching Subsystem (NSS) and GPRS .................................................................................................................................................................................................................................... Impact on the NSS (Network Switching Subsystem)

Due to the introduction of GPRS in the GSM network new interfaces and network entities are introduced that have impact on the NSS. The new network entities for GPRS are: •

The SGSN

•

The GGSN

The new interfaces for the NSS are: •

The Gs interface between de MSC/VLR and the SGSN

•

The Gc interface between the HLR and GGSN

•

The Gr interface between the HLR and SGSN

•

The Gf interface between the EIR and the SGSN

•

The Gd interface between the SMS-MSC and the SGSN

Due to these new entities, the interfaces and the fact that the GPRS is an overlay network, for mobility management the procedures are adjusted to route calls to that network. This requires modification of signalling, protocols and databases. Figure 2-14 GPRS Impact on NSS

NSS Entity Requirements

In order to support GPRS with the existing GSM Network, some requirements are needed for the NSS entities. These requirements are divided in Hardware and Software updates to the NSS entities.

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Network Switching Subsystem (NSS) and GPRS

System Overview

Hardware requirements

The only hardware updates needed for the NSS entities are additional signalling links to support the new GPRS interfaces. This possibly means additional Protocol Handlers and Facility Interfaces. Software requirements

Software requirements needs to be split between the entities:

MSC/VLR Changes and Procedures

•

For the MSC/VLR it is required that the changes support the interworking over the Gs interface to the new packet network node SGSN that allows a co-existence of GPRS and the existing circuit switched network. Examples are combined mobility management procedures and the support of paging for circuit switched services via GPRS.

•

For the HLR it is required that the changes support GPRS subscriber data, feature data and mobility management data. Furthermore the changes should support the interworking with the GGSN over the Gcinterface and SGSN over the Gr interface to provide mobility management and subscriber data over the interfaces.

•

For the EIR no specific changes are needed. Only the Gf interface is defined to interwork with the SGSN. All procedures are described in the existing specifications.

•

For the AUC no changes are needed due to its co-location with the HLR. All authentication procedures apply for GPRS.

•

For the SMS-MSC it is required that the changes support the possibility to send SMS messages to a mobile station via the SGSN and GPRS service. The Gd interface is defined to support this interworking.

•

Modifications also need to be made for the C interface between the SMS-MSC and the HLR to route SMS calls to the GPRS network.

The Gs interface has an identical structure as the A interface to the BSC. The protocol stack uses the same lower levels. Modifications are implemented in the BSSAP stack to where the following procedures impact the communication between the mobile station and the network: •

Location Update with information received from the SGSN

•

Sending the Paging message via the SGSN

•

Receiving an IMSI Attach/Detach via the SGSN

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Network Switching Subsystem (NSS) and GPRS

System Overview

•

Sending a GPRS Reset message after MSC or VLR recovery

•

Furthermore modifications are needed to the Alerting, Identification and Information Procedures

Not only procedures need to be updated. Database information in the MSC/VLR needs to be changed as well:

HLR/AuC/EIR Changes and Procedures

•

In order to retrieve the location of the mobile station when a call enters the PLMN via the MSC the number of the attached (currently serving) SGSN is stored in the VLR.

•

The MSC is not in control of the detach when an MS is both IMSI and GPRS attached. This means the implicit detach timer is not activated in the MSC but in the SGSN which is in charge to monitor the timer and to send the detach message to the MSC.

The Gr/Gc/Gf interface has an identical structure as a MAP interface. The protocol stack uses the same lower levels, modifications are implemented in the MAP stack to where a number of procedures impact the communication between the mobile station and the network. The AuC does not have its own interface but receives the needed information relayed via the HLR. For the Gr interface the following applies: •

Authentication information received via the SGSN

•

Registration information received from the SGSN (GPRS attached, detached)

•

Receiving a Routing Area Update message from a SGSN

For the Gc interface the following applies: •

Send Routing information message received from a GGSN

For the Gf interface the following applies: •

Check IMEI message received via the SGSN

If the database changes for the HLR, then incorporate more information: •

For instance, to route the calls to the appropriate SGSN the SGSN number and address are stored

•

A list of GGSN parameter that this subscriber is associated with

•

What type of Packet Data Protocol this subscriber can use

•

A flag when the MS is not reachable for GPRS (MNRG)

•

The Quality of service profile for the subscriber

•

A flag to indicate that no PDP context or MM information is stored in the SGSN (MS purged)

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Network Switching Subsystem (NSS) and GPRS

SMS-MSC Changes and Procedures

System Overview

The Gd interface has an identical structure as a MAP interface. The protocol stack uses the same lower levels, modifications are implemented in the MAP stack to where a number procedures impact the communication between the mobile station and the network. For the Gd interface the following applies: •

SMS message transfer via the SGSN

The C interface between the HLR and SMS-MSC has an updated procedure that allows the network to send routing information to the HLR that the SMS message is send via the GPRS network. In the MSC the alert procedure needs to be updated. GPRS Recovery

The existing recovery procedures need to be extended to include messages being send to the appropriate GSNs. In case of an HLR failure, an HLR reset will trigger a reset message to be send to each SGSN that is known by the HLR. In case of an VLR failure, an VLR reset will trigger a reset message to be send to each associated SGSN.

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System Overview

The TCP/IP Suite .................................................................................................................................................................................................................................... Introduction

When two computers need to communicate with each other, it is necessary to connect them via a physical connection to enable them to pass messages back and forward. Either two computers reside in the same network or the two computers reside in different networks. Transmission Control Protocol/Internet Protocol (TCP/IP) is a set of protocols developed to allow computers (hosts) to communicate with each other across a network.

Internet

TCP/IP suite

The Internet is a world-wide collection of thousands of computer networks that can communicate with each other. All of them speak the same language, namely the TCP/IP protocol suite. Users of any of the Internet networks can reach users on any of the other networks. The most accurate name for the TCP/IP set of protocols is ″the TCP/IP suite″. TCP and IP are two of the protocols in this suite. Because TCP and IP are the best known of the protocols, it has become common to use the term TCP/IP to refer to the whole family. Figure 2-15 TCP/IP suite

Graphic Legend ARP

Address Resolution Protocol

FTP

File Transfer Protocol

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The TCP/IP Suite

The TCP/IP layers

System Overview

ARP

Address Resolution Protocol

ICMP

Internet Control Messaging Protocol

IP

Internet Protocol

RARP

Reverse Address Resolution Protocol

SMTP

Simple Mail Transfer Protocol

TCP

Transmission Control Protocol

TFTP

Trivial File Transfer Protocol

UDP

User Datagram Protocol

Like the OSI 7 layer reference model, TCP/IP is a layered set of protocols. Although the layering of TCP/IP is not the same as the OSI model, the layers correspond with each other. The TCP/IP layering model can be divided in 5 layers: 1.

Physical layer

2.

Data layer

3.

Network layer

4.

Transport layer

5.

Application layer

Physical layer

The physical layer deals with the physical network hardware just as layer 1 in the OSI 7 layer model. Network interface

The network interface protocols deal with how to organise data into frames and how a host transmits these frames over a network. These protocols are similar to the layer 2 (data link) protocols in the OSI 7 layer model. Internet layer

The Internet layer protocols specify the format of the packets which are sent across the Internet as well as the mechanisms used to forward packets from a computer through one or more routers to a final destination. The protocols in this layer are similar to the layer 3 protocols in the OSI 7 layer model. Transport layer

The transport layer protocols in the TCP/IP suite ensure reliable transfer of messages. These protocols are similar to the layer 4 protocols in the OSI 7 layer model.

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System Overview

Application layer

The application layer protocols specify how an application uses an Internet. The application layer protocols correspond to layers 5, 6 and 7 in the OSI 7 layer model.

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System Overview

IP addressing .................................................................................................................................................................................................................................... IP Address

Every host or router on an Internet has an IP address or Internet address. All IP addresses consist of a unique 32 bit number. Each packet sent across an Internet must contain the IP address of the source and the IP address of the destination. The 32 bit IP addresses are seldom represented in binary format but they are represented in a dotted decimal format. Example

The 32 bit binary IP address 10000100 00110000 00000110 00000000 has the dotted decimal notation of: 132.48.6.0 Prefix and Suffix

The 32 bit IP address is divided into two sections, a prefix and a suffix. The IP address prefix is used to identify a particular network within the Internet and the IP address suffix is used to identify a particular host or router on that network. IP address classes

The problem with using an IP address containing prefixes and suffixes is the decision on how big to make each field. If the prefix field is small, only a few networks will be able to connect to the Internet. When the prefix field is increased, then the suffix field decreases, so fewer hosts can connect to a particular network with a given prefix. Since an Internet includes various types of networks, the developers of IP chose addressing schemes for both large and small networks. Therefore the IP addressing scheme is divided into classes. Figure 2-16 IP Addressing Scheme

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IP addressing

System Overview

IP addressing scheme classes:

Network and Host Numbers

•

Classes A, B and C are called primary classes because they are used for host addresses

•

Class D is used for multicasting, which allows packets to be directed to multiple hosts

•

Class E is reserved for future use

Network and host fields containing only 0s or 1s are used for different purposes. Network and Host Numbers

Router Addresses

Address class

Bits in prefix

Max. number of networks

Bits in suffix

Max. number of hosts per network

A

7

1261

24

16 million

B

14

16,3821

16

65,5341

C

21

2 million

8

2541

Routers are responsible for connecting various networks together. This means that a router is connected to at least two networks (with different prefixes). Therefore each router is assigned two or more IP addresses because a router with multiple network connections must have an IP address assigned to each connection. Figure 2-17 Router Address

Note: Not only routers have connections to more than one network. It is also possible to connect a computer to more than one.

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IP addressing

Control of IP addresses

System Overview

Each IP address prefix must be unique. This means that all networks connected to an Internet must have their own unique network address. Therefore all network addresses are assigned by the Internet Assigned Number Authority (IANA) to ensure each IP address prefix is unique. In case of a private Internet (Intranet), the choice of the IP addresses can be made by its owners.

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System Overview

Address Resolution .................................................................................................................................................................................................................................... Software and hardware addresses

Address resolution techniques

Although every host or router on an Internet has one (or more) IP addresses, these cannot be used for sending packets because the layer 2 network interface hardware does not understand IP addresses. IP addresses are virtual; software addresses, but if a packet must arrive at a certain host, the hardware address of that particular host is needed. A process must take place to translate an IP address into a hardware address. There are different techniques used for address resolution. Which technique is used depends upon: •

the type of hardware in the network

•

the number of networks a host may connect to or

•

the hardware addressing scheme that is used

Generally, there are three different address resolution techniques:

Table look up

•

Table look up

•

Closed-form computation

•

Message exchange

This technique in carrying out address resolution makes use of a binding table which contains IP addresses with the corresponding hardware addresses. Each host in the network has its own entry in the binding table. It is however necessary to have a separate binding table for each physical network and as such all IP addresses will contain the same prefix. Closed-form computation

Closed-form Computation

IP address

hardware address

183.76.8.1

0A:74:F8:12:46:C9

183.76.8.2

0A:59:32:B8:7F:18

183.76.8.3

0A:C4:BA:87:24:9E

183.76.8.4

0A:77:81:D8:36:42

183.76.8.5

0A:28:FA:11:1F:99

etc.

etc.

This technique of address resolution is used when dealing with networks, which allow configurable addresses. A mathematical computation is used to derive the hardware address directly from the

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Address Resolution

System Overview

IP address. The computation should be as simple as possible to reduce any delay. Example hardware address = IP address (suffix) hardware address = 194.76.4.4 (suffix) -> hardware address = 4 Address Resolution Protocol (ARP)

The protocol used to translate an IP address into a hardware address is called the Address Resolution Protocol. This technique of address resolution uses a “message based” approach to deriving a hardware address. The host sends a message containing the protocol address to a server(s) and in return, a message is sent containing the appropriate hardware address. There are two methods of message exchange resolution. Either a network is made up of several servers which will carry out all the resolution processes within the network, or each host on the network will answer address resolution requests for its address. Figure 2-18 Message Exchange Process

The process of an ARP message exchange: 1.

Host W begins to broadcast an ARP request message that contains host Ys IP address

2.

All hosts receive the ARP request message

3.

Host Y sends an ARP response message containing its corresponding address directly to host W. All other hosts will discard the ARP request message.

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System Overview

Internet Protocol (IP) .................................................................................................................................................................................................................................... IP service

The Internet Protocol (IP) is a procedure by which information (data) is sent from one computer to another. This protocol defines a datagram in which the data is transported. Routing is done by using an address that is unique for each computer or system. When data has to be sent, it will be divided into datagrams which also include the source and destination addresses. The network elements called routers will examine the destination address and as far as it is in their scope, send the datagram to another router. When a router (gateway) recognises the complete address, it will send the datagram to that corresponding computer.

Datagram & Packet

Datagrams are encapsulated in layer 2 packets for point to point transportation. If the datagram is larger than the maximum packet size, the datagram will be split into fragments and re-assembled again at the other side.

Connectionless

IP provides higher layer protocols (like TCP) a connectionless service, which means that no connection is established prior to the sending of the datagram.

IP header format

An IP datagram consists of a header part and a data part. The header contains a fixed part of 20 bytes (5 × 32 bit quantities) and an optional part of a variable length. Figure 2-19 IP Header Format

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Internet Protocol (IP)

System Overview

The different Header Fields are discussed below: Version

Indicates the version of Internet protocol. This is currently version 4

IHL

The Internet header (IHL) length field is used to specify the number of 32 bit quantities that make up the header. Minimum value is 5

Service Type

The service type field indicates the quality of service desired during transmission of the message through the Internet. For example, a message containing speech requires fast transmission and less reliability, but a file transfer message requires high reliability and normal transmission speed.

Total Length

The total length field is used to specify the total length of the datagram (header + data). Maximum length is 64KB, or 65.536 bytes

Identification

The identification field uniquely identifies a packet so that it can be distinguished from other packets; it is usually assigned when data is passed to the network layer from a higher layer. All packets of the same datagram contain the same value in the identification field.

Flags

The flags field indicates whether the packet is fragmented or whether it is the last fragment of the packet.

Fragment Offset

The fragment offset field indicates which fragment of the original packet this is. It is used to rebuild the full packet once all the fragments have been collected

Time to Live

The time to live field specifies the time a datagram will travel around in the network before it is destroyed. This prevents a datagram from travelling forever around a path that contains a loop. The field carries a positive integer value between 1 and 255; every time the datagram passes through a router, this value is reduced by 1. When the value reaches 0, the datagram is discarded

Type

The type field identifies the next higher layer protocol using IP. For example, TCP (value = 6) or UDP (value = 17).

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Internet Protocol (IP)

System Overview

Version

Indicates the version of Internet protocol. This is currently version 4

Header Checksum

The header checksum is used to provide error checking on the header by itself. It is used because the header can change (for example, due to fragmentation)

Source IP Address

The source IP addresses is the Internet address of the originating host

Destination IP Address

The destination IP addresses is the Internet addresses of the terminating host.

Options and Padding

The options field is used to specify routing options and network testing. Padding can be added to ensure that the header is a multiple of 32 bits

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System Overview

Transmission Control Protocol (TCP) .................................................................................................................................................................................................................................... Features

The Transmission Control Protocol (TCP) provides a highly reliable transport service. Most Internet applications use the services of TCP to transport data between hosts. TCP offers seven major features:

TCP header format

•

Connection orientated

•

Complete reliability

•

Full duplex communication

•

Stream interface

•

Reliable connection set-up

•

Graceful connection shut-down

A TCP header contains a fixed part of 20 bytes (5 × 32 bit quantities) and may be followed by header options. After the header 65,535-20-20 = 65,495 data bytes may follow, where the first 20 refers to the IP header and the second to the TCP header. Figure 2-20 TCP Header

The different TCP header fields are discussed below: Field

Description

SOURCE PORT and DESTINATION PORT

The source and destination port fields identify the relevant application layer services.

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Transmission Control Protocol (TCP)

System Overview

Field

Description

SEQUENCE NUMBER

The sequence number field specifies the sequence number of a segment of a message and is used to ensure that the segments of a message can be ordered properly

ACKNOWLEDGMENT NUMBER

The acknowledgment number field contains the sequence number of the next segment expected to be received. It indicates correct reception of all messages up to that sequence number.

DATA OFFSET

The data offset field indicates the start of the data within the segment, measured in 32 bit words, but that number is just the header length in words, so the effect is the same

FLAGS

URG - notes that the urgent pointer is valid ACK - notes that the acknowledgment number field is valid. PSH - causes the data in the message to be ″pushed″ through to the receiving application even if the buffer is not full RST - resets the connection SYN - resynchronises the sequence number. The SYN bit is used to establish connections FIN - marks that the sender has reached the end of its byte stream. The FIN bit is used to release a connection

WINDOW

The window field is used to specify how much data the receiver is willing to accept.

CHECKSUM

The checksum field is 16 bits long and it checksums the header and the data of the TCP message.

URGENT POINTER

The urgent pointer is used to indicate a byte offset from the current sequence number at which urgent data are to be found

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System Overview

User Datagram Protocol (UDP) .................................................................................................................................................................................................................................... Connectionless transport protocol

The TCP/IP suite also supports a connectionless transport protocol, User Datagram Protocol (UDP). UDP provides a way for applications to send a message without having to establish a connection. UDP allows the movement of data with the minimum requirement of network services. Figure 2-21 UDP Header Format

A UDP segment consists of an 8 byte header followed by the data: Field

Description

SOURCE PORT and DESTINATION PORT

The source and destination port fields identify the relevant application layer services.

LENGTH

The length field indicates the length of the total UDP segment, header and data

CHECKSUM

The checksum field is used to check for errors across the entire segment

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System Overview

TCP/IP Example .................................................................................................................................................................................................................................... Message Flow

A packet containing data is sent over a TCP/IP network and arrives at its receiving host. The packet passes through 5 TCP/IP layers: •

Layer 1 - This is the actual physical network hardware, for example, an ethernet. The packet arrives at the receiving host defined in its hardware address field.

•

Layer 2 - The network interface strips out the header containing the hardware address, performs a check and strips out the footer containing the check sequence. The payload is passed on to the Internet layer.

•

Layer 3 - The Internet layer analyses the IP header containing: source IP address, destination IP address, total length etc. The header is stripped out and the payload is passed on to the transport layer. The protocol of the transport layer (UDP or TCP) is defined in the type fields of the IP header.

•

Layer 4 - The transport layer protocols identify the destination of the data. TCP also performs some other tasks to ensure the reliability of the connection. The header is stripped out and the data is passed on to the application layer.

•

Layer 5 - The application layer presents the data to the user.

Figure 2-22 Message Flow

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3

Interfaces

Overview .................................................................................................................................................................................................................................... Purpose

Contents

This chapter describes the GSM and the new GPRS network interfaces. This chapter covers the following subjects: GSM System Interfaces

3-2

GPRS System Interfaces

3-4

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Interfaces

GSM System Interfaces .................................................................................................................................................................................................................................... Introduction

For the connection of the different nodes in the GSM network, different interfaces are defined in the GSM specifications. The following interfaces appear in the figure: Figure 3-1 GSM Interfaces

Um-Interface or Air Interface

Abis- Interface

The Um-Interface is the interface between the Base Transceiver Station (BTS-2000) and a Mobile Station (MS). The Um-Interface is required for supporting: •

Universal use of any compatible mobile station in a GSM network

•

A maximum spectral efficiency On the Um-Interface there are the following types of logical channels: Traffic channels, Broadcast channels, Common control channels and Dedicated control channels.

The Abis-Interface is the interface between the Base Station Controller (BSC) and the BTS and is used to carry the Um-Interface formatted 13 kbps data (speech data and signaling information) between them.

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GSM System Interfaces

Interfaces

The interface comprises traffic and control channels. Its physical transmission is based on the PCM30 (Pulse Code Modulation) transmission principles of the ITU-T (International Telecommunication Union - sector Telecommunication) at a data rate of 2048 kbps. The PCM30 frame consists of 32 channels, each carrying 64 kbps. The bit-stream of 64 kbps represents the transmission of 8000 samples per second, with each sample being coded into 8 bits. Functions implemented at the Abis-Interface are:

A-Interface

•

Voice - data traffic exchange

•

Signaling exchange between the BSC and the BTS

•

Transporting synchronization information from the BSC to the BTS

The A-Interface is used to carry the 64 kbps speech data and signaling information between the BSC and the MSC. It’s physical transmission is also based on the PCM30 principles of the ITU-T at a data rate of 2048 kbps. Timeslot 0 of the PCM30 frame is used for synchronization purposes. Timeslot 1 through 15 and 17 through 31 are used for exchanging the 64 kbps speech data. Timeslot 16 is used to transfer the SS No. 7 signaling between the BSC and the MSC.

Proprietary M-Interface

In the GSM network implementation of Lucent Technologies, the BSC includes the TRAU (Transcoder/Rate Adapter Unit). The TRAU adapts the transmission bit rate of the A interface (64 kbps) to the Abis-Interface (16 kbps). The interface between the physical BSC and the TRAU is known as the M-Interface. Each of the timeslots 1 through 15 and 17 through 31 on the M-Interface contains four multiplexed A-interface channels. Timeslot 0 is used for synchronization purposes. Timeslot 16 contains the signaling information which is transparently mapped from timeslot 16 of the A-interface.

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Interfaces

GPRS System Interfaces .................................................................................................................................................................................................................................... Gb Interface

The GBS connects to the BSS using the ETSI standardised open Gb interface. The Gb Interface is used to transport packet data traffic related to individual MS’s and general signaling information from the SGSN to the BSS and vice versa. Lucent NR 9.0 supports the Gb interface with the ETSI GPRS Phase 1 standardised layer 2 protocol Frame Relay (FR). The physical layer of this interface is supported with standard European E1 (2Mbit/s) trunks or single DS0 64 Kbit/s time-slots within an E1 line as specified by ETSI.

Gb Interface Protocol Stack Figure 3-2 Gb Interface Protocol Stack

The BSS will provide a Network Services Layer implementation to the ETSI GPRS standards. For NR 9.0, a minimal load sharing capability will be provided The BSSGP protocol operates BSSGP Virtual Connections (BVC) for the transmission of LLC-PDU frames between the SGSN and the BSS.

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Interfaces

The following apply: •

For NR 9.0 the FR protocol implementation shall support the transmission of packaged LLC frames over Point To Point (PTP) FR Virtual Circuits (VC)

•

The Backward Explicit Congestion Notification (BECN) / Forward Explicit Congestion Notification (FECN) and Discard Eligibility (DE) bits is never set by the BSS or Frame Relay Entities.

Abis Interface

When GPRS MAC and RLC layer functions are positioned remote to the BTS the information between the channel code unit (CCU) and the remote GPRS packet control unit (rPCU) is transferred in frames with a fixed length of 320 bits. Within these frames both GPRS data and the GPRS RLC/MAC associated control signals are transferred. The Abis interface should be the same if the PCU is positioned at the BSC site or at the SGSN. At the BSC, the PCU could be implemented as an adjunct unit to the BSC. At the SGSN, the BSC should be considered as transparent for 16 Kbit/s channels. In both cases, the PCU is referred to as the remote PCU. The remote PCU is considered a part of the BSC, and the signalling between the BSC and the PCU may be performed by using BSC internal signals. The in-band signalling between the CCU and the PCU functions, using PCU frames is required when the Abis interface is applied. The Abis interface for supporting the rPCU is a proprietary Lucent Technologies solution and it is only valid for coding schemes 1 and 2. For coding schemes 3 and 4 there will be a new structure.

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4

GPRS Signalling and Transmission Protocols

Overview .................................................................................................................................................................................................................................... Purpose

Contents

This chapter discusses the signalling and transmission protocols for the different GPRS interfaces, the GPRS network entities and the packet data logical channels for GPRS. This chapter contains information on the following topics: The GPRS Signalling Plane

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The GPRS Transmission Plane

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GGSN Protocols

4-6

SGSN Protocols

4-9

BSS Protocols

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GPRS MS Protocols

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GPRS Logical Channels

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Mapping of packet data logical channels onto physical channels

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GPRS MS

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GPRS Signalling and Transmission Protocols

The GPRS Signalling Plane .................................................................................................................................................................................................................................... Functions

The signalling plane consists of protocols for control and support of the transmission plane functions: •

Controlling the GPRS network access connections, such as attaching to and detaching from the GPRS network.

•

Controlling the attributes of an established network access connection, such as activation of a Packet Data Protocol (PDP) address. Controlling the routing path of an established network connection in order to support user mobility.

•

Controlling the assignment of network resources to meet changing user demands.

•

Providing supplementary services

Figure 4-1 Map Signalling

The Message Transfer Part (MTP) is responsible for the reliable transport of signalling information between the user parts. Level 2 controls the functions of the link; it is responsible for reliable message transfer. The level 3 functions handle procedures such as message routing and signalling network management. The Signalling Connection Control Part (SCCP) defines a means of transferring signalling data or management data without the need to establish a circuit. SCCP is really an addition of MTP. The Transaction Capability Application Part (TCAP) is used to manage the dialog between two network entities. The Mobile Application Part (MAP) protocol is used to transfer non-circuit-related signalling information between the network entities, i.e. between: ....................................................................................................................................................................................................................................

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The GPRS Signalling Plane

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SGSN <-> HLR SGSN <-> EIR SGSN <-> SMS-GMSC or SMS-IWMSC GGSN <-> HLR The information to be transferred is used during, for example, Location Updating, authentication, handover of established calls and transfer of charging information. BSSAP Signalling Figure 4-2 BSSAP Signalling

The Base Station System Application Part + (BSSAP+) is a subset of BSSAP procedures specifically for GPRS and supports signalling between the SGSN and MSC/VLR. It supports the following procedures: •

IMSI attach and detach via SGSN.

•

Location area updating via SGSN.

•

Paging via GPRS.

•

Alerting procedure.

•

Identification procedure.

•

Information procedure.

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GPRS Signalling and Transmission Protocols

The GPRS Transmission Plane .................................................................................................................................................................................................................................... The GPRS Transmission Plane

The transmission plane consists of a layered protocol structure providing user information transfer, along with associated information transfer control procedures (for example: flow control, error detection, error correction and error recovery). Figure 4-3 Transmission Plane

The GPRS Protocols

The transmission plane is made up of both GPRS specific protocols and open protocols such as the Internet Protocol (IP). The protocols are summarized below: •

GPRS Tunnelling Protocol (GTP)

•

Transmission Control Protocol (TCP) & User Datagram Protocol (UDP)

•

Internet Protocol (IP)

•

Subnetwork Dependent Convergence Protocol (SNDCP)

•

Logical Link Control (LLC)

•

Base Station System GPRS Protocol (BSSGP)

•

Network Service (NS)

•

Radio Link Control / Medium Access Control (RLC/MAC)

•

GSM Radio Frequency (GSM RF)

GPRS Tunnelling Protocol (GTP)

This protocol tunnels user data and signalling between GPRS support nodes in the GPRS backbone network.

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Transmission Control Protocol (TCP) & User Datagram Protocol (UDP)

TCP carries GTP Protocol Data Units (PDUs) in the GPRS backbone network for protocols that need a reliable connection. UDP carries GTP PDUs for protocols that do not need a reliable connection. Both TCP and UDP can be found in the TCP/IP suite. Internet Protocol (IP)

This is the GPRS backbone network protocol used for routing user data and control signalling. The GPRS backbone network may initially be based on the IP version 4 (IPv4) protocol. Ultimately, IP version 6 (IPv6) shall be supported. Subnetwork Dependent Convergence Protocol (SNDCP)

This transmission functionality maps the network level PDUs onto the underlying GPRS specific network. Logical Link Control (LLC)

This layer provides a highly reliable ciphered logical link. LLC shall be independent of the underlying radio interface protocols in order to allow GPRS to be used on different radio systems. Base Station System GPRS Protocol (BSSGP)

This layer conveys routing and Quality of Service (QoS) information between BSS and SGSN. BSSGP does not perform error correction. Network Service (NS)

This layer transports BSSGP PDUs. NS is based on the Frame Relay. Radio Link Control / Medium Access Control (RLC/MAC)

This layer contains two functions: The RLC function provides a radio solution dependent reliable link. The MAC function controls the access signalling procedures for the radio channel, and the mapping of LLC frames onto the GSM physical channel. GSM Radio Frequency (GSM RF)

This is the standard GSM RF interface.

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GGSN Protocols .................................................................................................................................................................................................................................... GPRS Tunnelling Protocol (GTP)

The GPRS Tunnelling Protocol (GTP) is the protocol between GPRS Support Nodes (GSNs) in the GPRS backbone network. It includes both signalling and data transfer procedures. GTP is defined both for the Gn interface between GSNs within a PLMN, and the Gp interface between GSNs in different PLMNs. In the signalling plane, GTP specifies a tunnel control and management protocol which allows the SGSN to provide GPRS network access for a MS. Signalling is used to create, modify and delete tunnels. In the transmission plane, GTP uses a tunnelling mechanism to provide a service for carrying user data packets. The choice of path is dependent on whether the user data to be tunneled requires a reliable connection or not. The GTP protocol is implemented only by SGSNs and GGSNs. No other system entities need to be aware of GTP. GPRS MSs are connected to a SGSN without being aware of GTP. Figure 4-4 LLC Frame Numberf

All fields in the GTP header shall always be present but the content of the fields differs depending on if the header is used for signalling messages or T-PDUs.

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The GTP header consists of the following fields:

User Datagram Protocol (UDP)

Transmission Control Protocol (TCP)

Internet Protocol (IP)

Field

Description

Version

Version shall be set to 0 to indicate the first version of GTP.

Reserved

Reserved bits for future use that shall be set to 1.

LFN

LFN is a flag indicating if LLC Frame Number is included or not.

Message Type

Message Type indicates the type of GTP message.

Length

The Length field indicates the length in octets of the GTP message (G-PDU).

Sequence Number

The Sequence Number is a transaction identity for signalling messages and an increasing sequence number for tunneled PDUs (T-PDUs).

Flow Label

Flow Label identifies unambiguously a GTP flow.

LLC Frame Number

The LLC Frame Number is used at the inter SGSN routing update procedure to co-ordinate the data transmission on the link layer between the MS and SGSN.

X

The spare bits X indicate the unused bits which shall be set to 0 by the sending side and which shall not be evaluated by the receiving side.

TID

This is the tunnel identifier that points out MM and PDP contexts.

UDP carries GTP Protocol Data Units (PDUs) for protocols that do not need a reliable connection (for example IP). UDP provides protection against corrupted GTP PDUs. UDP can be found in the TCP/IP suite. TCP carries GTP Protocol Data Units (PDUs) in the GPRS backbone network for protocols that need a reliable connection. TCP can be found in the TCP/IP suite. This is the GPRS backbone network protocol used for routing user data and control signalling. The GPRS backbone network may initially be based on the IP version 4 (IPv4) protocol. Ultimately, IP version 6 (IPv6) shall be supported. IP can be found in the TCP/IP suite.

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GGSN Protocols

GGSN activity

GPRS Signalling and Transmission Protocols

A packet from an external data network arrives at the GGSN and will be encapsulated with a GTP header, a UDP or a TCP header and an IP header. If the resulting IP datagram is larger than the Maximum Transfer Unit (MTU), fragmentation of the IP datagram will occur. Figure 4-5 GGSN Activity

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SGSN Protocols .................................................................................................................................................................................................................................... Subnetwork Dependent Convergence Protocol (SNDCP)

Network layer protocols are intended to be capable of operating over services derived from a wide variety of subnetworks and data links. GPRS supports several network layer protocols providing protocol transparency for the users of the service. Introduction of new network layer protocols to be transferred over GPRS shall be possible without any changes to GPRS. Therefore, all functions related to transfer of Network layer Protocol Data Units (N-PDUs) shall be carried out in a transparent way by the GPRS network entities. This is one of the requirements for GPRS SNDCP. Another requirement for the Sub Network Dependent Convergence Protocol (SNDCP) is to provide functions that help to improve channel efficiency. This requirement is fulfilled by means of compression techniques.

Multiplexing of different protocols

The set of protocol entities above SNDCP consists of commonly used network protocols. They all use the same SNDCP entity, which then performs multiplexing of data coming from different sources to be sent using the service provided by the LLC layer. The Network Service Access Point Identifier (NSAPI) is an index to the PDP context of the PDP that is using the services provided by SNDCP. Each active NSAPI shall use the services provided by the Service Access Point Identifier (SAPI) in the LLC layer. Several NSAPIs may be associated with the same SAPI. Figure 4-6 Multiplexing different protocols

SNDCP Service Primitives

Below the service primitives used for communication between the SNDCP layer and other layers are explained.

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SGSN Protocols

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SN-DATA

The request primitive is used by the SNDCP user for acknowledged transmission of N-PDU. The successful transmission of SN-PDU shall be confirmed by the LLC layer. The request primitive conveys NSAPI to identify the PDP using the service. The indication primitive is used by the SNDCP entity to deliver the received N-PDU to the SNDCP user. Successful reception has been acknowledged by the LLC layer.

SN-UNITDATA

SNDCP Service Functions

The request primitive is used by the SNDCP user for unacknowledged transmission of N-PDU. The request primitive conveys NSAPI to identify the PDP using the service and protection mode to identify the requested transmission mode. The indication primitive is used by the SNDCP entity to deliver the received N-PDU to the SNDCP user. SNDCP shall perform the following functions: •

Mapping of SN-DATA primitives onto LL-DATA primitives.

•

Mapping of SN-UNITDATA primitives onto LL-UNITDATA primitives.

•

Multiplexing of N-PDUs from one or several network layer entities onto the appropriate LLC connection.

•

Establishment, re-establishment and release of acknowledged peer-to-peer LLC operation.

•

N-PDU buffering at SNDCP for acknowledged service.

•

Management of delivery sequence for each NSAPI, independently.

•

Compression of redundant protocol control information (for example TCP/IP header) at the transmitting entity and decompression at the receiving entity. The compression method is specific to the particular network layer or transport layer protocols in use.

•

Compression of redundant user data at the transmitting entity and decompression at the receiving entity. Data compression is performed independently for each SAPI, and may be performed independently for each PDP context.

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•

Segmentation and re-assembly. The output of the compression functions is segmented to the maximum length of LL-PDU. These procedures are independent of the particular network layer protocol in use. Negotiation of the XID parameters between peer SNDCP entities using XID exchange.

Figure 4-7 SNDCP Service Model

The figure above shows the transmission flow through the SNDCP layer. The order of functions is as follows: •

Protocol control information compression.

•

User data compression.

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SGSN Protocols

SNDCP Header

GPRS Signalling and Transmission Protocols

•

Segmentation of compressed information into SN-DATA or SN-UNITDATA PDUs.

•

The order of functions is vice versa in the reception flow:

•

Re-assembly of SN-PDUs to N-PDUs.

•

User data decompression.

•

Protocol control information decompression.

This is an SNDCP header used for SN-DATA PDUs: Figure 4-8 SNDCP Header

For SNDCP headers used for SN-UNITDATA, some additional are added. This comprises the segment number field, the extension (E) bit and the N-PDU number field which is used to identify a particular N-PDU. The SNDCP header contains the following fields: Field

Description

X

Spare bit (set to 0).

C

The Compression © indicator is used to indicate whether or not the compression fields (DCOMP and PCOMP) are included.

T

The Type (T) bit is used to specify the type of PDU (SN-DATA PDU or SN-UNITDATA PDU).

M

The More (M) bit is used to indicate the last segment of the N-PDU.

NSAPI

The Network Service Access Point Identifier (NSAPI) is used to identify the user of SNDCP.

DCOMP

Data compression coding (DCOMP) is used to indicate whether or not data compression has taken place and points to the data compression identifier negotiated dynamically.

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Logical Link Control (LLC)

GPRS Signalling and Transmission Protocols

Field

Description

PCOMP

Protocol control information compression coding (PCOMP) is used to indicate whether or not control compression has taken place and points to the protocol control information compression identifier negotiated dynamically.

The LLC layer provides reliable transfer of data between the MS and the SGSN, retransmission during handovers and flow control between the MS and the SGSN. Figure 4-9 LLC FrameFormat

Address field

The address field consists of a single octet. The format of the address field is as follows: Figure 4-10 llc_address_field

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SGSN Protocols

GPRS Signalling and Transmission Protocols

The different fields are discussed below: Field

Description

PD

The Protocol Discriminator (PD) bit indicates whether a frame is an LLC frame or belongs to a different protocol.

C/R

The Command/Response (C/R) bit identifies a frame as either a command or a response.

X

Spare bit.

SAPI

The Service Access Point Identifier (SAPI) identifies a Logical Link Entity (LLE) that should process an LLC frame and it also identifies a layer 3 entity that is to receive information carried by the LLC frame.

Control field

The control field typically consists of between one and three octets although may under some circumstances be comprised of up to 36 octets. The control field identifies the type of frame. Four types of control field formats are specified: •

I format - confirmed information transfer.

•

S format - supervisory functions.

•

UI format - unconfirmed information transfer.

•

U format - control functions.

Figure 4-11 Control Field

The format of the control field is as follows:llc •

A - Acknowledgement request bit

•

E- Encryption function bit

•

Mn- Unnumbered function bit

•

N(R) - Transmitter receive sequence number

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•

N(S) - Transmitter send sequence number

•

N(U) - Transmitter unconfirmed sequence number

•

P/F - Poll bit, when issued as a command, Final bit, when issued as a response

•

PM - Protected mode bit

•

Sn - Supervisory function bit

•

X - Spare bit

Information field

The information field of a frame, when present, follows the control field. Frame Check Sequence (FCS) field

The FCS field shall consist of a 24 bit Cyclic Redundancy Check (CRC) code. The CRC is used to detect bit errors in the frame header and information fields. Base Station System GPRS Protocol (BSSGP)

The primary functions of the BSSGP include the following: •

In the downlink, the provision by an SGSN to a BSS of radio related information used by the RLC/MAC function.

•

In the uplink, the provision by a BSS to an SGSN of radio related information derived from the RLC/MAC function.

•

The provision of functionality to enable two physically distinct nodes, an SGSN and a BSS, to operate node management control functions.

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SGSN Protocols

GPRS Signalling and Transmission Protocols

BSSGP Service Model

BBSGP maps LLC, GPRS mobility management (GMM) and network management (NM) on one frame. Figure 4-12 BSSGP Service Model

•

BSSGP provides functions controlling the transfer of LLC frames passed between an SGSN and an MS across the Gb interface.

•

RL (relay) provides functions controlling the transfer of LLC frames between the RLC/MAC layer and the BSSGP layer.

•

GMM provides functions associated with GPRS mobility management between an SGSN and a BSS. GMM functions deal with paging, radio status and radio access capabilities etc.

•

NM provides functions associated with Gb-interface and BSS SGSN node management. NM functions deal with flow control, status and resets etc.

SGSN Activity

Data and signalling messages arrive at the SGSN via the Gn interface. The IP datagrams are collected by the IP layer and are reassembled if fragmentation has occurred either at the SGSN or at any IP router along the Gn interface. Any additional processes are carried out at this layer before the payload is passed up to either UDP or TCP. At the UDP/TCP layer, more processes are carried out such as determining the checksum value before this payload is passed up to GTP. AT the GTP layer, the GTP header is stripped off resulting in the PDU being ready for onward transmission across the Gb interface towards the BSS. As such, the PDU can be said to have been tunneled across the Gn interface. To travel across the Gb interface, the PDU ....................................................................................................................................................................................................................................

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requires further modification. This is carried out by the Subnetwork Dependent Convergence Protocol (SNDCP), the Logical Link Protocol (LLC) and the Base Station System GPRS Protocol (BSSGP) before being carried towards the BSS on the Gb interface via a Frame Relay network. Figure 4-13 SGSN Activity

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GPRS Signalling and Transmission Protocols

BSS Protocols .................................................................................................................................................................................................................................... RLC/MAC block structure

The RLC/MAC block consists of a MAC header and an RLC data block or RLC/MAC control block. The RLC/MAC control block is the part of a RLC/MAC block carrying a control message between RLC/MAC entities. It does not contain an RLC header. Figure 4-14 RLC/MAC Control Block

Radio Link Control (RLC) layer

The RLC function is responsible for the following: •

RLC provides service primitives for the transfer of LLC PDUs between the LLC layer in the SGSN and the MAC layer.

•

RLC performs segmentation and re-assembly of LLC PDUs into RLC/MAC blocks.

•

RLC provides a Backward Error Correction (BEC) for reliable data transfer and enables the selective retransmission of unsuccessfully delivered RLC/MAC blocks.

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RLC data block

The structure of the RLC data blocks are dependent upon the direction of the data transfer (uplink or downlink). Figure 4-15 Uplink RLC Data Block

Figure 4-16 Downlink RLC Data Block

The following fields comprise the RLC data blocks: Field

Description

FBI

The Final Block Indicator (FBI) bit indicates that the downlink RLC data block is the last RLC data block of the downlink TBF.

TI

The TLLI Indicator (TI) bit indicates the presence of an optional TLLI field within the RLC data block.

TFI

The Temporary Flow Identifier (TFI) field identifies the Temporary Block Flow (TBF) to which the RLC data block belongs.

E

The Extension (E) bit is used to indicate the presence of an optional octet in the RLC data block header.

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BSS Protocols

Medium Access Control (MAC) layer

GPRS Signalling and Transmission Protocols

Field

Description

BSN

The Block Sequence Number (BSN) field carries the sequence number of each RLC data block within the TBF.

M

The More (M) bit is used to indicate that more information is to follow.

Length Indicator

The Length Indicator (LI) is used to delimit LLC frames within the RLC data block. The first LI is used to specify the length of the first LLC frame, the second LI indicates the length of the next LLC frame.

TLLI

The TLLI field contains a Temporary Logical Link Identity (TLLI). This value is carried only in the first three RLC data blocks to be transferred in the uplink.

RLC data

The RLC data field contains octets from one or more LLC PDUs.

spare

The number of spare bits depends on the channel coding scheme being used.

The main function of the MAC layer is the control of multiple MSs sharing a common resource on the GPRS air interface. The RLC data block is passed down to the MAC layer where a MAC header is added. The MAC procedures support the provision of Temporary Block Flows (TBFs) that allow the point-to-point transfer of signalling and user data within a cell between the network and a MS. The structure of the MAC headers are dependent upon the direction of the data transfer (uplink or downlink). Figure 4-17 Uplink Mac Header Format

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Figure 4-18 Downlink Mac Header Format

The different MAC header fields are discussed below: Field

Description

USF

The Uplink State Flag (USF) field is used to indicate which MS is allocated the GPRS resource.

R

The Retry (R) bit shall indicate whether the mobile station transmitted the channel request message one time or more than one time during its most recent channel access.

S/P

The Supplementary/Polling (S/P) bit is used to indicate whether the RRBP field is valid or not valid.

RRBP

The Relative Reserved Block Period (RRBP) field specifies a single uplink block in which the mobile station shall transmit either a PACKET CONTROL ACKNOWLEDGEMENT or a PACCH block to the network.

Payload Type

The Payload Type field shall indicate the type of data contained in remainder of the RLC/MAC block.

SI

The Stall Indicator (SI) bit indicates whether the mobile’s transmission has stalled.

Countdown Value

The Countdown Value (CV) field is sent by the mobile station to allow the network to calculate the number of RLC data blocks remaining for the current uplink connection.

Temporary Block Flow (TBF)

A Temporary Block Flow (TBF) is a physical connection used by the BSS and the MS to support the unidirectional transfer of LLC PDUs on packet data physical channels. The TBF is allocated radio resource on one or more PDCHs and comprises a number of RLC/MAC blocks

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carrying one or more LLC PDUs. A TBF is temporary and is maintained only for the duration of the data transfer. The physical layer consists of two sub-layers: •

Physical RF layer.

•

Physical link layer.

Figure 4-19 Air Interface

Physical RF layer

The physical RF layer performs the modulation of the physical waveforms based on the sequence of bits received from the physical link layer. The physical RF layer also demodulates received waveforms into a sequence of bits which are transferred to the physical link layer for interpretation. The GSM physical RF layer is used as a basis for GPRS. Physical link layer

The purpose of the physical link layer is to convey information across the GSM radio interface, including RLC/MAC information. The physical link layer supports multiple MSs sharing a single physical channel. The physical link layer provides communication between MSs and the Network. The physical link layer control functions provide the services necessary to maintain communications capability over the physical radio channel between the network and MSs. Functions at the physical link layer include: •

Forward Error Correction (FEC) coding, allowing the detection and correction of transmitted code words and the indication of uncorrectable code words.

•

Rectangular interleaving of one Radio Block over four bursts in consecutive TDMA frames.

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•

Procedures for detecting physical link congestion.

•

Synchronisation procedures, including determining and adjusting the MS timing advance parameters.

•

Monitoring and evaluation procedures for radio link signal quality.

•

Cell selection and re-selection procedures.

•

Transmitter power control procedures.

•

Battery power conservation procedures, for example Discontinuous Reception (DRX) procedures.

BSS Activity

Data and signalling messages arrive at the BSS via the Gb interface. The frames arriving at the Packet Control Unit (PCU) pass through BSSGP where the information and signalling messages are separated into LLC frames, GPRS Mobility Management (GMM) information and Network Management (NM) information. With regards to data and signalling messages destined for the GPRS MS, the LLC frames pass through a relay entity (LLC relay) before entering the RLC and the MAC layer respectively. The RLC/MAC layer provides services for information transfer over the physical layer. Figure 4-20 BSS Activity

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GPRS Signalling and Transmission Protocols

GPRS MS Protocols .................................................................................................................................................................................................................................... GPRS MS activity

At the GPRS MS, the PDUs pass through the protocol stack in the reverse order. The four consecutive air interface bursts are re-assembled and passed to the RLC/MAC layer. Once all the RLC data blocks for a particular LLC PDU have been received, the LLC frame is re-assembled and passed up to the LLC layer. Here the Frame Check Sequence (FCS) is calculated and any retransmissions are activated if necessary, otherwise the payload area is passed up to the SNDCP layer. At the SNDCP layer, the PDUs are re-assembled and the information and control fields are decompressed. Finally, the PDUs are passed up to the IP/X.25 layer. Figure 4-21 MS Activity

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The GPRS Air Interface .................................................................................................................................................................................................................................... Packet data logical channels for GPRS

One or more packet data logical channels can be transmitted on a physical channel. There are different types of packet data logical channels. The type of packet data logical channel is determined by the function of the information transmitted over it. Figure 4-22 Logical channels for GPRS

The following types of packet data logical channels are defined: •

Packet Common Control Channels (PCCCH)

•

Packet Broadcast Control Channel (PBCCH)

•

Packet Dedicated Control Channels (PDCCH)

•

Packet Data Traffic Channels (PDTCH)

Note: The PDTCH carries packet data, and the other types control information (signalling).

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GPRS Logical Channels .................................................................................................................................................................................................................................... Packet Common Control Channels (PCCCH)

Packet Broadcast Control Channel (PBCCH)

PCCCH comprises packet data logical channels for common control signalling used for packet data as described below: •

Packet Random Access Channel (PRACH) For uplink only PRACH is used by MS to initiate uplink transfer for sending data or signalling information.

•

Packet Paging Channel (PPCH) For downlink only PPCH is used to page an MS prior to downlink packet transfer. PPCH uses paging groups in order to allow usage of discontinuous reception. PPCH can be used for paging of both circuit switched and packet data services. The paging for circuit switched services on PPCH is applicable for class A and B GPRS MSs.

•

Packet Access Grant Channel (PAGCH) For downlink only PAGCH is used in the packet transfer establishment phase to send resource assignment to an MS prior to packet transfer. It is used to allocate one or several PDTCHs.

•

Packet Notification Channel (PNCH) For downlink only PNCH is used to send a Point To Multipoint (PNCH will be standardised in the future) - Multicast (PTM-M) notification to a group of MSs prior to a PTM-M packet transfer. A ’PTM-M new message’ indicator may optionally be sent on all individual paging channels to inform MSs interested in PTM-M when they need to listen to PNCH. The PNCH will be standardized in the future.

PBCCH broadcasts packet data specific system information. If PBCCH is not allocated, the packet data specific system information is broadcast on the Broadcast Control Channel (BCCH). The PBCCH is only found on the downlink.

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GPRS Logical Channels

Packet Dedicated Control Channels (PDCCH)

Packet Data Traffic Channels (PDTCH)

GPRS Signalling and Transmission Protocols

Packet Dedicated Control Channels (PDCCH) is comprised of the following: •

Packet Associated Control Channel (PACCH) PACCH transfers signalling information related to a given MS. The signalling information includes for example, acknowledgments and power control information. PACCH carries also resource assignment and reassignment messages, comprising the assignment of a capacity for PDTCH(s) and for further occurrences of PACCH. The PACCH shares resources with PDTCHs, that are currently assigned to one MS. Additionally, an MS that is currently involved in packet transfer, can be paged for circuit switched services on PACCH. The PACCH can be found on both uplink and downlink.

•

Packet Timing advance Control Channel, uplink (PTCCH/U) PTCCH/U is used to transmit random access burst to allow estimation of the timing advance for one MS in packet transfer mode.

•

Packet Timing advance Control Channel, downlink (PTCCH/D) PTCCH/D is used to transmit timing advance information updates to several MSs. One PTCCH/D is paired with several PTCCH/U’s.

PDTCH is a channel allocated for data transfer. It is temporarily dedicated to one MS or to a group of MSs in the Point To Multipoint - Multicast (PTM-M) case. In multislot operation, one MS may use multiple PDTCHs in parallel for individual packet transfer. All packet data traffic channels are uni-directional: •

uplink (PDTCH/U), for a mobile originated packet transfer.

•

downlink (PDTCH/D), for a mobile terminated packet transfer.

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Mapping of packet data logical channels onto physical channels .................................................................................................................................................................................................................................... Overview

A Packet Data Channel (PDCH) is a physical time-slot that has been allocated for the use of GPRS. Different packet data logical channels can occur on the same physical channel (i.e. PDCH). The sharing of the physical channel is based on blocks of 4 consecutive bursts. Whenever the PCCCH is not allocated, the CCCH shall be used to initiate a packet transfer. One given MS may use only a subset of the PCCCH, the subset being mapped onto one physical channel (i.e. PDCH). Packet data logical channels are mapped dynamically onto a 52-multiframe. If it exists, PCCCH is mapped on one or several physical channels according to a 52-multiframe, In that case the PCCCH, PBCCH and PDTCH share same physical channels (PDCHs). GPRS Logical Channels: Group

Name

Direction

Function

PBCCH

PBCCH

downlink

Broadcast

PCCCH

PRACH

PTCH

52-Multiframe

Random Access

PPCH

downlink

Paging

PAGCH

downlink

Access Grant

PNCH

downlink

Multicast

PDTCH

Downlink & uplink

Data

PACCH

Downlink & uplink

Associated Control

The mapping in time of the logical channels is defined by a multiframe structure. The 52-multiframe structure for PDCH consists of 52 TDMA frames, divided into 12 blocks (of 4 frames), 2 idle frames and 2 frames used for the PTCCH. Figure 4-23 52 Multiframe

X - Idle frame ....................................................................................................................................................................................................................................

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T - Frame used for PTCCH B0 - B11 - Radio blocks Channel Configuration

The figure below gives an example of a possible channel configuration. Note that the BCCH channel is transmitted in time-slot 0 on the first defined frequency. It must always be present to enable the mobile stations to find the broadcast channels more easily Figure 4-24 Time-Slot Configuration

Uplink State Flag

1.

Channels that can be assigned to GPRS only (not supported by Lucent)

2.

Channels that can be dynamically assigned to either GPRS or circuit switched service

3.

Channels that can be assigned to circuit switched services only

The Uplink State Flag (USF) is used to allow multiplexing of of multiple MSs in uplink direction on a Packet Data Channel (PDCH). It is be used in dynamic and extended dynamic medium access modes.Three bits at the beginning of each Radio Block that is sent on the downlink is comprised by the USF. In that way it enables the coding of eight different USF states which are used to multiplex the uplink traffic. One USF value is assigned only to one MS per PDCH. On the PCCCH, one USF value is used to indicates the PRACH. The other USF values are used to reserve the uplink for different mobile stations.On PDCHs which are not carrying PCCCH, the eight USF values are used to reserve the uplink direction for different mobile stations. One of the USF values has to be used to prevent any collision on the uplink channel, if a mobile station without an USF is using an uplink channel. The USF is either pointing to the next uplink Radio Block or the sequence of four uplink Radio Blocks starting with the next uplink Radio Block.

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GPRS Signalling and Transmission Protocols

Temporary Block Flow

A Temporary Block Flow (TBF) is a physical connection that is used by the two RR entities in the MS and the BSS to support the unidirectional transfer of Logical Link Control (LLC) Packet Data Units (PDUs) on packet data physical channels. It is the allocated radio resource on one or more PDCHs and it comprises a number of RLC/MAC blocks carrying one or more LLC PDUs. A Temporary Block Flow is only temporary and also only maintained for the duration of a specific data transfer.

Temporary Flow Identity

For every Temporary Block Flow there is a Temporary Flow Identity (TFI) assigned by the network. This assigned TFI is always unique among all the other concurrent TBFs in each direction and is used instead of the mobile station identity in the RLC/MAC layer. On the opposite direction, the same TFI value may be used at the same time. It is assigned in a resource assignment message that precedes the transfer of LLC frames belonging to one TBF to or from the mobile station. The same TFI is included in every RLC header of a RLC/MAC data block belonging to a specific TBF and may be used in the control messages (here other addressings can be used, e.g. TLLI) associated to the LLC frame transfer in order to address the peer RLC entities.

Quality of Service (QoS)

For GPRS there are four different parameters for Quality of Service (QoS) •

Service precedence (priority)

•

Reliability

•

Delay

•

Throughput Service precedence (priority of service) This parameter is used for indicating the priority of maintaining the service. Service precedence parameters specifiies which packets have a priority and which packets could be discarded.

Three different levels of service precedence are defined: •

High precedence (high priority) This service commitments will be maintained prior to all other precedence levels

•

Normal precedence (normal priority) This service commitments will be maintained prior to all Low priority users

•

Low precedence (low priority) This service commitments will be maintained after all the other service precedences have been completed.

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Reliability

GPRS Signalling and Transmission Protocols

The Reliability parameters indicate the different transmission characteristics that are required by an application. There are four different reliability parameters: •

Probability of loss of Service Data Units (SDUs)

•

Duplication of SDUs

•

Mis-sequencing of SDUs

•

Corruption of SDUs

The table below shows the different Reliability classes with the different reliability parameters and also give examples of application characteristics. Reliability classes Reliability class

Lost SDU prob. (a)

Duplicate SDU prob.

Out of Sequence SDU prob.

Corrupt SDU prob. (b)

Example of application characteristics.

1

109

109

109

109

Error sensitive, no error correction capability, limited error tolerance capability.

2

10 4

105

105

106

Error sensitive, limited error correction capability, good error tolerance capability.

3

10 2

105

105

102

Not error sensitive, error correction capability and/or very good error tolerance capability.

In GPRS there is a protection against buffer overflow or protocol malfunction. For each SDU GPRS uses a maximum holding time after which the SDU is discarded. There are also different parameters for the maximum holding tme of a SDU depending on the protocols used (e.g. TCP/IP)

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The ″Corrupt SDU probability″ indicates the probability that a SDU might be delivered with an undetected error. Delay

In the GPRS network data is temporarily stored at network nodes during transmission. Any delay that occurs is due to technical transmission characteristicsof the system and has to be minimised for a particular delay class. The maximum delay values are defined for the mean delay and the 95-percentile delay that might occur by the transfer of data through a GPRS network. All delay parameters are end-to-end transfer delays in the transmission of SDUs through a GPRS network. The transfer delays include the following parameters: •

Radio channel access delay (uplink direction)

•

Radio channel scheduling delay (downlink direction)

•

Radio channel transit delay (uplink and/or downlink direction)

•

GPRS-network transit delay (multiple hops)

Delay values Delay (maximum values) SDU size: 128 octets Delay Class

Mean Transfer Delay (sec)

95 percentile Delay (sec)

Mean Transfer Delay (sec)

95 percentile Delay (sec)

1. (Predictive)

< 0.5

< 1.5

<2

<7

2. (Predictive)

<5

< 25

< 15

< 75

3. (Predictive)

< 50

< 250

< 75

< 375

4. (Best Effort) Throughput

SDU size: 1024 octets

Unspecified

The troughput parameter indicates the user data throughput requested by the user.

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It is defined by two negotiable parameters: •

Maximum bit rate

•

Mean bit rate (includes, for example for bursty transmissions, the periods in which no data is transmitted) The maximum and mean bit rates can be negotiated to a value up to the Information Transfer Rate value.

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GPRS Signalling and Transmission Protocols

GPRS MS .................................................................................................................................................................................................................................... Mobile Station Equipment

The current market view on GPRS terminals is that Class B and C MSs will be available in Q2 2000. This is the general view held by all terminal manufacturers. Three types of terminal class will be supported: •

Class A Mobile Station (MS) These will support simultaneous attach, activation, monitor, invocation and traffic. I.e. A subscriber will be able to make and/or receive calls on the two services (GSM and GPRS) simultaneously, subject to Quality of Service) QoS subscribed to by the end user.

•

Class B MS These will support simultaneous attach, activation and monitor. They will only support limited simultaneous invocation such that GPRS virtual circuits will not be cleared down due to the presence of circuit switched traffic. Under these circumstances, the GPRS virtual connection is then busy or held. Simultaneous traffic is not supported as in the Class A MS. Subscribers can make calls on either service but not at the same time, but selection of the appropriate service is automatic by the MS.

•

Class C MS These will support only non-simultaneous attach, alternate use only. If both services are supported then the subscriber can make and / or receive calls only from the manually or default selected service. Status of the service not selected is detached or not reachable during the session. The ability to send and receive SMS messages is optional. Lucent is working closely with terminal manufacturers with regards to compatibility and availability of GPRS terminals.

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5

GPRS Procedures

Overview .................................................................................................................................................................................................................................... Purpose

Contents

This chapter discusses the GPRS Procedures

This chapter contains information on the following topics: Mobility Management

5-2

GPRS Attach Procedure

5-5

Detach Procedures

5-10

Routing Area Update

5-15

Combined RA / LA Update Procedure

5-21

PDP Context Activation Procedure

5-29

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5-1

GPRS Procedures

Mobility Management .................................................................................................................................................................................................................................... IDLE TO READY STATE

For the mobile to move from the idle to ready state, it must first perform a GPRS Attach. Once attached, the mobile will be known to the network i.e. the SGSN. The Mobility Management will be active at the Mobile Station and the SGSN following the attach sequence. When in the ready state, the PDP context is activated which establishes a packet data session (and the packet data networks) with the mobile. With a valid PDP context Protocol Data Units (PDU) may be transferred. For every LLCPDU received in the SGSN, a ready timer is re-started . There are two timers, one in the MS which is activated when a packet is sent and one in the SGSN when a packet is received.

READY to STANDBY STATE

For the mobile to move from the idle to ready state, it must first perform a GPRS Attach. Once attached, the mobile will be known to the network i.e. the SGSN. The Mobility Management will be active at the Mobile Station and the SGSN following the attach sequence.

STANDBY to READY

The MS and SGSN will enter the Ready state when the PDUs have been either transmitted or received.

STANDBY to IDLE

When this state is reached, a second timer is started. When the timer expires, or a MAP message ’Cancel Location’ is received from the HLR then a return to Idle state is performed and the MM and PDP context are removed from the MS, SGSN and the GGSN.

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Mobility Management

READY to IDLE

GPRS Procedures

This state can only be reached if either a GPRS detach or ’Cancel Location’ message is received. When either of these occur, the MM and PDP contexts are removed as the MS is no longer attached to the GPRS network. Figure 5-1 GPRS Attach/Detach States

GPRS Mobility Management (GMM) and Session Management (SM) services, are enhancements operated directly over the GPRS defined Logical Link Control (LLC) layer between the Mobile Station (MS) and the SSGN. READY State Timer

STANDBY State

READY state timer: •

Initiated when the MS or network sends a signalling or data packets

•

MS does routing area update on crossing a cell boundary

•

Move to STANDBY state on READY timer expiry

•

Default timer value of 44 seconds

STANDBY state: •

Initiated on expiry of READY timer

•

MS does routing area update on crossing a routing area boundary

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Mobility Management

GPRS Procedures

•

MS has to be paged to deliver packets

Figure 5-2 GPRS GMM/SM Control Plane

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GPRS Procedures

GPRS Attach Procedure .................................................................................................................................................................................................................................... Overview

In GPRS, the attach is made to the SGSN. In this attach procedure, the mobile station shall provide its identity and an indication of which type of attach that is to be executed. The identity (provided by the network) shall be the mobiles Packet-TIMSI (P-TIMSI) or IMSI. If the mobile has a valid P-TIMSI, the P-TIMSI and the Routing Area Identity (RAI) with the P-TIMSI shall be provided. The IMSI shall only be provided if the mobile does not have a valid P-TIMSI. Those different attach types are GPRS attach and GPRS / IMSI attach. After executing the GPRS attach, the mobile is in READY state and MM contexts are established in the mobile and the SGSN. The mobile or the SGSN may then activate PDP contexts. The next figure illustrates the combined GPRS / IMSI Attach procedure.

GPRS Attach Procedure Diagram

GPRS Attach Procedure

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5-5

GPRS Attach Procedure

GPRS Procedures

GPRS Attach Procedure

............................................................................................................................................................

1

The MS initiates the attach procedure by the transmission of an Attach Request (IMSI or P-TMSI and old RAI, Classmark, CKSN, Attach Type, DRX Parameters, old P-TMSI Signature) message to the SGSN. IMSI shall be included if the MS does not have a valid P-TMSI available. If the MS has a valid P-TMSI, then P-TMSI and the old RAI associated with P-TMSI shall be included. Classmark contains the MS’s GPRS multislot capabilities and supported GPRS ciphering algorithms in addition to the existing classmark parameters defined in GSM 04.08. Attach Type indicates which type of attach that is to be performed, i.e., GPRS attach only, GPRS Attach while already IMSI attached, or combined GPRS / IMSI attach. DRX Parameters indicates whether the MS uses discontinuous reception or not. If the MS uses discontinuous reception, then DRX Parameters also indicate when the MS is in a non-sleep mode able to receive paging requests and channel assignments. If the MS uses P-TMSI for identifying itself and if it has also stored its old P-TMSI Signature, then the MS shall include the old P-TMSI Signature in the Attach Request message. ............................................................................................................................................................

2

If the MS identifies itself with P-TMSI and the SGSN has changed since detach, the new SGSN sends an Identification Request (P-TMSI, old RAI, and old P-TMSI Signature) to the old SGSN to request the IMSI. The old SGSN responds with Identification Response (IMSI, Authentication Triplets). If the MS is not known in the old SGSN, the old SGSN responds with an appropriate error cause. The old SGSN also validates the old P-TMSI Signature and responds with an appropriate error cause if it does not match the value stored in the old SGSN. ............................................................................................................................................................

3

If the MS is unknown in both the old and new SGSN, the SGSN sends an Identity Request (Identity Type = IMSI) to the MS. The MS responds with Identity Response (IMSI). ............................................................................................................................................................

4

The authentication functions are defined in the subclause ″Security Function″. If no MM context for the MS exists anywhere in the network, then authentication is mandatory. Ciphering procedures are described in subclause ″Security Function″. If P-TMSI allocation is going to be done, and if the network supports ciphering, ciphering mode shall be set. ............................................................................................................................................................

5

The equipment checking functions are defined in the subclause ″Identity Check Procedures″. Equipment checking is optional.

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GPRS Procedures

............................................................................................................................................................

6

If the SGSN number has changed since the GPRS detach, or if it is the very first attach, then the SGSN informs the HLR: •

(6a) The SGSN sends an Update Location (SGSN Number, SGSN Address, and IMSI) to the HLR.

•

(6b) The HLR sends Cancel Location (IMSI, Cancellation Type) to the old SGSN with Cancellation Type set to Update Procedure.

•

(6c) The old SGSN acknowledges with Cancel Location Ack (IMSI). If there are any ongoing procedures for that MS, the old SGSN shall wait until these procedures are finished before removing the MM and PDP contexts.

•

(6d) The HLR sends Insert Subscriber Data (IMSI, GPRS subscription data) to the new SGSN.

•

(6e) The new SGSN validates the MS’s presence in the (new) RA. If due to regional subscription restrictions the MS is not allowed to attach in the RA, the SGSN rejects the Attach Request with an appropriate cause, and may return an Insert Subscriber Data Ack (IMSI, SGSN Area Restricted) message to the HLR. If subscription checking fails for other reasons, the SGSN rejects the Attach Request with an appropriate cause and returns an Insert Subscriber Data Ack (IMSI, Cause) message to the HLR. If all checks are successful then the SGSN constructs a MM context for the MS and returns an Insert Subscriber Data Ack (IMSI) message to the HLR.

•

(6f) The HLR acknowledges the Update Location message by sending an Update Location Ack to the SGSN after the cancelling of old MM context and insertion of new MM context are finished. If the Update Location is rejected by the HLR, the SGSN rejects the Attach Request from the MS with an appropriate cause.

............................................................................................................................................................

7

If Attach Type in step 1 indicated GPRS Attach while already IMSI attached, or combined GPRS / IMSI attach, then the VLR shall be updated if the Gs interface is installed. The VLR number is derived from the RA information. The SGSN starts the location update procedure towards the new MSC/VLR upon receipt of the first Insert

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5-7

GPRS Attach Procedure

GPRS Procedures

Subscriber Data message from the HLR in step 6 d). This operation marks the MS as GPRS-attached in the VLR. •

(7a) The SGSN sends a Location Update Request (new LAI, IMSI, SGSN Number, and Location Update Type) message to the VLR. Location Update Type shall indicate IMSI attach if Attach Type indicated combined GPRS / IMSI attach. Otherwise, Location Update Type shall indicate normal location update. The VLR creates an association with the SGSN by storing SGSN Number.

•

(7b) If the LA update is inter-MSC, the new VLR sends Update Location (IMSI, new VLR) to the HLR.

•

(7c) If the LA update is inter-MSC, the HLR sends a Cancel Location (IMSI) to the old VLR.

•

(7d) The old VLR acknowledges with Cancel Location Ack (IMSI).

•

(7e) If the LA update is inter-MSC, the HLR sends Insert Subscriber Data (IMSI, GSM subscriber data) to the new VLR.

•

(7f) The VLR acknowledges with Insert Subscriber Data Ack (IMSI).

•

(7g) After finishing the inter-MSC location update procedures, the HLR responds with Update Location Ack (IMSI) to the new VLR.

•

(7h) The VLR responds with Location Update Accept (VLR TMSI) to the SGSN.

............................................................................................................................................................

8

The SGSN selects Radio Priority SMS, and sends an Attach Accept (P-TMSI, VLR TMSI, and P-TMSI Signature, Radio Priority SMS) message to the MS. P-TMSI is included if the SGSN allocates a new P-TMSI. ............................................................................................................................................................

9

If P-TMSI or VLR TMSI was changed, the MS acknowledges the received TMSI(s) with Attach Complete (P-TMSI, VLR TMSI). ............................................................................................................................................................

10

If VLR TMSI was changed, the SGSN confirms the VLR TMSI re-allocation by sending TMSI Reallocation Complete (VLR TMSI) to the VLR. E ND OF STEPS ............................................................................................................................................................

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GPRS Attach Procedure

GPRS Procedures

Attach Request failure

If the Attach Request cannot be accepted, the SGSN returns an Attach Reject (IMSI, Cause) message to the MS. Note

All the procedures and steps are according to the ETSI specifications 03.60 Version 6.4.0.

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5-9

GPRS Procedures

Detach Procedures .................................................................................................................................................................................................................................... Overview

With the detach procedure, the MS informs the network that it requires a GPRS and/or IMSI detach. The network then informs the MS that it has been GPRS detached. There are three different detach types: •

IMSI detach

•

GPRS detach

•

Combined GPRS / IMSI detach (MS-initiated only).

There are two ways in which the MS is detached from GPRS: •

Explicit detach: The detach request is explicitly from the network or the MS.

•

Implicit detach: The network detaches the MS (without notifying the MS) after a configuration dependent time after the mobile reachable timer expired or after an irrecoverable radio error causes disconnection of the logical link.

In the explicit detach case, the SGSN sends a Detach Request to the MS or vice versa. An IMSI detach could be done in two different ways by the MS, depending if it´s GPRS-attached or not:

MS-Initiated Detach Procedure Diagram

•

A Detach Request message from an GPRS-attached mobile is send to the SGSN, indicating an IMSI detach. This is also possible in combination with a GPRS detach.

•

If a mobile is not attached to GPRS, the IMSI detach is done as already defined in GSM.

MS-Initiated Detach Procedure

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Detach Procedures

GPRS Procedures

MS-Initiated Detach Procedure 1

............................................................................................................................................................

The MS detaches by sending Detach Request (Detach Type, Switch Off) to the SGSN. Detach Type indicates which type of detach that is to be performed, i.e., GPRS Detach only, IMSI Detach only or combined GPRS and IMSI Detach. Switch Off indicates whether the detach is due to a switch off situation or not. ............................................................................................................................................................

2

If GPRS detach, the active PDP contexts in the GGSNs regarding this particular MS are deactivated by the SGSN sending Delete PDP Context Request (TID) to the GGSNs. The GGSNs acknowledge with Delete PDP Context Response (TID). ............................................................................................................................................................

3

If IMSI detach, the SGSN sends IMSI Detach Indication (IMSI) to the VLR. ............................................................................................................................................................

4

If the MS wants to remain IMSI-attached and is doing a GPRS detach, the SGSN sends a GPRS Detach Indication (IMSI) message to the VLR. The VLR removes the association with the SGSN and handles paging and location update without going via the SGSN. ............................................................................................................................................................

5

If Switch Off indicates that the detach is not due to a switch off situation, the SGSN sends a Detach Accept to the MS. E ND OF STEPS ............................................................................................................................................................

Note

All the procedures and steps are according to the ETSI specifications 03.60 Version 6.4.0.

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5-11

Detach Procedures

GPRS Procedures

SGSN-Initiated Detach Procedure Diagram

SGSN-Initiated Detach Procedure 1

SGSN-Initiated Detach Procedure

............................................................................................................................................................

The SGSN informs the MS that it has been detached by sending Detach Request (Detach Type) to the MS. Detach Type indicates if the MS is requested to make a new attach and PDP context activation for the previously activated PDP contexts. If so, the attach procedure shall be initiated when the detach procedure is completed. ............................................................................................................................................................

2

The active PDP contexts in the GGSNs regarding this particular MS are deactivated by the SGSN sending Delete PDP Context Request (TID) messages to the GGSNs. The GGSNs acknowledge with Delete PDP Context Response (TID) messages. ............................................................................................................................................................

3

If the MS was both IMSI- and GPRS-attached, the SGSN sends a GPRS Detach Indication (IMSI) message to the VLR. The VLR removes the association with the SGSN and handles paging and location update without going via the SGSN. ............................................................................................................................................................

4

The MS sends a Detach Accept message to the SGSN any time after step 1. E ND OF STEPS ............................................................................................................................................................

Note

All the procedures and steps are according to the ETSI specifications 03.60 Version 6.4.0.

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HLR-Initiated Detach Procedure Diagram

HLR-Initiated Detach Procedure 1

This HLR-Initiated Detach Procedure is done by the HLR and the HLR uses this procedure for operator-determined purposes to request a removal of a subscriber´s MM and PDP contexts at the SGSN.

............................................................................................................................................................

If the HLR wants to request the immediate deletion of a subscriber’s MM and PDP contexts from the SGSN, the HLR shall send a Cancel Location (IMSI, Cancellation Type) message to the SGSN with Cancellation Type set to Subscription Withdrawn. ............................................................................................................................................................

2

The SGSN informs the MS that it has been detached by sending Detach Request (Detach Type) to the MS. Detach Type shall indicate that the MS is not requested to make a new attach and PDP context activation. ............................................................................................................................................................

3

The active PDP contexts in the GGSNs regarding this particular MS are deactivated by the SGSN sending Delete PDP Context Request (TID) messages to the GGSNs. The GGSNs acknowledge with Delete PDP Context Response (TID) messages. ............................................................................................................................................................

4

If the MS was both IMSI- and GPRS-attached, the SGSN sends a GPRS Detach Indication (IMSI) message to the VLR. The VLR removes the association with the SGSN and handles paging and location update without going via the SGSN. ............................................................................................................................................................

5

The MS sends a Detach Accept message to the SGSN any time after step 2.

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............................................................................................................................................................

6

The SGSN shall confirm the deletion of the MM and PDP contexts with a Cancel Location Ack (IMSI) message. E ND OF STEPS ............................................................................................................................................................

Note

All the procedures and steps are according to the ETSI specifications 03.60 Version 6.4.0.

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Routing Area Update .................................................................................................................................................................................................................................... Overview

The routing area update takes place: •

when a GPRS attached MS detects that it has entered a new routing area

•

when the periodic routing area update timer has expired

•

when a suspended MS is not resumed by the BSS.

There are two different routing area updates:

Intra SGSN Routing Area Update Diagram

Intra SGSN Routing Area Update Procedure 1

•

Intra SGSN Routing Area Update

•

Inter SGSN Routing Area Update

Intra SGSN Routing Area Update

............................................................................................................................................................

The MS sends a Routing Area Update Request (old RAI, old P-TMSI Signature, and Update Type) to the SGSN. Update Type shall indicate RA update or periodic RA update. The BSS shall add the Cell Global Identity including the RAC and LAC of the cell where the message was received before passing the message to the SGSN, see GSM 08.18. ............................................................................................................................................................

2

Security functions may be executed. These procedures are defined in subclause ″Security Function″. ............................................................................................................................................................

3

The SGSN validates the MS’s presence in the new RA. If due to regional subscription restrictions the MS is not allowed to be attached in the RA, or if subscription checking fails, then the SGSN rejects the routing area update with an appropriate cause. If all checks are

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successful then the SGSN updates the MM context for the MS. A new P-TMSI may be allocated. A Routing Area Update Accept (P-TMSI, P-TMSI Signature) is returned to the MS. ............................................................................................................................................................

4

If P-TMSI was reallocated, the MS acknowledges the new P-TMSI with Routing Area Update Complete (P-TMSI). E ND OF STEPS ............................................................................................................................................................

Routing area update procedure failure

If the routing area update procedure fails a maximum allowable number of times, or if the SGSN returns a Routing Area Update Reject (Cause) message, the MS shall enter IDLE state. Note

All the procedures and steps are according to the ETSI specifications 03.60 Version 6.4.0. Inter SGSN Routing Area Update Diagram

Inter SGSN Routing Area Update

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Inter SGSN Routing Area Update Procedure 1

............................................................................................................................................................

The MS sends a Routing Area Update Request (old RAI, old P-TMSI Signature, and Update Type) to the new SGSN. Update Type shall indicate RA update or periodic RA update. The BSS shall add the Cell Global Identity including the RAC and LAC of the cell where the message was received before passing the message to the SGSN. ............................................................................................................................................................

2

The new SGSN sends SGSN Context Request (old RAI, TLLI, old P-TMSI Signature, and New SGSN Address) to the old SGSN to get the MM and PDP contexts for the MS. The old SGSN validates the old P-TMSI Signature and responds with an appropriate error cause if it does not match the value stored in the old SGSN. This should initiate the security functions in the new SGSN. If the security functions authenticate the MS correctly, the new SGSN shall send an SGSN Context Request (old RAI, TLLI, MS Validated, and New SGSN Address) message to the old SGSN. MS Validated indicates that the new SGSN has authenticated the MS. If the old P-TMSI Signature was valid or if the new SGSN indicates that it has authenticated the MS, the old SGSN stops assigning SNDCP N-PDU numbers to downlink N-PDUs received, and responds with SGSN Context Response (MM Context, PDP Contexts). If the MS is not known in the old SGSN, the old SGSN responds with an appropriate error cause. The old SGSN stores New SGSN Address, to allow the old SGSN to forward data packets to the new SGSN. Each PDP Context includes the SNDCP Send N-PDU Number for the next downlink N-PDU to be sent in acknowledged mode to the MS, the SNDCP Receive N-PDU Number for the next uplink N-PDU to be received in acknowledged mode from the MS, the GTP sequence number for the next downlink N-PDU to be sent to the MS and the GTP sequence number for the next uplink N-PDU to be tunnelled to the GGSN. The old SGSN starts a timer and stops the transmission of N-PDUs to the MS. ............................................................................................................................................................

3

Security functions may be executed. These procedures are defined in subclause ″Security Function″. Ciphering mode shall be set if ciphering is supported. ............................................................................................................................................................

4

The new SGSN sends an SGSN Context Acknowledge message to the old SGSN. This informs the old SGSN that the new SGSN is ready to receive data packets belonging to the activated PDP contexts. The old SGSN marks in its context that the MSC/VLR association and the

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information in the GGSNs and the HLR are invalid. This triggers the MSC/VLR, the GGSNs, and the HLR to be updated if the MS initiates a routing area update procedure back to the old SGSN before completing the ongoing routing area update procedure. If the security functions do not authenticate the MS correctly, then the routing area update shall be rejected, and the new SGSN shall send a reject indication to the old SGSN. The old SGSN shall continue as if the SGSN Context Request was never received. ............................................................................................................................................................

5

The old SGSN duplicates the buffered N-PDUs and starts tunnelling them to the new SGSN. Additional N-PDUs received from the GGSN before the timer described in step 2 expires are also duplicated and tunnelled to the new SGSN. N-PDUs that were already sent to the MS in acknowledged mode and that are not yet acknowledged by the MS are tunnelled together with the SNDCP N-PDU number. No N-PDUs shall be forwarded to the new SGSN after expiry of the timer described in step 2. ............................................................................................................................................................

6

The new SGSN sends Update PDP Context Request (new SGSN Address, TID, QoS Negotiated) to the GGSNs concerned. The GGSNs update their PDP context fields and return Update PDP Context Response (TID). ............................................................................................................................................................

7

The new SGSN informs the HLR of the change of SGSN by sending Update Location (SGSN Number, SGSN Address, IMSI) to the HLR. ............................................................................................................................................................

8

The HLR sends Cancel Location (IMSI, Cancellation Type) to the old SGSN with Cancellation Type set to Update Procedure. If the timer described in step 2 is not running, then the old SGSN removes the MM and PDP contexts. Otherwise, the contexts are removed only when the timer expires. This allows the old SGSN to complete the forwarding of N-PDUs. It also ensures that the MM and PDP contexts are kept in the old SGSN in case the MS initiates another inter SGSN routing area update before completing the ongoing routing area update to the new SGSN. The old SGSN acknowledges with Cancel Location Ack (IMSI). ............................................................................................................................................................

9

The HLR sends Insert Subscriber Data (IMSI, GPRS subscription data) to the new SGSN. The new SGSN validates the MS’s presence in the (new) RA. If due to regional subscription restrictions the MS is not allowed to be attached in the RA, the SGSN rejects the Routing Area Update Request with an appropriate cause, and may return an

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Insert Subscriber Data Ack (IMSI, SGSN Area Restricted) message to the HLR. If all checks are successful then the SGSN constructs a MM context for the MS and returns an Insert Subscriber Data Ack (IMSI) message to the HLR. ............................................................................................................................................................

10

The HLR acknowledges the Update Location by sending Update Location Ack (IMSI) to the new SGSN. ............................................................................................................................................................

11

The new SGSN validates the MS’s presence in the new RA. If due to roaming restrictions the MS is not allowed to be attached in the SGSN, or if subscription checking fails, then the new SGSN rejects the routing area update with an appropriate cause. If all checks are successful then the new SGSN constructs MM and PDP contexts for the MS. A logical link is established between the new SGSN and the MS. The new SGSN responds to the MS with Routing Area Update Accept (P-TMSI, P-TMSI Signature, and Receive N-PDU Number). Receive N-PDU Number contains the acknowledgments for each acknowledged-mode NSAPI used by the MS, thereby confirming all mobile-originated N-PDUs successfully transferred before the start of the update procedure. ............................................................................................................................................................

12

The MS acknowledges the new P-TMSI with a Routing Area Update Complete (P-TMSI, Receive N-PDU Number). Receive N-PDU Number contains the acknowledgments for each acknowledged-mode NSAPI used by the MS, thereby confirming all mobile-terminated N-PDUs successfully transferred before the start of the update procedure. If Receive N-PDU Number confirms reception of N-PDUs that were forwarded from the old SGSN, then these N-PDUs shall be discarded by the new SGSN. LLC and SNDCP in the MS are reset. E ND OF STEPS ............................................................................................................................................................

Rejected routing area update

In the case of a rejected routing area update operation, due to regional subscription or roaming restrictions, the new SGSN shall not construct a MM context. A reject shall be returned to the MS with an appropriate cause. The MS shall not re-attempt a routing area update to that RA. The RAI value shall be deleted when the MS is powered-up. If the SGSN is unable to update the PDP context in one or more GGSNs, then the SGSN shall deactivate the corresponding PDP contexts as described in subclause ″PDP Context Deactivation .................................................................................................................................................................................................................................... 401–380–061 Issue RFA Version , May 2000

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Initiated by SGSN Procedure″. This shall not cause the SGSN to reject the routing area update. If the timer described in step 2 expires and no Cancel Location (IMSI) was received from the HLR, then the old SGSN shall stop forwarding N-PDUs to the new SGSN. If the routing area update procedure fails a maximum allowable number of times, or if the SGSN returns a Routing Area Update Reject (Cause) message, the MS shall enter IDLE state. Note

All the procedures and steps are according to the ETSI specifications 03.60 Version 6.4.0.

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Combined RA / LA Update Procedure .................................................................................................................................................................................................................................... Overview

Combined Intra SGSN RA / LA Update Diagram

Combined Intra SGSN RA / LA Update Procedure 1

There are two different Combined RA / LA Update procedures: •

Combined Intra SGSN RA / LA Update

•

Combined Inter SGSN RA / LA Update

Combined Intra SGSN RA / LA Update

............................................................................................................................................................

The MS sends a Routing Area Update Request (old RAI, old P-TMSI Signature, and Update Type) to the SGSN. Update Type shall indicate combined RA / LA update, or, if the MS wants to perform an IMSI attach, combined RA / LA update with IMSI attach requested. The BSS shall add the Cell Global Identity including the RAC and LAC of the cell where the message was received before passing the message to the SGSN. ............................................................................................................................................................

2

Security functions may be executed. This procedure is defined in subclause ″Security Function″.

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............................................................................................................................................................

3

If the association has to be established, if Update Type indicates combined RA / LA update with IMSI attach requested, or if the LA changed with the routing area update, then the SGSN sends a Location Update Request (new LAI, IMSI, SGSN Number, Location Update Type) to the VLR. Location Update Type shall indicate IMSI attach if Update Type in step 1 indicated combined RA / LA update with IMSI attach requested. Otherwise, Location Update Type shall indicate normal location update. The VLR number is translated from the RAI via a table in the SGSN. The VLR creates or updates the association with the SGSN by storing SGSN Number ............................................................................................................................................................

4

If the subscriber data in the VLR is marked as not confirmed by the HLR, then the new VLR informs the HLR. The HLR cancels the data in the old VLR and inserts subscriber data in the new VLR (this signalling is not modified from existing GSM signalling and is included here for illustrative purposes): •

(4a) The new VLR sends an Update Location (new VLR) to the HLR.

•

(4b) The HLR cancels the data in the old VLR by sending Cancel Location (IMSI) to the old VLR.

•

(4c) The old VLR acknowledges with Cancel Location Ack (IMSI).

•

(4d) The HLR sends Insert Subscriber Data (IMSI, GSM subscriber data) to the new VLR.

•

(4e) The new VLR acknowledges with Insert Subscriber Data Ack (IMSI).

•

(4f) The HLR responds with Update Location Ack (IMSI) to the new VLR.

............................................................................................................................................................

5

The new VLR allocates a new VLR TMSI and responds with Location Update Accept (VLR TMSI) to the SGSN. VLR TMSI is optional if the VLR has not changed. ............................................................................................................................................................

6

The SGSN validates the MS’s presence in the new RA. If due to regional subscription restrictions the MS is not allowed to be attached in the RA, or if subscription checking fails, then the SGSN rejects the routing area update with an appropriate cause. If all checks are successful then the SGSN updates the MM context for the MS. A new P-TMSI may be allocated. The SGSN responds to the MS with

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Routing Area Update Accept (P-TMSI, VLR TMSI, and P-TMSI Signature). ............................................................................................................................................................

7

If a new P-TMSI or VLR TMSI was received, then the MS confirms the reallocation of the TMSIs by sending Routing Area Update Complete (P-TMSI, VLR TMSI) message to the SGSN. ............................................................................................................................................................

8

The SGSN sends TMSI Reallocation Complete (VLR TMSI) to the VLR if the VLR TMSI is confirmed by the MS. E ND OF STEPS ............................................................................................................................................................

Routing area update procedure failure

If the routing area update procedure fails a maximum allowable number of times, or if the SGSN returns a Routing Area Update Reject (Cause) message, the MS shall enter IDLE state. If the Location Update Accept message indicates a reject, then this should be indicated to the MS, and the MS shall not access non-GPRS services until a successful Location Update is performed. Note

All the procedures and steps are according to the ETSI specifications 03.60 Version 6.4.0.

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Combined Inter SGSN RA / LA Update Diagram

Combined Inter SGSN RA / LA Update Procedure 1

GPRS Procedures

Combined Inter SGSN RA / LA Update

............................................................................................................................................................

The MS sends a Routing Area Update Request (old RAI, old P-TMSI Signature, and Update Type) to the new SGSN. Update Type shall indicate combined RA / LA update, or, if the MS wants to perform an IMSI attach, combined RA / LA update with IMSI attach requested. The BSS shall add the Cell Global Identity including the RAC and LAC of the cell where the message was received before passing the message to the SGSN. ............................................................................................................................................................

2

The new SGSN sends SGSN Context Request (old RAI, TLLI, old P-TMSI Signature, and New SGSN Address) to the old SGSN to get the MM and PDP contexts for the MS. The old SGSN validates the old P-TMSI Signature and responds with an appropriate error cause if it does not match the value stored in the old SGSN. This should

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initiate the security functions in the new SGSN. If the security functions authenticate the MS correctly, the new SGSN shall send an SGSN Context Request (old RAI, TLLI, MS Validated, and New SGSN Address) message to the old SGSN. MS Validated indicates that the new SGSN has authenticated the MS. If the old P-TMSI Signature was valid or if the new SGSN indicates that it has authenticated the MS, the old SGSN stops assigning SNDCP N-PDU numbers to downlink N-PDUs received, and responds with SGSN Context Response (MM Context, PDP Contexts). If the MS is not known in the old SGSN, the old SGSN responds with an appropriate error cause. The old SGSN stores New SGSN Address until the old MM context is cancelled, to allow the old SGSN to forward data packets to the new SGSN. Each PDP Context includes the SNDCP Send N-PDU Number for the next downlink N-PDU to be sent in acknowledged mode to the MS, the SNDCP Receive N-PDU Number for the next uplink N-PDU to be received in acknowledged mode from the MS, the GTP sequence number for the next downlink N-PDU to be sent to the MS and the GTP sequence number for the next uplink N-PDU to be tunnelled to the GGSN. The old SGSN starts a timer and stops the downlink transfer. ............................................................................................................................................................

3

Security functions may be executed. These procedures are defined in subclause ″Security Function″. Ciphering mode shall be set if ciphering is supported. ............................................................................................................................................................

4

The new SGSN sends an SGSN Context Acknowledge message to the old SGSN. This informs the old SGSN that the new SGSN is ready to receive data packets belonging to the activated PDP contexts. The old SGSN marks in its context that the MSC/VLR association and the information in the GGSNs and the HLR are invalid. This triggers the MSC/VLR, the GGSNs, and the HLR to be updated if the MS initiates a routing area update procedure back to the old SGSN before completing the ongoing routing area update procedure. If the security functions do not authenticate the MS correctly, then the routing area update shall be rejected, and the new SGSN shall send a reject indication to the old SGSN. The old SGSN shall continue as if the SGSN Context Request was never received. ............................................................................................................................................................

5

The old SGSN duplicates the buffered N-PDUs and starts tunnelling them to the new SGSN. Additional N-PDUs received from the GGSN before the timer described in step 2 expires are also duplicated and tunnelled to the new SGSN. N-PDUs that were already sent to the MS in acknowledged mode and that are not yet acknowledged by the MS

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are tunnelled together with the SNDCP N-PDU number. No N-PDUs shall be forwarded to the new SGSN after expiry of the timer described in step 2. ............................................................................................................................................................

6

The new SGSN sends Update PDP Context Request (new SGSN Address, TID, QoS Negotiated) to the GGSNs concerned. The GGSNs update their PDP context fields and return an Update PDP Context Response (TID). ............................................................................................................................................................

7

The new SGSN informs the HLR of the change of SGSN by sending Update Location (SGSN Number, SGSN Address, and IMSI) to the HLR. ............................................................................................................................................................

8

The HLR sends Cancel Location (IMSI, Cancellation Type) to the old SGSN with Cancellation Type set to Update Procedure. If the timer described in step 2 is not running, then the old SGSN removes the MM and PDP contexts. Otherwise, the contexts are removed only when the timer expires. This allows the old SGSN to complete the forwarding of N-PDUs. It also ensures that the MM and PDP contexts are kept in the old SGSN in case the MS initiates another inter SGSN routing area update before completing the ongoing routing area update to the new SGSN. The old SGSN acknowledges with Cancel Location Ack (IMSI). ............................................................................................................................................................

9

The HLR sends Insert Subscriber Data (IMSI, GPRS subscription data) to the new SGSN. The new SGSN validates the MS’s presence in the (new) RA. If due to regional subscription restrictions the MS is not allowed to be attached in the RA, the SGSN rejects the Routing Area Update Request with an appropriate cause, and may return an Insert Subscriber Data Ack (IMSI, SGSN Area Restricted) message to the HLR. If all checks are successful then the SGSN constructs a MM context for the MS and returns an Insert Subscriber Data Ack (IMSI) message to the HLR. ............................................................................................................................................................

10

The HLR acknowledges the Update Location by sending Update Location Ack (IMSI) to the new SGSN. ............................................................................................................................................................

11

If the association has to be established, if Update Type indicates combined RA / LA update with IMSI attach requested, or if the LA changed with the routing area update, then the new SGSN sends a Location Update Request (new LAI, IMSI, SGSN Number, Location

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Update Type) to the VLR. Location Update Type shall indicate IMSI attach if Update Type in step 1 indicated combined RA / LA update with IMSI attach requested. Otherwise, Location Update Type shall indicate normal location update. The VLR number is translated from the RAI via a table in the SGSN. The SGSN starts the location update procedure towards the new MSC/VLR upon receipt of the first Insert Subscriber Data message from the HLR in step 9). The VLR creates or updates the association with the SGSN by storing SGSN Number. ............................................................................................................................................................

12

If the subscriber data in the VLR is marked as not confirmed by the HLR, the new VLR informs the HLR. The HLR cancels the old VLR and inserts subscriber data in the new VLR (this signalling is not modified from existing GSM signalling and is included here for illustrative purposes): •

(12a) The new VLR sends an Update Location (new VLR) to the HLR.

•

(12b) The HLR cancels the data in the old VLR by sending Cancel Location (IMSI) to the old VLR.

•

(12c) The old VLR acknowledges with Cancel Location Ack (IMSI).

•

(12d) The HLR sends Insert Subscriber Data (IMSI, GSM subscriber data) to the new VLR.

•

(12e) The new VLR acknowledges with Insert Subscriber Data Ack (IMSI).

•

(12f) The HLR responds with Update Location Ack (IMSI) to the new VLR.

............................................................................................................................................................

13

The new VLR allocates a new TMSI and responds with Location Update Accept (VLR TMSI) to the SGSN. VLR TMSI is optional if the VLR has not changed. ............................................................................................................................................................

14

The new SGSN validates the MS’s presence in the new RA. If due to roaming restrictions the MS is not allowed to be attached in the SGSN, or if subscription checking fails, then the SGSN rejects the routing area update with an appropriate cause. If all checks are successful then the new SGSN establishes MM and PDP contexts for the MS. A logical link is established between the new SGSN and the MS. The new SGSN responds to the MS with Routing Area Update Accept (P-TMSI, VLR TMSI, P-TMSI Signature, and Receive N-PDU Number). Receive N-PDU Number contains the acknowledgments for each acknowledged-mode NSAPI used by the MS, thereby confirming

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all mobile-originated N-PDUs successfully transferred before the start of the update procedure. ............................................................................................................................................................

15

The MS confirms the reallocation of the TMSIs by sending Routing Area Update Complete (P-TMSI, VLR TMSI, and Receive N-PDU Number) to the SGSN. Receive N-PDU Number contains the acknowledgments for each acknowledged-mode NSAPI used by the MS, thereby confirming all mobile-terminated N-PDUs successfully transferred before the start of the update procedure. If Receive N-PDU Number confirms reception of N-PDUs that were forwarded from the old SGSN, then these N-PDUs shall be discarded by the new SGSN. LLC and SNDCP in the MS are reset. ............................................................................................................................................................

16

The new SGSN sends TMSI Reallocation Complete (VLR TMSI) to the new VLR if the MS confirms the VLR TMSI. E ND OF STEPS ............................................................................................................................................................

Rejected routing area update

In the case of a rejected routing area update operation, due to regional subscription or roaming restrictions, the new SGSN shall not construct a MM context. A reject shall be returned to the MS with an appropriate cause. The MS shall not re-attempt a routing area update to that RA. The RAI value shall be deleted when the MS is powered-up. If the SGSN is unable to update the PDP context in one or more GGSNs, then the SGSN shall deactivate the corresponding PDP contexts as described in subclause ″PDP Context Deactivation Initiated by SGSN Procedure″. This shall not cause the SGSN to reject the routing area update. If the routing area update procedure fails a maximum allowable number of times, or if the SGSN returns a Routing Area Update Reject (Cause) message, the MS shall enter IDLE state. If the timer described in step 2 expires and no Cancel Location (IMSI) was received from the HLR, then the old SGSN shall stop forwarding N-PDUs to the new SGSN. If the Location Update Accept message indicates a reject, then this should be indicated to the MS, and the MS shall not access non-GPRS services until a successful location update is performed. Note

All the procedures and steps are according to the ETSI specifications 03.60 Version 6.4.0. ....................................................................................................................................................................................................................................

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PDP Context Activation Procedure .................................................................................................................................................................................................................................... Overview

The PDP context is a description of each PDP address of a subscriber and contains mapping and routing information for transferring PDUs for that particular PDP address between the mobile and the GGSN. A PDP context exists of •

Mobile Station

•

GGSN

•

SGSN

and exists in either one of the two states

PDP Context Activation Procedure Diagram

PDP Context Activation Procedure 1

•

Active

•

Inactive.

PDP Context Activation Procedure

............................................................................................................................................................

The MS sends an Activate PDP Context Request (NSAPI, TI, PDP Type, PDP Address, Access Point Name, QoS Requested, and PDP Configuration Options) message to the SGSN. The MS shall use PDP Address to indicate whether it requires the use of a static PDP address or whether it requires the use of a dynamic PDP address. The MS shall leave PDP Address empty to request a dynamic PDP address. The MS may use Access Point Name to select a reference point to a certain external network. Access Point Name is a logical name referring to the external packet data network that the subscriber wishes to connect to. QoS Requested indicates the desired QoS profile. PDP Configuration Options may be used to request optional

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PDP Context Activation Procedure

GPRS Procedures

PDP parameters from the GGSN (see GSM 09.60). PDP Configuration Options is sent transparently through the SGSN. ............................................................................................................................................................

2

Security functions may be executed. These procedures are defined in subclause ″Security Function″. ............................................................................................................................................................

3

The SGSN validates the Activate PDP Context Request using PDP Type (optional), PDP Address (optional), and Access Point Name (optional) provided by the MS and the PDP context subscription records. The validation criteria, the APN selection criteria, and the mapping from APN to a GGSN are described in annex A. If a GGSN address can be derived, the SGSN creates a TID for the requested PDP context by combining the IMSI stored in the MM context with the NSAPI received from the MS. If the MS requests a dynamic address, then the SGSN lets a GGSN allocate the dynamic address. The SGSN may restrict the requested QoS attributes given its capabilities, the current load, and the subscribed QoS profile. The SGSN sends a Create PDP Context Request (PDP Type, PDP Address, Access Point Name, QoS Negotiated, TID, MSISDN, Selection Mode, and PDP Configuration Options) message to the affected GGSN. Access Point Name shall be the APN Network Identifier of the APN selected according to the procedure described in annex A. PDP Address shall be empty if a dynamic address is requested. The GGSN may use Access Point Name to find an external network. Selection Mode indicates whether a subscribed APN was selected, or whether a non-subscribed APN sent by MS or a non-subscribed APN chosen by SGSN was selected. Selection Mode is set according to annex A. The GGSN may use Selection Mode when deciding whether to accept or reject the PDP context activation. For example, if an APN requires subscription, then the GGSN is configured to accept only the PDP context activation that requests a subscribed APN as indicated by the SGSN with Selection Mode. The GGSN creates a new entry in its PDP context table and generates a Charging Id. The new entry allows the GGSN to route PDP PDUs between the SGSN and the external PDP network, and to start charging. The GGSN may further restrict QoS Negotiated given its capabilities and the current load. The GGSN then returns a Create PDP Context Response (TID, PDP Address, BB Protocol, Reordering Required, PDP Configuration Options, QoS Negotiated, Charging Id, Cause) message to the SGSN. PDP Address is included if the GGSN allocated a PDP address. BB Protocol indicates whether TCP or UDP shall be used to transport user data on the backbone network between the SGSN and GGSN. Reordering Required indicates whether the SGSN shall reorder N-PDUs before

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PDP Context Activation Procedure

GPRS Procedures

delivering the N-PDUs to the MS. PDP Configuration Options contain optional PDP parameters that the GGSN may transfer to the MS. These optional PDP parameters may be requested by the MS in the Activate PDP Context Request message, or may be sent unsolicited by the GGSN. PDP Configuration Options is sent transparently through the SGSN. The Create PDP Context messages are sent over the GPRS backbone network. If QoS Negotiated received from the SGSN is incompatible with the PDP context being activated (e.g., the reliability class is insufficient to support the PDP type), then the GGSN rejects the Create PDP Context Request message. The compatible QoS profiles are configured by the GGSN operator. ............................................................................................................................................................

4

The SGSN inserts the NSAPI along with the GGSN address in its PDP context. If the MS has requested a dynamic address, the PDP address received from the GGSN is inserted in the PDP context. The SGSN selects Radio Priority based on QoS Negotiated, and returns an Activate PDP Context Accept (PDP Type, PDP Address, TI, QoS Negotiated, Radio Priority, and PDP Configuration Options) message to the MS. The SGSN is now able to route PDP PDUs between the GGSN and the MS, and to start charging. E ND OF STEPS ............................................................................................................................................................

Quality of Service (QoS)

For each PDP Address a different quality of service (QoS) profile may be requested. For example, some PDP addresses may be associated with E-mail that can tolerate lengthy response times. Other applications cannot tolerate delay and demand a very high level of throughput, interactive applications being one example. These different requirements are reflected in the QoS profile. If a QoS requirement is beyond the capabilities of a PLMN, the PLMN negotiates the QoS profile as close as possible to the requested QoS profile. The MS either accepts the negotiated QoS profile, or deactivates the PDP context. PDP Context Activation Procedure failure

If the PDP Context Activation Procedure fails or if the SGSN returns an Activate PDP Context Reject (Cause, PDP Configuration Options) message, then the MS may attempt another activation to the same APN up to a maximum number of attempts. Note

All the procedures and steps are according to the ETSI specifications 03.60 Version 6.4.0. .................................................................................................................................................................................................................................... 401–380–061 Issue RFA Version , May 2000

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PDP Context Activation Procedure

Successful NetworkRequested PDP Context Activation Procedure Diagram

Successful NetworkRequested PDP Context Activation Procedure 1

GPRS Procedures

Successful Network-Requested PDP Context Activation Procedure

............................................................................................................................................................

When receiving a PDP PDU the GGSN determines if the Network-Requested PDP Context Activation procedure has to be initiated. The GGSN may store subsequent PDUs received for the same PDP address. ............................................................................................................................................................

2

The GGSN may send a Send Routing Information for GPRS (IMSI) message to the HLR. If the HLR determines that the request can be served, it returns a Send Routing Information for GPRS Ack (IMSI, SGSN Address, Mobile Station Not Reachable Reason) message to the GGSN. The Mobile Station Not Reachable Reason parameter is included if the MNRG flag is set in the HLR. The Mobile Station Not Reachable Reason parameter indicates the reason for the setting of the MNRG flag as stored in the MNRR record (see GSM 03.40). If the MNRR record indicates a reason other than ’No Paging Response’, the HLR shall include the GGSN number in the GGSN-list of the subscriber. If the HLR determines that the request cannot be served (e.g., IMSI unknown in HLR), the HLR shall send a Send Routing Information for GPRS Ack (IMSI, MAP Error Cause) message. Map Error Cause indicates the reason for the negative response.

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PDP Context Activation Procedure

GPRS Procedures

............................................................................................................................................................

3

If the SGSN address is present and either Mobile Station Not Reachable Reason is not present or Mobile Station Not Reachable Reason indicates ’No Paging Response’, the GGSN shall send a PDU Notification Request (IMSI, PDP Type, PDP Address) message to the SGSN indicated by the HLR. Otherwise, the GGSN shall set the MNRG flag for that MS. The SGSN returns a PDU Notification Response (Cause) message to the GGSN in order to acknowledge that it shall request the MS to activate the PDP context indicated with PDP Address. ............................................................................................................................................................

4

The SGSN sends a Request PDP Context Activation (TI, PDP Type, and PDP Address) message to request the MS to activate the indicated PDP context. ............................................................................................................................................................

5

The PDP context is activated with the PDP Context Activation procedure. E ND OF STEPS ............................................................................................................................................................

Network-requested PDP context activation procedure failure

If the network-requested PDP context activation procedure was not successful, the reason is as well indicated: •

″IMSI not known″ The SGSN has no MM context for that IMSI.

•

″MS GPRS Detached″. The MM state of the MS is IDLE.

Note

All the procedures and steps are according to the ETSI specifications 03.60 Version 6.4.0.

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6

Call Management

Overview .................................................................................................................................................................................................................................... Purpose

Contents

This chapter discusses the BSS Mobile Originated Packet Transfer and the BSS Mobile Terminated Packet Transfer. This chapter covers the following subjects: GPRS - BSS Mobile Originated Packet Transfer

6-2

GPRS - BSS Mobile Terminated Packet Transfer

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6-1

Call Management

GPRS - BSS Mobile Originated Packet Transfer .................................................................................................................................................................................................................................... Multiple Access

An MS initiates a packet transfer by making Packet Channel Request on the PRACH or the RACH. The network responds on PAGCH or AGCH respectively. It is possible to use a one or two phase packet access method. In the one phase access, the network responds to the channel request for Packet Transfer with the immediate assignment reserving the resources on PDCHs for uplink transfer of a number of Radio Blocks. Opposite to the one phase access, the two phase access offers the possibility to the mobile station to transfer information about its capability to the network. In the two phase access, the network responds to the channel request with the immediate assignment which reserves the one uplink radio block for transmitting the packet resource request message which carries the complete description of the requested resources for the uplink transfer. Thereafter, the network responds with the Packet Resource assignment reserving resources for the uplink transfer. If there is no response to the Packet Channel Request within a predefined time period, the MS makes a retry after a random backoff time.

Uplink Data Transfer

Efficient and flexible utilization of the available spectrum for a packet data traffic (one or more PDCHs in a cell) can be obtained using a multi-slot channel reservation scheme. Blocks from one MS can be sent on different PDCHs simultaneously, thus reducing the packet delay for transmission across the air interface. The bandwidth may be varied by allocating one to eight time slots in each TDMA frame depending on the number of available PDCHs multi-slot capabilities of the MS and the current system load. The master slave channel concept requires mechanisms for efficient utilisation of PDCH uplink(s). Therefore, the Uplink State Flag (USF) is used on PDCHs. The 3 bit USF at the beginning of each Radio Block that is sent on the downlink points to the next uplink Radio Block. It enables the coding of 8 different USF states which are used to multiplex the uplink traffic. The channel reservation command includes the list of allocated PDCHs and the corresponding USF state per channel. To an MS, the USF marks whether it can use the next uplink radio block on the respective PDCH for transmission. An MS monitors the USF and according to the USF value, identifies PDCHs that are assigned to it and starts transmission. This allows efficient multiplexing of blocks

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401–380–061 Issue RFA Version , May 2000

GPRS - BSS Mobile Originated Packet Transfer

Call Management

from a number of MSs on a single PDCH. Additionally, the channel reservation command can be sent to the MS even before the total number of requested PDCHs is free. Thus, the status flags not only result in a highly dynamic reservation but also allow interruption of transmission in favour of pending or high priority messages. On the PCCH, one USF value is used to denote PRACH (USF=FREE). The other USF values USF=R1/R2/[0085].R7 are used to reserve the uplink for different MSs. After the blocks have been transmitted in the reserved time slots, an acknowledgment should follow from the BSS and sent to the PACCH. In the case of an acknowledgment, which includes a bitmap of correctly or erroneous received blocks, a Packet Resource Assignment for retransmission, timing advance and power control , only those blocks listed as erroneous are retransmitted. Figure 6-1 GPRS Mobile Originated Packet Transfer

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6-3

Call Management

GPRS - BSS Mobile Terminated Packet Transfer .................................................................................................................................................................................................................................... Overview

A SGSN initiates a packet transfer to a mobile station that is in the standby state by sending a Packet Paging Request on the PPCH or PCH downlink. The MS responds to this paging request by initiating a procedure for page response very similar to the packet access procedure described earlier. The paging procedure is followed by the Packet Resource assignment for downlink frame transfer containing the list of PDCHs to be used Since an identifier, e.g. TFI is included in each Radio Block, it is possible to multiplex Radio Blocks destined for different MSs on the same PDCH downlink. It is also possible to interrupt a data transmission to one MS if a higher priority data or a pending control message is to be sent to some other MS. If more than one PDCH is available for the downlink traffic, and provided that the MS is capable of monitoring multiple PDCHs, blocks belonging to the same frame can be transferred on different PDCHs in parallel. The network obtains acknowledgments for downlink transmission by polling the MS. The MS sends the ACK/NACK message in the reserved Radio Block which is allocated in the polling process. In the case of a negative acknowledgment, only those blocks listed as erroneous are retransmitted. Figure 6-2 GPRS Mobile Terminated Packet Transfer

....................................................................................................................................................................................................................................

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7

Radio Resource Management

Overview .................................................................................................................................................................................................................................... Purpose

Contents

This chapter discusses Radio Resource Management.

This chapter covers the following subjects: PCU Functionality

7-2

Multislotting Operation Effects

7-3

Channel Coding Schemes

7-5

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7-1

Radio Resource Management

PCU Functionality .................................................................................................................................................................................................................................... Overview

In the downlink direction, the PCU receives data from the Gb interface unit in the form of logical Link Control (LLC). Protocol Data Units (PDUs). Its task is to segment them into Radio Link Control (RLC) blocks and schedule the transmission at the radio interface. In the uplink direction, the PCU receives data in the form of RLC blocks from the CCU. Its task is to reassemble the RLC blocks into complete LLC frames, which are then transferred via the Gb interface to the SSGN. The PCU needs to do this for each MS context established at the radio interface. Up to 7 or 8 subscribers are allowed to share the same radio resource (TS) in each direction. To achieve higher data rates for packet transfers, the PCU is able to assign multiple radio resources to a single user.

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401–380–061 Issue RFA Version , May 2000

Radio Resource Management

Multislotting Operation Effects .................................................................................................................................................................................................................................... Overview

GPRS is different from the original GSM specification in that it allows a single MS to transmit data simultaneously on multiple time slots. The following is a comparison of two types of operation: •

When there is only one Packet Data Channel (PDCH) available in the cell, it is considered to be a single slot operation. The master PDCH (MPDCH) supports both data traffic and random access.

•

When there are up to eight PDCHs available in a cell, and the MSs are able to operate on eight time slots simultaneously, eight slot operation occurs. Channel 8 is used as the MPDCH and supports both control signalling and data transmission. The other channels are used as slave PDCHs (SPDCHs) and support only data traffic.

To compare the efficiency of channel utilisation, the overall input load and throughput are divided by the number of slots used. The base station is capable of capture, and both uplink and downlink errors are included. In the single slot operation as the load exceeds 4kbs per slot the throughput reaches the maximum value of 4 kbs. The delay becomes unbounded at this point. In the eight slot operation when the input load increases the maximum load increases 5kbs per slot, 40 kbs total. The delay explodes when the input load reaches 5 kbs per slot. In single slot operation, the maximum throughput is lower because the channel used by GPRS has to handle both traffic and control information. With multiple slots, the additional channels only have to carry traffic. Blocking increases as the load goes up. For eight slot operation, the blocking rate is very low (less than 0.1%). The blocking remains the same even when the delay becomes intolerable. With single slot operation, blocking becomes a serious problem. When the input load is as low as 2.5 kbs per slot, the blocking is already more than 5%. As the load increases, the blocking goes higher. To summarise the comparison of single slot and eight slot operation, throughput is defined in terms of the user data that is received successfully. In single slot operation, part of the channel is used for random access, so there is less user data transmitted per unit time and the data needs to wait longer to be served. With the service rate lower

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7-3

Multislotting Operation Effects

Radio Resource Management

in the single slot case, the delay is longer, there is more blocking and the maximum throughput is lower. Figure 7-1 Operation Effects

Figure 7-2 Segmentation

....................................................................................................................................................................................................................................

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401–380–061 Issue RFA Version , May 2000

Radio Resource Management

Channel Coding Schemes .................................................................................................................................................................................................................................... Overview

For GPRS, four different coding schemes have been defined: CS1 (high error detection) - CS4 (low error detection) •

CS1, for instance, defines intensive error detection mechanism and will be applied, if the radio conditions are bad.

•

The better the radio conditions get, the less error detection is necessary and the higher the throughput can be chosen. This is achieved by choosing a higher coding scheme and is done under the control of the PCU.

•

The first release supports only CS1 and CS2 !

•

The feature Switching Coding Scheme provides the automatic switch between CS1 and CS2.

•

Increase of bandwidth for GPRS data transfers by using a coding scheme with a lower protection scheme whenever the transmission quality allows it.

•

Start always with CS1 !

•

For uplink/downlink the PCU is the master.

Figure 7-3 Channel Coding Schemes

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7-5

8

Future Enhancements

Overview .................................................................................................................................................................................................................................... Purpose

This chapter describes the concept of Enhanced Data rates for GSM Evolution (EDGE)

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8-1

Future Enhancements

Enhanced Data rates for GSM Evolution (EDGE) .................................................................................................................................................................................................................................... EDGE

EDGE is a concept for Enhanced Data rates for GSM Evolution: •

Higher spectral efficiency due to 8-PSK modulation (3 bits per symbol) vs. GMSK for GPRS (1 bit per symbol)

•

Packet data service EGPRS reuses the GPRS architecture

•

EGPRS and GPRS mobiles can be multiplexed on the same time slot

•

8 modulation and coding schemes proposed: MCS -1 [0085]. MCS - 8

•

EGPRS supports pure Link Adaptation (LA) mode or a combined LS and Incremental Redundancy (IR) mode. Enhanced Data Rates for GSM Evolution (EDGE) is currently under consideration in the Lucent Technologies work plan and is scheduled for later release. Lucent are active participants in the working group meetings in evaluating various technology proposals (like 8PSK vs. other coding options) for EDGE and as a result of these meetings EDGE compliance is being integrated into all Lucent equipment

EGPRS Modulation and Coding Schemes Coding Scheme

Mod.

Code Rate

RLC Payload Bits Octets

Max Data Rate kbps

Blocks Family # IR sub Per blocks 20ms

MSC 1

G

0.53

176 (22)

8.8

1

C

2

MSC 2

M

0.66

224 (28)

11.2

1

B

2

MSC 3

S

0.85

296 (37)

14.8

1

A

3

MSC 4

K

1

352 (44)

17.6

1

C

3

MSC 5

8-

0.37

448 (56)

22.4

1

B

2

MSC 6

P

0.49

592 (74)

29.6

1

A

2

MSC 7

S

0.76

896 (112)

44.8

2

B

3

MSC 8

K

1

1184 (148)

59.2

2

A

3

....................................................................................................................................................................................................................................

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401–380–061 Issue RFA Version , May 2000

Enhanced Data rates for GSM Evolution (EDGE)

Future Enhancements

EGPRS Combined LA and IR mode •

The whole RLS block is convolutional encoded with a rate 1/3 code

•

Maximum three puncturing schemes to derive 3 sub-blocks: P1 P3 for re-transmitting any MCS can be selected based on the current link quality.

•

First P1 is sent. If it cannot be decoded, P2 and P3 are subsequently transmitted until the receiver can successfully decode the RLC block via soft combining of all received sub-blocks.

•

The code rate is dynamically adjusted according to the experienced radio condition without using explicit measurements.

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8-3

Glossary

A

A

Interface between BSC and MSC Abis

Interface between BSC and BTS ACC

Advanced Communications Card AGCH

Access Grant Channel APN

Access Point Name ARQ

Automatic Retransmission on Request AVL

Automatic Vehicle Location ....................................................................................................................................................................................................................................

B

BCCH

Broadcast Control Channel BSC

Base Station Controller BCF-2000

Base-Station Controller Frame-2000 BSS

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G L O S S A R Y G L - 1

BSSGP

Base Station Subsystem GPRS Protocol BTS-2000

Base Transceiver Station-2000 BVC

BSSGP Virtual Connection BVCI

BSSGP Virtual Connection Identifier ....................................................................................................................................................................................................................................

C

CCCH

Common Control Channel CCF

Cell Control Function CCU

Channel Codec Unit CEWS

Cell Workstation CG

Charging Gateway CS

Circuit Switched Traffic ....................................................................................................................................................................................................................................

D

DNS

Domain Name Server ....................................................................................................................................................................................................................................

E

EDGE

Enhanced Data Rates for GSM Evolution EIR

Equipment Identity Register ETSI

European Telecommunications Standards Institue ....................................................................................................................................................................................................................................

F

FEC

Forward Explicit Congestion ....................................................................................................................................................................................................................................

G L O S S A R Y G L - 2

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FOA

First Office Application FN

Frame Number FR

Frame Relay ....................................................................................................................................................................................................................................

G

Gb

Interface between SGSN and BSC Gd

Interface between SMS-GMSC/IWMSC and SGSN Gi

Interface between GPRS and external data network Gn

Interface between two GSNs within same PLMN Gp

Interface between two GSNs in different PLMNs Gr

Interface between an SGSN and HLR Gs

Interface between SGSN and MSC GBIU

Gb Interface Unit GBN

GPRS Backbone Network GBS

GPRS Backbone System GGSN

Gateway GPRS Support Node GMM

GPRS Mobility Management GMSC

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G L O S S A R Y G L - 3

GPRS

General Packet Radio Service GSE

GPRS Signalling Entity GSM

Global System for Mobile Communications GSN

GPRS Support Node GTP

GPRS Tunneling Protocol GVM

GPRS Virtual Machine GWS

GPRS Workstation ....................................................................................................................................................................................................................................

H

HLR

Home Location Register HSCD

High Speed Circuit switched Data ....................................................................................................................................................................................................................................

I

I/F

Interfac IMEI

International Mobile station Equipment Identity IMSI

International Mobile Subscriber Identity IMW

Integrated Maintenance Workstation IP

Internet Protocol IWMSC

Inter-Working MSC

....................................................................................................................................................................................................................................

G L O S S A R Y G L - 4

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401–380–061 Issue RFA Version , May 2000

....................................................................................................................................................................................................................................

L

LAC

Location Area Code LAN

Local Area Network LLC

Logical Link Control ....................................................................................................................................................................................................................................

M

M

Interface between BSC and STF Mg

Interface between BSC and PGU MAC

Medium Access Layer MS

Mobile Station MSC

Mobile-services Switching Centre ....................................................................................................................................................................................................................................

N

NE

Network Element NEM

Network Element Manager NMC

Network Management Center N-PDU

Network-Protocol Data Unit NS_VC

Network Service Virtual Connection ....................................................................................................................................................................................................................................

O

OA

Interface between OMC and BSS OA&M

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G L O S S A R Y G L - 5

OMC-2000

Operations and Maintenance Center-2000 OMC-G

Operation and Maintenance Centre for GBS ....................................................................................................................................................................................................................................

P

PACCH

Packet Associated Control Channel PBCCH

Packet Broadcast Control Channel PCH

Paging Channel PCCCH

Packet Common Control Channel PCM

Pulse Code Modulation PCU

Packet Control Unit PDCH

Packet Data Channel PDN

Packet Data Network PDP

Packet Data Protocols PDU

Protocol Data Unit PGU

PCU & Gb Interface Unit PLMN

Public Land Mobile Network PSTN

Public Switched Telecommunication Network PTCH

Packet Traffic Channel ....................................................................................................................................................................................................................................

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PTM

Point–To–Multipoint PTM-G

Point-To-Multipoint Group Call PTP

Point–To–Point PVC

Permanent Virtual Channel ....................................................................................................................................................................................................................................

Q

QoS

Quality of Service ....................................................................................................................................................................................................................................

R

RACH

Random Access Channel RF

Radio Frequency RIL

Radio Interface Layer RLC

Radio Link Control ....................................................................................................................................................................................................................................

S

SAPI

Service Access Point Identifier SGSN

Serving GPRS Support Node SM

Session Manager SMS-SC

SMS-Center SNDCP

Subnetwork Dependent Convergence Protocol SRS

Sub-Rate Switch

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G L O S S A R Y G L - 7

SS

Supplementary Services SSS

Switching Sub-System STF

Speech Transcoder Frame SW

Software ....................................................................................................................................................................................................................................

T

TCP

Transmission Control Protocol TCP/IP

Transmission Control Protocol/Internet Protocol TRC

Transcoder ....................................................................................................................................................................................................................................

U

UDP

User Datagram Protocol Um

Interface between MS and BSS UMTS

Universal Mobile Telecommunications System USF

Uplink State Flag ....................................................................................................................................................................................................................................

V

VLR

Visitor Location Register VPLMN

Visited PLMN VSAT

Very Small Aperture Terminal ....................................................................................................................................................................................................................................

X

X.25

Packet Switching Protocol ....................................................................................................................................................................................................................................

G L O S S A R Y G L - 8

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Index

........................................................

GPRS Attach Procedure, 5-5

B BSS Protocols, 4-18 ........................................................ F

PDP Context Activation Procedure, 5-29

GPRS Services, 1-7

Enhanced Data rates for GSM Evolution (EDGE), 8-2 ........................................................

GPRS Signalling and Transmission Protocols, 4-1

GPRS Benefits, 1-8

GPRS Introduction to the BCF, 2-34 GPRS introduction to the BTS, 2-33

GPRS Impact on the Network Switching Subsystem (NSS), 2-31 ........................................................ I

GPRS MS Protocols, 4-24

Combined RA / LA Update Procedure, 5-21

Interfaces, 3-1

New Network Area, 2-18 New Network Elements Functional Entities, 2-19 New Network Interfaces, 2-28 ........................................................ R

L

Lucent Base Station Subsystem, 2-5

Multislotting Operation Effects, 7-3 PCU Functionality, 7-2 ........................................................ S SGSN Protocols, 4-9 ........................................................ T

Detach Procedures, 5-10

Radio Resource Management, 7-1 Channel Coding Schemes, 7-5

Internet Protocol (IP), 2-59 IP addressing, 2-54 ........................................................

Network Switching Subsystem (NSS), 2-11 Network Switching Subsystem (NSS) and GPRS, 2-47

GSM System Interfaces, 3-2

GPRS MS, 4-34

GPRS Procedures, 5-1

N

GPRS System Interfaces, 3-4

GPRS Logical Channels, 4-26

GPRS Network Architecture, 2-2

Mobility Management, 5-2 ........................................................

GPRS Impact on the Base Station Subsystem (BSS), 2-30

GPRS Development and History, 1-5

Mapping of packet data logical channels onto physical channels, 4-28 Mobile Station, 2-4

GSM Elements Affected by GPRS, 2-30

GGSN Protocols, 4-6

GPRS Input for the OMC, 2-38

M

Routing Area Update, 5-15

Frame Relay, 2-24 Future Enhancements, 8-1

G

........................................................

The GPRS Air Interface, 4-25

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I N D E X I N - 1

The GPRS Backbone System (GBS), 2-16 The GPRS Signalling Plane, 4-2 The GPRS Transmission Plane, 4-4 The TCP/IP layers, 2-52 The TCP/IP Suite, 2-51 Transmission Control Protocol (TCP), 2-62 ........................................................ U

User Datagram Protocol (UDP), 2-64 ........................................................ W

What is GPRS, 1-2

....................................................................................................................................................................................................................................

I N D E X I N - 2

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401–380–061 Issue RFA Version , May 2000