GPRS

GPRS Overview Manual

GSM Network Release 9.0

401–380–061Issue RFA Version

May 2000

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401–380–061 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

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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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401–380–061Issue RFA Version , May 2000

Lucent Technologies C O N T E N T Si 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

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3 Interfaces

Overview 3-1

GSM System Interfaces 3-2

GPRS System Interfaces 3-4

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4 GPRS Signalling and Transmission Protocols

Overview 4-1

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C O N T E N T Si v

Lucent Technologies 401–380–061Issue RFA Version , May 2000

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

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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

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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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Lucent Technologies C O N T E N T Sv

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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

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8 Future Enhancements

Overview 8-1

Enhanced Data rates for GSM Evolution (EDGE) 8-2

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GL Glossary GL-1

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IN Index IN-1

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C O N T E N T Sv i


List of Figures

1 Introduction

1-1 GSM System Architecture 1-2

1-2 GPRS System Architecture 1-3

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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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Lucent Technologies F I G U R E Sv 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

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3 Interfaces

3-1 GSM Interfaces 3-2

3-2 Gb Interface Protocol Stack 3-4

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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 Sv i i i


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

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5 GPRS Procedures

5-1 GPRS Attach/Detach States 5-3

5-2 GPRS GMM/SM Control Plane 5-4

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6 Call Management

6-1 GPRS Mobile Originated Packet Transfer 6-3

6-2 GPRS Mobile Terminated Packet Transfer 6-4

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7-1 Operation Effects 7-4

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Lucent Technologies F I G U R E Si x

7-2 Segmentation 7-4

7-3 Channel Coding Schemes 7-5

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F I G U R E Sx


About this information product

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

Purpose General Packet Radio Services (GPRS) has been specified to optimisethe way data is carried over GSM networks with new requirements forfeatures, network capacity and bearer services.

The technology allows GSM license holders to share physicalresources on a dynamic, flexable basis between packet data servicesand other GSM services.

This GPRS Overview manual presents a detailed description of theGPRS system.

Reason for reissue This document has been updated to increase the overall level ofinformation provided to users.

Safety labels There are no safety labels associated with this information product

Conventions used There are no special conventions used in this information product

Related documentation The following documents can provide additional useful information:

• GPRS Introduction Procedure (401–380–060)

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


Lucent Technologies x i

1 Introduction

Overview....................................................................................................................................................................................................................................

Purpose General Packet Radio Services (GPRS) has been specified to optimisethe way data is carried over GSM networks with new requirements forfeatures, 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 throughoutthe world. This section also lists the history of GPRS, the servicesprovided & 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 CircuitSwitched Data)

1-8

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Lucent Technologies 1 - 1

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

Introduction GPRS is a data service for GSM, the European standard digitalcellular service. GPRS is a packet-switched mobile data service, it is awireless packet based network. GPRS, further enhancing GSMnetworks to carry data, is also an important component in the GSMevolution entitled GSM+. GPRS enables high-speed mobile datausage.

GPRS provides a packet data service for GSM where Time-Slots (TS)on the air interface can be assigned to GPRS over which the packetdata from several mobile stations (MS) is multiplexed. GPRS, furtherenhancing GSM networks to carry data.

The GSM system architecture includes, the air interface (Um), the Abis

and the A Interface and others mentioned later in this document. TheGSM functionality is between the Mobile station (MS), the BaseStation 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 theBase Station Controller (BSC) which manages the radio resource andcontrols handovers. A BSC can manage several BTSs. Through theMSC, the GSM system communicates to other networks such as thePublic Switched Telephone Network (PSTN), Integrated ServicesDigital Network (ISDN), Circuit Switched Public Data Network(CSPDN) and Packet Switched Public Data Network (PSPDN). GSMspecifies 4 databases, the Home Location Register (HLR), the Visitor

Figure 1-1 GSM System Architecture

Introduction

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1 - 2 Lucent Technologies 401–380–061Issue RFA Version , May 2000

Location Register (VLR) and the Authentication Centre (AUC) andEquipment Identity Register (EIR).

The ETSI Standard introduces two new elements, the Serving GPRSSupport Node (SGSN) and the Gateway GPRS Support Node (GGSN)(Shown in the diagram below as shadowed objects) are introduced tocreate an end-to-end packet transfer mode.

The HLR is enhanced with GPRS subscriber data and routinginformation. 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 LandMobile Network (PLMN) is supported by a new logical network nodecalled the GPRS Support Node (GSN). The Gateway GPRS SupportNode (GGSN) acts as a logical interface to external packet datanetworks. The Serving GPRS Support Node (SGSN) is responsible forthe delivery of packets to the MSs within its service area. Within theGPRS network, Protocol Data Units (PDUs) are encapsulated at theoriginating GSN and decapsulated at the destination GSN. In betweenthe GSNs, Internet Protocol (IP) is used as the backbone to transferPDUs. This whole process is defined as tunnelling in GPRS. TheGGSN also maintains routing information used to tunnel the PDUs tothe SGSN that is currently serving the MS. All GPRS user relateddata needed by the SGSN to perform the routing and data transferfunctionality is stored within the HLR.

Figure 1-2 GPRS System Architecture

What is General Packet Radio Service(GPRS) ?

Introduction

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The European Telecommunications Standards Institute (ETSI) hasspecified GPRS as an overlay to the existing GSM network to providepacket data services. In order to operate a GPRS service over a GSMnetwork, new functionality has to be introduced into existing GSMNetwork Elements and new Networks elements have to be integratedinto the existing operators GSM networks. The Base StationSubsystem (BSS) of GSM is upgraded to support GPRS over the airinterface. The BSS works with the GPRS Backbone System (GBS) toprovide GPRS service in a similar manner to its interaction with theSwitching subsystem for the circuit switched services.

The GPRS backbone system manages the GPRS sessions set upbetween the mobile terminal and the network, by providing functionssuch as admission control, Mobility Management and SessionManagement. Subscriber and equipment information is shared betweenGPRS and the switched functions of GSM by the use of a commonHLR and the co-ordination of data between the VLR and the GPRSsupport nodes of the GBS. The GBS is comprised of two newnetwork elements, the Serving GPRS Support Node (SGSN) and theGateway GPRS Support Node (GGSN). GPRS will be the IndustryStandard interface for mobile packet systems.

The maximum data rate is 171.2 kbps gross rate.

What is General Packet Radio Service(GPRS) ?

Introduction

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

Development Over the last ten years, there have been numerous predictions thatMobile Data is about to explode in the marketplace and indeed, mostof the data trends confirm this. With the rapidly advancing technologyit does appear that mobile data will become a widespread reality, butperhaps not quite as quickly as first thought. Until now, the only GSMdata services available have been the Short Message Service (SMS)and low speed bearer services for fax and data transmission at9.6kbps. The general take up of these services has been slow and onlya very small percentage of mobile users (estimated at 3-5%) areenabled for data services.

The current data rate for GSM is 9.6 kbps. To maintain competitiveedge, modifications and enhancements will need to be made. Theproposed enhancements will mean an increase in the amount of userdata to be carried across the network. These have included the HighSpeed Circuit Switched Data (HSCD) which has data rates up to 57.6kbps and General Packet Radio Service (GPRS) which has up to171.2 kbps.

History The following section lists the main development dates associatedwith GPRS.

• GPRS has been established at the European TelecommunicationsStandards 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 basedNETwork (NSFnet) funded to provide regionalsites & backbone

1991 Gopher is introduced

1991 Commercial Internet Exchange CCIX7 set up forcommercial traffic

1992 First Cellular Digital Packet Data (CDPD)specifications appear

1992 World-wide web is introduced

Introduction

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Date Event

1993 Wireless Data Cellular Digital Packet Data(CDPD) forum started

1994 GPRS introduced to ETSI subcommittees & firstcommercial CDPP networks

1998 GPRS Phase 1 standards published

Development/History Introduction

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

Introduction The services provided by GPRS are extensive. GPRS is ideal forsending & receiving bursty data via the Mobile Station (MS). Thisenables the user to send information via e-mail and also have accessto Mobile Internet/Intranet Services, like Emerging services, andWWW access.

It could also be used for the following:

• E-Commerce, Credit Card checks, Ticketing

• Vertical Market ApplicationsThese 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 asTele-Traffic control, Automatic Vehicle location (AVL)

• Location Services, LCS (ETSI Specified)

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

Introduction

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The Benefits GPRS Provides (Compared to Circuit SwitchedData)....................................................................................................................................................................................................................................

Introduction The data transferred is encapsulated into short packets with a headercontaining the origin and destination address. The packets are thensent individually over the transmission network. Packets originatingfrom one user may take different routes through the network to thereceiver. Packets originating from many users can be interleaved, sothat the transmission capacity is shared. No pre-set time-slots areused. Instead, network capacity is allocated when needed and releasedwhen not needed. This is called statistical multiplexing, in contrast tostatic time division multiplexing. In static time division multiplexing,time-slots are reserved for one user for the length of the connectionregardless of whether it is used or not, as with PCM lines and GSMvoice and circuit switched data.

GPRS upgrades GSM data services to be more compatible withLANs, WANs and the Internet. GPRS uses radio resources only whenthere is data to be sent or received, and so is well adapted to the verybursty nature of data applications. Furthermore, it provides fastconnectivity and high throughput.

While the current GSM system was originally designed for voicesessions, the main objective of GPRS is to offer access to standarddata networks such as TCP/IP. These networks consider GPRS to benormal 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. Theoperator benefits of GPRS are:

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

• The possibility to offer new, innovative services. New usersegments such as telemetry of electric meters will becomeaccessible to the operator

• The ability to profit with idle capacity that would otherwise beused only to cover peak-hour traffic. Many users can use onetime-slot simultaneously

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

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

Introduction

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• Profitable to the operator (value added service, efficient use ofchannels)

• 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 jointhe Internet boom with true IP connectivity

• The possibility to offer new, innovative services. New marketsegments such as telemetry of electric meters will becomeaccessible to the operator

• The ability to profit with idle capacity that would otherwise beused only to cover peak-hour traffic. Multiple users can use onetime-slot simultaneously

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

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

• Profitable to the operator (value added service, efficient use ofchannels)


• Reuse of existing network infrastructure

• Due to the wide GSM coverage, GPRS will offer true globalmass market wireless access to the Internet and otherpacket-based networks

• Applications will be user-friendly with a seamless on-linenetwork connection independent of time and place. All existingTCP/IP-based applications can be used with GPRS as if theywere connected to a LAN

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

• GPRS makes using existing applications easier and enables newapplications

• High bit rates in peak-hour, and uncompressed data rates of171.2kbps

• The existing e-mail subscriber base in the Internet gives even thevery first GPRS user a large group of ’B-subscribers’ tocommunicate with


The Benefits GPRS Provides (Compared toCircuit Switched Data)

Introduction

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2 System Overview

Overview....................................................................................................................................................................................................................................

Purpose This chapter describes the basic layout of the GPRS systemarchitecture in terms of the major entities involved.

Contents 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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GPRS Network Architecture....................................................................................................................................................................................................................................

Overview GPRS is an overlay on the existing GSM structure, which means thatan existing GSM network is used with added new GPRS networkentities. The new GPRS network entities are, the Gateway GPRSSupport Node (GGSN), the Serving GPRS Support Node (GGSN) andadditional functionality in the BSS.

GPRS will require modifications and enhancements to the existingGSM network architecture to enable it to support both packet andswitched data.

GSM System Entities The GSM system entities represent groupings of specific wirelessfunctionality.

A Public Land Mobile Network (PLMN) includes the followingsystem 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)

System Overview

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• Other Network Elements

Figure 2-1 GSM System Architecture

GPRS Network Architecture System Overview

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Mobile Station....................................................................................................................................................................................................................................

Overview The Mobile Station (MS) represents the terminal equipment used bythe 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 anappropriate SIM can access the system using various mobileequipment. The equipment identity is not linked to a particularsubscriber. Validity checks made on the MS equipment are performedindependently of the authentication checks made on the MS subscriberinformation.

Functions of a MobileStation

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

Types of Mobile Stations: Mobile stations can come in different power classes, which define themaximum RF power level that the unit can transmit. For GSM 900there are five power classes, for GSM 1800 there are three powerclasses. The mobile station output power is specified in the GSMSpecifications 05.05.

Power Classes

Class Max RF Power (Watts)

GSM 900 GSM 1800

I – 1

II 8 0.25

III 5 4

IV 2 –

System Overview

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Class Max RF Power (Watts)

V 0.8 –

Vehicular and portable units can be either class I or II, whileHandheld units can be class III, IV or V. Typical vehicular andportable stations are of power class II or III while the typicalhandheld is of power class IV.

Lucent Base StationSubsystem

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)

Functions of the BaseTransceiver Station (BTS)

Signalling data intended for the mobile station is inserted in thecorrect signalling channel on the air interface. This signalling andtraffic data is protected against transmission errors, interleaved, andencrypted 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, datachannels, and signalling data. Since the data to be transmitted cansometimes become partially corrupted by the fading effect, the datamust be appropriately protected. Additional check bits are generatedfor this purpose, which make it possible to detect transmission errorsand to reconstruct the original data to a certain degree.

Encryption andDecryption

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

Mobile Station System Overview

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

Interleaving The sub-blocks of a data block created by channel coding aredistributed over several TDMA frames (interleaving). Because of theinterleaving, only isolated sub-blocks are affected by interferencevariables. This increases the overall interference resistivity of thechannels, since minor errors can be corrected with the aid of thecheck bits inserted during channel coding. After they have beenreceived, the interleaved sub-blocks are recomposed into completedata blocks, checked for errors, and corrected, if necessary.

Burst Formation The interleaved and encrypted data is packed into bursts. A burst is atime segment of the radio frequency carrier that is the same length asa time slot and therefore constitutes the physical content of a timeslot.

The burst types are listed below:

• Normal Burst - Transmission of voice and signalling data

• Dummy Burst - Sent in unoccupied time slots on the BCCHcarrier

• Access Burst - Request for a connection, location update, andresponses to a paging cell

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

• Frequency Correction Burst - Corrects the transmit and receivefrequencies of the mobile station

Delay Correction Because of the varying distances between mobile radio stations, theradio signals may have different delay times. For this reason, controlsare necessary to equalise these delays. For an existing connection, thegroup delay is constantly changing because of the movement of themobile station. For this reason, deviations from the correct time arecontinuously measured at the BTS-2000, and the correctionparameters are automatically inserted and transmitted to the mobilestation.

Modulation The modulator has the task of converting the serial data stream into aGMSK-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 isgenerated in parallel to this signal recovery.


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Call Handling Functions Call handling functions include all the functions that are required forsetting up, maintaining, and releasing connections. These functions arecontrolled by the BSC. The BTS-2000 is the executing element in theGSM 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 ChannelManagement

The BSC informs the BTS-2000 of all relevant parameters, suchchannel type, carrier frequency, time slot number, channel coding, andrate adaption. The BSC determines what is to be sent over thesignalling channels. The BTS-2000 must send the messages associatedto the various channels at the right times in accord with its channelconfiguration. Only the correction parameters for the delay areinserted automatically by the BTS-2000 itself.

Detection of Loss ofConnection

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

Connection ControlMeasurements

The BTS-2000 conducts internally different measurements on eachvoice/data channel for monitoring the transmission quality.

These include the following measurements:

• Receive field strength measurement (taken over one SACCHperiod)

• Receive field strength measurement (taken over a subset of theTDMA frames)

• Signal quality measurement (bit error rate; taken over oneSACCH period)

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


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Control and Supervisionof the STF-2000

The BTS-2000 performs the synchronisation between the STF-2000and the BTS-2000 and also controls the functions of the STF-2000.This operation is performed by means of the appropriate control bitsincluded in the TRAU-Frames exchanged between the BTS-2000 andthe STF-2000.

Functions forTransmission Quality

Improvement

The following BTS-2000 functions improve the quality oftransmission to the mobile station:

• Frequency Hopping

• Antenna Diversity

• Transmit Power Control

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

Antenna Diversity The antenna diversity function serves to improve the reception quality.It is enabled by installing two spatially separated reception antennasfor each cell, each of which is connected to its own transmission pathin the transmitter.

Transmit Power Control BTS-2000 transmit power control is optional in the GSM system andcan be activated and deactivated by the OMC-2000 (operation andMaintenance Centre). The aim of transmit power control is to use alow transmit power that will enable problem-free high-qualitytransmission of voice/data.

Functions of the BaseStation Controller Frame

(BCF-2000)

The BCF-2000 is the central control module in the GSM network. Itis connected in the transmission paths between the BTS-2000 and theSTF-2000. A BCF-2000 can manage a number of BTSs through theAbis-links. It is connected to the STF-2000 via an M-link.

The functions of the BCF-2000 are performed either autonomously orunder control of the OMC-2000 and are related to:

• Call handling

• Operations and Maintenance


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Call handling functions:

• Management of the BTS-2000 radio terminals and the assignedradio frequencies

• Establishing and holding supervising calls for all subordinateBTSs

• Handling of signalling connections to the mobile stations (LAPDà Link Access Procedure on the D-Channel) and RIL3 (RadioInterface Layer-3) and to the MSC (CCS7 à Common ChannelSignalling No. 7) and BSSAP (Base Station System ApplicationPart)

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

• RF power control and handover management

Operations andMaintenance

• Configuration Management to control the various BSS elements

• Fault Management to detect, localise and correct system faults

• Performance Management to control the measurements initiatedby the OMC in order to obtain statistical data (e.g. for planningand analysis). Statistical data can be gathered by recordinginformation in connection with special events, and readingspecial event counters. Performance Management gathers therequested 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, aswell as to the memory of the other network elements

Functions of the SpeechTranscoder Frame

(STF-2000)

• Speech transcoding

• Data transmission between the A- and the M-interface

• 4 : 1 multiplexing

• Through-switching of any channel

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


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

4 : 1 Multiplexing The STF-2000 combines four 16kbps M-interface channels into one64kbps traffic channel. In total, the STF-2000 multiplexes fourA-interfaces into one M-interface.

Through-switching of anyChannel

The STF-2000 switches any channels, e.g. the CCS7 signallingchannel, between the BSC and the MSC through transparently.

Functionality of theOperations and

Maintenance Centre(OMC–2000)

The OMC-2000 (Operations and Maintenance Centre) manages theBSS-2000 (Base Station Subsystem) and the 5ESS-2000 Switch MSC(Mobile-services Switching Centre) in a GSM network.. It providesoperation and maintenance control capabilities from a central (remote)location.

To perform daily operational and maintenance routines, theOMC-2000 provides the following functions:

Function Provided forBSS-2000

Provided for5ESS-2000 SwitchMSC

ConfigurationManagement

X

Fault Management X

PerformanceManagement

X X

SystemAdministration

X

Switchover toredundant ports

X

On-line access viaterminal-orientedinterface

X

ConfigurationManagement

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

• Centralised storage of BSS network configuration data


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2 - 1 0 Lucent Technologies 401–380–061Issue RFA Version , May 2000

• Managing object states (e.g. restarting a piece of equipment thathas failed)

• Software administration for BSS loadable units

Fault Management

• Alarms indicating abnormal conditions for the BSS

• Alarm management functions (acknowledging and clearingalarms)

• Alarm correlation

• Fault tracking records

• Support for external alarms

Performance Management

• Gathering Performance Measurements

• Storing Performance Measurements

• Analysing Performance Measurements

System Administration

• Workstation administration (adding and modifying workstationinformation)

• User administration (adding and modifying user accounts)

• Loading error definition files

• Maintaining the network clock

Switchover to redundantports

Switchover to redundant ports provides a means of fast recovery ofthe possible link failure causes (e.g. a physical link failure betweenthe OMC-2000 and the connected BSSs, etc.). Switchover toredundant ports enables the operator to quickly switch over from afaulty X.25 connection to another X.25 connection.

Network SwitchingSubsystem (NSS)

Mobile-services Switching Centre (MSC) performs the switchingfunctions for all mobile stations located in the geographic areacovered by its assigned BSSs. Functions performed include interfacingwith the Public Switched Telephone Network (PSTN) as well as withthe other MSCs and other system entities, such as the HLR, in thePLMN.

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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Lucent Technologies 2 - 1 1

• Handling location registration and ensuring interworking betweenMobile 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 fixednetwork (e.g. charging)

Functions of the Home Location Register (HLR):

The Home Location Register (HLR) contains the identities of mobilesubscribers (IMSI), their service parameters, and their locationinformation.

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 subscriberparameters and location information for all mobile subscriberscurrently located in the geographical area (i.e. cells) controlled by theMSC.

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 theequipment validation procedure when a MS accesses the system. Itcontains the identity of the mobile station equipment (IMEI) whichmay be valid, suspect, or known to be fraudulent.


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The EIR contains:

• White or Valid list. This is a list of valid MS equipment identitiesList

• Grey or Monitored list. of suspected mobiles under observation

• Black or Prohibited list. List of mobiles for which any service isbarred

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 authoriseservice using Ki

• To generate a unique pattern called the Cipher Key (Kc) neededfor 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 andAuthorisation

X X X

Admission Control X X X

Message Screening X

Packet Terminal Adaptation X

Charging Data Collection X X

Packet Routing & Transfer:

Relay X X X X

Routing X X X X

Address Translation andMapping

X X X

Encapsulation X X X

Tunnelling X X

Compression X X

Ciphering X X

Mobility Management X X X X


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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 SGSNcurrently serving this MS.

SGSN Address The IP address of the SGSN currentlyserving this MS.

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

MS Purged for GPRS Indicates that the MM and PDPcontexts of the MS are deleted fromthe SGSN.

MNRG Indicates that the MS is not reachablethrough an SGSN, and that the MS ismarked as not reachable for GPRS atthe SGSN and possibly at the GGSN.

GGSN-list The GSN number and optional IPaddress pair related to the GGSN thatshall be contacted when activity fromthe MS is detected and MNRG is set.The GSN number shall be either thenumber of the GGSN or theprotocol-converting GSN as describedin the subclauses″MAP-based GGSN -HLR Signalling″ and ″GTP andMAP-based GGSN - HLR Signalling″.


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Field Description

Each IMSI contains zero or more of the following PDP contextsubscription 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 dynamicaddressing is allowed.

Access Point Name A label according to DNS namingconventions describing the access pointto the external packet data network.

QoS Profile Subscribed The quality of service profilesubscribed. QoS Profile Subscribed isthe default level if a particular QoSprofile is not requested.

VPLMN Address Allowed Specifies whether the MS is allowed touse the APN in the domain of theHPLMN only, or additionally the APNin the domain of the VPLMN.


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

Introduction The GBS represents the packet switching network that provides GPRSconnectivity between the BSS and external packet data networks tosupport GPRS terminals. The GBS comprises several different typesof network elements as well as the interconnecting transmissionhardware (e.g. routers, repeaters) and the transmission links betweenthem.

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, aswell as session management for any mobile GPRS user that has beenassociated with this SGSN. In order to achieve this task, the SGSNholds interfaces to the GSM subscriber databases: HLR, VLR, AUCand EIR. The SGSNs also hold the interfaces to the BSSs, andprovides the authentication and encryption services for securetransmission of user data.

The GGSN provides connectivity to external Packet Data Networks(PDNs). The ETSI standards specify the Internet and X.25 networksas external PDNs. The GGSN also provides address translationservices. Rate adaptation services between the GBS and externalnetworks may also be included in the GGSN. The Border Gatewayprovides connectivity to another Operator’s GPRS network.

New interfaces will be required to connect the new entities to theexisting GSM network elements. These interfaces will be pre-fixedwith the character ’G’ and will support both traffic and signalconnections.

Figure 2-2 The Principal GPRS Network Architecture

System Overview

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Unlike circuit switched services, packet services allow concurrentusage of the same resources by multiple users. In order to supportGPRS in a GSM network, the BSS has to be upgraded to supportpacket services and a GPRS Backbone System (GBS) has to be addedto the basic GSM network to provide packet connection from GPRScapable mobile stations to other packet users, both fixed and mobile.

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

• A GPRS operator managed IP domain and Domain Server to maplogical names for each element connected to the GBS domain toIP addresses

• Multiple Serving GPRS Support Nodes (SGSN) which providepacket service management for GPRS subscribers

• Multiple Gateway GPRS Support Nodes GGSNs which providesubscribers with access to external packet data networks andPublic Land Mobile Networks PLMNs

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

• A Performance Gateway function that collects Measurement Datafrom the GSNs and forwards to a Performance Monitoring Centre

• A Charging Gateway function that collects Accounting Data fromthe GSNs and forwards to a Billing Centre

The IP domain may be entirely operator provisioned or part of alarger IP network operated as a Virtual Private Network domain. TheNetwork supporting the IP domain is called the GPRS BackboneNetwork (GBN).

Figure 2-3 Architecture Overview

The GPRS Backbone System (GBS) System Overview

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New Network Area....................................................................................................................................................................................................................................

Overview GPRS introduces a new network area, the Routing Area.

Routing Area A Routing Area (RA) can consist of one or more cells and is alwaysserved by only one SGSN. However, one SGSN could serve morethan one Routing Area.

Location Area A Location Area (LA) can contain one or more Routing Areas, butone Routing Area could not span more than one Location Area.

Figure 2-4 Location and Routing Areas

System Overview

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New Network Elements - Functional Entities....................................................................................................................................................................................................................................

The SGSN For GPRS the GSM Base Station Subsystem (BSS) requires upgradingto support packet capabilities. This is done by adding the functionalityof a Packet Control Unit which provides true packet access over theGSM radio interface with no changes to the radio interface. Newlogical radio packet channels provide packet access to the GPRS BSSand the PCU handles these packet channels and forwards packets tothe SGSN.

The SGSN is a new network element that is the master of packetaccess to the GPRS system. In a similar way to the MSC for GSM,the SGSN provides service to Mobile Stations for packet transfer. TheSGSN is the master of packet transmission through the GPRS system.The SGSN provides Admission Control, Packet Service Managementand GPRS Mobility Management.

Unlike the MSC, the SGSN additionally provides several access leveloptions in the form of multiple Quality of Service (QoS) options andSession Management.

SGSN Connections

The SGSN contains the following connections:

• Connection to the GSM BSS via theGb - interface

• Connection to the HLR via theGr - interface

• Connection to the EIR via theGf- interface

• Connection to the GSM MSC/VLR via theGs - interface

• Connection to the SMS - SC via theGd- interface

• Connection to other PLMNs via theGp - 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, AddressTranslation, Address Resolution, IP Functions)

• GPRS Mobility & Session Management (PDP Context, HLRUpdates)

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

• GSM Circuit Switched Interactions (Paging, etc)

• BSS Queue Management (Queuing of data/users)

System Overview

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• Data Packet Counting (Billing)

• Gb Resource Management (Flow Control of BVCs over Gb,Frame Relay - PVC, NS - VC for support of BVCs, Support ofE1 Physical Layer)

The GGSN The GGSN is a new network element that provides access from theGBS to external packet data networks such as the Internet. Thegateway is primarily an IP router. The GGSN provides routing acrossthe GBS on GPRS Tunnelling Protocol (GTP) request from the SGSNand out onto the external network. This entity is therefore responsiblefor managing both routing of traffic from multiple SGSNs and accessto the external network this it is connected. The GGSN providesdynamic IP addresses on request from a SGSN, if a static address isnot requested by the MS and manages routing of requests fromexternal Packet Data Networks (PDN) to both PDP active andnon-PDP active, GPRS attached MSs.

The GGSN and the SGSN functions may be combined in a singlephysical unit or in different physical nodes. The connection betweenthe GGSN and the SGSN, i.e. the Gn interface, utilises IP routingfunctionality and as such, standard IP routers may be found on thisinterface between the two GSNs (GPRS Support Nodes). When theGGSN and the SGSN reside in different locations, the connection ismade via the Gp interface. The Gp interface has the same functionalityas the Gn interface with additional security such as firewall.

GGSN Connections

The GGSN contains the following connections:

• Connection to the SGSN via theGn - interface

• Connection to other PDNs via theGi - interface

• Connection to other PLMNs via theGp - interface

GGSN Functions

The GGSN carries out the following functions:

• Access Control (Firewall between GBS and PDN / Messagescreening)

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

• Data/Packet countingThe GGSN is the first point of interconnection from a PLMN toa PDN.

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

New Network Elements - FunctionalEntities

System Overview

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The GSM Phase 2+ GPRS Standards introduces the Packet ControlUnit (PCU) as the functional entity that handles all packet trafficrelated tasks within a BSS or a cell.

It can be implemented in the Base Transceiver Station (BTS), thencalled Integrated Packet Control Unit (iPCU), as well as in the BaseStation Controller Frame (BCF-2000), then it is called Remote PacketControl Unit (rPCU) (According to the Lucent terminology).

The Packet Control Unit (PCU) is the unit that adds the packetfunctionality to the Base Station System (BSS). It controls the radiointerface which allows multiple users to access the same radioresource

Additionally it also provides the Gb interface.

In the downlink direction, the Packet Control Unit (PCU) receivesdata from the Gb interface unit (GBIU) in the form of Logical LinkControl (LLC) Protocol Data Units (PDUs). Its task is to segmentthem into Radio Link Control blocks (RLC) and schedule thetransmission at the radio interface per slot and per mobile station.

In the uplink direction, the Packet Control Unit (PCU) receives datain form of Radio Link Control blocks (RLC) from the Channel CodecUnit (CCU). Its task is to reassemble the Radio Link Control blocks(RLC) into complete Logical Link Control frames, which then aretransferred via the Gb interface to the Serving GPRS Support Node(SGSN).

Figure 2-5 Placement of PCU within the Lucent BSS


System Overview

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The Packet Control Unit (PCU) needs to do this for each mobilecontext established at the radio interface. Up to eight subscribers areallowed to share the same radio resource in each direction, i.e. PDCH.

To achieve higher data rates for packet transfers, the Packet ControlUnit (PCU) is able to assign multiple radio resources to a single user.The Packet Control Unit (PCU) is a logical, not a physical unitimplemented in the Base Station System (BSS).

The Gb Interface Unit(GBIU)

The GBIU is a term that is used by Lucent Technologies to cover allfunctions that are provided by the Gb interface. The Gb interface hasbeen introduced by the Standards to provide packet data transportfunctionality between the BSS area and the GPRS backbone system.

The Gb interface is an open standard interface allowing GPRSequipment from different vendors to co-operate.

IT comprises Frame Relay (FR), Network Services (NS) and the BaseStation Subsystem GPRS Protocol (BSSGP). In the downlink theGBIU receives PDU’s from the SGSN and forwards them to theaddressed PCU or the GSE, if it is a signalling PDU. In the uplink theGBIU receives PDU’s from the PCU or the GSE and transfers themto the SGSN. The data link and subnetwork layer of the Gb interfaceis based on Frame Relay. The Gb interface allows load sharingthrough the usage of multiple links and provides limited protectionagainst link failures

The GPRS Signalling Entity(GSE)

The GPRS Signalling Entity (GSE) is a Lucent Technologies term toidentify a functional entity that summons all signalling functionalityrelated to the BSS Gb protocol.

The signalling functionality of the BSS Gb protocol comprises thecontrol of the Gb interface, as well as the handling of paging of GPRSattached mobiles.

The Channel Codec Unit(CCU)

The Channel Codec Unit (CCU) is a unit located in the BaseTransceiver Station (BTS).

In the downlink direction, the Channel Codec Unit (CCU) receives theRLC block from the PCU. It generates a Frame Check Sequence foreach block and appends it to the RLC block before transmission overthe radio interface.

The Channel Codec Unit (CCU) applies fourfold rectangularinterleaving to the Radio Link Control blocks (RLC). They arethereafter transferred to the Mobile Station over the radio interface.

In the uplink direction the Channel Codec Unit (CCU) receives theRadio Link Control blocks (RLC) over the radio interface from the


System Overview

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Mobile Station. The Channel Codec Unit (CCU) is responsible forde-interleaving and for checking the Frame Check Sequence in orderto detect erroneous Radio Link Control blocks (RLC). The Radio LinkControl blocks (RLC) are then transferred to the Packet Control Unit(PCU) for further processing. Non erroneous Radio Link Controlblocks are transferred.

An additional task of the Channel Codec Unit (CCU) is the handlingof timing advance.

For a newly accessing mobile, the Channel Codec Unit (CCU) isresponsible to determine the initial timing advance. The determinedtiming 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 ChannelCodec Unit (CCU) handles the continuous timing advance procedure.

The Cell Control Function(CCF)

The Cell Control Function (CCF) is a Lucent Technologies term. It isused to characterise all GSM functionality in the Base Station System(BSS) that is necessary for providing circuit switched services relatedto one cell.

The Cell Control Function (CCF) carries out the following standardGSM function:

• Administration of radio resources associated with the cell

The GSM Phase 2+ GPRS Standards require that it shall be possibleto support GPRS in a call even if there is no dedicated controlchannel for GPRS traffic defined.

As a consequence the Cell Control Function (CCF) needs to:

• support broadcast of GPRS System Information on the BroadcastControl 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 mobileson the Access Grant Channel (AGCH)


System Overview

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

Frame Relay Frame Relay is a high-speed communications technology that is usedin lots of networks throughout the world to connect Local AreaNetworks (LAN), System Network Architecture (SNA), Internet andeven 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 anaddress that is used by the network to determine the destination of theframe. The frames travel through a series of switches within the framerelay network and arrive at their destination.

Frame relay is a connection oriented packet service protocol thatmultiplexes many logical data connections over a single physicaltransmission link. It provides fast packet switching (more efficientthan X.25) and is optimized for high throughput and low end-to-enddelay.

Figure 2-6 Frame Relay Network

System Overview

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Frame Relay is based on the following three convergent parameters:

1. Increasing demand for high throughput

2. Highly reliable physical network

3. Intelligent end systemsA low protocol overhead is responsible to allow a highthroughput. The data link protocol is cut down, there are nosequence numbers, only address field (Data Link ConnectionIdentifier, DLCI) and a cyclic redundancy check (CRC). There isno network layer in Frame Relay .

No Error Correction byFrame Relay

There is no time consuming error correction in Frame Relay networks.Only error detection is done by the CRC and corrupted frames arediscarded. The retransmission is done only by end systems.

No Flow Control by FrameRelay

There is no flow control in Frame Relay networks. Special bitsprovide a simple congestion notification and the congestion control inthe network is done by discarding frames.

In case of a link failure there is no explicit rerouting mechanism in aFrame Relay network.

Frame Relay Terms:

• User to Network Interface (UNI)Specifies signaling and management functions between a framerelay 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 inGPRS 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

Frame Relay System Overview

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Frame Relay Structure The structure of Frame Relay contains the following fields:

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

• Address Field: This field is the comprise of two octects. It isused to carry the Data Link Connection Identifier (DLCI) whichis needed for routing the frame between different nodes. In theaddress field there is also an Address Field Extension (EA) thatindicates the last octet in the address field. There are also somebits to indicate whether a frame has encountered some congestedresources, the Forward Explicit Congestion Notification (FECN)and the Backward Explicit Congestion Notification (BECN).Another bit, the Discard Eligibilty bit (DE) is used in case ofcongestion in a network to indicate a specific frame that can bediscarded.

• Information Field: The purpose of this field is to carry the userinformation

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

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

Figure 2-7 Frame Relay Structure


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• DE Discard eligibility indicator

Frame Relayimplementation 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 runin user mode on the GWS.

Figure 2-8 Frame Relay Network


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

Overview New Interfaces will be required to connect the new entities to theexisting GSM Network Elements. These Interfaces will be pre-fixedwith the character G and will support both traffic and signalconnections. The diagram below displays the new interfaces.

Interface Connectivity

Interface Connectivity

Interface Connecting

Gb Between SGSN and BSS

Gn Between SGSN and GGSN or between twoSGSNs

Gi From GGSN to an external network

Gs Between MSC/VLR and SGSN to allowco-ordination of location information and paging

Gc, Gr MAP interfaces between the HLR andGGSN/SGSN to support authentication

Gf Interface to EIR to support the check IMEIprocedure

Figure 2-9 New GPRS Interfaces

System Overview

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Interface Connecting

Gd Interface from SMSC to the SGSN to allow SMStraffic to be carried over the GPRS channels

Gp Equivalent to the Gn, except that the connectedGSNs are in different networks

New Network Interfaces System Overview

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

Overview There are GBS implications on several existing GSM networkelements. These are , the BSS, OMC, MSC, VLR, HLR AUC andEIR. Several other new network elements are required by GPRSwhich the GBS feature has impact upon, these are the SGSN, GGSN,OMC-G, DNS and Data Gateways (CG and Performance Gateway).

Shared Network Resources The figure below shows how network resources will be shared. TheHLR & VLR record field size have been extended to accommodatefor GPRS.

GPRS Impact on the BaseStation Subsystem (BSS)

GPRS Impact on the Base Station Subsystem (BSS)

Element Description of changes required

BSC New Interface to new GPRS elements, Gb to theSGSN. New functionality to handle packet data,Remote Packet Control Unit (rPCU). Note: Ifcurrent link capacity is not sufficient to supportGPRS and GSM Circuit Switched (CS) traffic, thenadditional interface boards (M interface for nailedup connections) would need to be added

Figure 2-10 Shared Network Resources

System Overview

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BTS Software Modifications to handle packet data forhandling the GPRS traffic. Additional processingrequirements to support GPRS. The Abis interfacehas to be adapted to support GPRS

OMC O & M modifications to cover overlaid packetnetwork.

GPRS Impact on theNetwork Switching

Subsystem (NSS)

GPRS Impact on the Network Switching Subsystem (NSS)


MSC/VLR The Mobile switching Centre / Visitor LocationRegister (VLR) needs to be updated to allow forthe efficient co-ordination of circuit switched callsand GPRS packet data services. Also a newinterface (Gs) is needed between the MSC/VLRand the SSGN.

HLR The Home Location Register (HLR) needs to beupdated to store and manage new GPRS subscriberdata. To manage the new GPRS subscriber data,two new interfaces are created, (Gc) between theGGSN and the HLR, and (Gr) between the SGSNand HLR.

GSM Elements Affected by GPRS System Overview

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

Overview The introduction of GPRS to the Base Station System (BSS) is asmooth introduction (software update). Call processing will still bepossible while introducing the GPRS functionality.

Preconditions for GPRS Introduction:

1. All network elements are running at least at NR 8.2

2. Software release 9.0 available with appropriate″CustomerSpecific Database″

3. All cabling activities for Gb interface completed

4. Additional hardware for STF in place (if needed)

BSS GPRS Features (NR9.0)

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 codingscheme 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 uplinkdirection and 250 in downlink direction

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

System Overview

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

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

Abis - PCU Interface Abis - PCU Interface:

• Interface between CCU and Remote PCU

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

• 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 onthe Um Interface

The PCU schedules 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 The CCU reports to PCU

• Receive Level

• Receive Quality

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

The GPRS Um Interface The GPRS Um Interface

• BTS knows only Channel PDCH

• Mapping of logical Channels PACCH, PBCCH, PCCCH, PDTCHis done by PCU (Future release)

• BTS supports Frequency Hopping for GPRS

System Overview

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

Overview The GPRS functionality within the BCF-2000 is assigned to oneserver. Hence an extra server including an Advanced CommunicationCard (ACC) card will be required as a GPRS extension unit perBCF-2000.

GPRS workstation (GWS) One new type of logical workstation will be implemented. The newworkstation is called GPRS workstation (GWS). This leads to areduction of four Cell Workstations per BCF-2000. There will be oneGWS instance per BCF. Adding a GWS to a BCF–2000 requires nohardware changes, because every available server can come up as aGPRS workstation.

rPCU Integration into theBCF-2000

Figure 2-11 rPCU Integration into the BCF-2000

System Overview

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Distribution of functionality

All GPRS relevant units in the BCF are placed in the GPRSworkstation.

The GPRS Signalling Entity (GSE), the Gb Interface Unit (GBIU) andthe Packet Control Unit (PCU) are located in the GPRS Workstation.These three new UNIX processes will be combined into the GPRSVirtual Machine (GVM). The ACC card will have a new software andbe the holder of the RLC/MAC scheduler. There will be no GPRSspecific 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 receivedfrom 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 receivedfrom the SGSN. The non-connection related parts of the GPRSMobility Management (GMM) and of the Network Management (NM)functionality is also handled by the GSE.

Figure 2-12 Distribution of functionality

GPRS Introduction to the BCF-2000 System Overview

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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 FaultManagement (FM)

By analyzing the BSSGP Virtual Identifier and the primitive type, it isdecided by the BSSGP layer whether a received Protocol Data Unit(PDU) must be routed to the GSE or not. As a consequence, the GSEreceives only PDU′s which contain the signalling BSSGP VirtualConnection. It also receives all paging messages from the Gb InterfaceUnit (GBIU). These paging messages are analyzed by the PAGERprocess and they are forwarded to the Line Transmission VirtualMachines (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 VirtualConnection (NSVC)

• The Gb interface is not involved in dynamic switching (staticswitching)


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GWS Recovery procedures The recovery procedures for the GWS are listed below:

• Creation of a GBIU (via database or OMC)

• BCC recognises that GPRS is enabledChecking the LCA flag

• SRS-Handler selects suitable server as GWSSelection 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 allGVM UNIX processes have to be established)

• Creation of at least one NSVC

• Configuration of PCU

Reliability Parameters 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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GPRS Input for the OMC-2000 part....................................................................................................................................................................................................................................

Overview The following pages describe the impact of GPRS on the OMC-2000.

GPRS Support for BSS Before a complete set of new General Packet Radio Service(GPRS)-related objects (GBIU, PCU, and at least one NSVC) can becreated, the following conditions must be met:

• The NECONN object associated with the BSS must have itsGPRS 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 NSVCobject.

Reset of GPRS Support

If the GPRS Supported parameter in the BSS is reset from True toFalse to stop any support of GPRS traffic, any active GPRS-relatedmeasurement groups are not deleted automatically. In addition, theBSS continues to″collect″ GPRS measurement data even though noneof the counters associated with those measurements are incremented.To optimise your data collection activities, delete any GPRSmeasurement groups before resetting the GPRS Supported parameteron the BSS to False.

Important! Before you disable GPRS in the BSS, you must manuallychange 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 beselected:

• 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, theGPRS 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 youset its GPRS Supported parameter to False), you must do thefollowing:

• Under the BTS, delete any contained PCU object

• Make sure no RTs have CHNs configured with a channel type ofTCHFullandPDCH

• In the BTS, set the GPRS Supported parameter to False

System Overview

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• Manually delete all NSVC objects

• Under the BSS, ensure that there is no GBIU objectOnce the above conditions are met, you can set the BSS GPRSSupported parameter to False.

GPRS Support for BTS The parent BSS must have its GPRS Supported parameter set to Truebefore 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 thefollowing:

• Delete any contained PCU object.

• Make sure no contained CHNs are configured with a ChannelType of TCHFullandPDCH.

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

GPRS Support for RT In order to support GPRS functionality, the BTS must be able to mapnew logical channels on the RTs. To support GPRS communications, anew channel type, the Traffic Channel Fullrate and Packet DataChannel (TCHFullAndPDCH), is added.

At any given time, only one RT within a BTS–2000 can supportGPRS channels. Thus, the maximum number of channels that can beconfigured as PDCHs is 8.

To determine which of the RTs within a BTS–2000 has GPRSchannels assigned, you can open the RT Browser or RT Detail Viewand look at the GPRS Active column. The OMC-2000 sets the valueof this parameter to Y automatically as soon as a channel on an RT isconfigured as a PDCH.

Before Configuration

When no channels are configured as GPRS channels, such as whenyou are configuring the first one, all RTs will show″False″ in theGPRS Active column.

Display RT channel usage

The RT channel usage dialog displays information associated withGPRS communications, that is a Channel Status that indicates busyPDCH, only when GPRS capability exists for an RT.

GPRS Support for CHN Before traffic can move across the network, you must first configurethe channels (CHNs) on the Radio Terminals (RTs). To support GPRScapabilities, a new channel type TCGFullAndPDCH is added.

The Channel object (CHN) is also known as a physical channel. Itrepresents one physical time-slot in the air interface on an RT. There

GPRS Input for the OMC-2000 part System Overview

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are up to eight different channels for every RT. Every channel createdmust be configured, which includes assigning a channel type todesignate its function.

For GPRS additional channel types are defined:

• Packet Data Traffic Channel (PDTCH) which belongs to the classPacket Data Channel and will be used for Uplink and Downlinkdirection

• Packet Associated Control Channel (PACCH) which belongs tothe class Packet Data Channel and will be used for Uplink andDownlink direction

• Packet Timing Advance Control Channel (PTCCH) whichbelongs to the Class Packet Data Channel and will be used forUplink direction

GPRS Channel Description

• PDTCH - This corresponds to the resource allocated to a singlemobile station on one physical channel for user datatransmission. One PDTCH has an instantaneous bit rate of 0 to22.8 Kbit/s. When a channel is configured as a PDCH, it is ashared resource and can be used either for circuit switched orpacket switched operation. The BSS determines how it is usedbased on the number of requests for each type service, andaccording to resource availability. Creating a channel of this typedoes not mean that it will be used for GPRS services, even it isavailable and required.

• PACCH - Used to carry signalling information associated with aPDTCH.

• PTCCH - Used in the uplink to transmit random bursts to allowfor the estimation of the timing advance for one mobile stationon the packet transfer mode, and in the downlink to transmittiming advance updates for one or several mobile stations. Theexisting control channels handle all GPRS-specific informationand control operations.

The following information will help you to create a CHN object tosupport 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 TypeTCHFullAndPDCH to support GPRS.

• Shared resources must have a Frequency Hopping Relationship(frequency usage) value of 255, which means they are notallowed to be part of a Frequency Hopping scheme.

• All shared resources assigned within one BTS must be containedin the same RT.


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GPRS Support for a TRC The allocation of the bearer channel by the Network Services VirtualConnection (NSVC) object is done by reference to a TRC object,which has been configured to carry GPRS data. This means that the64Kb/s channel is passed transparently through the transcoder. To dothis and avoid confusion with existing CCSS7 signalling channels, anew 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 thePacket Control Unit (PCU). There is one functional PCU for eachBTS supporting GPRS. Since the PCU is a child object of the BTS,you must delete it before you disable GPRS capabilities of the parentBTS object.

Prerequisites

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

• The BTS parameter, GPRS Supported, indicates if GPRSfunctionality is supported by the BTS. It must be set to Truebefore 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 affectingparameter is used to determine if GPRS capability is supportedby a BTS-2000. A mobile station to do a cell reselection alsouses it. Values can range from 0 through 7.

• Routing Area Code (RAC) - The value of this service affectingparameter is determined by each network using the structure,which is specified in the GSM standards. Values can range from1 through 253, and must match the value set at the SGSN.

• BVCI - The BSSGP Virtual Connection Identifier. The value ofthis service-affecting attribute identifies the BSSGP VirtualConnection used between the PCU and SGSN. Values can rangefrom 2 through 181, and must be unique within the BTS-2000.

• Max(imum) Number of PDCHs Allowed - This parameterdetermines the maximum number of idle TCHFullAndPDCHwithin a BTS-2000 that the PCU can allocate for GPRS serviceat any time. Once this number has been reached, no morechannels can be assigned for GPRS service even if more idleTCHFullAndPDCH channels are available. Values can range from1 through 8. Default is 8.


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• Number of PDCHs Available - This attribute maintains a runningcount of the number of radio channels available for GPRS. For achannel to be counted it must be configured asTCHFullAndPDCH and Unlocked and Enabled.

• Priority Access THR - This parameter, sometimes, referred to asthe packet access class indicator, indicates whether or not amobile station of a certain priority class is authorised to do arandom 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 indicatesthe maximum time allowed for a mobile station to requestnon-discontinuous (non-DRX) reception mode after packettransfer 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 transfermode

- Maximum of 2 seconds



- Maximum of 16 seconds (default)



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

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

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


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• Power Control Timer T_Avg_T - This parameter defines thesignal strength filter period for power control in packet transfermode. Value can range from 0 through 25.

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

Network Services VirtualConnection (NSVC) Object

The Network Services Virtual Connection (NSVC) object is a child ofthe Gb Interface Unit (GBUI) object. This object is available only ifthe OMC is GPRS enabled, and if its parent BSS object has its GPRSSupported 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 forcreating an NSVC object.Do this as follows:

1. Obtain the list of available TRCs under a TCG of typeSTF-2000

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

3. If a TRC exists, ensure that the TRC Type field is set toGPRS

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 createdand activated, as long as at least one NSVC is unlocked and enabled,GPRS operations can begin. No association needs to be made betweenthe 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. Itis on of the two Network Services mapping elements. Values canrange from 0 through 65535, and must be unique within the BSS.


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

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

Gb Interface Unit (GBUI)Object

Each BSS is capable of supporting up to 31 NSVC objects for GPRSdata, where one bearer channel represents one 64 Kb/s timeslot on anM-link.

The allocation of the bearer channel is accomplished by referencing aTranscoder (TRC) object that has been configured to carry GPRSdata. The channel is passed through the TRC transparently.

The Network Services (NS) layer sits above Frame Relay, and isresponsible for the correct routing of data between the SGSN and theBSS. This is done by setting up Network Services Virtual Connections(NSVCs). These NSVCs are identified by their NS_VCI. This valueuniquely identifies the NSVC within the SGSN.

The OMC-2000 uses point-to-point connections, so the NetworkServices Virtual Connection Identifier (NS_VCI)-to-DLCI mappingmust be the same at the BSS and the Serving GPRS Service Node(SGSN). The mapping of the NS_VCI-toDLCI to bearer channelrelationship is contained in the NSVC objects. There is a limit of oneNSVC per bearer channel. Up to 31 NSVC objects are contained bythe GBIU object.

Once the data has been delivered to the BSS, the GBIU determinesthe final destination of each data packet within the BSS. This data iscontained in the BSSGP layer. The transfer of BSSGP data isaccomplished with the setting up of a BSSGP Virtual Connection(BVC). These BVCs exist between the BSSGP layers of the SGSNand the final destination within the BSS. To uniquely identify thedestination within a BSS each BVC is given a BSSGP VirtualConnection Identifier (BVCI), which must be unique within a BSS.The BVCI is a parameter with the Packet Control Unit (PCU). Itidentifies the BSSGP Virtual Connection used between the PCU andSGSN.

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 theBSS.


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How Packets Are Routed

Data traffic is forwarded to the PCU responsible for the BTS-2000where the mobile is currently located. Signalling traffic is passed tothe GPRS Signalling Entity (GSE) for processing.

The GSE is a BSS entity, which is not visible on the OMC-2000. Touniquely identify a PCU or GSE within an SGSN domain, a NetworkServices Element Identifier (NSEI) is provided at the NetworkServices layer. The NSEI uniquely identifies a BSS within an SGSN.It is, therefore, the combination of the NSEI plus the BVCI, whichuniquely identifies the final destination of each BSSGP packet withinan SGSN domain.

Prerequisites

The following are prerequisites to create a GBIU object:

• The GPRS Supported parameter in the parent BSS must be set toTrue

• No GBUI object currently exists in the BSS

GBIU Attributes

GBIU Attributes:

• NSEI - The Network Service Entity Identifier. The NSEI is aservice-affecting attribute that provides the network managementfunctionality required operating the Gb interface. The BSS andthe SGSN to determine the NSVC that provides service to aBSSGP Virtual Connection Identifier (BVCI) within the PCU usethe NSEI. Values can range from 0 through 65535, and must beunique within the SGSN.

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

• 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 oftime after which the BSS may send a flow control message to theSGSN for a specific BSSGP Virtual Connection (BVC) or mobilestation. The valid range is 1 through 10 seconds, and must matchthe value set at the SGSN. (Default=1)


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• BSSGP Timer Th - This timer defines the period of time afterwhich the SGSN will change the flow control settings for aparticular mobile to the default values. For the BSS to preventdefault values from being assigned by the SGSN,FLOW_CONTROL_MS messages must be sent before expirationof the Th timer. This timer value must be greater than BSSGPTimer 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 howoften the NSVC test procedure is performed. Values can range 1second through 60 seconds (Default=10)

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

• Frame Relay Counter N392 - This counter works with N393counter to provide a way to detest service affecting conditions bydetecting N392 errors in the last N393 events. The value of thiscounter must be less than or equal to the N393 counter. Valuescan range from 1 through 10 (Default=3)

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

• Frame Relay Counter N392 - This counter works with N393counter to provide a way to detest service affecting conditions bydetecting N392 errors in the last N393 events. The value of thiscounter must be less than or equal to the N393 counter. Valuescan range from 1 through 10. (Default=3)

• Frame Relay Counter N393 - This counter works with N392counter to provide a way to detect service affecting conditions bydetecting N393 errors in the last N393 events. The value of thiscounter must be greater than or equal to the N392 counter. Valuescan range from 1 through 10 (Default=4)

STF-2000 Lucent is able to support transparent 64 Kbit/s channels for thepurposes of providing an entry level physical Gb interface provisionedusing STF nailed up 64kbps per time–slot on E1 links.


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Network Switching Subsystem (NSS) and GPRS....................................................................................................................................................................................................................................

Impact on the NSS(Network Switching

Subsystem)

Due to the introduction of GPRS in the GSM network new interfacesand 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 isan overlay network, for mobility management the procedures areadjusted to route calls to that network. This requires modification ofsignalling, protocols and databases.

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

Figure 2-14 GPRS Impact on NSS

System Overview

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Hardware requirements

The only hardware updates needed for the NSS entities are additionalsignalling links to support the new GPRS interfaces. This possiblymeans additional Protocol Handlers and Facility Interfaces.

Software requirements

Software requirements needs to be split between the entities:

• For the MSC/VLR it is required that the changes support theinterworking over the Gs interface to the new packet networknode SGSN that allows a co-existence of GPRS and the existingcircuit switched network. Examples are combined mobilitymanagement procedures and the support of paging for circuitswitched services via GPRS.

• For the HLR it is required that the changes support GPRSsubscriber data, feature data and mobility management data.Furthermore the changes should support the interworking withthe GGSN over the Gcinterface and SGSN over the Gr interfaceto provide mobility management and subscriber data over theinterfaces.

• For the EIR no specific changes are needed. Only the Gf

interface is defined to interwork with the SGSN. All proceduresare described in the existing specifications.

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

• For the SMS-MSC it is required that the changes support thepossibility to send SMS messages to a mobile station via theSGSN and GPRS service. The Gd interface is defined to supportthis interworking.

• Modifications also need to be made for the C interface betweenthe SMS-MSC and the HLR to route SMS calls to the GPRSnetwork.

MSC/VLR Changes andProcedures

The Gs interface has an identical structure as the A interface to theBSC. The protocol stack uses the same lower levels.

Modifications are implemented in the BSSAP stack to where thefollowing procedures impact the communication between the mobilestation 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

Network Switching Subsystem (NSS) andGPRS

System Overview

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• 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 theMSC/VLR needs to be changed as well:

• In order to retrieve the location of the mobile station when a callenters 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 bothIMSI and GPRS attached. This means the implicit detach timer isnot activated in the MSC but in the SGSN which is in charge tomonitor the timer and to send the detach message to the MSC.

HLR/AuC/EIR Changes andProcedures

The Gr/Gc/Gf interface has an identical structure as a MAP interface.The protocol stack uses the same lower levels, modifications areimplemented in the MAP stack to where a number of proceduresimpact the communication between the mobile station and thenetwork. The AuC does not have its own interface but receives theneeded information relayed via the HLR.

For the Gr interface the following applies:

• Authentication information received via the SGSN

• Registration information received from the SGSN (GPRSattached, 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 moreinformation:

• For instance, to route the calls to the appropriate SGSN theSGSN 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 isstored in the SGSN (MS purged)


System Overview

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SMS-MSC Changes andProcedures

The Gd interface has an identical structure as a MAP interface. Theprotocol stack uses the same lower levels, modifications areimplemented in the MAP stack to where a number procedures impactthe 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 updatedprocedure that allows the network to send routing information to theHLR 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 includemessages being send to the appropriate GSNs.

In case of an HLR failure, an HLR reset will trigger a reset messageto be send to each SGSN that is known by the HLR.

In case of an VLR failure, an VLR reset will trigger a reset messageto be send to each associated SGSN.


System Overview

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

Introduction When two computers need to communicate with each other, it isnecessary to connect them via a physical connection to enable them topass messages back and forward. Either two computers reside in thesame network or the two computers reside in different networks.

Transmission Control Protocol/Internet Protocol (TCP/IP) is a set ofprotocols developed to allow computers (hosts) to communicate witheach other across a network.

Internet The Internet is a world-wide collection of thousands of computernetworks that can communicate with each other. All of them speak thesame language, namely the TCP/IP protocol suite. Users of any of theInternet networks can reach users on any of the other networks.

TCP/IP suite The most accurate name for the TCP/IP set of protocols is″theTCP/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 hasbecome common to use the term TCP/IP to refer to the whole family.

Graphic Legend

ARP Address Resolution Protocol

FTP File Transfer Protocol

Figure 2-15 TCP/IP suite

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

The TCP/IP layers Like the OSI 7 layer reference model, TCP/IP is a layered set ofprotocols. Although the layering of TCP/IP is not the same as the OSImodel, 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 aslayer 1 in the OSI 7 layer model.

Network interface

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

Internet layer

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

Transport layer

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

The TCP/IP Suite System Overview

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Application layer

The application layer protocols specify how an application uses anInternet. The application layer protocols correspond to layers 5, 6 and7 in the OSI 7 layer model.

The TCP/IP Suite System Overview

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IP addressing....................................................................................................................................................................................................................................

IP Address Every host or router on an Internet has an IP address or Internetaddress. All IP addresses consist of a unique 32 bit number. Eachpacket sent across an Internet must contain the IP address of thesource and the IP address of the destination.

The 32 bit IP addresses are seldom represented in binary format butthey 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 asuffix. The IP address prefix is used to identify a particular networkwithin the Internet and the IP address suffix is used to identify aparticular host or router on that network.

IP address classes The problem with using an IP address containing prefixes and suffixesis the decision on how big to make each field. If the prefix field issmall, only a few networks will be able to connect to the Internet.When the prefix field is increased, then the suffix field decreases, sofewer hosts can connect to a particular network with a given prefix.

Since an Internet includes various types of networks, the developersof 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

System Overview

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IP addressing scheme classes:

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

• Class D is used for multicasting, which allows packets to bedirected to multiple hosts

• Class E is reserved for future use

Network and HostNumbers

Network and host fields containing only 0s or 1s are used for differentpurposes.

Network and Host Numbers

Addressclass

Bits inprefix

Max.number ofnetworks

Bits insuffix

Max.number ofhosts pernetwork

A 7 1261 24 16 million

B 14 16,3821 16 65,5341

C 21 2 million 8 2541

Router Addresses Routers are responsible for connecting various networks together. Thismeans that a router is connected to at least two networks (withdifferent prefixes). Therefore each router is assigned two or more IPaddresses because a router with multiple network connections musthave an IP address assigned to each connection.

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

Figure 2-17 Router Address

IP addressing System Overview

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Control of IP addresses Each IP address prefix must be unique. This means that all networksconnected to an Internet must have their own unique network address.Therefore all network addresses are assigned by the Internet AssignedNumber Authority (IANA) to ensure each IP address prefix is unique.

In case of a private Internet (Intranet), the choice of the IP addressescan be made by its owners.

IP addressing System Overview

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Address Resolution....................................................................................................................................................................................................................................

Software and hardwareaddresses

Although every host or router on an Internet has one (or more) IPaddresses, these cannot be used for sending packets because the layer2 network interface hardware does not understand IP addresses. IPaddresses are virtual; software addresses, but if a packet must arrive ata certain host, the hardware address of that particular host is needed.A process must take place to translate an IP address into a hardwareaddress.

Address resolutiontechniques

There are different techniques used for address resolution. Whichtechnique 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

• Closed-form computation

• Message exchange

Table look up This technique in carrying out address resolution makes use of abinding table which contains IP addresses with the correspondinghardware addresses. Each host in the network has its own entry in thebinding table.

It is however necessary to have a separate binding table for eachphysical network and as such all IP addresses will contain the sameprefix.

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.

Closed-form Computation This technique of address resolution is used when dealing withnetworks, which allow configurable addresses. A mathematicalcomputation is used to derive the hardware address directly from the

System Overview

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IP address. The computation should be as simple as possible to reduceany delay.

Example

hardware address = IP address (suffix)

hardware address = 194.76.4.4 (suffix) -> hardware address = 4

Address ResolutionProtocol (ARP)

The protocol used to translate an IP address into a hardware address iscalled the Address Resolution Protocol. This technique of addressresolution uses a “message based” approach to deriving a hardwareaddress. The host sends a message containing the protocol address toa server(s) and in return, a message is sent containing the appropriatehardware address.

There are two methods of message exchange resolution. Either anetwork is made up of several servers which will carry out all theresolution processes within the network, or each host on the networkwill answer address resolution requests for its address.

The process of an ARP message exchange:

1. Host W begins to broadcast an ARP request message thatcontains host Ys IP address

2. All hosts receive the ARP request message

3. Host Y sends an ARP response message containing itscorresponding address directly to host W. All other hosts willdiscard the ARP request message.

Figure 2-18 Message Exchange Process

Address Resolution System Overview

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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 adatagram in which the data is transported. Routing is done by usingan address that is unique for each computer or system. When data hasto be sent, it will be divided into datagrams which also include thesource and destination addresses. The network elements called routerswill 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 thatcorresponding computer.

Datagram & Packet Datagrams are encapsulated in layer 2 packets for point to pointtransportation. If the datagram is larger than the maximum packetsize, the datagram will be split into fragments and re-assembled againat the other side.

Connectionless IP provides higher layer protocols (like TCP) aconnectionlessservice,which means that no connection is established prior to the sending ofthe datagram.

IP header format An IP datagram consists of a header part and a data part. The headercontains a fixed part of 20 bytes (5× 32 bit quantities) and anoptional part of a variable length.

Figure 2-19 IP Header Format

System Overview

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The different Header Fields are discussed below:

Version Indicates the version of Internet protocol. Thisis currently version 4

IHL The Internet header (IHL) length field is usedto specify the number of 32 bit quantities thatmake up the header. Minimum value is 5

Service Type The service type field indicates the quality ofservice desired during transmission of themessage through the Internet. For example, amessage containing speech requires fasttransmission and less reliability, but a filetransfer message requires high reliability andnormal transmission speed.

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

Identification The identification field uniquely identifies apacket so that it can be distinguished fromother packets; it is usually assigned when datais passed to the network layer from a higherlayer. All packets of the same datagram containthe same value in the identification field.

Flags The flags field indicates whether the packet isfragmented or whether it is the last fragment ofthe packet.

Fragment Offset The fragment offset field indicates whichfragment of the original packet this is. It isused to rebuild the full packet once all thefragments have been collected

Time to Live The time to live field specifies the time adatagram will travel around in the networkbefore it is destroyed. This prevents a datagramfrom travelling forever around a path thatcontains a loop. The field carries a positiveinteger value between 1 and 255; every timethe datagram passes through a router, thisvalue is reduced by 1. When the value reaches0, the datagram is discarded

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

Internet Protocol (IP) System Overview

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Version Indicates the version of Internet protocol. Thisis currently version 4

Header Checksum The header checksum is used to provide errorchecking on the header by itself. It is usedbecause the header can change (for example,due to fragmentation)

Source IP Address The source IP addresses is the Internet addressof the originating host

Destination IPAddress

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

Options andPadding

The options field is used to specify routingoptions and network testing. Padding can beadded to ensure that the header is a multiple of32 bits

Internet Protocol (IP) System Overview

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

Features The Transmission Control Protocol (TCP) provides a highly reliabletransport service. Most Internet applications use the services of TCPto transport data between hosts.

TCP offers seven major features:

• Connection orientated

• Complete reliability

• Full duplex communication

• Stream interface

• Reliable connection set-up

• Graceful connection shut-down

TCP header format A TCP header contains a fixed part of 20 bytes (5× 32 bit quantities)and may be followed by header options. After the header65,535-20-20 = 65,495 data bytes may follow, where the first 20refers to the IP header and the second to the TCP header.

The different TCP header fields are discussed below:

Field Description

SOURCE PORT andDESTINATION PORT

The source and destination port fieldsidentify the relevant application layerservices.

Figure 2-20 TCP Header

System Overview

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Field Description

SEQUENCENUMBER

The sequence number field specifies thesequence number of a segment of amessage and is used to ensure that thesegments of a message can be orderedproperly

ACKNOWLEDG-MENT NUMBER

The acknowledgment number field containsthe sequence number of the next segmentexpected to be received. It indicates correctreception of all messages up to thatsequence number.

DATA OFFSET The data offset field indicates the start ofthe data within the segment, measured in32 bit words, but that number is just theheader length in words, so the effect is thesame

FLAGS URG - notes that the urgent pointer is valid

ACK - notes that the acknowledgmentnumber field is valid.

PSH - causes the data in the message to be″pushed″ through to the receivingapplication even if the buffer is not full

RST - resets the connection

SYN - resynchronises the sequence number.The SYN bit is used to establishconnections

FIN - marks that the sender has reached theend of its byte stream. The FIN bit is usedto release a connection

WINDOW The window field is used to specify howmuch data the receiver is willing to accept.

CHECKSUM The checksum field is 16 bits long and itchecksums the header and the data of theTCP message.

URGENT POINTER The urgent pointer is used to indicate abyte offset from the current sequencenumber at which urgent data are to befound

Transmission Control Protocol (TCP) System Overview

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User Datagram Protocol (UDP)....................................................................................................................................................................................................................................

Connectionless transportprotocol

The TCP/IP suite also supports a connectionless transport protocol,User Datagram Protocol (UDP). UDP provides a way for applicationsto send a message without having to establish a connection. UDPallows the movement of data with the minimum requirement ofnetwork services.

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

Field Description

SOURCE PORT andDESTINATIONPORT

The source and destination port fieldsidentify the relevant application layerservices.

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

CHECKSUM The checksum field is used to check forerrors across the entire segment

Figure 2-21 UDP Header Format

System Overview

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TCP/IP Example....................................................................................................................................................................................................................................

Message Flow A packet containing data is sent over a TCP/IP network and arrives atits receiving host.

The packet passes through 5 TCP/IP layers:

• Layer 1 - This is the actual physical network hardware, forexample, an ethernet. The packet arrives at the receiving hostdefined in its hardware address field.

• Layer 2 - The network interface strips out the header containingthe hardware address, performs a check and strips out the footercontaining the check sequence. The payload is passed on to theInternet layer.

• Layer 3 - The Internet layer analyses the IP header containing:source IP address, destination IP address, total length etc. Theheader is stripped out and the payload is passed on to thetransport 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 ofthe data. TCP also performs some other tasks to ensure thereliability of the connection. The header is stripped out and thedata is passed on to the application layer.

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

Figure 2-22 Message Flow

System Overview

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3 Interfaces

Overview....................................................................................................................................................................................................................................

Purpose This chapter describes the GSM and the new GPRS networkinterfaces.

Contents This chapter covers the following subjects:

GSM System Interfaces 3-2

GPRS System Interfaces 3-4

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



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

Introduction For the connection of the different nodes in the GSM network,different interfaces are defined in the GSM specifications. Thefollowing interfaces appear in the figure:

Um-Interface or AirInterface

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

• Universal use of any compatible mobile station in a GSMnetwork

• A maximum spectral efficiencyOn the Um-Interface there are the following types of logicalchannels: Traffic channels, Broadcast channels, Common controlchannels and Dedicated control channels.

Abis - Interface The Abis-Interface is the interface between the Base Station Controller(BSC) and the BTS and is used to carry the Um-Interface formatted13 kbps data (speech data and signaling information) between them.

Figure 3-1 GSM Interfaces

Interfaces

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


The interface comprises traffic and control channels. Its physicaltransmission is based on the PCM30 (Pulse Code Modulation)transmission principles of the ITU-T (International TelecommunicationUnion - sector Telecommunication) at a data rate of 2048 kbps. ThePCM30 frame consists of 32 channels, each carrying 64 kbps. Thebit-stream of 64 kbps represents the transmission of 8000 samples persecond, with each sample being coded into 8 bits.

Functions implemented at the Abis-Interface are:

• Voice - data traffic exchange

• Signaling exchange between the BSC and the BTS

• Transporting synchronization information from the BSC to theBTS

A-Interface The A-Interface is used to carry the 64 kbps speech data and signalinginformation between the BSC and the MSC. It’s physical transmissionis also based on the PCM30 principles of the ITU-T at a data rate of2048 kbps.

Timeslot 0 of the PCM30 frame is used for synchronization purposes.Timeslot 1 through 15 and 17 through 31 are used for exchanging the64 kbps speech data. Timeslot 16 is used to transfer the SS No. 7signaling between the BSC and the MSC.

Proprietary M-Interface In the GSM network implementation of Lucent Technologies, the BSCincludes the TRAU (Transcoder/Rate Adapter Unit). The TRAUadapts the transmission bit rate of the A interface (64 kbps) to theAbis-Interface (16 kbps). The interface between the physical BSC andthe TRAU is known as the M-Interface. Each of the timeslots 1through 15 and 17 through 31 on the M-Interface contains fourmultiplexed A-interface channels. Timeslot 0 is used forsynchronization purposes. Timeslot 16 contains the signalinginformation which is transparently mapped from timeslot 16 of theA-interface.

GSM System Interfaces Interfaces

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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 trafficrelated to individual MS’s and general signaling information from theSGSN to the BSS and vice versa. Lucent NR 9.0 supports the Gb

interface with the ETSI GPRS Phase 1 standardised layer 2 protocolFrame Relay (FR). The physical layer of this interface is supportedwith standard European E1 (2Mbit/s) trunks or single DS0 64 Kbit/stime-slots within an E1 line as specified by ETSI.

Gb Interface Protocol Stack

The BSS will provide a Network Services Layer implementation tothe ETSI GPRS standards. For NR 9.0, a minimal load sharingcapability will be provided

The BSSGP protocol operates BSSGP Virtual Connections (BVC) forthe transmission of LLC-PDU frames between the SGSN and theBSS.

Figure 3-2 G b Interface Protocol Stack

Interfaces

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


The following apply:

• For NR 9.0 the FR protocol implementation shall support thetransmission 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 DiscardEligibility (DE) bits is never set by the BSS or Frame RelayEntities.

Abis Interface

When GPRS MAC and RLC layer functions are positioned remote tothe BTS the information between the channel code unit (CCU) andthe remote GPRS packet control unit (rPCU) is transferred in frameswith a fixed length of 320 bits. Within these frames both GPRS dataand the GPRS RLC/MAC associated control signals are transferred.

The Abis interface should be the same if the PCU is positioned at theBSC site or at the SGSN. At the BSC, the PCU could be implementedas an adjunct unit to the BSC. At the SGSN, the BSC should beconsidered as transparent for 16 Kbit/s channels. In both cases, thePCU is referred to as the remote PCU.

The remote PCU is considered a part of the BSC, and the signallingbetween the BSC and the PCU may be performed by using BSCinternal signals. The in-band signalling between the CCU and thePCU functions, using PCU frames is required when the Abis interfaceis applied.

The Abis interface for supporting the rPCU is a proprietary LucentTechnologies solution and it is only valid for coding schemes 1 and 2.For coding schemes 3 and 4 there will be a new structure.

GPRS System Interfaces Interfaces

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4 GPRS Signalling andTransmission Protocols

Overview....................................................................................................................................................................................................................................

Purpose This chapter discusses the signalling and transmission protocols forthe different GPRS interfaces, the GPRS network entities and thepacket data logical channels for GPRS.

Contents This chapter contains information on the following topics:

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

GPRS Logical Channels 4-26

Mapping of packet data logical channels ontophysical channels

4-28

GPRS MS 4-34

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



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

Functions The signalling plane consists of protocols for control and support ofthe transmission plane functions:

• Controlling the GPRS network access connections, such asattaching to and detaching from the GPRS network.

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

• Controlling the assignment of network resources to meetchanging user demands.

• Providing supplementary services

The Message Transfer Part (MTP) is responsible for the reliabletransport of signalling information between the user parts.

Level 2 controls the functions of the link; it is responsible for reliablemessage transfer.

The level 3 functions handle procedures such as message routing andsignalling network management.

The Signalling Connection Control Part (SCCP) defines a means oftransferring signalling data or management data without the need toestablish a circuit. SCCP is really an addition of MTP.

The Transaction Capability Application Part (TCAP) is used tomanage the dialog between two network entities.

The Mobile Application Part (MAP) protocol is used to transfernon-circuit-related signalling information between the network entities,i.e. between:

Figure 4-1 Map Signalling

GPRS Signalling and Transmission Protocols

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


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 andtransfer of charging information.

BSSAP Signalling

The Base Station System Application Part + (BSSAP+) is a subset ofBSSAP procedures specifically for GPRS and supports signallingbetween 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.

Figure 4-2 BSSAP Signalling

The GPRS Signalling Plane GPRS Signalling and Transmission Protocols

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



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

The GPRS TransmissionPlane

The transmission plane consists of a layered protocol structureproviding user information transfer, along with associated informationtransfer control procedures (for example: flow control, error detection,error correction and error recovery).

The GPRS Protocols The transmission plane is made up of both GPRS specific protocolsand 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 supportnodes in the GPRS backbone network.

Figure 4-3 Transmission Plane


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


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

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

Internet Protocol (IP)

This is the GPRS backbone network protocol used for routing userdata and control signalling. The GPRS backbone network may initiallybe 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 theunderlying GPRS specific network.

Logical Link Control (LLC)

This layer provides a highly reliable ciphered logical link. LLC shallbe independent of the underlying radio interface protocols in order toallow GPRS to be used on different radio systems.

Base Station System GPRS Protocol (BSSGP)

This layer conveys routing and Quality of Service (QoS) informationbetween 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 radiosolution dependent reliable link. The MAC function controls theaccess signalling procedures for the radio channel, and the mapping ofLLC frames onto the GSM physical channel.

GSM Radio Frequency (GSM RF)

This is the standard GSM RF interface.

The GPRS Transmission Plane GPRS Signalling and Transmission Protocols

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



GGSN Protocols....................................................................................................................................................................................................................................

GPRS Tunnelling Protocol(GTP)

The GPRS Tunnelling Protocol (GTP) is the protocol between GPRSSupport Nodes

(GSNs) in the GPRS backbone network. It includes both signallingand data transfer procedures. GTP is defined both for the Gn interfacebetween GSNs within a PLMN, and the Gp interface between GSNsin different PLMNs. In the signalling plane, GTP specifies a tunnelcontrol and management protocol which allows the SGSN to provideGPRS network access for a MS. Signalling is used to create, modifyand delete tunnels.

In the transmission plane, GTP uses a tunnelling mechanism toprovide a service for carrying user data packets. The choice of path isdependent on whether the user data to be tunneled requires a reliableconnection or not. The GTP protocol is implemented only by SGSNsand GGSNs. No other system entities need to be aware of GTP. GPRSMSs are connected to a SGSN without being aware of GTP.

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

Figure 4-4 LLC Frame Numberf


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


The GTP header consists of the following fields:

Field Description

Version Version shall be set to 0 to indicate the firstversion of GTP.

Reserved Reserved bits for future use that shall be setto 1.

LFN LFN is a flag indicating if LLC FrameNumber is included or not.

Message Type Message Type indicates the type of GTPmessage.

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

Sequence Number The Sequence Number is a transactionidentity for signalling messages and anincreasing sequence number for tunneledPDUs (T-PDUs).

Flow Label Flow Label identifies unambiguously a GTPflow.

LLC Frame Number The LLC Frame Number is used at the interSGSN routing update procedure toco-ordinate the data transmission on the linklayer between the MS and SGSN.

X The spare bits X indicate the unused bitswhich shall be set to 0 by the sending sideand which shall not be evaluated by thereceiving side.

TID This is the tunnel identifier that points outMM and PDP contexts.

User Datagram Protocol(UDP)

UDP carries GTP Protocol Data Units (PDUs) for protocols that donot need a reliable connection (for example IP). UDP providesprotection against corrupted GTP PDUs. UDP can be found in theTCP/IP suite.

Transmission ControlProtocol (TCP)

TCP carries GTP Protocol Data Units (PDUs) in the GPRS backbonenetwork for protocols that need a reliable connection. TCP can befound in the TCP/IP suite.

Internet Protocol (IP) This is the GPRS backbone network protocol used for routing userdata and control signalling. The GPRS backbone network may initiallybe 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.

GGSN Protocols GPRS Signalling and Transmission Protocols

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



GGSN activity A packet from an external data network arrives at the GGSN and willbe encapsulated with a GTP header, a UDP or a TCP header and an IPheader. If the resulting IP datagram is larger than the MaximumTransfer Unit (MTU), fragmentation of the IP datagram will occur.

Figure 4-5 GGSN Activity

GGSN Protocols GPRS Signalling and Transmission Protocols

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


SGSN Protocols....................................................................................................................................................................................................................................

Subnetwork DependentConvergence Protocol

(SNDCP)

Network layer protocols are intended to be capable of operating overservices derived from a wide variety of subnetworks and data links.GPRS supports several network layer protocols providing protocoltransparency for the users of the service.

Introduction of new network layer protocols to be transferred overGPRS shall be possible without any changes to GPRS. Therefore, allfunctions related to transfer of Network layer Protocol Data Units(N-PDUs) shall be carried out in a transparent way by the GPRSnetwork entities. This is one of the requirements for GPRS SNDCP.Another requirement for the Sub Network Dependent ConvergenceProtocol (SNDCP) is to provide functions that help to improvechannel efficiency. This requirement is fulfilled by means ofcompression techniques.

Multiplexing of differentprotocols

The set of protocol entities above SNDCP consists of commonly usednetwork protocols. They all use the same SNDCP entity, which thenperforms multiplexing of data coming from different sources to besent using the service provided by the LLC layer.

The Network Service Access Point Identifier (NSAPI) is an index tothe PDP context of the PDP that is using the services provided bySNDCP. Each active NSAPI shall use the services provided by theService Access Point Identifier (SAPI) in the LLC layer. SeveralNSAPIs may be associated with the same SAPI.

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

Figure 4-6 Multiplexing different protocols


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SN-DATA The request primitive is used by the SNDCP user for acknowledgedtransmission of N-PDU. The successful transmission of SN-PDU shallbe confirmed by the LLC layer.

The request primitive conveys NSAPI to identify the PDP using theservice. The indication primitive is used by the SNDCP entity todeliver the received N-PDU to the SNDCP user. Successful receptionhas been acknowledged by the LLC layer.

SN-UNITDATA The request primitive is used by the SNDCP user for unacknowledgedtransmission of N-PDU. The request primitive conveys NSAPI toidentify the PDP using the service and protection mode to identify therequested transmission mode. The indication primitive is used by theSNDCP entity to deliver the received N-PDU to the SNDCP user.

SNDCP Service Functions SNDCP shall perform the following functions:

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

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

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

• Establishment, re-establishment and release of acknowledgedpeer-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 (forexample TCP/IP header) at the transmitting entity anddecompression at the receiving entity. The compression method isspecific to the particular network layer or transport layerprotocols in use.

• Compression of redundant user data at the transmitting entity anddecompression at the receiving entity. Data compression isperformed independently for each SAPI, and may be performedindependently for each PDP context.

SGSN Protocols GPRS Signalling and Transmission Protocols

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• Segmentation and re-assembly. The output of the compressionfunctions is segmented to the maximum length of LL-PDU.These procedures are independent of the particular network layerprotocol in use. Negotiation of the XID parameters between peerSNDCP entities using XID exchange.

The figure above shows the transmission flow through the SNDCPlayer.

The order of functions is as follows:

• Protocol control information compression.

• User data compression.

Figure 4-7 SNDCP Service Model


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• Segmentation of compressed information into SN-DATA orSN-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.

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

For SNDCP headers used for SN-UNITDATA, some additional areadded. This comprises the segment number field, the extension (E) bitand the N-PDU number field which is used to identify a particularN-PDU.

The SNDCP header contains the following fields:

Field Description

X Spare bit (set to 0).

C The Compression © indicator is used to indicatewhether or not the compression fields (DCOMPand PCOMP) are included.

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

M The More (M) bit is used to indicate the lastsegment 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 toindicate whether or not data compression has takenplace and points to the data compression identifiernegotiated dynamically.

Figure 4-8 SNDCP Header


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Field Description

PCOMP Protocol control information compression coding(PCOMP) is used to indicate whether or notcontrol compression has taken place and points tothe protocol control information compressionidentifier negotiated dynamically.

Logical Link Control (LLC) The LLC layer provides reliable transfer of data between the MS andthe SGSN, retransmission during handovers and flow control betweenthe MS and the SGSN.

Address field

The address field consists of a single octet. The format of the addressfield is as follows:

Figure 4-9 LLC FrameFormat

Figure 4-10 llc_address_field


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The different fields are discussed below:

Field Description

PD The Protocol Discriminator (PD) bit indicates whethera frame is an LLC frame or belongs to a differentprotocol.

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

X Spare bit.

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

Control field

The control field typically consists of between one and three octetsalthough may under some circumstances be comprised of up to 36octets. 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.

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

Figure 4-11 Control Field


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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 issuedas 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 controlfield.

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 headerand information fields.

Base Station System GPRSProtocol (BSSGP)

The primary functions of the BSSGP include the following:

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

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

• The provision of functionality to enable two physically distinctnodes, an SGSN and a BSS, to operate node management controlfunctions.


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BSSGP Service Model

BBSGP maps LLC, GPRS mobility management (GMM) and networkmanagement (NM) on one frame.

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

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

• GMM provides functions associated with GPRS mobilitymanagement between an SGSN and a BSS. GMM functions dealwith 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 iffragmentation has occurred either at the SGSN or at any IP routeralong the Gn interface. Any additional processes are carried out at thislayer before the payload is passed up to either UDP or TCP.

At the UDP/TCP layer, more processes are carried out such asdetermining the checksum value before this payload is passed up toGTP. AT the GTP layer, the GTP header is stripped off resulting in thePDU being ready for onward transmission across the Gb interfacetowards the BSS. As such, the PDU can be said to have been tunneledacross the Gn interface. To travel across the Gb interface, the PDU

Figure 4-12 BSSGP Service Model


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requires further modification. This is carried out by the SubnetworkDependent Convergence Protocol (SNDCP), the Logical Link Protocol(LLC) and the Base Station System GPRS Protocol (BSSGP) beforebeing carried towards the BSS on the Gb interface via a Frame Relaynetwork.

Figure 4-13 SGSN Activity


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BSS Protocols....................................................................................................................................................................................................................................

RLC/MAC block structure The RLC/MAC block consists of a MAC header and an RLC datablock or RLC/MAC control block. The RLC/MAC control block isthe part of a RLC/MAC block carrying a control message betweenRLC/MAC entities. It does not contain an RLC header.

Radio Link Control (RLC)layer

The RLC function is responsible for the following:

• RLC provides service primitives for the transfer of LLC PDUsbetween the LLC layer in the SGSN and the MAC layer.

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

• RLC provides a Backward Error Correction (BEC) for reliabledata transfer and enables the selective retransmission ofunsuccessfully delivered RLC/MAC blocks.

Figure 4-14 RLC/MAC Control Block


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RLC data block

The structure of the RLC data blocks are dependent upon the directionof the data transfer (uplink or downlink).

The following fields comprise the RLC data blocks:

Field Description

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

TI The TLLI Indicator (TI) bit indicates the presenceof an optional TLLI field within the RLC datablock.

TFI The Temporary Flow Identifier (TFI) fieldidentifies the Temporary Block Flow (TBF) towhich the RLC data block belongs.

E The Extension (E) bit is used to indicate thepresence of an optional octet in the RLC datablock header.

Figure 4-15 Uplink RLC Data Block

Figure 4-16 Downlink RLC Data Block

BSS Protocols GPRS Signalling and Transmission Protocols

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Field Description

BSN The Block Sequence Number (BSN) field carriesthe sequence number of each RLC data blockwithin the TBF.

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

LengthIndicator

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

TLLI The TLLI field contains a Temporary Logical LinkIdentity (TLLI). This value is carried only in thefirst three RLC data blocks to be transferred in theuplink.

RLC data The RLC data field contains octets from one ormore LLC PDUs.

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

Medium Access Control(MAC) layer

The main function of the MAC layer is the control of multiple MSssharing a common resource on the GPRS air interface. The RLC datablock is passed down to the MAC layer where a MAC header isadded. The MAC procedures support the provision of TemporaryBlock Flows (TBFs) that allow the point-to-point transfer of signallingand user data within a cell between the network and a MS.

The structure of the MAC headers are dependent upon the direction ofthe data transfer (uplink or downlink).

Figure 4-17 Uplink Mac Header Format


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The different MAC header fields are discussed below:

Field Description

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

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

S/P The Supplementary/Polling (S/P) bit is used toindicate whether the RRBP field is valid or notvalid.

RRBP The Relative Reserved Block Period (RRBP) fieldspecifies a single uplink block in which the mobilestation shall transmit either a PACKET CONTROLACKNOWLEDGEMENT or a PACCH block to thenetwork.

Payload Type The Payload Type field shall indicate the type ofdata contained in remainder of the RLC/MACblock.

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

CountdownValue

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

Temporary Block Flow (TBF)

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

Figure 4-18 Downlink Mac Header Format


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carrying one or more LLC PDUs. A TBF is temporary and ismaintained only for the duration of the data transfer.

The physical layer consists of two sub-layers:

• Physical RF layer.

• Physical link layer.

Physical RF layer

The physical RF layer performs the modulation of the physicalwaveforms based on the sequence of bits received from the physicallink layer. The physical RF layer also demodulates receivedwaveforms into a sequence of bits which are transferred to thephysical link layer for interpretation. The GSM physical RF layer isused as a basis for GPRS.

Physical link layer

The purpose of the physical link layer is to convey information acrossthe GSM radio interface, including RLC/MAC information. Thephysical link layer supports multiple MSs sharing a single physicalchannel. The physical link layer provides communication betweenMSs and the Network. The physical link layer control functionsprovide the services necessary to maintain communications capabilityover the physical radio channel between the network and MSs.

Functions at the physical link layer include:

• Forward Error Correction (FEC) coding, allowing the detectionand correction of transmitted code words and the indication ofuncorrectable code words.

• Rectangular interleaving of one Radio Block over four bursts inconsecutive TDMA frames.

Figure 4-19 Air Interface


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


• Procedures for detecting physical link congestion.

• Synchronisation procedures, including determining and adjustingthe MS timing advance parameters.

• Monitoring and evaluation procedures for radio link signalquality.

• Cell selection and re-selection procedures.

• Transmitter power control procedures.

• Battery power conservation procedures, for exampleDiscontinuous 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 throughBSSGP where the information and signalling messages are separatedinto LLC frames, GPRS Mobility Management (GMM) informationand Network Management (NM) information.

With regards to data and signalling messages destined for the GPRSMS, the LLC frames pass through a relay entity (LLC relay) beforeentering the RLC and the MAC layer respectively.

The RLC/MAC layer provides services for information transfer overthe physical layer.

Figure 4-20 BSS Activity


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

GPRS MS activity At the GPRS MS, the PDUs pass through the protocol stack in thereverse order. The four consecutive air interface bursts arere-assembled and passed to the RLC/MAC layer. Once all the RLCdata blocks for a particular LLC PDU have been received, the LLCframe is re-assembled and passed up to the LLC layer. Here theFrame Check Sequence (FCS) is calculated and any retransmissionsare activated if necessary, otherwise the payload area is passed up tothe SNDCP layer.

At the SNDCP layer, the PDUs are re-assembled and the informationand control fields are decompressed. Finally, the PDUs are passed upto the IP/X.25 layer.

Figure 4-21 MS Activity


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The GPRS Air Interface....................................................................................................................................................................................................................................

Packet data logicalchannels for GPRS

One or more packet data logical channels can be transmitted on aphysical channel. There are different types of packet data logicalchannels. The type of packet data logical channel is determined by thefunction of the information transmitted over it.

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 controlinformation (signalling).

Figure 4-22 Logical channels for GPRS


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GPRS Logical Channels....................................................................................................................................................................................................................................

Packet Common ControlChannels (PCCCH)

PCCCH comprises packet data logical channels for common controlsignalling used for packet data as described below:

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

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

• Packet Access Grant Channel (PAGCH)For downlink only PAGCH is used in the packet transferestablishment phase to send resource assignment to an MS priorto 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 allindividual paging channels to inform MSs interested in PTM-Mwhen they need to listen to PNCH. The PNCH will bestandardized in the future.

Packet Broadcast ControlChannel (PBCCH)

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


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Packet Dedicated ControlChannels (PDCCH)

Packet Dedicated Control Channels (PDCCH) is comprised of thefollowing:

• 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 carriesalso resource assignment and reassignment messages, comprisingthe assignment of a capacity for PDTCH(s) and for furtheroccurrences of PACCH. The PACCH shares resources withPDTCHs, that are currently assigned to one MS. Additionally, anMS that is currently involved in packet transfer, can be paged forcircuit switched services on PACCH. The PACCH can be foundon both uplink and downlink.

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

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

Packet Data TrafficChannels (PDTCH)

PDTCH is a channel allocated for data transfer. It is temporarilydedicated to one MS or to a group of MSs in the Point To Multipoint- Multicast (PTM-M) case. In multislot operation, one MS may usemultiple 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.

GPRS Logical Channels GPRS Signalling and Transmission Protocols

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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 beenallocated for the use of GPRS. Different packet data logical channelscan occur on the same physical channel (i.e. PDCH). The sharing ofthe physical channel is based on blocks of 4 consecutive bursts.

Whenever the PCCCH is not allocated, the CCCH shall be used toinitiate a packet transfer. One given MS may use only a subset of thePCCCH, the subset being mapped onto one physical channel (i.e.PDCH).

Packet data logical channels are mapped dynamically onto a52-multiframe. If it exists, PCCCH is mapped on one or severalphysical channels according to a 52-multiframe, In that case thePCCCH, PBCCH and PDTCH share same physical channels(PDCHs).

GPRS Logical Channels:

Group Name Direction Function

PBCCH PBCCH downlink Broadcast

PCCCH PRACH RandomAccess

PPCH downlink Paging

PAGCH downlink Access Grant

PNCH downlink Multicast

PTCH PDTCH Downlink &uplink

Data

PACCH Downlink &uplink

AssociatedControl

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

X - Idle frame

Figure 4-23 52 Multiframe


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T - Frame used for PTCCH

B0 - B11 - Radio blocks

Channel Configuration The figure below gives an example of a possible channelconfiguration. Note that the BCCH channel is transmitted in time-slot0 on the first defined frequency. It must always be present to enablethe mobile stations to find the broadcast channels more easily

1. Channels that can be assigned to GPRS only (not supported byLucent)

2. Channels that can be dynamically assigned to either GPRS orcircuit switched service

3. Channels that can be assigned to circuit switched services only

Uplink State Flag The Uplink State Flag (USF) is used to allow multiplexing of ofmultiple MSs in uplink direction on a Packet Data Channel (PDCH).It is be used in dynamic and extended dynamic medium accessmodes.Three bits at the beginning of each Radio Block that is sent onthe downlink is comprised by the USF. In that way it enables thecoding of eight different USF states which are used to multiplex theuplink traffic.

One USF value is assigned only to one MS per PDCH. On thePCCCH, one USF value is used to indicates the PRACH. The otherUSF values are used to reserve the uplink for different mobilestations.On PDCHs which are not carrying PCCCH, the eight USFvalues are used to reserve the uplink direction for different mobilestations. One of the USF values has to be used to prevent anycollision on the uplink channel, if a mobile station without an USF isusing an uplink channel. The USF is either pointing to the next uplinkRadio Block or the sequence of four uplink Radio Blocks startingwith the next uplink Radio Block.

Figure 4-24 Time-Slot Configuration

Mapping of packet data logical channelsonto physical channels


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Temporary Block Flow A Temporary Block Flow (TBF) is a physical connection that is usedby the two RR entities in the MS and the BSS to support theunidirectional transfer of Logical Link Control (LLC) Packet DataUnits (PDUs) on packet data physical channels. It is the allocatedradio resource on one or more PDCHs and it comprises a number ofRLC/MAC blocks carrying one or more LLC PDUs. A TemporaryBlock Flow is only temporary and also only maintained for theduration 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 uniqueamong all the other concurrent TBFs in each direction and is usedinstead of the mobile station identity in the RLC/MAC layer. On theopposite direction, the same TFI value may be used at the same time.It is assigned in a resource assignment message that precedes thetransfer of LLC frames belonging to one TBF to or from the mobilestation. The same TFI is included in every RLC header of aRLC/MAC data block belonging to a specific TBF and may be usedin the control messages (here other addressings can be used, e.g.TLLI) associated to the LLC frame transfer in order to address thepeer RLC entities.

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

• Service precedence (priority)

• Reliability

• Delay

• ThroughputService precedence (priority of service)This parameter is used for indicating the priority of maintainingthe service. Service precedence parameters specifiies whichpackets 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 otherprecedence levels

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

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



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Reliability The Reliability parameters indicate the different transmissioncharacteristics 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 thedifferent reliability parameters and also give examples of applicationcharacteristics.

Reliability classes

Reliabil-ity class

LostSDUprob.(a)

Dupli-cateSDUprob.

Out ofSequenceSDUprob.

Cor-ruptSDUprob.(b)

Example ofapplicationcharacteristics.

1 109 109 109 109 Error sensitive,no errorcorrectioncapability,limited errortolerancecapability.

2 104 105 105 106 Error sensitive,limited errorcorrectioncapability, gooderror tolerancecapability.

3 102 105 105 102 Not errorsensitive, errorcorrectioncapability and/orvery good errortolerancecapability.

In GPRS there is a protection against buffer overflow or protocolmalfunction. For each SDU GPRS uses a maximum holding time afterwhich the SDU is discarded. There are also different parameters forthe 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 SDUmight be delivered with an undetected error.

Delay In the GPRS network data is temporarily stored at network nodesduring transmission. Any delay that occurs is due to technicaltransmission characteristicsof the system and has to be minimised fora particular delay class. The maximum delay values are defined forthe mean delay and the 95-percentile delay that might occur by thetransfer of data through a GPRS network. All delay parameters areend-to-end transfer delays in the transmission of SDUs through aGPRS 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 SDU size: 1024 octets

DelayClass

MeanTransferDelay(sec)

95percentileDelay(sec)

MeanTransferDelay (sec)

95 percentileDelay (sec)

1.(Predic-tive)

< 0.5 < 1.5 < 2 < 7

2.(Predic-tive)

< 5 < 25 < 15 < 75

3.(Predic-tive)

< 50 < 250 < 75 < 375

4. (BestEffort)

Unspecified

Throughput The troughput parameter indicates the user data throughput requestedby 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, theperiods in which no data is transmitted)The maximum and mean bit rates can be negotiated to a value upto the Information Transfer Rate value.



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GPRS MS....................................................................................................................................................................................................................................

Mobile Station Equipment The current market view on GPRS terminals is that Class B and CMSs will be available in Q2 2000. This is the general view held by allterminal 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 makeand/or receive calls on the two services (GSM and GPRS)simultaneously, subject to Quality of Service) QoS subscribed toby the end user.

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

• Class C MSThese will support only non-simultaneous attach, alternate useonly. If both services are supported then the subscriber can makeand / or receive calls only from the manually or default selectedservice. Status of the service not selected is detached or notreachable during the session. The ability to send and receiveSMS messages is optional.Lucent is working closely with terminal manufacturers withregards to compatibility and availability of GPRS terminals.


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5 GPRS Procedures

Overview....................................................................................................................................................................................................................................

Purpose This chapter discusses the GPRS Procedures

Contents 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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Mobility Management....................................................................................................................................................................................................................................

IDLE TO READY STATE For the mobile to move from the idle to ready state, it must firstperform a GPRS Attach. Once attached, the mobile will be known tothe network i.e. the SGSN. The Mobility Management will be activeat the Mobile Station and the SGSN following the attach sequence.

When in the ready state, the PDP context is activated whichestablishes a packet data session (and the packet data networks) withthe mobile. With a valid PDP context Protocol Data Units (PDU) maybe transferred. For every LLCPDU received in the SGSN, a readytimer is re-started . There are two timers, one in the MS which isactivated when a packet is sent and one in the SGSN when a packet isreceived.

READY to STANDBYSTATE

For the mobile to move from the idle to ready state, it must firstperform a GPRS Attach. Once attached, the mobile will be known tothe network i.e. the SGSN. The Mobility Management will be activeat 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 havebeen either transmitted or received.

STANDBY to IDLE When this state is reached, a second timer is started. When the timerexpires, or a MAP message ’Cancel Location’ is received from theHLR then a return to Idle state is performed and the MM and PDPcontext are removed from the MS, SGSN and the GGSN.

GPRS Procedures

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READY to IDLE This state can only be reached if either a GPRS detach or ’CancelLocation’ message is received. When either of these occur, the MMand PDP contexts are removed as the MS is no longer attached to theGPRS network.

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

READY State Timer READY state timer:

• Initiated when the MS or network sends a signalling or datapackets

• 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 STANDBY state:

• Initiated on expiry of READY timer

• MS does routing area update on crossing a routing area boundary

Figure 5-1 GPRS Attach/Detach States

Mobility Management GPRS Procedures

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



• MS has to be paged to deliver packets

Figure 5-2 GPRS GMM/SM Control Plane

Mobility Management 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 whichtype of attach that is to be executed. The identity (provided by thenetwork) shall be the mobiles Packet-TIMSI (P-TIMSI) or IMSI. Ifthe mobile has a valid P-TIMSI, the P-TIMSI and the Routing AreaIdentity (RAI) with the P-TIMSI shall be provided. The IMSI shallonly be provided if the mobile does not have a valid P-TIMSI. Thosedifferent attach types are GPRS attach and GPRS / IMSI attach.

After executing the GPRS attach, the mobile is in READY state andMM contexts are established in the mobile and the SGSN. The mobileor the SGSN may then activate PDP contexts.

The next figure illustrates the combined GPRS / IMSI Attachprocedure.

GPRS Attach ProcedureDiagram

GPRS Attach Procedure

GPRS Procedures

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



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

1 The MS initiates the attach procedure by the transmission of an AttachRequest (IMSI or P-TMSI and old RAI, Classmark, CKSN, AttachType, DRX Parameters, old P-TMSI Signature) message to the SGSN.IMSI shall be included if the MS does not have a valid P-TMSIavailable. If the MS has a valid P-TMSI, then P-TMSI and the oldRAI associated with P-TMSI shall be included. Classmark containsthe MS’s GPRS multislot capabilities and supported GPRS cipheringalgorithms in addition to the existing classmark parameters defined inGSM 04.08. Attach Type indicates which type of attach that is to beperformed, i.e., GPRS attach only, GPRS Attach while already IMSIattached, or combined GPRS / IMSI attach. DRX Parameters indicateswhether the MS uses discontinuous reception or not. If the MS usesdiscontinuous reception, then DRX Parameters also indicate when theMS is in a non-sleep mode able to receive paging requests andchannel assignments. If the MS uses P-TMSI for identifying itself andif it has also stored its old P-TMSI Signature, then the MS shallinclude the old P-TMSI Signature in the Attach Request message.

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

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

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

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

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

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

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

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

GPRS Attach Procedure GPRS Procedures

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


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

6 If the SGSN number has changed since the GPRS detach, or if it isthe 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 oldSGSN shall wait until these procedures are finished beforeremoving the MM and PDP contexts.

• (6d) The HLR sends Insert Subscriber Data (IMSI, GPRSsubscription 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 notallowed to attach in the RA, the SGSN rejects the Attach Requestwith an appropriate cause, and may return an Insert SubscriberData Ack (IMSI, SGSN Area Restricted) message to the HLR. Ifsubscription checking fails for other reasons, the SGSN rejectsthe Attach Request with an appropriate cause and returns anInsert Subscriber Data Ack (IMSI, Cause) message to the HLR.If all checks are successful then the SGSN constructs a MMcontext for the MS and returns an Insert Subscriber Data Ack(IMSI) message to the HLR.

• (6f) The HLR acknowledges the Update Location message bysending an Update Location Ack to the SGSN after thecancelling of old MM context and insertion of new MM contextare finished. If the Update Location is rejected by the HLR, theSGSN rejects the Attach Request from the MS with anappropriate cause.

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

7 If Attach Type in step 1 indicated GPRS Attach while already IMSIattached, or combined GPRS / IMSI attach, then the VLR shall beupdated if the Gs interface is installed. The VLR number is derivedfrom the RA information. The SGSN starts the location updateprocedure towards the new MSC/VLR upon receipt of the first Insert


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



Subscriber Data message from the HLR in step 6 d). This operationmarks 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 theVLR. Location Update Type shall indicate IMSI attach if AttachType indicated combined GPRS / IMSI attach. Otherwise,Location Update Type shall indicate normal location update. TheVLR creates an association with the SGSN by storing SGSNNumber.

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

• (7c) If the LA update is inter-MSC, the HLR sends a CancelLocation (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 InsertSubscriber 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 newVLR.

• (7h) The VLR responds with Location Update Accept (VLRTMSI) 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 newP-TMSI.

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

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

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

10 If VLR TMSI was changed, the SGSN confirms the VLR TMSIre-allocation by sending TMSI Reallocation Complete (VLR TMSI) tothe VLR.


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


E N D O F S T E P S............................................................................................................................................................

Attach Request failure

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

Note

All the procedures and steps are according to the ETSI specifications03.60 Version 6.4.0.


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



Detach Procedures....................................................................................................................................................................................................................................

Overview With the detach procedure, the MS informs the network that itrequires a GPRS and/or IMSI detach. The network then informs theMS 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 networkor the MS.

• Implicit detach: The network detaches the MS (without notifyingthe MS) after a configuration dependent time after the mobilereachable timer expired or after an irrecoverable radio errorcauses disconnection of the logical link.

In the explicit detach case, the SGSN sends a Detach Request to theMS or vice versa.

An IMSI detach could be done in two different ways by the MS,depending if it´s GPRS-attached or not:

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

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

MS-Initiated DetachProcedure Diagram

MS-Initiated Detach Procedure

GPRS Procedures

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


MS-Initiated DetachProcedure

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

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

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

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

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

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

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

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

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

5 If Switch Off indicates that the detach is not due to a switch offsituation, the SGSN sends a Detach Accept to the MS.

Note


Detach Procedures GPRS Procedures

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



E N D O F S T E P S............................................................................................................................................................

SGSN-Initiated DetachProcedure Diagram

SGSN-Initiated Detach Procedure

SGSN-Initiated DetachProcedure

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

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

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

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

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

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

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

4 The MS sends a Detach Accept message to the SGSN any time afterstep 1.

Note



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


E N D O F S T E P S............................................................................................................................................................

HLR-Initiated DetachProcedure Diagram

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

HLR-Initiated DetachProcedure

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

1 If the HLR wants to request the immediate deletion of a subscriber’sMM and PDP contexts from the SGSN, the HLR shall send a CancelLocation (IMSI, Cancellation Type) message to the SGSN withCancellation Type set to Subscription Withdrawn.

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

2 The SGSN informs the MS that it has been detached by sendingDetach Request (Detach Type) to the MS. Detach Type shall indicatethat the MS is not requested to make a new attach and PDP contextactivation.

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

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

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

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

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

5 The MS sends a Detach Accept message to the SGSN any time afterstep 2.


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



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

6 The SGSN shall confirm the deletion of the MM and PDP contextswith a Cancel Location Ack (IMSI) message.

Note



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


E N D O F S T E P S............................................................................................................................................................

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

Overview The routing area update takes place:

• when a GPRS attached MS detects that it has entered a newrouting 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

• Inter SGSN Routing Area Update

Intra SGSN Routing AreaUpdate Diagram

Intra SGSN Routing Area Update

Intra SGSN Routing AreaUpdate Procedure

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

1 The MS sends a Routing Area Update Request (old RAI, old P-TMSISignature, and Update Type) to the SGSN. Update Type shall indicateRA update or periodic RA update. The BSS shall add the Cell GlobalIdentity including the RAC and LAC of the cell where the messagewas received before passing the message to the SGSN, see GSM08.18.

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

2 Security functions may be executed. These procedures are defined insubclause″Security Function″.

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

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

GPRS Procedures

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



successful then the SGSN updates the MM context for the MS. A newP-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-TMSIwith Routing Area Update Complete (P-TMSI).

Routing area update procedure failure

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

Note


Inter SGSN Routing AreaUpdate Diagram

Inter SGSN Routing Area Update

Routing Area Update GPRS Procedures

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


E N D O F S T E P S............................................................................................................................................................

Inter SGSN Routing AreaUpdate Procedure

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

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

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

2 The new SGSN sends SGSN Context Request (old RAI, TLLI, oldP-TMSI Signature, and New SGSN Address) to the old SGSN to getthe MM and PDP contexts for the MS. The old SGSN validates theold P-TMSI Signature and responds with an appropriate error cause ifit does not match the value stored in the old SGSN. This shouldinitiate the security functions in the new SGSN. If the securityfunctions authenticate the MS correctly, the new SGSN shall send anSGSN Context Request (old RAI, TLLI, MS Validated, and NewSGSN Address) message to the old SGSN. MS Validated indicatesthat the new SGSN has authenticated the MS. If the old P-TMSISignature was valid or if the new SGSN indicates that it hasauthenticated the MS, the old SGSN stops assigning SNDCP N-PDUnumbers to downlink N-PDUs received, and responds with SGSNContext Response (MM Context, PDP Contexts). If the MS is notknown in the old SGSN, the old SGSN responds with an appropriateerror cause. The old SGSN stores New SGSN Address, to allow theold SGSN to forward data packets to the new SGSN. Each PDPContext includes the SNDCP Send N-PDU Number for the nextdownlink N-PDU to be sent in acknowledged mode to the MS, theSNDCP Receive N-PDU Number for the next uplink N-PDU to bereceived in acknowledged mode from the MS, the GTP sequencenumber for the next downlink N-PDU to be sent to the MS and theGTP sequence number for the next uplink N-PDU to be tunnelled tothe GGSN. The old SGSN starts a timer and stops the transmission ofN-PDUs to the MS.

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

3 Security functions may be executed. These procedures are defined insubclause″Security Function″. Ciphering mode shall be set ifciphering is supported.

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

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


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



information in the GGSNs and the HLR are invalid. This triggers theMSC/VLR, the GGSNs, and the HLR to be updated if the MSinitiates a routing area update procedure back to the old SGSN beforecompleting the ongoing routing area update procedure. If the securityfunctions do not authenticate the MS correctly, then the routing areaupdate shall be rejected, and the new SGSN shall send a rejectindication to the old SGSN. The old SGSN shall continue as if theSGSN Context Request was never received.

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

5 The old SGSN duplicates the buffered N-PDUs and starts tunnellingthem to the new SGSN. Additional N-PDUs received from the GGSNbefore the timer described in step 2 expires are also duplicated andtunnelled to the new SGSN. N-PDUs that were already sent to the MSin acknowledged mode and that are not yet acknowledged by the MSare tunnelled together with the SNDCP N-PDU number. No N-PDUsshall be forwarded to the new SGSN after expiry of the timerdescribed in step 2.

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

6 The new SGSN sends Update PDP Context Request (new SGSNAddress, TID, QoS Negotiated) to the GGSNs concerned. The GGSNsupdate their PDP context fields and return Update PDP ContextResponse (TID).

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

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

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

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

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

9 The HLR sends Insert Subscriber Data (IMSI, GPRS subscriptiondata) to the new SGSN. The new SGSN validates the MS’s presencein the (new) RA. If due to regional subscription restrictions the MS isnot allowed to be attached in the RA, the SGSN rejects the RoutingArea Update Request with an appropriate cause, and may return an


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


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

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

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

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

11 The new SGSN validates the MS’s presence in the new RA. If due toroaming restrictions the MS is not allowed to be attached in theSGSN, or if subscription checking fails, then the new SGSN rejectsthe routing area update with an appropriate cause. If all checks aresuccessful then the new SGSN constructs MM and PDP contexts forthe MS. A logical link is established between the new SGSN and theMS. The new SGSN responds to the MS with Routing Area UpdateAccept (P-TMSI, P-TMSI Signature, and Receive N-PDU Number).Receive N-PDU Number contains the acknowledgments for eachacknowledged-mode NSAPI used by the MS, thereby confirming allmobile-originated N-PDUs successfully transferred before the start ofthe update procedure.

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

12 The MS acknowledges the new P-TMSI with a Routing Area UpdateComplete (P-TMSI, Receive N-PDU Number). Receive N-PDUNumber contains the acknowledgments for each acknowledged-modeNSAPI used by the MS, thereby confirming all mobile-terminatedN-PDUs successfully transferred before the start of the updateprocedure. If Receive N-PDU Number confirms reception of N-PDUsthat were forwarded from the old SGSN, then these N-PDUs shall bediscarded by the new SGSN. LLC and SNDCP in the MS are reset.

Rejected routing area update

In the case of a rejected routing area update operation, due to regionalsubscription or roaming restrictions, the new SGSN shall not constructa MM context. A reject shall be returned to the MS with anappropriate cause. The MS shall not re-attempt a routing area updateto that RA. The RAI value shall be deleted when the MS ispowered-up.

If the SGSN is unable to update the PDP context in one or moreGGSNs, then the SGSN shall deactivate the corresponding PDPcontexts as described in subclause″PDP Context Deactivation


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



E N D O F S T E P S............................................................................................................................................................

Initiated by SGSN Procedure″. This shall not cause the SGSN toreject the routing area update. If the timer described in step 2 expiresand no Cancel Location (IMSI) was received from the HLR, then theold SGSN shall stop forwarding N-PDUs to the new SGSN.

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

Note



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

Overview 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 Diagram

Combined Intra SGSN RA / LA Update

Combined Intra SGSN RA /LA Update Procedure

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

1 The MS sends a Routing Area Update Request (old RAI, old P-TMSISignature, and Update Type) to the SGSN. Update Type shall indicatecombined RA / LA update, or, if the MS wants to perform an IMSIattach, combined RA / LA update with IMSI attach requested. TheBSS shall add the Cell Global Identity including the RAC and LACof the cell where the message was received before passing themessage to the SGSN.

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

2 Security functions may be executed. This procedure is defined insubclause″Security Function″.

GPRS Procedures

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



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

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

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

4 If the subscriber data in the VLR is marked as not confirmed by theHLR, then the new VLR informs the HLR.

The HLR cancels the data in the old VLR and inserts subscriber datain the new VLR (this signalling is not modified from existing GSMsignalling and is included here for illustrative purposes):

• (4a) The new VLR sends an Update Location (new VLR) to theHLR.

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

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

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

• (4e) The new VLR acknowledges with Insert Subscriber DataAck (IMSI).

• (4f) The HLR responds with Update Location Ack (IMSI) to thenew VLR.

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

5 The new VLR allocates a new VLR TMSI and responds withLocation Update Accept (VLR TMSI) to the SGSN. VLR TMSI isoptional if the VLR has not changed.

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

6 The SGSN validates the MS’s presence in the new RA. If due toregional subscription restrictions the MS is not allowed to be attachedin the RA, or if subscription checking fails, then the SGSN rejects therouting area update with an appropriate cause. If all checks aresuccessful then the SGSN updates the MM context for the MS. A newP-TMSI may be allocated. The SGSN responds to the MS with

Combined RA / LA Update Procedure GPRS Procedures

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


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

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

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

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

8 The SGSN sends TMSI Reallocation Complete (VLR TMSI) to theVLR if the VLR TMSI is confirmed by the MS.

Routing area update procedure failure

If the routing area update procedure fails a maximum allowablenumber of times, or if the SGSN returns a Routing Area UpdateReject (Cause) message, the MS shall enter IDLE state. If theLocation Update Accept message indicates a reject, then this shouldbe indicated to the MS, and the MS shall not access non-GPRSservices until a successful Location Update is performed.

Note



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E N D O F S T E P S............................................................................................................................................................

Combined Inter SGSN RA /LA Update Diagram

Combined Inter SGSN RA / LA Update

Combined Inter SGSN RA /LA Update Procedure

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

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

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

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


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


initiate the security functions in the new SGSN. If the securityfunctions authenticate the MS correctly, the new SGSN shall send anSGSN Context Request (old RAI, TLLI, MS Validated, and NewSGSN Address) message to the old SGSN. MS Validated indicatesthat the new SGSN has authenticated the MS. If the old P-TMSISignature was valid or if the new SGSN indicates that it hasauthenticated the MS, the old SGSN stops assigning SNDCP N-PDUnumbers to downlink N-PDUs received, and responds with SGSNContext Response (MM Context, PDP Contexts). If the MS is notknown in the old SGSN, the old SGSN responds with an appropriateerror cause. The old SGSN stores New SGSN Address until the oldMM context is cancelled, to allow the old SGSN to forward datapackets to the new SGSN. Each PDP Context includes the SNDCPSend N-PDU Number for the next downlink N-PDU to be sent inacknowledged mode to the MS, the SNDCP Receive N-PDU Numberfor the next uplink N-PDU to be received in acknowledged modefrom the MS, the GTP sequence number for the next downlinkN-PDU to be sent to the MS and the GTP sequence number for thenext uplink N-PDU to be tunnelled to the GGSN. The old SGSNstarts a timer and stops the downlink transfer.

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

3 Security functions may be executed. These procedures are defined insubclause″Security Function″. Ciphering mode shall be set ifciphering is supported.

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

4 The new SGSN sends an SGSN Context Acknowledge message to theold SGSN. This informs the old SGSN that the new SGSN is ready toreceive data packets belonging to the activated PDP contexts. The oldSGSN marks in its context that the MSC/VLR association and theinformation in the GGSNs and the HLR are invalid. This triggers theMSC/VLR, the GGSNs, and the HLR to be updated if the MSinitiates a routing area update procedure back to the old SGSN beforecompleting the ongoing routing area update procedure. If the securityfunctions do not authenticate the MS correctly, then the routing areaupdate shall be rejected, and the new SGSN shall send a rejectindication to the old SGSN. The old SGSN shall continue as if theSGSN Context Request was never received.

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

5 The old SGSN duplicates the buffered N-PDUs and starts tunnellingthem to the new SGSN. Additional N-PDUs received from the GGSNbefore the timer described in step 2 expires are also duplicated andtunnelled to the new SGSN. N-PDUs that were already sent to the MSin acknowledged mode and that are not yet acknowledged by the MS


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



are tunnelled together with the SNDCP N-PDU number. No N-PDUsshall be forwarded to the new SGSN after expiry of the timerdescribed in step 2.

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

6 The new SGSN sends Update PDP Context Request (new SGSNAddress, TID, QoS Negotiated) to the GGSNs concerned. The GGSNsupdate their PDP context fields and return an Update PDP ContextResponse (TID).

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

7 The new SGSN informs the HLR of the change of SGSN by sendingUpdate Location (SGSN Number, SGSN Address, and IMSI) to theHLR.

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

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

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

9 The HLR sends Insert Subscriber Data (IMSI, GPRS subscriptiondata) to the new SGSN. The new SGSN validates the MS’s presencein the (new) RA. If due to regional subscription restrictions the MS isnot allowed to be attached in the RA, the SGSN rejects the RoutingArea Update Request with an appropriate cause, and may return anInsert Subscriber Data Ack (IMSI, SGSN Area Restricted) message tothe HLR. If all checks are successful then the SGSN constructs a MMcontext for the MS and returns an Insert Subscriber Data Ack (IMSI)message to the HLR.

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

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

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

11 If the association has to be established, if Update Type indicatescombined RA / LA update with IMSI attach requested, or if the LAchanged with the routing area update, then the new SGSN sends aLocation Update Request (new LAI, IMSI, SGSN Number, Location


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


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

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

12 If the subscriber data in the VLR is marked as not confirmed by theHLR, the new VLR informs the HLR.

The HLR cancels the old VLR and inserts subscriber data in the newVLR (this signalling is not modified from existing GSM signallingand is included here for illustrative purposes):

• (12a) The new VLR sends an Update Location (new VLR) to theHLR.

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

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

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

• (12e) The new VLR acknowledges with Insert Subscriber DataAck (IMSI).

• (12f) The HLR responds with Update Location Ack (IMSI) to thenew VLR.

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

13 The new VLR allocates a new TMSI and responds with LocationUpdate Accept (VLR TMSI) to the SGSN. VLR TMSI is optional ifthe VLR has not changed.

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

14 The new SGSN validates the MS’s presence in the new RA. If due toroaming restrictions the MS is not allowed to be attached in theSGSN, or if subscription checking fails, then the SGSN rejects therouting area update with an appropriate cause. If all checks aresuccessful then the new SGSN establishes MM and PDP contexts forthe MS. A logical link is established between the new SGSN and theMS. The new SGSN responds to the MS with Routing Area UpdateAccept (P-TMSI, VLR TMSI, P-TMSI Signature, and Receive N-PDUNumber). Receive N-PDU Number contains the acknowledgments foreach acknowledged-mode NSAPI used by the MS, thereby confirming


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



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

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

15 The MS confirms the reallocation of the TMSIs by sending RoutingArea Update Complete (P-TMSI, VLR TMSI, and Receive N-PDUNumber) to the SGSN. Receive N-PDU Number contains theacknowledgments for each acknowledged-mode NSAPI used by theMS, thereby confirming all mobile-terminated N-PDUs successfullytransferred before the start of the update procedure. If Receive N-PDUNumber confirms reception of N-PDUs that were forwarded from theold 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) tothe new VLR if the MS confirms the VLR TMSI.

Rejected routing area update

In the case of a rejected routing area update operation, due to regionalsubscription or roaming restrictions, the new SGSN shall not constructa MM context. A reject shall be returned to the MS with anappropriate cause. The MS shall not re-attempt a routing area updateto that RA. The RAI value shall be deleted when the MS ispowered-up.

If the SGSN is unable to update the PDP context in one or moreGGSNs, then the SGSN shall deactivate the corresponding PDPcontexts as described in subclause″PDP Context DeactivationInitiated by SGSN Procedure″. This shall not cause the SGSN toreject the routing area update.

If the routing area update procedure fails a maximum allowablenumber of times, or if the SGSN returns a Routing Area UpdateReject (Cause) message, the MS shall enter IDLE state. If the timerdescribed in step 2 expires and no Cancel Location (IMSI) wasreceived from the HLR, then the old SGSN shall stop forwardingN-PDUs to the new SGSN. If the Location Update Accept messageindicates a reject, then this should be indicated to the MS, and the MSshall not access non-GPRS services until a successful location updateis performed.

Note



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


E N D O F S T E P S............................................................................................................................................................

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

Overview The PDP context is a description of each PDP address of a subscriberand contains mapping and routing information for transferring PDUsfor 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

• Active

• Inactive.

PDP Context ActivationProcedure Diagram

PDP Context Activation Procedure

PDP Context ActivationProcedure

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

1 The MS sends an Activate PDP Context Request (NSAPI, TI, PDPType, PDP Address, Access Point Name, QoS Requested, and PDPConfiguration Options) message to the SGSN. The MS shall use PDPAddress to indicate whether it requires the use of a static PDP addressor whether it requires the use of a dynamic PDP address. The MSshall leave PDP Address empty to request a dynamic PDP address.The MS may use Access Point Name to select a reference point to acertain external network. Access Point Name is a logical namereferring to the external packet data network that the subscriberwishes to connect to. QoS Requested indicates the desired QoSprofile. PDP Configuration Options may be used to request optional

GPRS Procedures

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



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

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

2 Security functions may be executed. These procedures are defined insubclause″Security Function″.

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

3 The SGSN validates the Activate PDP Context Request using PDPType (optional), PDP Address (optional), and Access Point Name(optional) provided by the MS and the PDP context subscriptionrecords. The validation criteria, the APN selection criteria, and themapping from APN to a GGSN are described in annex A.

If a GGSN address can be derived, the SGSN creates a TID for therequested PDP context by combining the IMSI stored in the MMcontext with the NSAPI received from the MS. If the MS requests adynamic address, then the SGSN lets a GGSN allocate the dynamicaddress. The SGSN may restrict the requested QoS attributes given itscapabilities, the current load, and the subscribed QoS profile. TheSGSN 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 APNselected according to the procedure described in annex A. PDPAddress shall be empty if a dynamic address is requested. The GGSNmay use Access Point Name to find an external network. SelectionMode indicates whether a subscribed APN was selected, or whether anon-subscribed APN sent by MS or a non-subscribed APN chosen bySGSN was selected. Selection Mode is set according to annex A. TheGGSN may use Selection Mode when deciding whether to accept orreject the PDP context activation. For example, if an APN requiressubscription, then the GGSN is configured to accept only the PDPcontext activation that requests a subscribed APN as indicated by theSGSN with Selection Mode. The GGSN creates a new entry in itsPDP context table and generates a Charging Id. The new entry allowsthe GGSN to route PDP PDUs between the SGSN and the externalPDP network, and to start charging. The GGSN may further restrictQoS Negotiated given its capabilities and the current load. The GGSNthen returns a Create PDP Context Response (TID, PDP Address, BBProtocol, Reordering Required, PDP Configuration Options, QoSNegotiated, Charging Id, Cause) message to the SGSN. PDP Addressis included if the GGSN allocated a PDP address. BB Protocolindicates whether TCP or UDP shall be used to transport user data onthe backbone network between the SGSN and GGSN. ReorderingRequired indicates whether the SGSN shall reorder N-PDUs before

PDP Context Activation Procedure GPRS Procedures

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


delivering the N-PDUs to the MS. PDP Configuration Options containoptional PDP parameters that the GGSN may transfer to the MS.These optional PDP parameters may be requested by the MS in theActivate PDP Context Request message, or may be sent unsolicited bythe GGSN. PDP Configuration Options is sent transparently throughthe SGSN. The Create PDP Context messages are sent over the GPRSbackbone network.

If QoS Negotiated received from the SGSN is incompatible with thePDP context being activated (e.g., the reliability class is insufficient tosupport the PDP type), then the GGSN rejects the Create PDP ContextRequest message. The compatible QoS profiles are configured by theGGSN operator.

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

4 The SGSN inserts the NSAPI along with the GGSN address in itsPDP context. If the MS has requested a dynamic address, the PDPaddress received from the GGSN is inserted in the PDP context. TheSGSN selects Radio Priority based on QoS Negotiated, and returns anActivate PDP Context Accept (PDP Type, PDP Address, TI, QoSNegotiated, Radio Priority, and PDP Configuration Options) messageto the MS. The SGSN is now able to route PDP PDUs between theGGSN and the MS, and to start charging.

Quality of Service (QoS)

For each PDP Address a different quality of service (QoS) profile maybe requested. For example, some PDP addresses may be associatedwith E-mail that can tolerate lengthy response times. Otherapplications cannot tolerate delay and demand a very high level ofthroughput, interactive applications being one example. These differentrequirements are reflected in the QoS profile. If a QoS requirement isbeyond the capabilities of a PLMN, the PLMN negotiates the QoSprofile as close as possible to the requested QoS profile. The MSeither accepts the negotiated QoS profile, or deactivates the PDPcontext.

PDP Context Activation Procedure failure

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

Note



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



E N D O F S T E P S............................................................................................................................................................

Successful Network-Requested PDP Context

Activation ProcedureDiagram

Successful Network-Requested PDP Context Activation Procedure

Successful Network-Requested PDP Context

Activation Procedure ............................................................................................................................................................

1 When receiving a PDP PDU the GGSN determines if theNetwork-Requested PDP Context Activation procedure has to beinitiated. The GGSN may store subsequent PDUs received for thesame 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 beserved, it returns a Send Routing Information for GPRS Ack (IMSI,SGSN Address, Mobile Station Not Reachable Reason) message to theGGSN. The Mobile Station Not Reachable Reason parameter isincluded if the MNRG flag is set in the HLR. The Mobile Station NotReachable Reason parameter indicates the reason for the setting of theMNRG flag as stored in the MNRR record (see GSM 03.40). If theMNRR record indicates a reason other than ’No Paging Response’,the HLR shall include the GGSN number in the GGSN-list of thesubscriber.

If the HLR determines that the request cannot be served (e.g., IMSIunknown in HLR), the HLR shall send a Send Routing Informationfor GPRS Ack (IMSI, MAP Error Cause) message. Map Error Causeindicates the reason for the negative response.


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


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

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

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

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

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

5 The PDP context is activated with the PDP Context Activationprocedure.

Network-requested PDP context activation procedure failure

If the network-requested PDP context activation procedure was notsuccessful, 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



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



E N D O F S T E P S............................................................................................................................................................

6 Call Management

Overview....................................................................................................................................................................................................................................

Purpose This chapter discusses the BSS Mobile Originated Packet Transfer andthe BSS Mobile Terminated Packet Transfer.


GPRS - BSS Mobile Originated Packet Transfer 6-2

GPRS - BSS Mobile Terminated Packet Transfer 6-4

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



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

Multiple Access An MS initiates a packet transfer by making Packet Channel Requeston the PRACH or the RACH. The network responds on PAGCH orAGCH respectively. It is possible to use a one or two phase packetaccess method.

In the one phase access, the network responds to the channel requestfor Packet Transfer with the immediate assignment reserving theresources on PDCHs for uplink transfer of a number of Radio Blocks.

Opposite to the one phase access, the two phase access offers thepossibility to the mobile station to transfer information about itscapability to the network.

In the two phase access, the network responds to the channel requestwith the immediate assignment which reserves the one uplink radioblock for transmitting the packet resource request message whichcarries the complete description of the requested resources for theuplink transfer. Thereafter, the network responds with the PacketResource assignment reserving resources for the uplink transfer.

If there is no response to the Packet Channel Request within apredefined time period, the MS makes a retry after a random backofftime.

Uplink Data Transfer Efficient and flexible utilization of the available spectrum for a packetdata traffic (one or more PDCHs in a cell) can be obtained using amulti-slot channel reservation scheme. Blocks from one MS can besent on different PDCHs simultaneously, thus reducing the packetdelay for transmission across the air interface. The bandwidth may bevaried by allocating one to eight time slots in each TDMA framedepending on the number of available PDCHs multi-slot capabilitiesof the MS and the current system load.

The master slave channel concept requires mechanisms for efficientutilisation of PDCH uplink(s). Therefore, the Uplink State Flag (USF)is used on PDCHs. The 3 bit USF at the beginning of each RadioBlock that is sent on the downlink points to the next uplink RadioBlock. It enables the coding of 8 different USF states which are usedto multiplex the uplink traffic.

The channel reservation command includes the list of allocatedPDCHs and the corresponding USF state per channel. To an MS, theUSF marks whether it can use the next uplink radio block on therespective PDCH for transmission. An MS monitors the USF andaccording to the USF value, identifies PDCHs that are assigned to itand starts transmission. This allows efficient multiplexing of blocks

Call Management

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


from a number of MSs on a single PDCH. Additionally, the channelreservation command can be sent to the MS even before the totalnumber of requested PDCHs is free. Thus, the status flags not onlyresult in a highly dynamic reservation but also allow interruption oftransmission in favour of pending or high priority messages. On thePCCH, one USF value is used to denote PRACH (USF=FREE). Theother USF values USF=R1/R2/[0085].R7 are used to reserve theuplink for different MSs. After the blocks have been transmitted in thereserved time slots, an acknowledgment should follow from the BSSand sent to the PACCH.

In the case of an acknowledgment, which includes a bitmap ofcorrectly or erroneous received blocks, a Packet Resource Assignmentfor retransmission, timing advance and power control , only thoseblocks listed as erroneous are retransmitted.

Figure 6-1 GPRS Mobile Originated Packet Transfer

GPRS - BSS Mobile Originated PacketTransfer

Call Management

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



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

Overview A SGSN initiates a packet transfer to a mobile station that is in thestandby state by sending a Packet Paging Request on the PPCH orPCH downlink. The MS responds to this paging request by initiating aprocedure for page response very similar to the packet accessprocedure described earlier. The paging procedure is followed by thePacket Resource assignment for downlink frame transfer containingthe list of PDCHs to be used

Since an identifier, e.g. TFI is included in each Radio Block, it ispossible to multiplex Radio Blocks destined for different MSs on thesame PDCH downlink. It is also possible to interrupt a datatransmission to one MS if a higher priority data or a pending controlmessage is to be sent to some other MS. If more than one PDCH isavailable for the downlink traffic, and provided that the MS is capableof monitoring multiple PDCHs, blocks belonging to the same framecan be transferred on different PDCHs in parallel.

The network obtains acknowledgments for downlink transmission bypolling the MS. The MS sends the ACK/NACK message in thereserved Radio Block which is allocated in the polling process. In thecase of a negative acknowledgment, only those blocks listed aserroneous are retransmitted.

Figure 6-2 GPRS Mobile Terminated Packet Transfer

Call Management

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



Overview....................................................................................................................................................................................................................................

Purpose This chapter discusses Radio Resource Management.


PCU Functionality 7-2

Multislotting Operation Effects 7-3

Channel Coding Schemes 7-5

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



PCU Functionality....................................................................................................................................................................................................................................

Overview In the downlink direction, the PCU receives data from the Gb

interface unit in the form of logical Link Control (LLC). ProtocolData Units (PDUs). Its task is to segment them into Radio LinkControl (RLC) blocks and schedule the transmission at the radiointerface.

In the uplink direction, the PCU receives data in the form of RLCblocks from the CCU. Its task is to reassemble the RLC blocks intocomplete LLC frames, which are then transferred via the Gb interfaceto the SSGN.

The PCU needs to do this for each MS context established at theradio interface. Up to 7 or 8 subscribers are allowed to share the sameradio resource (TS) in each direction.

To achieve higher data rates for packet transfers, the PCU is able toassign multiple radio resources to a single user.


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


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

Overview GPRS is different from the original GSM specification in that itallows a single MS to transmit data simultaneously on multiple timeslots.

The following is a comparison of two types of operation:

• When there is only one Packet Data Channel (PDCH) availablein the cell, it is considered to be a single slot operation. Themaster PDCH (MPDCH) supports both data traffic and randomaccess.

• When there are up to eight PDCHs available in a cell, and theMSs are able to operate on eight time slots simultaneously, eightslot operation occurs. Channel 8 is used as the MPDCH andsupports both control signalling and data transmission. The otherchannels are used as slave PDCHs (SPDCHs) and support onlydata traffic.

To compare the efficiency of channel utilisation, the overall input loadand throughput are divided by the number of slots used. The basestation is capable of capture, and both uplink and downlink errors areincluded.

In the single slot operation as the load exceeds 4kbs per slot thethroughput reaches the maximum value of 4 kbs. The delay becomesunbounded at this point. In the eight slot operation when the inputload increases the maximum load increases 5kbs per slot, 40 kbs total.The delay explodes when the input load reaches 5 kbs per slot. Insingle slot operation, the maximum throughput is lower because thechannel used by GPRS has to handle both traffic and controlinformation. With multiple slots, the additional channels only have tocarry traffic.

Blocking increases as the load goes up. For eight slot operation, theblocking rate is very low (less than 0.1%). The blocking remains thesame even when the delay becomes intolerable. With single slotoperation, blocking becomes a serious problem. When the input loadis 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 receivedsuccessfully. In single slot operation, part of the channel is used forrandom access, so there is less user data transmitted per unit time andthe data needs to wait longer to be served. With the service rate lower


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



in the single slot case, the delay is longer, there is more blocking andthe maximum throughput is lower.

Figure 7-1 Operation Effects

Figure 7-2 Segmentation

Multislotting Operation Effects 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 mechanismand will be applied, if the radio conditions are bad.

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

• The first release supports only CS1 and CS2 !

• The feature Switching Coding Scheme provides the automaticswitch between CS1 and CS2.

• Increase of bandwidth for GPRS data transfers by using a codingscheme with a lower protection scheme whenever thetransmission quality allows it.

• Start always with CS1 !

• For uplink/downlink the PCU is the master.

Figure 7-3 Channel Coding Schemes


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



8 Future Enhancements

Overview....................................................................................................................................................................................................................................

Purpose This chapter describes the concept of Enhanced Data rates for GSMEvolution (EDGE)

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



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 persymbol) 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 timeslot

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

• EGPRS supports pure Link Adaptation (LA) mode or a combinedLS and Incremental Redundancy (IR) mode.Enhanced Data Rates for GSM Evolution (EDGE) is currentlyunder consideration in the Lucent Technologies work plan and isscheduled for later release.Lucent are active participants in the working group meetings inevaluating various technology proposals (like 8PSK vs. othercoding options) for EDGE and as a result of these meetingsEDGE compliance is being integrated into all Lucent equipment

EGPRS Modulation and Coding Schemes

CodingScheme

Mod. CodeRate

RLCPayloadBitsOctets

MaxDataRatekbps

BlocksPer20ms

Family # IRsubblocks

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

Future Enhancements

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


EGPRS Combined LA and IR mode

• The whole RLS block is convolutional encoded with a rate 1/3code

• Maximum three puncturing schemes to derive 3 sub-blocks: P1 -P3 for re-transmitting any MCS can be selected based on thecurrent link quality.

• First P1 is sent. If it cannot be decoded, P2 and P3 aresubsequently transmitted until the receiver can successfullydecode the RLC block via soft combining of all receivedsub-blocks.

• The code rate is dynamically adjusted according to theexperienced radio condition without using explicit measurements.

Enhanced Data rates for GSM Evolution(EDGE)

Future Enhancements

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



Glossary

A AInterface between BSC and MSC

Abis

Interface between BSC and BTS

ACCAdvanced Communications Card

AGCHAccess Grant Channel

APNAccess Point Name

ARQAutomatic Retransmission on Request

AVLAutomatic Vehicle Location

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

B BCCHBroadcast Control Channel

BSCBase Station Controller

BCF-2000Base-Station Controller Frame-2000

BSSBase Station System

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


Lucent Technologies G L O S S A R YG L - 1

BSSGPBase Station Subsystem GPRS Protocol

BTS-2000Base Transceiver Station-2000

BVCBSSGP Virtual Connection

BVCIBSSGP Virtual Connection Identifier

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

C CCCHCommon Control Channel

CCFCell Control Function

CCUChannel Codec Unit

CEWSCell Workstation

CGCharging Gateway

CSCircuit Switched Traffic

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

D DNSDomain Name Server

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

E EDGEEnhanced Data Rates for GSM Evolution

EIREquipment Identity Register

ETSIEuropean Telecommunications Standards Institue

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

F FECForward Explicit Congestion

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

G L O S S A R YG L - 2


FOAFirst Office Application

FNFrame Number

FRFrame Relay

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

G GbInterface between SGSN and BSC

GdInterface between SMS-GMSC/IWMSC and SGSN

GiInterface between GPRS and external data network

GnInterface between two GSNs within same PLMN

GpInterface between two GSNs in different PLMNs

GrInterface between an SGSN and HLR

GsInterface between SGSN and MSC

GBIUGb Interface Unit

GBNGPRS Backbone Network

GBSGPRS Backbone System

GGSNGateway GPRS Support Node

GMMGPRS Mobility Management

GMSCGateway MSC (towards PSTN)

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



GPRSGeneral Packet Radio Service

GSEGPRS Signalling Entity

GSMGlobal System for Mobile Communications

GSNGPRS Support Node

GTPGPRS Tunneling Protocol

GVMGPRS Virtual Machine

GWSGPRS Workstation

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

H HLRHome Location Register

HSCDHigh Speed Circuit switched Data

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

I I/FInterfac

IMEIInternational Mobile station Equipment Identity

IMSIInternational Mobile Subscriber Identity

IMWIntegrated Maintenance Workstation

IPInternet Protocol

IWMSCInter-Working MSC

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



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

L LACLocation Area Code

LANLocal Area Network

LLCLogical Link Control

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

M MInterface between BSC and STF

MgInterface between BSC and PGU

MACMedium Access Layer

MSMobile Station

MSCMobile-services Switching Centre

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

N NENetwork Element

NEMNetwork Element Manager

NMCNetwork Management Center

N-PDUNetwork-Protocol Data Unit

NS_VCNetwork Service Virtual Connection

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

O OAInterface between OMC and BSS

OA&MOperations Administration & Maintenance

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



OMC-2000Operations and Maintenance Center-2000

OMC-GOperation and Maintenance Centre for GBS

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

P PACCHPacket Associated Control Channel

PBCCHPacket Broadcast Control Channel

PCHPaging Channel

PCCCHPacket Common Control Channel

PCMPulse Code Modulation

PCUPacket Control Unit

PDCHPacket Data Channel

PDNPacket Data Network

PDPPacket Data Protocols

PDUProtocol Data Unit

PGUPCU & Gb Interface Unit

PLMNPublic Land Mobile Network

PSTNPublic Switched Telecommunication Network

PTCHPacket Traffic Channel

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



PTMPoint–To–Multipoint

PTM-GPoint-To-Multipoint Group Call

PTPPoint–To–Point

PVCPermanent Virtual Channel

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

Q QoSQuality of Service

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

R RACHRandom Access Channel

RFRadio Frequency

RILRadio Interface Layer

RLCRadio Link Control

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

S SAPIService Access Point Identifier

SGSNServing GPRS Support Node

SMSession Manager

SMS-SCSMS-Center

SNDCPSubnetwork Dependent Convergence Protocol

SRSSub-Rate Switch

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



SSSupplementary Services

SSSSwitching Sub-System

STFSpeech Transcoder Frame

SWSoftware

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

T TCPTransmission Control Protocol

TCP/IPTransmission Control Protocol/Internet Protocol

TRCTranscoder

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

U UDPUser Datagram Protocol

UmInterface between MS and BSS

UMTSUniversal Mobile Telecommunications System

USFUplink State Flag

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

V VLRVisitor Location Register

VPLMNVisited PLMN

VSATVery Small Aperture Terminal

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

X X.25Packet Switching Protocol

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



Index

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

B BSS Protocols,4-18........................................................

F Frame Relay,2-24

Future Enhancements,8-1

Enhanced Data rates forGSM Evolution(EDGE), 8-2

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

G GGSN Protocols,4-6

GPRS Benefits,1-8

GPRS Development andHistory, 1-5

GPRS Input for the OMC,2-38

GPRS Introduction to theBCF, 2-34

GPRS introduction to theBTS, 2-33

GPRS Logical Channels,4-26

GPRS MS,4-34

GPRS MS Protocols,4-24

GPRS NetworkArchitecture,2-2

GPRS Procedures,5-1

Combined RA / LAUpdate Procedure,5-21

Detach Procedures,5-10

GPRS Attach Procedure,5-5

PDP Context ActivationProcedure,5-29

Routing Area Update,5-15

GPRS Services,1-7

GPRS Signalling andTransmission Protocols,4-1

GSM Elements Affected byGPRS,2-30

GPRS Impact on theBase StationSubsystem (BSS),2-30

GPRS Impact on theNetwork SwitchingSubsystem (NSS),2-31

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

I Interfaces,3-1

GPRS SystemInterfaces,3-4

GSM System Interfaces,3-2

Internet Protocol (IP),2-59

IP addressing,2-54........................................................

L Lucent Base StationSubsystem,2-5

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

M Mapping of packet datalogical channels ontophysical channels,4-28

Mobile Station,2-4

Mobility Management,5-2........................................................

N Network SwitchingSubsystem (NSS),2-11

Network SwitchingSubsystem (NSS) andGPRS,2-47

New Network Area,2-18

New Network Elements -Functional Entities,2-19

New Network Interfaces,2-28

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

R Radio ResourceManagement,7-1

Channel CodingSchemes,7-5

Multislotting OperationEffects, 7-3

PCU Functionality,7-2........................................................

S SGSN Protocols,4-9........................................................

T The GPRS Air Interface,4-25

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


Lucent Technologies I N D E XI N - 1

The GPRS BackboneSystem (GBS),2-16

The GPRS SignallingPlane,4-2

The GPRS TransmissionPlane,4-4

The TCP/IP layers,2-52

The TCP/IP Suite,2-51

Transmission ControlProtocol (TCP),2-62

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

U User Datagram Protocol(UDP), 2-64

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

W What is GPRS,1-2

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

I N D E XI N - 2


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