02-introduction to gprs

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GPRSSYS

Introduction to GPRS

Training Document

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The information in this document is subject to change without notice and describes only theproduct defined in the introduction of this documentation. This document is intended for theuse of Nokia's customers only for the purposes of the agreement under which the document issubmitted, and no part of it may be reproduced or transmitted in any form or means withoutthe prior written permission of Nokia. The document has been prepared to be used by

professional and properly trained personnel, and the customer assumes full responsibilitywhen using it. Nokia welcomes customer comments as part of the process of continuousdevelopment and improvement of the documentation.

The information or statements given in this document concerning the suitability, capacity, orperformance of the mentioned hardware or software products cannot be considered bindingbut shall be defined in the agreement made between Nokia and the customer. However,Nokia has made all reasonable efforts to ensure that the instructions contained in thedocument are adequate and free of material errors and omissions. Nokia will, if necessary,explain issues which may not be covered by the document.

Nokia's liability for any errors in the document is limited to the documentary correction oferrors. NOKIA WILL NOT BE RESPONSIBLE IN ANY EVENT FOR ERRORS IN THISDOCUMENT OR FOR ANY DAMAGES, INCIDENTAL OR CONSEQUENTIAL (INCLUDINGMONETARY LOSSES), that might arise from the use of this document or the information in it.

This document and the product it describes are considered protected by copyright accordingto the applicable laws.

NOKIA logo is a registered trademark of Nokia Oyj.

Other product names mentioned in this document may be trademarks of their respectivecompanies, and they are mentioned for identification purposes only.

Copyright Nokia Oyj 2004. All rights reserved.

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Contents

Contents

1 Module objectives ..................................................................................4

2 Background ............................................................................................52.1 The Internet..............................................................................................52.2 Mobile Communications...........................................................................7

3 Do you remember GSM? .......................................................................93.1 The GSM subsystems............................................................................103.1.1 Network Switching Subsystem (NSS) ....................................................103.1.2 Base Station Subsystem (BSS)..............................................................113.1.3 Network Management Subsystem (NMS)..............................................123.1.4 Nokia GSM network architecture............................................................133.2 The GSM radio interface concept...........................................................143.2.1 Duplex transmission...............................................................................143.2.2 Multiple Access ......................................................................................153.2.3 The GSM frequency bands ....................................................................16

4 Overview of GPRS................................................................................174.1 Circuit and Packet Switched...................................................................174.2 GSM and packet orientated services .....................................................194.2.1 GSM drawbacks.....................................................................................214.2.2 How to overcome the above shortcomings? - GPRS.............................244.3 GPRS standardisation............................................................................26

5 Services, users and operators............................................................285.1 GPRS applications.................................................................................285.1.1 Service examples...................................................................................285.1.2 Push to talk (PoC) ..................................................................................305.2 GPRS users ...........................................................................................315.3 GPRS operator's role .............................................................................325.3.1 Mobile access operator ..........................................................................325.3.2 Full-service provider model ....................................................................33

6 Key points.............................................................................................34

7 Review Questions ................................................................................35

Appendix A: ETSI GPRS Phase 2........................................................................36

Appendix B: ETSI GPRS documents..................................................................37

References 38

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1 Module objectives

At the end of the module, the participant will be able to:

Describe the relationship between GPRS and GSM

Describe the difference between packet switching and circuit switching and

the meaning of these to data services

Describe some benefits of GPRS

to end-users

to operators

List some business reasons for GPRS

List some possible GPRS applications that would generate revenue

without using any references.



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2 Background

In the 90s of the last centuries, two technologies were the driving forces for

economic growth: The Internet and the mobile communication technology.

2.1 The Internet

The Internet story began in 1969 as a university research project. The predecessor of

the todays Internet the ARPANET - was funded by military research

organisations. In its first 30 years of existence, the Internet was primarily used by

government organisations and research institutes. The Internets huge success was

triggered in 1989 by Tim Berners-Lee, who proposed the World Wide Web (WWW

or Web). Only one year later, the Web became reality with the inauguration of the

first implementation of a primitive Web browser. The browser technology enabled

Internet-illiterates to easily access network servers such as ftp-servers or easily

sending electronic messages (emails). The release of the Mosaic browser in 1993 and

the Netscape Browser in 1994 enabled millions of PC users to easily and quickly get

into the Internet.

The browser technology enabled many computer users to easily enhance the value

added of their PC. At the same time, the prices for computer technology dropped. It

was the combination of the two facts, which resulted in an enormous growth of

Internet users. Nowadays, we can already observe, that in countries with a high level

of Internet user penetration, the growth of Internet users is slowing down. In

countries with a low Internet penetration level, huge growth rates still can beexpected. The figure below indicates who the internet grew over the last years. In the

year 2002 there were an estimated 540 million Internet users, and 840 million

Internet users are forecasted for the year 2005.

eTForecasts0

100

200

300

400

500

600

700

800

900

1989 1990 1995 1999 2000 2002 2005

inmillion

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Figure 1. World-wide Internet user growth

What were the driving forces for the exponential growth of the Internet?

Low-cost personal computers

One reason for the enormous growth rates of the Internet is rooted in the

fact, that the platform for the browser software the pc became cheaper

and more powerful over the recent years.

E-mail

One of the most popular applications between users of the Internet is the

ability to easily transfer messages. Emails are not only used by private users.

Business to business communication and business to consumer

communication via email becomes more and more common.

Web content

Given a growing number of Internet users, a wide range of content can beaccessed fast and easily in the Internet and often even free of charge. In the

recent years, not only text files could be downloaded, but also music and

video clips. This triggered in the mean time a major discussion on how to

protect the copy rights of digital information. Digital rights management will

be a major challenge for Internet business cases in the near future

Intranets

Within larger companies, which are often a located at multi sites, a range of

different Intranet solutions were in use. The Internet and the browser

technology forms nowadays a unified graphical user interface, with which

company employees can access corporate information without any

knowledge of the underlying transmission or data base technology. fast access on the last mile

Many fixed network operators are offering to private and business users a

fast access to the Internet. ISDN and xDSL (digital subscriber line)

guarantee a fast access to the Internet. Also the capacity of backbone routers

doubled about every 20 months, so that many users can nowadays

conveniently download huge files at moderate speed. Mobile communication

standards were optimised for narrowband voice transmission. To support a

higher data rate access for mobile subscribers, new standards were

developed. The most important ones are HSCSD, GPRS, EGDE (in GSM)

and UMTS.

These is just a small list of applications, which triggered the Internet success up tonow, and these applications will play an important role also in the future. Services

envisioned for a future Internet are among others

Web based cellular phones

mobile commerce

business to business electronic commerce

Web based radio and TV



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2.2 Mobile Communications

Mobile communication is the second success story of the 90s. There is a wide range

of mobile communication technologies, but the second generation mobilecommunication solution GSM is dominating the market. The success of the mobile

communication business becomes visible, when we just look to some facts and

trends.

Mobile traffic is growing faster than fixed traffic: in September 2002 there are

more than one billion mobile subscribers, and about 70% of them were using

GSM. It is predicted that in 10 years the number of mobiles will exceed the

number of PSTN (Public Switched Telephone Network) lines. In Finland and

the Scandinavian countries, the number of mobiles has already exceeded the

number of fixed lines. Furthermore, 1 in 18 people on this earth use GSM to

make phone calls today.

The unit cost of mobile phone call has been decreasing rapidly due tocompetition as the number of mobile telecommunication operators increase in

each country. Mobile operators have to stay competitive to capture and retain

markets by setting competitive tariffs and by offering value-added services.

There is a limit to which any operator can decrease tariffs, so offering value

added services to subscribers is the best solution to staying competitive.

The cost of radio spectrum has increased exponentially and the sale of new

spectrum has been used to offset the national debt in some countries. Mobile

operators are seeking good returns for these investments.

Mobile users are hungry for data services, and this is demonstrated by the

huge success of SMS (Short Message Service) and WAP (Wireless

Application Protocol) services. Despite its not-so-user-friendly user interfaceand relatively high tariffs, SMS traffic is booming. In September 2002, about

27 million SMS messages were sent. SMS is therefore the most successful

data communication service currently in use. Operators are currently

launching the Multimedia Messaging Service (MMS), which represents a user

friendly platform to transmit enhanced message. The MMS messages then can

transfer music, stills, short videos, and of course text messages.

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0

200

400

600

800

1000

1200

1400

Dec 97 Dec 98 Dec 99 Dec 00 Dec 01 Dec 02 Dec 03 Dec 04 Dec 05

estimates

inmillion

Figure 2. GSM growth rates world wide

Based on the above trends and the rapid growth of mobile and data communications,

it is clear that there will be a great demand for mobile data communication services

in the future. For an operator, offering value-added services and interesting content

is the key to increasing revenue and keeping ahead of the competition. Mobile data

services make it possible to offer innovative, segmented services to different user

groups, attract new subscribers, and reduce churn. Data users may also be the busiestspeech users, so capturing their business can also increase speech revenues.

Data services offer the opportunity to increase revenue by providing much more than

simply a mobile connection. Data services also provide additional revenue from the

type of content accessed and the amount of content transferred during that

connection.



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3 Do you remember GSM?

GSM (Global System for Mobile communications) was the first and most successful

digital cellular system (2G). Its standardisation includes services, subsysteminterfaces, and protocol architecture. It has been implemented in more than 160

countries. In Europe and Asia Pacific the 900 and 1800 MHz solutions are in use. In

North America, some part of South America and Asia, GSM 1900 is applied, i.e. the

duplex frequency bands can be found in the 1900 MHz band. Variants of GSM have

been deployed for different frequency ranges and applications. Examples are GSM

850 and GSM-Railway. The services provided by GSM include voice, circuit

switched data, and SMS.

For any mobile communication system to function the following components and

functionality are needed:

Base stations spaced regularly throughout the coverage area

Switching units to switch calls between base stations and between base

stations and external networks

Interfaces to Public Switched Telephone Networks (PSTN), Public Data

Networks (PDN), and other Public Land Mobile Networks (PLMN)

Mobile stations (MSs) containing Mobile Equipment (ME) and SIM cards

with unique subscriber identification such as IMSI (International Mobile

Subscriber Identity) and IMEI (International Mobile Equipment Identity)

Authentication units that are capable of authenticating subscribers by the use

of special codes and algorithms

Encryption units that ensure that all information transmitted on the airinterface is encrypted so that is secure

Speech and data compression so as to maximise the use of limited radio

resources

Databases to store subscriber details such as IMSI, security data, and

subscription information

Location management so that the current location of the subscriber can be

known and used for incoming calls

Units to co-ordinate handover between base stations when the mobile

subscriber is moving within the coverage area

Power control to minimise the transmitted power by the user

Network Management Centre that facilitates the management of the network

and collections of statistics pertaining to network performance

Billing Centre that logs subscribers call activity and generates billing records

Signalling links that are needed for the various building blocks to

communicate with each other.

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3.1 The GSM subsystems

The GSM network is divided into three subsystems:

Network Switching Subsystem (NSS)

Base Station Subsystem (BSS)

Network Management Subsystem (NMS).

These subsystems are shown in Figure 3.

BSC

BTS

BTS

TRAU

BSC

BTS

BTS

TRAU

BSS

BSS

NSS

MSC/VLR GMSC

HLREIR AC

PSTN/ISDN

MS

NMS

A

A

Um

Figure 3. GSM Public Land Mobile Network

3.1.1 Network Switching Subsystem (NSS)

The main elements of Network Switching Subsystem are (see Figure 3):

Mobile Services Switching Centre (MSC)

Visitor Location Register (VLR)

Home Location Register (HLR)

The MSC is responsible for controlling calls in the mobile network. It identifies the

origin and destination of a call (either a mobile station or a fixed telephone in both

cases), as well as the type of call. An MSC acting as a bridge between a mobile



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network and a fixed network is called a Gateway MSC. An MSC is normally

integrated with a VLR, which maintains information related to the subscribers who

are currently in the service area of the MSC. The VLR carries out location

registrations and updates. The MSC associated with it initiates the paging process. A

VLR database is always temporary in the sense that the data is held as long as thesubscriber is within its service area, whereas the HLR maintains a permanent register

of the subscribers. In addition to the fixed data, the HLR also maintains a temporary

database that contains the current location of its customers. This data is required for

routing calls.

In addition, there are two more elements in the NSS: the Authentication Centre

(AC) and the Equipment Identity Register (EIR). They are used in order to

provide security and are usually implemented as part of HLR. The subscriber and the

mobile station have to be identified and authorised before accessing the network.

To sum up, the main functions of NSS are:

Call control

This identifies the subscriber, establishes a call and clears the connection after the

conversation is over.

Charging

This collects the charging information about a call such as the numbers of the caller

and the called subscriber, and the time and type of the transaction, and transfers it to

the Billing Centre.

Mobility management

This maintains information about the location of the subscriber.

Signalling with other

This applies to interfaces with the BSS and PSTN.

Subscriber data handling

This is the permanent data storage in the HLR and temporary storage of relevant data

in the VLR.

Locating the subscriber

This locates a subscriber before establishing a call.

3.1.2 Base Station Subsystem (BSS)

The Base Station Subsystem consists of the following elements (see Figure 3):

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Base Station Controller (BSC)

Base Transceiver Station (BTS)

Transcoder and Rate Adaptation Unit (TRAU) (often just called Transcoder

(TC)

The Base Station Controller (BSC) is the central network element of the BSS and it

controls the radio network. The main responsibilities of the BSC are: Connection

establishment between MS and NSS, mobility management, statistical raw data

collection, and air interface and A interface signalling support.

The Base Transceiver Station (BTS) is a network element maintaining the air

interface. It takes care of air interface signalling, air interface ciphering, and speech

processing. In this context, speech processing refers to all the functions that the BTS

performs in order to guarantee an error-free connection between the MS and the

BTS.

The Transcoder and Rate Adaptation Unit (TRAU) is a BSS element taking careof speech transcoding, that is, it is capable of converting speech from one digital

coding format to another and vice versa, to maximise the use of radio resources.

3.1.3 Network Management Subsystem (NMS)

TheNetwork Management Subsystem (NMS) is the third subsystem of the GSM

network.

BSC

HLR/AC/EIR

TCSM

MSC/VLR

UnixWorkstations

Database andCommunications

Servers

NMS/2000

GSM Network

Router

DataCommunicationsNetwork (DCN)

Figure 4. NMS and the GSM network

The purpose of the NMS is to monitor various functions and elements of the

network. These tasks are carried out in the Nokia Solution by the NMS/2000 that



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consists of a number of workstations, servers, and a router that connects to a data

communications network (DCN).

The operator workstations are connected to the database and communication servers

via a local area network (LAN). The database server stores the managementinformation about the network. The communication server takes care of the data

communication between the NMS and the equipment in the GSM network known as

network elements. This communication is carried over the data communications

network which connects to the NMS via a router. The DCN is normally implemented

using an X.25 packet switching network.

The functions of the NMS can be divided into three categories:

Fault management

Configuration management

Performance management

These functions cover the whole of the GSM network elements from the level ofindividual BTSs, up to MSCs and HLRs.

3.1.4 Nokia GSM network architecture

The following network picture contains equipment from a typical Nokia GSM

network.

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Mobile StationsBase Station Subsystem Network Management Subsystem

BaseTransceiverStations

Base StationController

Transcoder

Submultiplexer

Digital CrossConnect

A-Interface Air Interface X.25 Interface Abis Interface

IN Service Control PointShort MessageService Centre

Voicemail

Mobile Switching Centre/

Visitor Location Register

Home Location Register/Authentication Centre/Equipment IdentityRegister

Network Switching Subsystem

PSTN/ISDN

CommunicationsServer

DataCommunication

Network

Database Server

Workstations

NetworkPlanningSystem

NetworkMeasurementSystem

TCP/IP

Data CommunicationsServer

Figure 5. Nokia GSM network architecture

3.2 The GSM radio interface concept

The radio interface is the main bottleneck in terms of available transmission

resources for the operator. In addition to that, due to the nature of the radio interface,

a huge amount of features have to be added to make the transmission both reliable

and safe. This section repeats shortly wireless key aspects.

3.2.1 Duplex transmission

Duplex is communication in a two-way direction on two frequencies. One frequency

is used to talk and the other one to listen. This is the modern way of cellular

communication.

There are two common ways to realise duplex transmission:

Frequency Division Duplex (FDD)

In this case, frequency resources are allocated to the mobile communication

system. Some of the frequency bands are allocated to uplink communication



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only, while other frequency bands are used for downlink communication. In

other words duplex transmission is enabled by using different frequency

bands, or, uplink and downlink are separated by frequency.

Time Division Duplex (TDD)In this case, one carrier frequency band is used for uplink and downlink

communication. The transmission is organised in time frames. Within in

each time frame, some time resources are used for uplink transmission,

while the remaining ones are used for downlink transmission.

Frequency Division Duplex Time Division Duplex

frequency

time

frequency

time

Uplink

Uplink

Uplink

UplinkDownlink

Downlink

Downlink

Downlink

Figure 6. FDD and TDD

3.2.2 Multiple Access

Two multiple access principles are combined in the GSM radio interface solution:

Frequency Division Multiple Access (FDMA)

In order to enable multiple access the frequency range is broken down into

unique carriers and distributed to the users. That way multiple users can

operate in a particular frequency spectrum.

Time Division Multiple Access (TDMA)

Multiple access is made possible by dividing on frequency band (carrier)into different slices of time. Hereby a time resource called timeslot is

cyclically allocated to one subscriber. Consequently, several subscribers can

use the same carrier and again, multiple access is archived.

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frequency

time

mobil

eph

one1

mobil

eph

one4

mobil

eph

one2

mobil

eph

one3

carrier band 200 kHz

TDMA frame= 8 timeslots

012345

76

012345

76

0123

45

frequency

tim

e

TDMA frame

FrequencyDivision

MultipleAccess

TimeDivision

MultipleAccess

Figure 7. FDMA and TDMA

3.2.3 The GSM frequency bands

Every GSM radio interface solution is using FDD, combined with FDMA and

TDMA. An FDMA carrier has 200 kHz bandwidth, on which TDMA is applied. A

TDMA frame last approximately 4.615 ms and houses 8 timeslots. In Europe,

Australia, most parts of Asia and South America, GSM 900 and GSM 1800 are

available. In North America, some parts of Asia and South America, there is GSM

1900. Numbers such as 900 and 1900 indicate, which frequency bands are applied.

GSM 900, 1800 and 1900 are the most commonly used frequency bands, which are

listed here:

GSM 900 (standard GSM, P-GSM, Primary GSM)

UL: 890 915 MHz and DL: 935 960 MHz

124 carrier frequency bands

GSM 1800 (DCS 1800)

UL: 1710 1785 MHz and DL: 1805 1880 MHz


GSM 1900 (PCS 1900)

UL: 1850 1910MHz and DL: 1930 1990 MHz




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4 Overview of GPRS

The existing GSM networks are based on circuit switching techniques. For data

services that are based on Internet Protocol (IP) such as e-mail and web browsing,GSM circuit switching is inefficient.

GSM Release '97 has introduced the General Packet Radio Service (GPRS) which

maintains the GSM BSS access technologies but provides packet switched data

services to the mobile station (MS).

4.1 Circuit and Packet Switched

Circuit switched connections

Standard GSM uses circuit switched (CS) connections. Each time a connection is

required between two points, a link is established between them, and network

resources are reserved and dedicated for a subscriber's use for the entire duration of

the call. Circuit switched connections have relatively low delay in the network and

have traditionally been used in fixed and mobile networks for speech and data.

Packet switched connections

Data networks, such as the Internet, Frame Relay and X.25 use packet switched (PS)

connections. With packet switching, the user data is organised in packets

(datagrams), each packet having an identifier or address that is used by routers(switching elements) in the network to pass the packet to its intended destination.

Hereby each packet is routed individually. GPRS brings packet switching techniques

to GSM networks.

A packet switched connection can be either connection less or connection orientated.

What is the difference between the two terms?

Connection orientated network service (CONS)

A service is connection orientated, when signalling takes place to establish an end-

to-end connection, to maintain it, and to release it. The signalling information is used

by the end points of the transmission to agree in the terms on how the transmissionhas to take place. For instance, the transport protocol TCP (Transfer Control

Protocol) is offering a connection orientated network service to higher layer

protocols, such as http or SMTP. TCP makes the connection reliable and well

organised.

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Connectionless network service (CLNS)

Each packet is transmitted independently. There is no mutual agreement in the end

points of the transmission on how to organise the user data transfer. IP is the best

known example of a connectionless network service.

The figure below gives a comparison between circuit switched and packet switched

network solutions.

Telephonenetworks

Packet switched

Datanetworks

Physical circuitPCM-tsl(CONS)

End-to-end connection (call)establishment needed

Dedicated resources (e.g. PCM-tsl) for oneuser are reserved during callestablishment

Only 30 - 40% of resources areeffectively used for speech transfer

Speech is transferred in real time Speech does not accept delays Errors in transmission are not so critical

for speech Charging is usually based on time

Virtual circuit (VC) No VCX.25 IP

(CONS) (CLNS)

Resources are shared between different usersessions, not dedicated

Resources are requested on demand, moreefficient use

Packets are not sent in real time bufferingand delay (in classical packet networks, e.g. IP)

Error correction and detection possible Charging is usually based on volume number

of packets

Circuit switched

Figure 8. Circuit switched vs. Packet switched

Since the mid 90s, real-time services atop of a packet switched infrastructure gained

increasing importance.

Real Time (RT)A real-time service is given, when the user data transfer between the source and

destination is done within a time limit. A 300 ms delay is already noticeable delay

for speech. There a protocols which support real time service, such as the Internet

protocol RTP (Real-Time Protocol).

If real-time services are offered via packet switched networks, also arrival jitter

affects the perceived QoS. Arrival jitter must be adjusted.

In mobile networks, two real-time QoS classes are normally considered:



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conversational class: which is used for services like speech. The round trip

delay is very limited.

streaming class: which is used for services such as downloading video clips.

There may be arrival jitter; there may be even an interruption during thetransmission. Here, it must guaranteed, that there is always enough data in

the memory of the receiver to give the user a continuous service.

Non-real Time (NRT)

Packet switched networks such as X.25 and IP were originally developed for bursty,

but non-time critical services, such as downloading emails and files. Nowadays, two

non-real time QoS classes are in use in the mobile communication business:

interactive class: which is used for FTP or SNMP signalling. When a

computer (client) gets connected to a server, signalling takes place between

the two network elements. A response to a request is hereby expected within

a certain time limit, i.e. delays are allowed, but not too long delays otherwise one party closes down the communication.

background class: which is for instance used for downloading files after

successfully login in a file server. This is not time critical, and large delays

are allowed. Transmission bandwidth is only used, when available.

In classical packet switched network, bandwidth in a packet switched (PS) network

is not reserved continuously, as is the case with circuit switching. Instead, network

bandwidth is allocated when required and released when not needed. The

requirements in terms of QoS were therefore quite different in circuit and packet

switched networks. Consequently, separate network solution for circuit switched andpacket switched services evolved.

Nowadays, some packet switched network such as ATM can be used to transmit

circuit switched services. We could create the impression to the user that there is a

permanent connection between the two ends of the connection; but in practice, the

connection is only there when data is being transmitted. This is referred to as a

virtual connection. Data packets from different users are statistically multiplexed by

the first router onto a single transmission path. Statistical multiplexing means that

the user data may have variable delay in the network. Therefore, a particular Quality

of Service (QoS) must be negotiated between the data user and the network to

provide an appropriate level of service for various data applications.

4.2 GSM and packet orientated services

While working in the company, an employee can access the Internet and download

data from and Internet server. The employee has the feeling, that he can directly

retrieve the information from the Internet. He is not aware of the underlying

transmission network infrastructure.

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contentcontent

Networkserver

Figure 9. Internet service as perceived from the subscribers

The employee is using his laptop also in his home office. How can the employee get

connected to Internet? The employee has a telephone and a modem. He is connecting

his computer to the modem and telephone. Then he is activating a program, with

which he can dial in to the Internet. But what does that mean, that he is dial in to the

Internet? The employee (or the software on his laptop) is dialing the telephonenumber of a remote access server (RAS). A RAS is a network element, which

interfaces a telephone network and a data network, such as the Internet. In the

dialing in process, a circuit switched connection is established via the telephony

network to the RAS. Then the RAS and the (dial-in software on the) laptop

negotiate, how the packet switched user data are transmitted via the circuit switched

connection. Also authentication can take place between the two devices. If

everything goes fine, the user has a circuit connection to the Internet. The employee

has no idea, how the telephony network looks like, or how many exchanges are

within the circuit switched transmission part. All he wants to do, it to serve in the

Internet at low cost, high data rates, high reliability, and high security.

What kind of service was offered to the user by the telephony network operator? A

bit tunnel (bearer) between the users end device (laptop) and the Internet.

contentcontent

Networkserver

telephony

networkinfrastructure

ModemRemote Access Server

PacketData

Networke.g. Internet

Telco is offering a bearer (= bit tunnel)to the requested Packet Data Network



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Figure 10. Data service offered by a PSTN-operator: access to requestedPacket Data Networks

What is the difference, when the employee is using a GSM mobile phone instead ofa fixed network phone to get connected to the Internet? There is none. The PLMN

operator is offering the same service as the fixed network operator, namely, a bit

tunnel, so that packet data can be exchanged between the employees laptop and the

Internet.

But does the subscriber really perceive the service, offered to him by mobile

operator in the same way as service, offered to him by a fixed network operator?

Over the last 10 years, triggered by the Internet, the packet switched traffic was

growing exponentially. But are packet switched services a success story in the

mobile communication business?

The answer is no although GSM was specified from the beginning to allow packet

switched data transfer, it is rarely used for that. With GSM, a bit tunnel (bearer) canbe established between the MS and the Internet, a corporate network, an intranet, and

so on.

4.2.1 GSM drawbacks

What kind of drawbacks does a subscriber perceive, when accessing a Packet Data

Network via GSM?

a download takes too long

GSM was specified in such a way, that packet data transmission was

supported. But the maximum data rate is limited to 9.6 kbps. Often, it iseven less, because the transmission has to take place in the acknowledged

mode. When during the transmission via the radio interface, some data has

been corrupted, it must be retransmitted. Often a subscriber must expect data

rates of less that 8 kbps. Consequently, when a subscriber wants to

download a larger file, it takes a long time.

only text SMS is supported

SMS is the only packet switched application, which is successful. Some

operators gain even more 10% of their revenues by the SMS-service. A short

message is a text based message, which can be sent from MS to MS. (Some

operators also offer the option to sent an SMS-message from the Internet to

mobile stations.) But an SMS message is limited to 160 characters. Thetransmission of music samples, pictures, graphical short messages, etc. is not

supported. This limits the potential of SMS. In some markets, there is

already a saturation in SMS in order to make mobile services more

attractive, an enhanced SMS service, or even a multimedia messaging

service (MMS) is required.

GSM is too expensive for serving in the Internet

When a subscriber gets connected to some packet data network, GSM is

offering a circuit switched service only, Circuit switched means, that traffic

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resources are permanently allocated to the subscribers use, including radio

interface resources.

Many packet switched subscriber applications have so-called bursty traffic

behaviour. They get connected to a network server, such as the email server.

They download the first file and read it. While they are reading the contentof the file, they are still connected to the email server, but they are not

transmitting anything. Within packet switched networks, the networks

transmission resources can be used by someone else. This is called statistical

multiplexing. By doing so, a fairly high transmission resource efficiency can

be gained. But in circuit switched networks like GSM, transmission

resources are allocated to the subscriber for the time of the connection. That

means, while the subscriber is reading the content of the first file, resources

are dedicated to him even if he is not actively using them and therefore

he has to pay the operator for them.

The subscriber perceives two drawbacks: If he is downloading something,

the GSM system is slow. And similar to the PSTN networks, he has to pay

for the time of the connection. If the subscriber wants to be always on, the

GSM network service becomes very expensive for him.

I had to pay for a connection, but didnt get any data at all (data

losses)

The mobile communications system GSM was optimised for speech

transmission. Traffic resources are allocated to the subscriber for the time of

the connection. The radio link is hereby the most sensitive part of the

transmission path. Due to the nature of the radio interface solution, there

may occur many problems, such as fading dips, obstacles in the transmission

path, interferers, or subscribers leaving the supply area of the PLMN. Both

the MS and the BTS generate measurement reports, including aspects such

as Bit Error Rate (BER) and Frame Erasure Rate (FER). The reports are sentto the BSC, which then decides, how to continue the radio link management.

If the MS and the BSC determine a too high error rate i.e. the quality of the

connection is too poor and no handover can be performed, the MS and the

BSC can initiate the call termination. The subscriber gets disconnected. For

a speech subscriber, this is annoying.

I a data call is disconnected during transmission of a file this result in

permanent data loss. If a file has been only partly downloaded, the

subscriber has actually got nothing at all. In contrast to circuit switched

services such as speech, data transmission is often organised in fragments,

called packets. Packets can be sent independently, and the delivery is not

time critical. In other words, they can be transmitted, whenever resources are

available. If there are problems on the radio interface, then the subscriber

cannot be served or will be served with a lower bit rate

The call establishment time is too long

The GSM network operator is not directly connected to the packet data

network, the subscriber wants to get connected to. Often, there are PSTNs

and the Internet within the transmission path. This may result in a high call

establishment time.



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I feel uneasy about the connection security

Many business users require a safe connection to the corporate network.

Many GSM operators currently only offer an access to the unsecured

Internet. This raises questions about the integrity of the data exchanged

between for example end devices and corporate networks. A valuablefunction would be an encrypted virtual connection from the GSM network to

the corporate network.

Not only the subscribers, but also the operators face the shortcomings of the GSM

system for packet switched applications:

inefficient use of the radio interface resources

The radio interface resources impose the main capacity restraint to a mobile

operator. The operator only has a limited amount of resources available; if

the resources are all in use, no additional subscribers can be served. Packet

switched subscribers get radio interface resources dedicated for the time forconnection. But they have a bursty traffic behaviour. Consequently, the

resources allocated to them are often not used. When a new GSM feature for

packet switched services is introduced, the operators expect it to offer a

solution, which improves the radio interface efficiency. It is then possible to

serve more packet switched subscribers on the given radio interface

resources, and consequently increase the potential to earn money.

marginal packet switched subscriber satisfaction

as can be seen above, many subscribers experience GSM as unsatisfactory

for packet switched applications. The above mentioned problems must be

solved to increase the subscriber satisfaction. If it is increased, more

subscribers are willing to use packet switched application via GSM (GPRS),and again, the potential to earn money is increased for the mobile operator.

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4.2.2 How to overcome the above shortcomings? - GPRS

The GSM Phase 2+ feature General Packet Radio Service (GPRS) overcomesmost of the limitations, mentioned above. We list here its main characteristics:

Bottleneck radio interface Um

The given capacities of the radio interface are the bottleneck for a GSM operator.

Therefore especially at this point new solutions were looked after:

One central task was to increase the data transmission rate for the subscriber. To do

so two new features were introduced:

FourCoding Schemes to increase the maximum net data rate. With

Coding Scheme CS-1, 9.05 kbps can be transmitted, with CS-2 13.4 kbps,

with CS-3 15.6 kbps, and with CS-4 21.4 kbps. In principle the increase of

the net data transfer rate was realised by reducing the redundancy. With CS-4 there is no redundancy at all! The coding schemes can change during the

transmission; GPRS is capable to dynamically adjust them in order to react

on the current radio link properties, which may be affected by the MS speed,

distance from the BTS, rain, etc. Currently, mainly CS-1 and CS-2 are in

use!

An increase of the data rate can be also realised by bundling physical

channels. In GPRS up to 8 time slots of a TDMA-frame can be dynamically

bundled for a single user, but in reality, most MS are limited to 3 timeslots.

Given channel bundling with up to 8 physical channels/time slots and CS-4

with a data rate of 21.4 kbps, a total of 171.2 kbps is available for a single

user. In reality, subscribers are normally limited to three time slots. And theycan only expect CS-1 and CS-2 in use. Therefore, data rate of up to 30 to 40

kbps can be expected.

Error! Objects cannot be created from editing field codes.

Figure 11. GPRS enabled increased data rates

Another central task was to increase the efficient use of the radio resources. This can

easily be shown with one example:

If there is one cell with two TRX, up to 15 Erlang voice traffic can be transmitted.

When an operator is planning his network, he has to reduce the probability of users

to be blocked from network access due to lack of free radio resources. If the operatoris planning a 2 percent blocking probability, on average only 9 Erlang of the cell are

used for voice calls. In a way the remaining resources are wasted.

As a result a network operator is interested in a mechanism to dynamically allocate

the spare resources to non-prioritised services. Especially packet orientated services

with no real-time demand, which show bursty data transmission behaviour, are

suitable.

With GPRS the dynamical allocation of radio resources to GSM and GPRS use is

possible so that these spare resources can be used. By prioritising of voice calls an

PLMN operator can serve all voice calls (circuit switched connection) by



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dynamically allocating free resources to these services, or by taking the resources

from GPRS users. A mechanism was included so that a logical connection between a

GPRS-subscriber and the PLMN is established even if there is no data transmission

via the air interface. The concept of dynamically allocate resources to GPRS users is

called capacity on demand.

0

2

4

6

8

10

12

14

16

1:00 PM 1:15 PM 1:30 PM 1:45 PM

TCH

0

2

4

6

8

10

12

14

16

3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00

TCH

GPRS packets can be transmittedusing free GSM capacity

Circuit switched traffic haspriority!

Figure 12. Increased radio interface efficiency

Physical channels are not only dynamical allocated between GSM and GPRS-subscribers, but a physical channel can also be used by several GPRS subscribers.

This again is an answer to the bursty transmission behaviour of many packet

switched services.

The asymmetric allocation of resources uplink and downlinkis also based on this

concept.

Access to Data Networks

Improvements are not only required in the radio interface organisation, and hence

within the BSS. Also the GSM NSS is upgraded with GPRS specific network

elements. The GPRS NSS is based on a packet switched data network, which has

direct access to PDNs (Packet Data Networks). By doing so, a speedy connectionestablishment and data transfer can be achieved. This should be realised within 0.5 to

1 seconds. The direct access to the PDNs also allows higher data transmission rates

also on the network side of the PLMN.

Quality of Service

The operator can prioritise services and/or subscribers. If there are packet orientated

services and applications which are e.g. more time sensitive or more critical of bit

errors, the operator may offer/ set different Quality of Service, both on the air

interface and on his terrestrial network.

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Evolution from GSM to UMTS

GPRS not only offers a more efficient use of the radio resources to an operator, but

also the option to gradually move to the 3rd

generation mobile communication

systems. This is realised in the GPRS by a strict separation of the Network SwitchingSubsystem (NSS) and the Base Station Subsystem (BSS). On the NSS side, new

network elements have to be introduced, while the BSS elements just have to be

enhanced. If the operator later on adds UMTS to his services, he can use the GPRS-

NSS side without modifications.

4.3 GPRS standardisation

The ETSI standardisation work on GPRS Phase 1 was officially finalised in

Q1/1998. It includes point-to-point (PTP) services and the complete basic GPRSinfrastructure. Air interface, mobility management, security, limited QoS, SMS

service, GPRS support nodes, and the GPRS backbone are all part of Phase 1.

The ETSI standardisation work on GPRS Phase 2 was frozen with GSM

Release 99. Some work items were included in the GSM Release 98. Phase 2

adds additional services like enhanced QoS support and point-to-multipoint

(PTM) connections. Some main point of GPRS phase 2 are the support of

IPv4 and IPv6

BSS co-ordination of radio resource allocation for class A GPRS services

Enhanced QoS support in GPRS

Charging and billing for GPRS AoC

Charging and billing for GPRS Pre-paid

Point-to-multipoint (PTM) services

Access to ISPs and intranets in GPRS Phase 2, separation of GPRS bearer

establishment and ISP service environment set-up

In GSM Release 4 (frozen March 2001) and GSM Release 5 (frozen June 2002),

QoS enhancements for the GPRS backbone were introduced to support packet

switched real-time services (on the long run). This goes hand-in-hand with the

introduction of the IP Multimedia Subsystem (IMS). The Nokia IP Multimedia

Subsystem can be combined with terminals supporting downloadable applications,creating exciting opportunities for application developers and operators to develop

and offer new IP multimedia services in GPRS and 3G networks. Further

information on network details is available in the architecture module.

At the end of the year 2002, more that 120 operators are commercially offering

GPRS and more than 40 operators are testing GPRS or building up a GPRS

infrastructure.

Note



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For additional information on the standardisation, see Appendix A: ETSI GPRS

Phase 2 and Appendix B: ETSI GPRS documents.

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5 Services, users and operators

5.1 GPRS applications

In addition to the traditional access selling business, as in the case of GSM, a GPRS

operator can now choose to enter the business of selling ISP and/or value-added

services (VAS) to customers. This would mean new sources of revenue from the

following:

Basic ISP functions (Internet access, WWW homepages, newsgroups, etc.)

Value-added services

Hosting value-added service providers

Brokering wireless access (WAP or non-WAP) to value-added serviceproviders

Providing business users access to their office LANs will probably make up a major

part of the revenue, at least in the beginning of GPRS. In the long run, with increased

GPRS penetration and cheaper GPRS mobile stations, one should not forget such

possibilities in the private user sector as, for example, on-line gaming and chatting.

5.1.1 Service examples

Today, person-to-person communication is mainly related to voice calls and Short

Message Service (SMS). Based on the GPRS infrastructure, in GSM and the nextgeneration system UMTS, person-to-person communications will evolve to new

types of messaging and telephony, including:

Chat (one to many)

Calendar and email (including synchronisation)

Rich call and video telephony

Picture messaging and multimedia messaging

Evolution of messaging will bring richer content into the messages. With multimedia

messaging, it is possible to combine the conventional short messages with much

richer content type photographs, images, and eventually also video clips. Inaddition to sending messages from one hand set to another, it is also possible to send

messages from handset to email.



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SMS

PictureMessaging

MultimediaMessageService

MobileMultimedia

Text Text &Graphics

Digitalimageinput

Newcontenttypes

Time

ersatility of Contentand User Benefits

Figure 13. Development of person-to-person messaging

In mid-2002, about 27 billion SMSs were sent globally. In the end of 2002,

more than 40 operators support MMS services already.

Already there are a number of value-added services via SMS. The same kind of

applications could be implemented using GPRS. The mobile subscriber would

then be able to enjoy the same services, only faster. Some typical VAS

examples today

Bus, train and airline information: arrivals, departures, delays, all busespassing the nearest street corner, etc.

Locating restaurants with a specific menu item

Weather information, news, sports headlines and scores

Buying products from Vending Machines using hand-held terminals

Lottery results sent to a user as soon they are known

Banking account balance and transactions, etc

Jokes, horoscope, and other entertainment information in the locality

Stock information

The real limitation is the imagination of the developers. Strategic alliances withvalue-added service providers might be an idea for many operators. Most of the

services that may become popular in the future have not yet been invented.

If SMS and MMS messages are transmitted via the GPRS infrastructure, there are

several benefits:

The SMS messages are no longer limited to 160 characters,

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The transmission of SMS messages is done via signalling resources. This

imposes major constrains in the GSM system, and limits the possibilities to

enhance the SMS feature.

MMS is offered via WAP. The WAP infrastructure can be regarded asexternal packet switched solution. GPRS is optimised for packet switched

data transfer, thus optimising WAP and MMS enabled services.

5.1.2 Push to talk (PoC)

Push to talk over Cellular (PoC) introduces a direct access one-to-one and one-

to-many voice communication service in the cellular network. It makes a service

that has proved popular among two-way radio users available through attractive

cellular phones, thus enhancing cellular services and bringing new businessopportunities in the domain of instant voice communications.

The principle of communication behind the service is simple just push to talk.

Thanks to the always-on(*connection, calls can be started to both individuals

and talk groups with just a push of a key. The call connection is direct. The users

can also form talk groups on an ad hoc basis without having to contact their

service providers, which facilitates spontaneous and flexible group

communication.

Error! Objects cannot be created from editing field codes.

Figure 14 Push to talk concept

Users can select the person or talk group they wish to talk to and then press the

Push to talk key or equivalent to start talking. The call is connected instantly.

Push to talk calls are one-way communication: while one person speaks, the

other(s) listen. The turns to speak are requested by pressing the key and granted

on a first-come-first-served basis. Push to talk speech is connected without the

recipient(s) answering and typically heard through the phone's built-in

loudspeaker. The basic idea is that the initiator of a call session is the first one to

talk instead of the receiver. Some examples of PoC use could be:

Family in the shopping mall communicating plans

Organizing transportation to school and evening activities

Group searching a missing person

A group of young people going out in the night

Discussing the game in a sports event



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Trying to decide on what video to rent at video rental store--spouse at video

store talking to family

A group coordinating where to meet for an evening out

Teenagers organizing a party or calling friends during the party

5.2 GPRS users

GPRS offers a new set of data services, which means new possibilities in the market,

that is, new types of subscribers and new types of operators. GPRS users can be

classified into three types and these are discussed next.

Private usersPrivate users' demand will be primarily for value-added services. They want access

to the Internet, personal messaging (e-mail) through a mobile hand-held all-in-one

communicator such as a WAP terminal or mobile enabled PDA.

Business users

The second and most important category of users is the business user who will want

secure access to corporate intranet IP networks for e-mail, intranet and Internet

browsing, database lookup and entry, etc. It is expected that most of the income will

be from this category of users as was the case in the early days of GSM. Business

users usually have a laptop and hence will not need an all in one communicator.

GPRS can also be used as a Mobile ISP for small enterprises whose staff are mobile

and need access to data services while on the move. A mobile operator can provide

complete ISP service package. Package pricing (bundling) of

e-mail, web services, and mobile voice can help to attract and retain mobile users.

GPRS can simply provide transparent access to the customers ISP. With these

options, the idea of a remote-office becomes a reality.

Industrial applications

The third category of users is industrial applications such as delay insensitive data

measurements from remote location, telematics, vending machines, transmission of

images from cab drivers to central locations, monitoring the performance of sicklypatients, and high-speed trains and trucks.

As with most technology available today, the fourth category of GPRS users are

applications which have not yet been invented, for which packet switched wireless

data transmission through GPRS may be the only choice. One example is computer

games played by users in a virtual reality and mobile environment.

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5.3 GPRS operator's role

One of the most important strategic decisions for the operator is how far down the

value chain should the operator invest. That is, how much service will the operatorprovide to the subscriber in terms of value-added services and how much will be

done by other companies or partners. This might have an impact on the operator's

business model.

We will now look at two possible operator roles; namely the mobile access operator

and the full-service provider models. Both of these models have some advantages

and disadvantages.

5.3.1 Mobile access operator

Internet

WWWWWW

ISP or

content

provider

Figure 15. Mobile access operator

In the mobile access operator model, an operator would act as a 'transparent bit-pipe',not adding one's own value-added services or acting as an ISP. The operator simply

sells the service of moving data packets between the subscriber and an ISP or other

external data networks. In this model, the operator has very limited possibilities for

differentiation when it comes to, for example, price, bit rate and availability, and is

very much in the hands of the ISP.

In addition, the ISPs control the end-customers through actual services and content

access. Choosing this path involves small risks for the operator the investment cost

is lower, but the opportunities for revenue are limited.



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5.3.2 Full-service provider model

In the full-service provider model, the operator adds value by offering services with

value to the end-user. Thus, the operator manages the GPRS network, ISP and other

networks which may offer value-added services to the subscriber. These servicesgive the operator an opportunity to differentiate:

customer loyalty

new customers and revenue streams

brand recognition

Contentproviders

Corporations

Internet

Multimedia

Service

Center

SMS,SMS,

HSCSD,HSCSD,GPRS,GPRS,

3rd3rd generationgeneration

Figure 16. Full-service provider

Choosing this path involves higher risk, since the investments are higher. In addition,

new competencies might be required (e.g. web designers), either within the own

company or together with strategic partners. But at the same time, the opportunities

for revenue are excellent.

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6 Key points

GPRS uses a packet-based switching technique which will enhance GSM data

services significantly, especially for bursty Internet/intranet traffic.

Some application examples:

Bus, train, airline real-time information

Locating restaurants and other entertainment venues based on current location

Lottery

E-commerce

Banking

E-mail

Web browsing

The main advantages of GPRS for users:

Instant access to data as if connected to an office LAN

Charging based on amount of data transferred (not the time connected)

Higher transmission speeds

The main advantages for operators:

Fast network roll-out with minimum investment

Excess voice capacity used for GPRS data

Smooth path to 3G services

In circuit switching, each time a connection is required between two points, a link

between the two points is established and the needed resources are reserved for the

use of that single call for the complete duration of the call.

In packet switching, the data to be transferred is divided up into packets, which are

then sent through the network and re-assembled at the receiving end.



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7 Review Questions

1. Give an example of a CS network and identify three characteristics.

2. Give an example of a packet switched network and identify three

characteristics.

3. Name two benefits of GPRS.

4. Give three examples of services that could be carried over GPRS.

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Appendix A: ETSI GPRS Phase 2

The ETSI standardisation work on the GPRS Phase 2 is on going. Some work

items will be included in the GSM Release 98 and the rest in later releases. The

GPRS Phase 2 work items are: GPRS mobile IP interworking

Modem and ISDN interworking in Phase 2 GPRS

BSS co-ordination of radio resource allocation for class A GPRS services

Enhanced QoS support in GPRS

Unstructured octet stream GPRS PDP type

Connecting an octet stream to port on Internet host

FIGS applied to GPRS

Charging and billing for GPRS AoC

Charging and billing for GPRS Pre-paid

Point-to-multipoint (PTM) services

Access to ISPs and intranets in GPRS Phase 2, separation of GPRS bearer

establishment and ISP service environment set-up

Access to ISPs and intranets in GPRS Phase 2, wireless/remote access to

LANs

It should be noted that there is on going work on only some of the work items

and not all the work items will be finalised.



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Appendix B: ETSI GPRS documents

Appendix B: ETSI GPRS documents

This page lists new technical specifications on GPRS. Latest version of

document is stated in the list if the document exists (December 1998).

Doc. Title Latest version Date

Stage 102.60 GPRS Service Description 6.1.0 1998-07

10.60 GPRS Program Management 5.4.2 1998-04

Stage 2

03.60 GPRS Service Description 6.2.0 1998-10

03.61 PTM-M Service Description 0.7.1 1997-01

03.62 PTM-G Service Description -

03.64 GPRS Radio Interface 6.1.0 1998-10

Stage 3

01.61 Ciphering Requirements 5.0.0 1997-10

04.60 RLC/MAC 6.2.0 1998-10

04.61 PTM-M Services -

04.62 PTM-G Services -

04.64 LLC 6.2.0 1998-11

04.65 SNDCP 6.2.0 1998-11

07.60 R and S Interfaces 6.2.1 1998-11

08.14 Gb Layer 1 6.0.0 1998-07

08.16 Gb Layer 2 6.1.0 1998-07

08.18 BSSGP 6.2.0 1998-10

09.16 Gs Layer 2 6.0.0 1998-04

09.18 Gs Layer 3 6.2.0 1998-10

09.60 GTP 6.2.0 1998-10

09.61 Gi 6.3.0 1998-10

12.15 GPRS Charging 7.0.0 1998-10

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References

Nokia GPRS Solution Description

Nokia GPRS System Description

GSM Specification 03.60 (GPRS Service Description R.97)

02-introduction to gprs

Documents