introduction to gprs_6 66916

8/10/2019 Introduction to GPRS_6 66916

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System Training

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 Networks' customers only for the purposes of the agreement under which thedocument is submitted, and no part of it may be reproduced or transmitted in any form ormeans without the prior written permission of Nokia Networks. The document has beenprepared to be used by professional and properly trained personnel, and the customer

assumes full responsibility when using it. Nokia Networks welcomes customer comments aspart of the process of continuous development and improvement of the documentation.

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Nokia Networks' liability for any errors in the document is limited to the documentarycorrection of errors. Nokia Networks WILL NOT BE RESPONSIBLE IN ANY EVENT FORERRORS IN THIS DOCUMENT OR FOR ANY DAMAGES, INCIDENTAL ORCONSEQUENTIAL (INCLUDING MONETARY LOSSES), that might arise from the use of thisdocument or the information in it.

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Copyright Nokia Oyj 2003. All rights reserved.


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Contents

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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) ........................................................... 123.1.3 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.................................................................................... 15

3.2.3 The GSM frequency bands .................................................................. 16

4 Overview of GPRS ............................................................................. 174.1 Circuit and Packet Switched ................................................................ 174.2 GSM and packet orientated services ................................................... 204.2.1 GSM drawbacks .................................................................................. 214.2.2 How to overcome the above shortcomings? - GPRS ........................... 254.3 GPRS standardisation ......................................................................... 27

5 Services, users and operators.......................................................... 295.1 GPRS applications............................................................................... 295.1.1 Service examples ................................................................................ 29

5.2 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 .......................................................................................... 35

7 Review Questions.............................................................................. 36


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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 foreconomic 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 militaryresearch 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, whoproposed 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 toeasily access network servers such as ftp-servers or easily sending electronic

messages (emails). The release of the Mosaic browser in 1993 and the NetscapeBrowser 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 technologydropped. 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 isslowing down. In countries with a low Internet penetration level, huge growth

rates still can be expected. The figure below indicates who the internet grew

over the last years. In the year 2002 there were an estimated 540 millionInternet users, and 840 million Internet users are forecasted for the year 2005.


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eTForecasts0

100

200

300

400

500600

700

800

900

1989 1990 1995 1999 2000 2002 2005

inmillion

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 byprivate 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 canbe accessed fast and easily in the Internet and often even free of

charge. In the recent years, not only text files could be downloaded, butalso music and video clips. This triggered in the mean time a majordiscussion 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, arange 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


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without any knowledge of the underlying transmission or data basetechnology.

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 cannowadays conveniently download huge files at moderate speed. Mobilecommunication standards were optimised for narrowband voice

transmission. To support a higher data rate access for mobile

subscribers, new standards were developed. The most important onesare HSCSD, GPRS, EGDE (in GSM) and UMTS.

These is just a small list of applications, which triggered the Internet success up

to now, 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

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% ofthem were using GSM. It is predicted that in 10 years the number ofmobiles 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 to

competition as the number of mobile telecommunication operators

increase in each country. Mobile operators have to stay competitive tocapture and retain markets by setting competitive tariffs and by offering

value-added services. There is a limit to which any operator can decreasetariffs, so offering value added services to subscribers is the best solution

to staying competitive.


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The cost of radio spectrum has increased exponentially and the sale ofnew 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 (WirelessApplication Protocol) services. Despite its not-so-user-friendly userinterface and 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 inuse. 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.

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

inmillio

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 datacommunication 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 busiest speech users, so capturingtheir business can also increase speech revenues.

Data services offer the opportunity to increase revenue by providing much morethan 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 mostsuccessful digital cellular system (2G). Its standardisation includes services,

subsystem interfaces, and protocol architecture. It has been implemented inmore than 160 countries. In Europe and Asia Pacific the 900 and 1800 MHzsolutions 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 1900MHz band. Variants of GSM have been deployed for different frequency rangesand 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 componentsand 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 SIMcards with unique subscriber identification such as IMSI (International

Mobile Subscriber Identity) and IMEI (International Mobile EquipmentIdentity)

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 radioresources

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

subscription information

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


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The MSC is responsible for controlling calls in the mobile network. It identifiesthe 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 network and a fixed network is called a Gateway MSC. An MSC isnormally integrated with a VLR, which maintains information related to thesubscribers 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 datais held as long as the subscriber 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 locationof its customers. This data is required for routing calls.

In addition, there are two more elements in the NSS: the AuthenticationCentre (AC)and the Equipment Identity Register (EIR). They are used in

order to provide security and are usually implemented as part of HLR. Thesubscriber 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, andtransfers 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.


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3.1.2 Base Station Subsystem (BSS)

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

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 BSSand 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 signallingsupport.

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

interface. It takes care of air interface signalling, air interface ciphering, andspeech processing. In this context, speech processing refers to all the functions

that the BTS performs in order to guarantee an error-free connection betweenthe MS and the BTS.

The Transcoder and Rate Adaptation Unit (TRAU)is a BSS element takingcare of 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 radioresources.

3.1.3 Network Management Subsystem (NMS)

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

GSM network.


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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/2000that consists of a number of workstations, servers, and a router that connects toa data communications network (DCN).

The operator workstations are connected to the database and communicationservers via a local area network (LAN). The database server stores the

management information about the network. The communication server takes

care of the data communication between the NMS and the equipment in theGSM network known as network elements. This communication is carried over

the data communications network which connects to the NMS via a router. TheDCN 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

of individual 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

TranscoderSubmultiplexer

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

Network

Measurement

System

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 transmissionresources 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 transmissionboth 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 ofcellular 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


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uplink communication only, while other frequency bands are used fordownlink communication. In other words duplex transmission is

enabled by using different frequency bands, or, uplink and downlink areseparated 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. Withinin each time frame, some time resources are used for uplinktransmission, 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 userscan 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 accessis archived.


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frequency

time

mobileph

one1

mobileph

one4

mobil

eph

one2

mobil

eph

one3

carrie band 200 kHz

TDMA frame=8 timeslots

012345

76

012345

76

012

345

frequency

time

TDMA frame

FrequencyDivisionMultiple

Access

TimeDivisionMultiple

Access

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 areavailable. In North America, some parts of Asia and South America, there isGSM 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 MHz124 carrier frequency bands

GSM 1800 (DCS 1800)UL:1710 1785 MHz and DL:1805 1880 MHz

374 carrier frequency bands GSM 1900 (PCS 1900)

UL:1850 1910MHz and DL:1930 1990 MHz299 carrier frequency bands


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4 Overview of GPRS

The existing GSM networks are based on circuit switching techniques. For dataservices 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 connectionis required between two points, a link is established between them, and network

resources are reserved and dedicated for a subscriber's use for the entireduration 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 packetswitching 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 signallinginformation is used by the end points of the transmission to agree in the termson how the transmission has 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 theend 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 packetswitched 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 a 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 roundtrip delay is very limited.

streaming class: which is used for services such as downloading videoclips. There may be arrival jitter, there may be even an interruption

during the transmission. Here, it must guaranteed, that there is alwaysenough data in the memory of the receiver to give the user a continuousservice.

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

expected within a certain time limit, i.e. delays are allowed, but not toolong 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, whenavailable.

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 notneeded. The requirements in terms of QoS were therefore quite different in

circuit and packet switched networks. Consequently, separate network solutionfor circuit switched and packet 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 thereis a permanent connection between the two ends of the connection; but in

practice, the connection is only there when data is being transmitted. This isreferred 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 thenetwork. Therefore, a particular Quality of Service (QoS) must be negotiated

between the data user and the network to provide an appropriate level of servicefor various data applications.


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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 theunderlying transmission network infrastructure.

contentcontent

Networkserver

Figure 9. Internet service as perceived from the subscribers

The employee is using his laptop also in his home office. How can theemployee get connected to Internet? The employee has a telephone and amodem. 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 onhis laptop) is dialing the telephone number of a remote access server (RAS). A

RAS is a network element, which interfaces a telephone network and a datanetwork, 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 telephonynetwork looks like, or how many exchanges are within the circuit switchedtransmission 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.


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contentcontent

Networkserver

telephonynetwork

infrastructure

ModemRemote Access Server

PacketData

Networke.g. Internet

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

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 of a 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 theemployees 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 networkoperator?

Over the last 10 years, triggered by the Internet, the packet switched traffic wasgrowing 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 allowpacket switched data transfer, it is rarely used for that. With GSM, a bit tunnel

(bearer) can be 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 longGSM was specified in such a way, that packet data transmission was


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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 radiointerface, 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 supportedSMS is the only packet switched application, which is successful. Someoperators 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-messagefrom the Internet to mobile stations.) But an SMS message is limited to

160 characters. The transmission of music samples, pictures, graphicalshort messages, etc. is not supported. This limits the potential of SMS.

In some markets, there is already a saturation in SMS in order tomake 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 isoffering a circuit switched service only, . Circuit switched means, that

traffic resources are permanently allocated to the subscribers use,including radio interface resources.

Many packet switched subscribers have a 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 arereading the content of the file, they are still connected to the emailserver, but they are not transmitting anything. Within packet switched

networks, the networks transmission resources can be used by someoneelse. This is called statistical multiplexing. By doing so, a fairly high

transmission resource efficiency can be gained. But in circuit switchednetworks like GSM, transmission resources are allocated to thesubscriber 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 topay the operator for them.

So the subscriber perceives two drawbacks: If he is downloading

something, the GSM system is slow. And similar to the PSTNnetworks, 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 speechtransmission. Traffic resources are allocated to the subscriber for the

time of the connection. The radio link is hereby the most sensitive partof the transmission path. Due to the nature of the radio interface

solution, there may occur many problems, such as fading dips, obstacles


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in the transmission path, interferers, or subscribers leaving the supplyarea of the PLMN. Both the MS and the BTS generate measurement

reports, including aspects such as Bit Error Rate (BER) and FrameErasure Rate (FER). The reports are sent to 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 connectionis too poor and no handover can be performed, the MS and the BSCcan initiate the call termination. The subscriber gets disconnected. For a

speech subscriber, this is annoying. But imagine, the call is not release for instance, when the subscriber has moved into a non-GSM-supply

area. The subscriber cannot make a call. But when the resources werenot released who is going to pay for them?But exactly the same happens in a data call. If a file has been only

partly downloaded, the subscriber has actually got nothing at all. He

thinks, he has to pay for a GSM service, which did not serve him well!

In contrast to circuit switched services such as speech, datatransmission is often organised in fragments, called packets. Packets

can be sent independently, and they are nowadays 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. But when the GSM subscriber returns into a GSM supplyarea, it would be very nice to continue the data download.

The call establishment time is too longThe GSM network operator often is not directly connected to the packetdata network, the subscriber wants to get connected to. Often, there are

PSTNs and the Internet within the transmission path. This may result ina high call establishment time.

I feel uneasy about the connection securityMany business women and men require a safe connection to the

corporate network. Many GSM operators currently only offer an accessto the unreliable Internet. This rises questions about the integrity ofthe data they exchange between their end devices and their corporate

network. As a minimum requirement, they need a 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 resourcesThe radio interface resources impose the main capacity restraint to amobile 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 resourcesdedicated for the time for connection. But they have a bursty traffic

behaviour. Consequently, the resources allocated to them are often not

used. If a new GSM feature for packet switched services are introduced,the operators expect it to offer a solution, which improves the radio


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interface efficiency. Then, they can serve more packet switchedsubscribers on the given radio interface resources, and consequently

increase their potential to earn money.

marginal packet switched subscriber satisfaction

as can be seen above, many subscribers feel GSM as unsatisfactoryfor packet switched applications. The above mentioned problems must

be solved to increase the subscriber satisfaction. If it is increased, moresubscribers are willing to use packet switched application viaGSM(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) overcomes

most of the limitations, mentioned above. We list here its main characteristics:

Bottleneck radio interface UmThe 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:

Four Coding Schemesto increase the maximum net data rate. With

Coding Scheme CS-1, 9.05 kbps can be transmitted, with CS-2 13.4kbps, 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 theredundancy. With CS-4 there is no redundancy at all! The coding

schemes can change during the transmission; GPRS is capable todynamically adjust them in order to react on the current radio linkproperties, 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 bundlingphysical

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 arelimited to 3 timeslots.

Given channel bundling with up to8 physical channels/time slots andCS-4 with a data rate of 21.4 kbps,

a total of 171.2 kbps is available

for a single user. But this istheory! In reality, subscribers are

normally limited to three timeslots. And they can only expect

CS-1 and CS-2 in use. Therefore,

data rate of up to 30 to 40 kbps

can be expected.

Figure 11. GPRS enabled increased data rates

Increased data transmission ratesvia newCoding Schemes

CS-1

9.05kbps

CS-2

13.4kbps

CS-315.6kbps

CS-421.4kbps

Bundlingof up to8 physical channels

Net transmission rate up to171.2 kbps


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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 betransmitted. 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 operator is planning a 2 percent blocking probability, onaverage only 9 Erlang of the cell are used for voice calls. In a way theremaining resources are wasted.

As a result a network operator is interested in a mechanism to dynamicallyallocate the spare resources to a non-prioritised services. Especially packet

orientated services with no real-time demand, which show bursty datatransmission behaviour, are suitable.With GPRS the dynamical allocation of radio resourcesto 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 dynamically allocating free resources to these services, or by taking theresources 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 dynamicallyallocate 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


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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 ofmany packet switched services.

The asymmetric allocation of resources uplink and downlink is also basedon 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 specificnetwork 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 speedyconnection establishment and data transfer can be achieved. This should berealised 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 packetorientated 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.

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 3rdgeneration mobile

communication systems. This is realised in the GPRS by a strict separation of

the Network Switching Subsystem (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 tohis 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 inQ1/1998. It includes point-to-point (PTP) services and the complete basic

GPRS infrastructure. Air interface, mobility management, security, limitedQoS, 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 GSMRelease 99. Some work items were included in the GSM Release 98. Phase 2

add additional services like enhanced QoS support and point-to-multipoint(PTM) connections.

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


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switched real-time services (on the long run). This goes hand-in-hand with theintroduction of the IP Multimedia Subsystem (IMS).

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

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, aGPRS operator can now choose to enter the business of selling ISP and/or

value-added services (VAS) to customers. This would mean new sources ofrevenue 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 service

providersProviding 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 next generation system UMTS, person-to-person communications willevolve 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. Withmultimedia messaging, it is possible to combine the conventional short

messages with much richer content type photographs, images, and eventuallyalso video clips. In addition 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

Versatility 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 ofapplications could be implemented using GPRS. The mobile subscriber wouldthen 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 not done via signalling resources.This imposes major constrains in the GSM system, and limits the

possibilities to enhance the SMS feature.

MMS is can offered via WAP. The WAP infrastructure can be regarded

as external packet switched solution. GPRS is optimised for packetswitched data transfer, thus optimising WAP and MMS enabledservices.

5.2 GPRS users

GPRS offers a new set of data services, which means new possibilities in themarket, that is, new types of subscribers and new types of operators. GPRSusers can be classified into three types and these are discussed next.

Private users

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

access to the Internet, personal messaging (e-mail) through a mobile hand-heldall-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 willwant 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 theincome 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 onecommunicator.

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 mobileusers. GPRS can simply provide transparent access to the customers ISP. Withthese 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 sickly patients, 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


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wireless data transmission through GPRS may be the only choice. One exampleis computer games played by users in a virtual reality and mobile environment.

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 theoperator provide to the subscriber in terms of value-added services and how

much will be done by other companies or partners. This might have an impacton the operator's business model.

We will now look at two possible operator roles; namely the mobile accessoperator 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 14. 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. Theoperator simply sells the service of moving data packets between the subscriber


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Choosing this path involves higher risk, since the investments are higher. Inaddition, new competencies might be required (e.g. web designers), either

within the own company or together with strategic partners. But at the sametime, the opportunities for revenue are excellent.


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6 Key points

GPRS uses a packet-based switching technique which will enhance GSM dataservices 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, alink between the two points is established and the needed resources are reservedfor 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, whichare 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 threecharacteristics.

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

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Appendix A: ETSI GPRS Phase 2

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

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

References

Nokia GPRS Solution Description

Nokia GPRS System Description

GSM Specification 03.60 (GPRS Service Description R.97)

introduction to gprs_6 66916

Documents