02-introduction to gprs
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GPRSSYS
Introduction to GPRS
Training Document
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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
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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
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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
374 carrier frequency bands
GSM 1900 (PCS 1900)
UL: 1850 1910MHz and DL: 1930 1990 MHz
299 carrier frequency bands
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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)