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Seminar Report
On
General Packet Radio Service (GPRS)
Course Title: Seminar
Course No.: ECE 4204
Date of Submission: 28-05-2013
Khulna University
Electronics and Communication Engineering Discipline
Khulna-9208
Submitted By
Group No-09
A. K. M. Tohidur Rahman
Student ID: 090918
S. M. M. Hossain Mahmud
Student ID: 090924
Tapan Kumar Biswas
Student ID: 090933
4th Year, 2nd Term
ECE Discipline
Khulna University
Khulna-9208
Submitted To
Sehrish Khan
Associate Professor
ECE Discipline
Khulna University
Khulna-9208
&
Dr. Md. Sohel Mahmud Sher
Associate Professor
ECE Discipline
Khulna University
Khulna-9208
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ACKNOWLEDGEMENT
I thank God Almighty for the successful completion of my seminar. I express my sincere
gratitude to Sehrish Khan, Associate Professor and Dr. Md. Sohel Mahmud Sher, Associate
Professor, ECE Discipline, Khulna University, Khulna-9208.
Finally, I wish to thank all my dear friends, for their whole-hearted cooperation, support and
encouragement.
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ABSTRACT
Today's mobile professionals need to stay in regular contact with important sources of
information such as the internet, email, corporate networks and remote databases. As demand
for Wide Area Networking (WAN) connectivity continues to grow, users and organizations
are seeking ways to make it more efficient and productive. One of the most promising new
technologies for this purpose is General Packet Radio Service (GPRS). GPRS is a packet-
switching data network that is overlaid on the existing cellular voice network, using the same
radio frequencies and cellular towers. When combined with the existing Global System for
Mobile communication (GSM), GPRS offers a complete voice and data solution with
significant advantages over other solutions. GPRS offers the flexibility and throughput of
packet switching. GPRS uses packet switching to transfer data from the mobile device to the
network and back. On a packet switched network a device can be always connected and ready
to send information without monopolizing the channel. Channels are shared in packet-
switched network, but in circuit-switched each channel is dedicated to one user. There are no
call up or suspend delays. By overlaying the GSM network, GPRS is able to take advantage
of the world's leading digital phone system. This is about three times as fast as the data
transmission speeds possible over today's fixed telecommunications networks and ten times
as fast as current Circuit Switched Data services on GSM networks.
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TABLE OF CONTENTS
Chapters Topics Pages
Chapter 1 Introduction 6
1.1 Need For a Wireless WAN Solution 6
1.2 A bit of history 7
1.2.1 First Generation Wireless Technology 7
1.2.2Second Generation Wireless Technology
7
1.2.3Second Generation Plus (2G+) Wireless Networks
7
Chapter 2 GPRS Overview 9
2.1 Who owns GPRS? 9
2.2 Goals of GPRS 9
2.3 Advantages of GPRS 10
2.4 Key NetworkFeatures of GPRS 11
2.4.1 Packet switching 11
2.4.2 Spectrum efficiency 12
2.4.3 Internet aware 12
Chapter 3 GPRS Architecture 14
3.1 GPRS Network Overview 14
3.2 Subscriber Terminal Devices 14
3.3 Radio Base Station Network 15
3.4 Network Switching and Services Infrastructure 15
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3.5 Additional Network Functionality 16
3.5.1 Serving GPRS Support Node (SGSN) 16
3.5.2 Gateway GPRS Support Node (GGSN) 16
3.6 Internal Backbone 17
3.7 GPRS Interfaces and Reference Points 17
Chapter 4 GPRS Protocol Architecture 20
4.1 Physical Layer 20
4.2 RLC/MAC Layer 22
4.3 LLC Layer 22
4.4 SNDCP Layer 22
4.5 BSSGP Layer 23
4.6 GTP Layer 24
Chapter 5 GPRS in Action 25
5.1 Attachment and Detachment Procedure 25
5.2 Session Management 25
5.3 Data Packet Routing 27
5.4 Location Management 28
5.5 Routing Update in GPRS 30
Chapter 6 GPRS Packet Data Channels 31
6.1 Time Slot Aggregation 31
6.2 Logical Channels in GPRS 32
6.3 Channel Coding 33
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Chapter 7 GPRS Security 34
7.1 Subscriber Identity Confidentiality 34
7.2 Identifying method 34
7.3 GPRS Authentication 35
7.4 GSM confidentiality 35
Chapter 8 GPRS Charging and Billing Techniques 37
Chapter 9 Limitations/ Problems RegardingGPRS Technology 38
Chapter 10 GPRS Applications 39
Chapter 11 Conclusion 42
Glossary 43
Reference 46
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CHAPTER 1
INTRODUCTION
Wireless wide area cellular network solutions have been around for many years.
Widespread adoption has been slow due to issues with coverage, cost, performance, and
secure remote access to business networks. The deployment of the Global System for Mobile
Communications (GSM) based General Packet Radio Service (GPRS) has the potential to
change this situation and to provide connectivity anytime and anywhere. GPRS is a packet
based radio service that enables always on connections, eliminating repetitive and time
consuming dial up connections. It will also provide real throughput in excess of 40 Kbps,
about the same speed as an excellent land line analog modem connection.
1.1 Need for a Wireless WAN Solution
Mobile workers who need to access information while they travel can do so using one
of two Wide Area Networking methods - wired or wireless. In the past, they relied mainly on
wired methods such as analog modems to connect over the public switched telephone
network (PSTN). However, users realized that using a dial up method to get a connection
were relatively tedious and time consuming, and connections were sometimes difficult to
maintain. In addition, as networking has progressed, the circuit- switched phone network has
proved to have limitations for data transmission compared to packet-switched networks such
as the Internet and corporate LANs. And finally, wired methods do not provide the same
degree of mobility as wireless solutions. The advent of wireless data communication through
the use of mobile phones and alphanumeric pagers has provided a higher degree of flexibility
over wired mobile connections. Today, users are able to connect their notebook and handheld
computers to data sources using mobile phone connection kits, and the data is sent over the
mobile phone network. However, mobile phones are still relatively slow in terms of data
throughput, and pagers can only display small amounts of information. Manufacturers are
rapidly developing a wide variety of new client devices, and advanced transmission
capabilities are also required. Mobile data users, businesses and other organizations have
asked for the freedom of wireless, but with the performance of wired connections. One of the
most promising technologies for meeting these needs is General Packet Radio Service
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(GPRS). This wireless data transmission technology can be used to send data over large
geographic areas to create the next evolution of wireless WANs (WWANs).
1.2 A BIT OF HISTORY
1.2.1 First Generation Wireless Technology
The first generation of wireless mobile communications was based on analog signaling.
Analog systems, implemented in North America, were known as Analog Mobile Phone Systems
(AMPS), while systems implemented in Europe and the rest of the worlds were typically identified as
a variation of Total Access Communication Systems (TACS). Analog systems were primarily based
on circuit-switched technology and designed for voice, not data.
1.2.2 Second Generation Wireless Technology
The second generation (2G) of the wireless mobile network was based on low band
digital data signaling. The most popular 2G wireless technology is known as Global Systems
for Mobile Communications (GSM). GSM technology is a combination of Frequency
Division Multiple Access (FDMA) and Time Division Multiple Access (TDMA). The first
GSM systems used a 25MHz frequency spectrum in the 900MHz band. FDMA is used to
divide the available 25MHz of bandwidth into 124 carrier frequencies of 200 kHz each. Each
frequency is then divided using a TDMA scheme into eight time slots. The use of separate
time slots for transmission and reception simplifies the electronics in the mobile units. Today,
GSM systems operate in the 900MHz and 1.8 GHz bands throughout the world with the
exception of the Americas where they operate in the 1.9 GHz band. While GSM technology
was developed in Europe, Code Division Multiple Access (CDMA) technology was
developed in North America. CDMA uses spread spectrum technology to break up speech
into small, digitized segments and encodes them to identify each call. The Second Generation
(2G) wireless networks mentioned above are also mostly based on circuit-switched
technology. 2G wireless networks are digital and expand the range of applications to more
advanced voice services, such as Called Line Identification. 2G wireless technology can
handle some data capabilities such as fax and short message service at the data rate of up to
9.6 kbps, but it is not suitable for web browsing and multimedia applications.
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1.2.3 Second Generation Plus (2G+) Wireless Networks
The effective data rate of 2G circuit-switched wireless systems is relatively slow for
today's Internet. As a result, GSM and other TDMA-based mobile system providers and
carriers have developed 2G+ technology that is packet- based and increases the data
communication speeds to as high as 384kbps. These 2G+ systems are based on the following
technologies High Speed Circuit-Switched Data (HSCSD), General Packet Radio Service
(GPRS) andEnhanced Data Rates for Global Evolution (EDGE)technologies. HSCSD is one
step towards 3G wide band mobile data networks. This circuit-switched technology improves
the data rates up to 57.6kbps by introducing 14.4 kbps data coding and by aggregating 4 radio
channels time slots of 14.4 kbps. GPRS is an intermediate step that is designed to allow the
GSM world to implement a full range of Internet services without waiting for the deployment
of full scale 3G wireless systems. GPRS uses a multiple of the 1 to 8 radio channel time slots
in the 200 kHz-frequency band allocated for a carrier frequency to enable data speeds of up to
115kbps. EDGE technology is a standard that has been specified to enhance the throughput
per time slot for both HSCSD and GPRS.
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Chapter 2
GPRS OVERVIEW
GPRS is a Mobile Data Service available to users of GSM and IS-136 mobile phones. GPRS is packet-switched and multiple users share the same transmission channel for
transmitting the data.
2.1 Who owns GPRS?
The GPRS specifications are written by the European Telecommunications Standard
Institute (ETSI), the European counterpart of the American National Standard Institute
(ANSI).GPRS stands for General Packet Radio System. GPRS provides packet radio access
for mobile Global System for Mobile Communications (GSM) and time-division multiple
access (TDMA) users.
GPRS is important as a migration step toward third-generation (3G) networks and
allows network operators to implement IP-based core architecture for data applications,
which will continue to be used and expanded for 3G services for integrated voice and data
applications.GPRS is a new bearer service for GSM that greatly improves and simplifies
wireless access to packet data networks, e.g., to the Internet. It applies a packet radio
principle to transfer user data packets in an efficient way between GSM mobile stations and
external packet data networks. Packets can be directly routed from the GPRS mobile stations
to packet switched networks. Networks based on the Internet Protocol (IP) (e.g., the global
Internet or private/ corporate intranets) and X.25 networks are also supported in the current
versions of GPRS.
2.2 Goals of GPRS
GPRS is the first step toward an end-to-end wireless infrastructure and has the following
goals:
Open architecture Consistent IP services Same infrastructure for different air interfaces Integrated telephony and Internet infrastructure
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Leverage industry investment in IP Service innovation independent of infrastructure
2.3 Advantages of GPRS
GPRS provides faster data transfer rates, always on connection, robust connectivity,
broad application support and strong security mechanisms.
Fast Data Transfer Rates
GPRS currently supports an average data rate of 115 Kbps, but this speed is only
achieved by dedicating all eight time slots to GPRS. Instead, carriers and terminal devices
will typically be configured to handle a specific number of time slots for upstream and
downstream data. For example, a GPRS device might be set to handle a maximum of four
slots downstream and two slots upstream. Under good radio conditions, this yields speeds of
approximately 50 Kbps downstream and 20 Kbps upstream. This is more than three times
faster than current 14.4-Kbps GSM networks and roughly equivalent to a good land line
analog modem connection. The aggregate cell site bandwidth is shared by voice and data
traffic. GPRS operators will vary in how they allocate the bandwidth. Typically, they will
configure the networks to give precedence to voice traffic; some may dedicate time slots to
data traffic to ensure a minimum level of service during busy voice traffic periods. Unused
voice capacity may be dynamically reallocated to data traffic. With its faster data transfer
rates, GPRS enables higher bandwidth applications not currently feasible on a GSM network.
Always-On Connection
An always on connection eliminates the lengthy delays required to reconnect to the
network to send and receive data. Information can also be pushed to the end user in real time.
GPRS allows providers to bill by the packet, rather than by the minute, thus enabling cost
effective always on subscriber services.
Robust Connectivity
GPRS improves data transmission integrity with a number of mechanisms. First, user
data is encoded with redundancies that improve its resistance to adverse radio conditions. The
amount of coding redundancy can be varied, depending on radio conditions. GPRS has
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defined four coding schemes CS1 through CS4. Initially, only CS1 and CS2 will be
supported, which allows approximately 9 and 13 Kbps in each time slot. If an error is
detected in a frame received in the base station, the frame may be repeatedly retransmitted
until properly received before passing it on to the GPRS core network.
Broad Application SupportLike the Internet, GPRS is based on packet-switched data. This means that all native
IP applications, such as email, Web access, instant messaging, and file transfers can run over
GPRS. In addition, its faster data transfer rates enable GPRS to accommodate higher-
bandwidth applications (such as multimedia Web content) not suited to slower GSM dial-up
connections. GPRS is particularly well suited for applications based on the WirelessApplication Protocol (WAP). WAP has gained widespread acceptance in a new breed of
micro browser enabled phones.
Security Support
GPRS builds on the proved authentication and security model used by GSM. At
session initiation, a user is authenticated using secret information contained on a smart card
called a Subscriber Identity Module (SIM). Authentication data is exchanged and validated
with records stored in the HLR network node. GPRS enables additional authentication using
protocols such as RADIUS before the subscriber is allowed access to the Internet or corporate
data networks. GPRS supports the ciphering of user data across the wireless interface from
the mobile terminal to the SGSN. In addition, higher level, end to end VPN encryption may
take place when a user connects to a private corporate network.
2.4 KEY NETWORK FEATURES OF GPRS
2.4.1 Packet switching
GPRS involves overlaying a packet based air interface on the existing circuit switched
GSM network. This gives the user an option to use a packet-based data service. With GPRS,
the information is split into separate but related "packets" before being transmitted and
reassembled at the receiving end. Packet switching is similar to a jigsawGPRS, the
information is split into separate but related "packets" before being transmitted andreassembled at the receiving end. Packet switching is similar to a jigsaw puzzle- the image
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that the puzzle represents is divided into pieces at the manufacturing factory and put into a
plastic bag. During transportation of the now boxed jigsaw from the factory to the end user,
the pieces get jumbled up. When the recipient empties the bag with all the pieces, they are
reassembled to form the original image. All the pieces are all related and fit together, but the
way they are transported and assembled varies.
Characteristic Circuit Switching Packet Switching
Need to establish a Connection
Dedicated Path
Bandwidth allocation
Potentially wasted bandwidth
Same path for all data
Congestion can occur at
Yes
Yes
Fixed
Yes
Yes
Setup time
No
No
Dynamic
No
No
Any time
2.4.2 Spectrum efficiency
Packet switching means that GPRS radio resources are used only when users are
actually sending or receiving data. Rather than dedicating a radio channel to a mobile data
user for a fixed period of time, the available radio resource can be concurrently shared
between several users. This efficient use of scarce radio resources means that large numbers
of GPRS users can potentially share the same bandwidth and be served from a single cell.
The actual number of users supported depends on the application being used and how much
data is being transferred. Because of the spectrum efficiency of GPRS, there is less need to
build in idle capacity that is only used in peak hours. GPRS therefore lets network operators
maximize the use of their network resources in a dynamic and flexible way, along with user
access to resources and revenues.
Table 1: Circuit switching vs. Packet
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2.4.3 Internet aware
For the first time, GPRS fully enables Mobile Internet functionality by allowing
interworking between the existing Internet and the new GPRS network. Any service that is
used over the fixed Internet today- File Transfer Protocol (FTP), web browsing, chat, email,
telnet- will be as available over the mobile network because of GPRS. In fact, many network
operators are considering the opportunity to use GPRS to help become wireless Internet
Service Providers in their own right.. There is a trend away from storing information locally
in specific software packages on PCs to remotely on the Internet .Each GPRS terminal can
potentially have its own IP address and will be addressable as such.
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Chapter 3
GPRS ARCHITECTURE
3.1 GPRS Network Overview
GPRS is a data network that overlays a second-generation GSM network. This data
overlay network provides packet data transport at rates from 9.6 to 171 kbps. Additionally,
multiple users can share the same air-interface resources simultaneously. GPRS attempts to
reuse the existing GSM network elements as much as possible, but to effectively build a
packet-based mobile cellular network, some new network elements, interfaces, and protocols
for handling packet traffic are required. To supply this capability, a GPRS network consists
of three basic components:
3.2 Subscriber Terminal Devices
Today, these devices are typically cell phones, but there are other devices such as
personal digital assistants (PDAs) with various input/output capabilities. All have integrated
radio transceivers.
Types of devices: GPRS devices are also classified by their ability to handle voice and
data calls. There are three such classifications:
Class A mode of operation: The MS is attached to both GPRS and other GSM services. The
mobile user can make and/or receive calls on the two services simultaneously, subject to the
quality of service (QoS) requirements, e.g. having a normal GSM voice call and receiving
GPRS data packets at the same time.
Class B mode of operation: The MS is attached to both GPRS and other GSM services, but
the MS can only operate one set of services at a time. The MS in idle mode (and packet idle
mode) is required to monitor paging channels (PCHs) for both circuit-switched and packet-
switched services. However, the practical behavior of the MS depends on the mode of
network operation. For example, one mode of network operation is defined so that when an
MS is engaged in packet data transfer, it will receive paging messages via the packet data
channel (PDCH) without degradation of the packet data transfer.
Class C mode of operation: The MS can only be attached to either the GSM network or theGPRS network. The selection is done manually and there are no simultaneous operations.
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3.3 Radio Base Station Network
Cellular networks are composed of small, low powered, terrestrial radio cells that
typically range in coverage area from tens of kilometers in sparsely populated rural areas to
less than 500 meters in densely populated urban areas. The frequencies used by the network
are reused again and again in different cells throughout the network to increase network
capacity.
3.4 Network Switching and Services Infrastructure
The traffic to and from the radio network is concentrated at a set of switching nodes
that interface to other fixed public or private networks. These nodes handle the call setup,
channel resource allocation, and the administration of subscriber services. These components
allow the GSM network to provide coverage as a user moves from an area covered by one
cell to an area covered by another cell. The network terminates the old cell connection and
immediately establishes a new cell connection. This process is designed to be transparent to
the user. In addition, users can roam or travel outside of a home coverage area to a new city,
region, or country. The arrival of the visitor is detected by the new system through an
automatic registration process. The new system informs the users home system of the new
location so that calls can be delivered.
Many registers are also maintained which contain information necessary for the
smooth functioning of the network. The HLR (Home Location Register) stores information
Figure 01: Functional View of GPRS Architecture [6]
Localareanetwork
Server
Router
Localareanetwork
Server
Router
Corporate 2
Corporate 1
Intra-PLMNbackbonenetwork
(IP based)
Serving GPRSSupport Node(SGSN)
Point-To-MultipointServiceCenter(PTM SC)
Gateway GPRSSupport Node(GGSN)
GPRSINFRASTRUCTURE
HLR/AuC
MSC
BSCBTS PacketnetworkPSTN
PacketnetworkSS7Network
Packetnetwork
Datanetwork(Internet)
Packetnetwork
Datanetwork(X.25)
Packetnetwork
Inter-PLMNBackbone
network
BorderGateway (BG)
Gb
Gr Gd
Gi.IP
Gi.X.25
Firewall
Firewall
Firewall
UmR/S
SMS-GMSC
Gr Gd
Gs
Gs
Gp
Gn
Gn
EIR
MAP-F
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about the current location of all subscribers of the network. This information is necessary for
routing all calls/messages to their intended destinations. A VLR (Visitor Location Register)
covers one or more cells and stores information about the subscribers currently under its area
of influence.
3.5 Additional Network Functionality
Although GPRS reuses existing GSM network elements, some new protocols,
interfaces and other network elements is required (see Figure 1). These include two major
core network elements, the Serving GPRS Support Node (SGSN) and the Gateway GPRS
Support Node (SGSN)
3.5.1 Serving GPRS Support Node (SGSN)
The SGSN is a main component of the GPRS network, which handles, e.g. the
mobility management and authentication and has register function. The SGSN is connected to
the BSC and is the service access point to the GPRS network for the GPRS MS. The SGSN
handles the protocol conversion from the IP used in the backbone network to the sub-
network-dependent convergence protocol (SNDCP) and logical link control (LLC) protocols
used between the SGSN and the MS. These protocols handle compression and ciphering. The
SGSN also handles the authentication of GPRS mobiles, and when the authentication is
successful; the SGSN handles the registration of an MS to the GPRS network and takes care
of its mobility management. When the MS wants to send (or receive) data to (from) external
networks, the SGSN relays the data between the SGSN and relevant GGSN (and vice versa).
3.5.2 Gateway GPRS Support Node (GGSN)
The GGSN is connected to the external networks like the Internet and the X.25. From
the external networks point of view, the GGSN is a router to a sub -network, because the
GGSN hides the GPRS infrastructure from the external networks. When the GGSN receives
data addressed to a specific user, it checks if the address is active. If it is, the GGSN forwards
the data to the SGSN serving the MS, but if the address is inactive, the data are discarded.
The mobile-originated packets are routed to the right network by the GGSN. The GGSN
tracks the MS with a precision of SGSN.
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3.6 Internal Backbone
The internal backbone is an IP based network used to carry packets between different
GSNs. Tunneling is used between SGSNs and GGSNs, so the internal backbone does not
need any information about domains outside the GPRS network. Signaling from a GSN to a
MSC, HLR or EIR is done using SS7.
Routing Area
GPRS introduces the concept of a routing area. This is much the same as a Location
Area in GSM, except that it will generally contain fewer cells. Because routing areas are
smaller than Location Areas, less radio resources are used when a paging message is
broadcast.
3.7 GPRS Interfaces and Reference Points
The GPRS system introduces new so-called G-interfaces to the GSM network
architecture. It is important to understand the function of every interface and reference point
because this gives an insight to the GPRS system and consequent evolution. Figure 02 gives a
logical architecture description with the interfaces and reference points of the GSM networkwith GPRS.
Figure 02: Logical architecture description with the interfaces and reference points oftheGSM network with GPRS [6]
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Connections of the GPRS system to the network and switching sub-system (NSS) part of
the GSM network are implemented through signaling system number 7 (SS7) network (Gc,
Gd, Gf, Gr, Gs), while the other interfaces and reference points are implemented through the
intra-PLMN backbone network (Gn), the inter-PLMN backbone network (Gp) or the external
networks (Gi). The different interfaces that the GPRS system uses are as follows:
Gb between an SGSN and a BSS. The Gb interface is the carrier of the GPRS trafficand signaling between the GSM radio network (BSS) and the GPRS part. Frame
relaybased network services (NSs) provide flow control for this interface.
Gc between the GGSN and the HLR. The GGSN may request location information fornetwork requested context activation only via this optional interface. The standard
also defines the use of a proxy GSN, which is used as a GPRS tunnelling protocol
(GTP) to mobile application part (MAP) protocol converter, thus avoiding
implementing MAP in GGSN.
Gd between the SMS-GMSC and an SGSN, and between SMS-IWMSC and anSGSN. The Gd interface allows more efficient use of the SMS services.
Gf between an SGSN and the Equipment Identity Register (EIR). The Gf gives theSGSN access to equipment information. In the EIR, the MSs are divided into three
lists: black list for stolen mobiles, grey list for mobiles under observation and white
list for other mobiles.
Gn between two GSNs within the same PLMN. The Gn provides a data and signalinginterface in the intra-PLMN backbone. The GTP is used in the Gn (and in the Gp)
interface over the IP-based backbone network.
Gp between two GSNs in various PLMNs. The Gp interface provides the samefunctionality as the Gn interface, but it also provides, with the BG and the Firewall,
all the functions needed in the inter-PLMN networking, i.e. security, routing, etc.
Gr between an SGSN and the HLR. The Gr gives the SGSN access to subscriberinformation in the HLR, which can be located in a different PLMN than the SGSN.
Gs between an SGSN and an MSC. The SGSN can send location data to the MSC orreceive paging requests from the MSC via this optional interface. The Gs interface
will greatly improve effective use of the radio and network resources in the combined
GSM/GPRS network. This interface uses BSSAP+ protocol.
Um between a MS and the GPRS fixed network part. The Um is the access interfacefor the MS to the GPRS network. The MS has a radio interface to the BTS, which is
the same interface used by the existing GSM network with some GPRS-specific
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changes. There are two different reference points in the GPRS network. The Gi is
GPRS-specific, but the R is common with the circuit-switched GSM network. The
two reference points in the GPRS are as follows:
Gi between a GGSN and an external network. The GPRS network is connected toexternal data networks via this interface. The GPRS system will support a variety of
data networks and that is why the Gi is not a standard interface, but merely a
reference point.
R between terminal equipment and mobile termination. This reference point connectsterminal equipment to mobile termination, thus allowing, e.g. a laptop-PC to transmit
data over the GSM phone. The physical R interface follows, e.g. the ITU-T V.24/V.28
or the PCMCIA PC-Card standards.
Therefore, GPRS requires modifications to numerous GSM network elements as
summarized below:
GSM Network
Element
Modification or Upgrade Required for GPRS
Subscriber Terminal A totally new subscriber terminal is required to access GPRS
services. These new terminals will be backward compatible with
GSM for voice calls.
BTS A software upgrade is required in the existing base transceiver site
(BTS).
BSC The base station controller (BSC) will also require a software
upgrade, as well as the installation of a new piece of hardware
called a packet control unit (PCU). The PCU directs the data
traffic to the GPRS network and can be a separate hardware
element associated with the BSC.
Core Network The deployment of GPRS requires the installation of new core
network elements called the Serving GPRS Support Node (SGSN)
and Gateway GPRS Support Node (GGSN).
Databases (VLR,
HLR and so on)
All the databases involved in the network will require software
upgrades to handle the new call models and functions introduced
by GPRS.
Table 2: Modifications on GSM Network
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Chapter 4
GPRS Protocol Architecture
The GPRS system introduces a whole new set of protocols for the GSM Phase 2+
network. The inter-working between the new network elements is done with new GPRS-
specific protocols. However, there are a number of existing protocols used at the lower layers
of the protocol stacks, namely, TCP/user datagram protocol (UDP) IP. Figure 03 shows the
transmission plane used in the GPRS system
4.1 Physical Layer
The physical layer has been separated into two distinct sub-layers, the physical RF
layer and the physical link layer.
The physical RF layer performs the modulation of the physical waveforms based on
the sequence of bits received from the physical link layer. The physical RF layer also
demodulates received waveforms into a sequence of bits that are transferred to the physical
link layer for interpretation. The GSM physical RF layer is defined in GSM 05 series
specifications, which define the following among other things:
The carrier frequency characteristics and GSM radio channel structures.
Figure 03: GPRS Protocol Architecture [15]
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The modulation of the transmitted waveforms and the raw data rates of GSMchannels.
Note that in the GPRS Rel97 radio interface, only the original GSM modulation method,
GMSK modulation, with the carrier bit rate of 270.833 kbps is defined. For one single
timeslot; this corresponds to the gross data rate of 22.8 kbps.
The transmitter and receiver characteristics and performance requirements.
Thephysical link layerprovides services for information transfer over a physical channel
between the MS and the network. These functions include data unit framing, data coding and
the detection and correction of physical medium transmission errors. The physical link layer
operates above the physical RF layer to provide a physical channel between the MS and the
network. The purpose of the physical link layer is to convey information across the GSM
radio interface, including RLC/MAC information. The physical link layer supports multiple
MSs sharing a single physical channel and provides communication between MSs and the
network. In addition, it provides the services necessary to maintain communications
capability over the physical radio channel between the network and MSs. Radio sub-system
link control procedures are specified in.
The physical link layer is responsible for the following:
Forward error correction (FEC) coding, allowing the detection and correction oftransmitted code words and the indication of uncorrectable code words. The coding
schemes are described in the section entitled Physical link layer.
Rectangular interleaving of one radio block over four bursts in consecutive TDMAframes, as specified in.
Procedures for detecting physical link congestion. The physical link layer controlfunctions include
Synchronization procedures, including means for determining and adjusting the MStiming advance to correct for variances in propagation delay,
Monitoring and evaluation procedures for radio link signal quality. Cell selection and re-selection procedures. Transmitter power control procedures. Battery power saving procedures, e.g. discontinuous reception (DRX) procedures.
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4.2 RLC/MAC Layer
The RLC/MAC layer provides services for information transfer over the physical
layer of the GPRS radio interface. These functions include backward error correction
procedures enabled by the selective re-transmission of erroneous blocks. The RLC function
offers a reliable radio link to the upper layers. The MAC function handles the channel
allocation and the multiplexing, i.e. the use of physical layer functions. The RLC/MAC layer
together form the open system interconnection (OSI) Layer 2 protocol for the Um interface
and uses the services of the physical link layer (see the section entitled Medium Access
Control and Radio Link Control Layer).
4.3 LLC Layer
The logical link control layer offers a secure and reliable logical link between the MS
and the SGSN to upper layers, and is independent of the lower layers. The LLC layer has two
transfer modesthe acknowledged and unacknowledged. The LLC conveys signaling, SMS
and SNDCP packets.
4.4 SNDCP Layer
The sub-network-dependent convergence protocol (SNDCP) is a mapping and
compression function between the network layer and lower layers. It also performs
segmentation, reassembling and multiplexing. The SNDCP protocol is specified in [11].
Signaling has various sets of protocols, which are used with the existing GSM network
elements. Internal signaling in the GPRS system is handled by protocols, which carry both
data and signaling (LLC, GTP and BSSGP). The GPRS control plane is shown in Figure 04.
Figure 05 describes how network protocols are multiplexed. NSAPI is the network
layer service access point identifier, which is used to identify the packet data protocol (PDP)
context at SNDCP level. Service access point identifier (SAPI) is used to identify the points
where LLC provides service to higher layers. SAPIs have different priorities. TLLI is the
temporary logical link identity, which unambiguously identifies the logical link between the
MS and the SGSN. The IP or the X.25 is the packet protocol offered to the subscriber by the
GPRS system.
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4.5 BSSGP Layer
The primary functions of the base station sub-system GPRS protocol (BSSGP)
include, in the downlink, the provision by an SGSN to a BSS of radio-related information
used by the RLC/MAC function; in the uplink, the provision by a BSS to an SGSN of radio-
related information derived from the RLC/MAC function; and the provision of functionality
to enable two physically distinct nodes, an SGSN and a BSS, to operate node management
control functions. The underlying network service is responsible for the transport of BSSGP
packet data units (PDUs) between a BSS and an SGSN.
Figure 04: GPRS control plane [15]
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4.6 GTP Layer
The GPRS tunneling protocol (GTP) is used to tunnel data and signaling between the
GSNs. The GTP can have proprietary extensions to allow proprietary features. The relay
function relays PDP (packet data protocol) PDUs between the Gb and the Gn interfaces.
Figure 05:Network rotocols multi lex 15
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Chapter 5
GPRS IN ACTION
When a user turns on a GPRS device, typically it will automatically scan for a local
GPRS channel. If an appropriate channel is detected, the device will attempt to attach to the
network. The SGSN receives the attach request, fetches subscriber profile information from
the subscribers HLR node, and authenticates the user. Ciphering may be established at this
point.
The SGSN uses the profile information (including the access point name, which identifies the
network and operator) to determine which GGSN to route to. The selected gateway may
perform a Remote Authentication Dial In User Service (RADIUS) authentication and allocate
a dynamic Internet Protocol (IP) address to the user before setting up connections to outside
networks. This process is called the packet data profile context activation and the setup may
vary from one carrier to the next. It may include additional functions like QoS management.
When the mobile device is powered off or moved out of a GPRS coverage area, its context is
deactivated and the device is detached from the network.
How does a GPRS work?
5.1 Attachment and Detachment Procedure
Before a mobile station can use GPRS services, it must register with an SGSN of the
GPRS network. The network checks if the user is authorized, copies the user profile from the
HLR to the SGSN, and assigns a packet temporary mobile subscriber identity (PTMSI) to the
user. This procedure is called GPRS attach. For mobile stations using both circuit switched
and packet switched services it is possible to perform combined GPRS/IMSI attach
procedures. The disconnection from the GPRS network is called GPRS detach. It can be
initiated by the mobile station or by the network (SGSN or HLR).
5.2 Session Management
To exchange data packets with external PDNs after a successful GPRS attach, a
mobile station must apply for one or more addresses used in the PDN and e.g. for an IP
address in case the PDN is an IP network. This address is called PDP address (Packet Data
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Protocol address). For each session, a so called PDP context is created, which describes the
characteristics of the session. It contains the PDP type (e.g., IPv4), the PDPaddress assigned
to the mobile station (e.g., 129.187.222.10), the requested QoS, and the address of a GGSN
that serves as the access point to the PDN. This context is stored in the MS, the SGSN, and
the GGSN.
With an active PDP context, the mobile station is visible for the external PDN and is
able to send and receive data packets. The mapping between the two addresses, PDP and
IMSI, enables the GGSN to transfer data packets between PDN and MS. A user may have
several simultaneous PDP contexts active at a given time. The allocation of the PDP address
can be static or dynamic. In the first case, the network operator of the users home PLMN
permanently assigns a PDP address to the user. In the second case, a PDP address is assigned
to the user upon activation of a PDP context. The PDP address can be assigned by the
operator ofthe users home-PLMN (dynamic home- PLMN PDP address) or by the operator
of the visited network (dynamic visited-PLMN PDP address). The GGSN is responsible for
the allocation and the activation/ deactivation of the PDP addresses.
Figure 06 shows the PDP context activation procedure. Using the message activate PDP
context request, the MS informs the SGSN about the requested PDP context. If dynamic
PDP address assignment is requested, the parameter PDP address will be left empty.
Figure 06: PDP context activation procedure [7]
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Afterward, usual security functions (e.g., authentication of the user) are performed. If access
is granted, the SGSN will send a create PDP context request message to the affected
GGSN. The latter creates a new entry in its PDP context table, which enables the GGSN to
route data packets between the SGSN and the external PDN. Afterward, the GGSN returns a
confirmation message create PDP context response to the SGSN, which contains the PDP
address in case dynamic PDP address allocation was requested. The SGSN updates its PDP
context table and confirms the activation of the new PDP context to the MS (activate PDP
context accepts).
GPRS also supports anonymous PDP context activation. In this case, security functions
as shown in Figure are skipped, and thus, the user (i.e., the IMSI) using the PDP context
remains unknown to the network. Anonymous context activation may be employed for pre-
paid services, where the user does not want to be identified. Only dynamic address allocation
is possible in this case.
5.3 Data Packet Routing
The main functions of the GGSN involve interaction with the external data network.
The GGSN updates the location directory using routing information supplied by the SGSNs
about the location of a MS and routes the external data network protocol packet encapsulated
over the GPRS backbone to the SGSN currently serving the MS. It also decapsulates and
forwards external data network packets to the appropriate data network and collect charging
data that is forwarded to a charging gateway.
In Figure 3, three different routing schemes are illustrated: mobile-originated message (path
1), network-initiated message when the MS is in its home network (path 2), and network-
initiated message when the MS has roamed to another GPRS operators network (path 3). In
these examples, the operators GPRS network consists of multiple GSNs (with a gateway and
serving functionality) and an intra-operator backbone network.
GPRS operators will allow roaming through an inter-operator backbone network. The
GPRS operators connect to the inter-operator network via a boarder gateway (BG), which can
provide the necessary interworking and routing protocols (for example, Border Gateway
Protocol [BGP]). It is also foreseeable that GPRS operators will implement QoS mechanisms
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over the inter-operator network to ensure service-level agreements (SLAs). The main benefits
of the architecture are its flexibility, scalability, interoperability, and roaming.
5.4Location Management
The main task of location management is to keep track of the users current location,
so that incoming packets can be routed to his or her MS. For this purpose, the MS frequently
sends location update messages to its current SGSN. If the MS sends updates rather seldom,
its location (e.g., its current cell) is not known exactly and paging is necessary for each down
link packet, resulting in a significant delivery delay. On the other hand, if location updates
happen very often, the MSs location is well known to the network, and the data packets can
be delivered without any additional paging delay. However, quite a lot of uplink radio
capacity and battery power is consumed for mobility management in this case. Thus, a good
location management strategy must be a compromise between these two extreme methods. A
state model shown in Figure 4 has been defined for location management in GPRS. A MS
can be in one of three states depending on its current traffic amount.
Figure 07: Data Routing Procedure [1]
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Fig 08: States of GPRS in a Mobile Station [10]
In idle state the MS is not reachable. Performing a GPRS attach, the MS gets into
ready state. With a GPRS detach it may disconnect from the network and fall back to idle
state. All PDP contexts will be deleted.
The standby state will be reached when an MS does not send any packets for a
longer period of time, and therefore the ready timer (which was started at GPRS attach)
expires. In idle state, no location updating is performed, i.e., the current location of the MS is
unknown to the network.
An MS in ready state (active state) informs its SGSN of every movement to a
new cell. For the location management of an MS in standby state, a GSM location area (LA)
is divided into several routing areas (RA). In general, an RA consists of several cells. The
SGSN will only be informed when an MS moves to a new RA; cell changes will not be
disclosed. To find out the current cell of an MS in standby state, paging of the MS within a
certain RA must be performed .For MSs in ready state, no paging is necessary.
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5.5 Routing Update in GPRS
When an MS that is in an active or a standby state moves from one routing area to
another within the service area of one SGSN, it must perform a routing update. The routing
area information in the SGSN is updated, and the success of the procedure is indicated in the
response message.
A cell-based routing update procedure is invoked when an active MS enters a new
cell. The MS sends a short message containing the identity of the MS and its new location
through GPRS channels to its current SGSN. This procedure is used only when the MS is in
the active state.
The inter-SGSN routing update is the most complicated routing update. The MSchanges from one SGSN area to another and it must establish a new connection to a new
SGSN. This means creating a new logical link context between the MS and the new
SGSNand informing the GGSN about the new location of the MS.
Figure 9: Routing Area Update [11]
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Chapter 6
GPRS Packet Data Channels
The channel allocation in GPRS is different from the original GSM. GPRS allows a
single mobile station to transmit on multiple time slots of the same TDMA frame
(multislotoperation). GPRS can combine multiple slots in a single transmission, the effective
bandwidth is increased the theoretical limit for GPRS is eight time slots. GPRS assigns a .5-
millisecond time slot to each data packet. The system is notified at the time of transmission as
to how many time slots or kbps is needed on both the sending and receiving devices. The
ability to combine only the required number of time slots for each transmission gives GPRS
the flexibility to support both low-speed and high-speed data applications in a single network.
6.1 Time Slot Aggregation
In conventional GSM, a channel is permanently allocated for a particular user during
the entire call period (whether data is transmitted or not). In contrast to this, in GPRS the
channels are only allocated when data packets are sent or received, and they are released after
the transmission. For bursty traffic this results in a much more efficient usage of the scarce
radio resources. With this principle, multiple users can share one physical channel. A cell
supporting GPRS may allocate physical channels for GPRS traffic. Such a physical channel is
denoted as packet data channel (PDCH). The PDCHs are taken from the common pool of all
channels available in the cell. Thus, the radio resources of a cell are shared by all GPRS and
non-GPRS mobile stations located in this cell. The mapping of physical channels to either
packet switched (GPRS) or circuit switched (conventional GSM) services can be performed
dynamically (capacity on demand principle, depending on the current traffic load, the priority
of the service, and the multislot class. A load supervision procedure monitors the load of the
PDCHs in the cell. According to the current demand, the number of channels allocated for
GPRS (i.e., the number of PDCHs) can be changed. Physical channels not currently in use by
conventional GSM can be allocated as PDCHs to increase the quality of service for GPRS.
When there is a resource demand for services with higher priority, PDCHs can be de-
allocated.
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6.2 Logical Channels in GPRS
On top of the physical channels, a series of logical channels are defined to perform a
multiplicity of functions, e.g., signaling, broadcast of general system information,
synchronization, channel assignment, paging, or payload transport. They can be divided into
two categories
Traffic channels Signaling (control) channels.
The packet data traffic channel (PDTCH) is employed for the transfer of user data. It is
assigned to one mobile station (or in the case of PTM to multiple mobile stations). One
mobile station can use several PDTCHs simultaneously.
The packet broadcast control channel (PBCCH) is a unidirectional point-to-multipoint
signaling channel from the base station subsystem (BSS) to the mobile stations. It is used by
the BSS to broadcast specific information about the organization of the GPRS radio network
to all GPRS mobile stations of a cell. Besides system information about GPRS, the PBCCH
should also broadcast important system information about circuit switched services, so that a
GSM/GPRS mobile station does not need to listen to the broadcast control channel (BCCH).
The packet common control channel (PCCCH) is a bidirectional point-to-multipoint
signaling channel that transports signaling information for network access management, e.g.,
for allocation of radio resources and paging. It consists of four sub-channels:
1. The packet random access channel (PRACH) is used by the mobile to request one ormore PDTCH.
2. The packet access grant channel (PAGCH) is used to allocate one or more PDTCH toa mobile station.
3. The packet paging channel (PPCH) is used by the BSS to find out the location of amobile station (paging) prior to downlink packet transmission.
4. The packet notification channel (PNCH) is used to inform a mobile station ofincoming PTM messages (multicast or group call).
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6.3 Channel Coding
Channel coding is used to protect the transmitted data packets against errors. The
channel coding technique in GPRS is quite similar to the one employed in conventional
GSM. The selection of coding schemes is transparent to the user and determines the level of
error correction the network users to send the data. The better the link is between the user and
the network, the less error correction is needed. Less error correction means higher
throughput. (Coding scheme 1 has the highest level of error correction.)
Scheme Data Rates(Kbps)
CS-1 9.05
CS-2 13.4
CS-3 16.6
CS-4 21.4
Table 3: Channel coding
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Chapter 7
GPRS SECURITY
GPRS is secure. It is an overlay on the existing GSM network. Hence it uses all
security features of the GSM network, along with its on options.
7.1 Subscriber Identity Confidentiality
The purpose of this function is to avoid an intruder to identity a subscriber on the
radio path (e.g. Traffic Channel or signaling resources) by listening to the signaling
exchanges. This function can be achieved by protecting the subscribers IMSI (International
Mobile Subscriber Index) and any signaling information elements. Therefore, a protected
identifying method should be used to identify a mobile subscriber instead of the IMSI on the
radio path. The signaling information elements that convey information about the mobile
subscriber identity must be transmitted in ciphered form. And also a ciphering method is
used.
7.2 Identifying method
The TMSI (Temporary Mobile Subscriber Index) is used in the method. Its a local
number and only valid in a given location area. The TMSI must be used together with the
LAI to avoid ambiguities. The network manages the databases (e.g. VLR) to keep the relation
between TMSIs and IMSIs. When a TMSI is received with an LAI that does not correspond
to the current VLR, the IMSI of the MS must be requested from the VLR in charge of the
indicated location area if its address is known; otherwise the IMSI is requested from the MS.
A new TMSI must be allocated in each location updating procedure. The allocation of a new
TMSI corresponds implicitly for the mobile to the de-allocation of the previous one. In the
fixed part of the network, the cancellation of the record for an MS in VLR implies the deal
location of the corresponding TMSI. When a new TMSI is allocated to an MS, it is
transmitted to the MS in a ciphered mode. The MS stores its current TMSI in a non-volatile
memory together with the LAI so that these data are not lost when the MS is switched off.
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7.3 GPRS Authentication
The GPRS authentication procedure is handled in the same way as in GSM with the
distinction that the procedures are executed in the SGSN. In some cases, the SGSN requests
the pairs for a MS from the HLR/AUC corresponding to the IMSI of the MS.
7.4 GSM confidentiality
The signaling information elements related to the user, such as IMSI, and Calling
subscriber directory number (mobile terminated or originated calls) need to be protected after
connection establishment. The user information such as short messages is transferred in a
connectionless packet mode over a signaling channel. It should be protected. And also User
information on Physical Connections (voice and non-voice communications) on traffic
channels over the radio interface should be protected. In order to achieve that confidentiality,
a ciphering method, key setting, the starting of the enciphering and deciphering processes and
synchronization are needed.
A key setting completes a process that allows the MS and the network to agree on the
key Kc using in the ciphering and deciphering algorithms .It is triggered by the authentication
procedure and initiated by the network. Key setting must occur on a DCCH not yet encryptedand soon after the identity of the mobile subscriber is known by the network.
The transmission of Kc to the MS is indirect. A Kc is generated on both sides using
the key generator algorithm A8 and the authentication process. At the network side, the
values of Kc are calculated in the AUC/HLR. At the MS side, the Kc is stored by the mobile
station until it is updated at the next authentication. The encryption of signaling and user data
is performed at the MS as well as at the BSS. This is a case called symmetric encryption, i.e.
ciphering and deciphering are performed with the same Kc and the A5 algorithm and start on
DCCH and TCH. This process can be described as follows: First, the network (i.e. BSS)
requests the MS to start its (de)ciphering process and starts its own deciphering process. The
MS then starts its ciphering and deciphering. The first ciphered message from the MS, which
reaches the network and is correctly ciphered leads to the start of the ciphering process on the
network sides. The enciphering stream at one end and deciphering stream at the other end
must be synchronized. GPRS confidentiality GPRS network still needs this security feature.
However the ciphering scope is different. The scope of GSM is between BTS and MS. The
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scope of GPRS is from the SGSN to the MS. A new ciphering algorithm GPRS-A5 is used
because of the nature of GPRS traffic. The ciphering is done in the Logical Link Control
(LLC) layer. The GPRS-Kc is handled by the SGSN independently from MSC.
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Chapter 8
GPRS CHARGING AND BILLING TECHNIQUES
As packet data is introduced into mobile systems, the question of how to bill for the
services arises. Always online and paying by the minute does not sound all that appealing.
Here, we describe the possibilities but it is totally depends on different service providers how
they want to charge their customers:
The SGSN and GGSN register all possible aspects of a GPRS user's behavior and
generate billing information accordingly. This information is gathered in so-called Charging
Data Records (CDR) and is delivered to a billing gateway.
The GPRS service charging can be based on the following parameters:
Volume: The amount of bytes transferred i.e. downloaded and uploaded. Duration: The duration of a PDP context session. Time: Date, time of day, and day of the week (enabling lower tariffs at off peak
hours).
Final destination: A subscriber could be charged for access to the specific network,such as through a proxy server.
Location The current location of the subscriber. Quality of Service: Pay more for higher network priority. SMS: The SGSN will produce specific CDRs for SMS. Served IMSI/subscriber: Different subscriber classes (different tariffs for frequent
users, businesses, or private users).
Reverse charging: The receiving subscriber is not charged for the received data;instead, the sending party is charged.
Free of charge: Specified data to be free of charge. Flat rate: A fixed monthly fee. Bearer service: Charging based on different bearer services (for an operator who has
several networks, such as GSM900 and GSM1800, and who wants to promote usage
of one of the networks). Or, perhaps the bearer service would be good for areas where
it would be cheaper for the operator to offer services from a wireless LAN rather than
from the GSM network.
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Chapter 9
LIMITATIONS/ PROBLEMS REGUARDING GPRS TECHNOLOGY
Although GPRS has many benefits there have been a few problems. Connection
speeds until the end of last year performed badly on some networks running at around
12Kbps, a far cry from the expected. This year however there do not seem to be as many
problems, probably due to the fact that operators are improving due to trial and error. GPRS
is after all a pretty new technology.
Another problem sometimes encountered is customer expectation. Many companies
have applications running on a 10 megabyte LAN and expect the same performance from
their GPRS devices. Although the connection speeds these days are pretty good it still is not
as fast as ISDN or Local Area Networks. To a certain extent operators have themselves to
blame for this, since in the past their marketing has tended to promote the speed aspects of
2.5 and 3G. Today, they are working hard to reduce expectation in this respect.
Earlier problems with things like mail servers not sending mail because of latency
problems to GPRS devices have all been pretty much eradicated through optimization
programs. People running Citrix Thin Client has also encountered problems with latency
although a few Thin Client forums suggest that Citrix are addressing the issue.
Deployment on some networks has been slow. There still is a major UK network
provider who does not offer the service.
GPRS roaming has not been implemented in many countries on a lot of networks as
yet. This is where a user can use the GPRS service from any network operator. At the
moment although your GSM mobile will work, GPRS may not work at all. Accesses by third
party application providers are having a lot of difficulty obtaining an APN from providers to
offer their own GPRS services. This somewhat limits services to that provided by the GPRS
operator.
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Chapter 10
GPRS APPLICATIONS
GPRS will enable a variety of new and unique services to the mobile wireless
subscriber. These mobile applications contain several unique characteristics that enhance the
value to the customers. First among them is mobility, the ability to maintain constant voice
and data communications while on the move. Second is immediacy, which allows subscribers
to obtain connectivity when needed, regardless of location and without a lengthy login
session. Finally, localization allows subscribers to obtain information relevant to their current
location.
Communications
Communications applications include all those in which it appears to the users that
they are using the mobile communications network purely as a pipe to access messages or
information.
Intranet Access
The first stage of enabling users to maintain contact with their office is through access
to e-mail, fax, and voice mail using unified messaging systems. Increasingly, files and data
on corporate networks are becoming accessible through corporate intranets that can be
protected through firewalls, by enabling secure tunnels.
Internet Access
As a critical mass of users is approached, more and more applications aimed at
general consumers are being placed on the Internet. The Internet is becoming an invaluable
tool for accessing corporate data as well as for the provision of product and service
information. More recently, companies have begun using the Internet as an environment for
carrying out business, through e-commerce.
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E-Mail and Fax
E-mail on mobile networks may take one of two forms. It is possible for e-mail to be
sent to a mobile user directly, or users can have an e-mail account maintained by their
network operator or their Internet service provider (ISP).
Unified Messaging
Unified messaging uses a single mailbox for all messages, including voice mail,
faxes, email, short message service (SMS), and pager messages. With the various mailboxes
in one place, unified messaging systems then allow for a variety of access methods to recover
messages of different types. Some will use text-to-voice systems to read e-mail and, less
commonly, faxes over a normal phone line, while most will allow the interrogation of the
contents of the various mailboxes through data access, such as the Internet. Others may be
configured to alert the user on the terminal type of their choice when messages are received.
Value-Added Services
Value-added services refer strictly to content provided by network operators to
increase the value of their service to their subscribers.
E-Commerce
E-commerce is defined as the carrying out of business on the Internet or data service.
This would include only those applications where a contract is established over the data
connection, such as for the purchase of goods, or services, as well as online banking
applications because of the similar requirements of user authentication and secure
transmission of sensitive data.
Banking
Specific banking functions that can be accomplished over a wireless connection
include balance checking, moving money between accounts, bill payment, and overdraft
alert.
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Location-Based Services
Location-based services provide the ability to link push or pull information services
with a users location. Examples include hotel and restaurant finders, roadside assistance, an d
city-specific news and information.
Advertising
Advertising may be offered to customers to subsidize the cost of voice or other
information services. Advertising may be location sensitive where, for example, a user
entering a mall would receive advertising specific to the stores in that mall.
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Chapter 11
CONCLUSION
In summary, GPRS presents an intermediate step in bring high speed Internet access
to GSM users as the industry moves towards implementing 3rd Generation mobile services,
known as UMTS (Universal Mobile Telephone Service). GPRS will thrive in both vertical
and horizontal markets where high-speed data transmission over wireless networks is
required. The deployment of GPRS networks will enable a plethora of new applications
ranging from mobile e-commerce to mobile corporate VPN access. Deployment of GPRS
will also have a great impact on the wireless data traffic volume by generating new sources of
revenue for the service providers, especially since any current GSM network user can
upgrade services to include high-speed data. The only question is how soon it takes off in
earnest and how to ensure that the technical and commercial features do not hinder its
widespread use.
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GLOSSARY
2G Second generation; generic name for second generation of digital
mobile networks (such as GSM, and so on)
3G Third generation; generic name for next-generation mobile networks
(Universal Mobile Telecommunications System [UMTS], IMT-2000)
BG Border gateway
BGP Border Gateway Protocol
BSC Base Station Controller
BTS Base transceiver station
CS Circuit switched
DCCH Dedicated control channel
DHCP Dynamic Host Configuration Protocol
DNS Domain Name System EDGE Enhanced data rates for GSM evolution;
upgrade to GPRS systems that require new base stations and claims to
increase bandwidth to 384 kbps
EIR Equipment Identity Register
GGSN Gateway GPRS Support Node
Gi Reference point between GPRS and an external packet data network
Gn Interface between two GSNs within the same PLMN
Gp Interface between two GSNs in different PLMNs
GPRS General Packet Radio Service; upgrade to existing 2G digital mobile
networks to provide higher-speed data services
GSM Global System for Mobile Communications; most widely deployed 2G
digital cellular mobile network standard
GSN GPRS Support Node (xGSN)
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GTP GPRS Tunneling Protocol
GW Gateway
HDLC High-Level Data Link Control
HLR Home location register
HSCSD High-speed circuit-switched data; software upgrade for cellular
networks that gives each subscriber 56K data
IMSI International Mobile Subscriber Index
IP Internet Protocol
ISP Internet service provider
LA Local Area
LLC Logical Link Control
MAC Medium Access Control
MM Mobility management
MS Mobile station
MSC Mobile services switching center
NAS Network access server
PCU Packet control unit
PDA Personal digital assistant
PDN Packet data network
PDP Packet Data Protocol
PLMN Public Land Mobile Network; generic name for all mobile wireless
networks that use earth base stations rather than satellites;
PSPDN Packet Switched Public Data Network
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PSTN Public Switched Telephone Network
PVC Permanent virtual circuit
QoS Quality of service
RADIUS Remote Authentication Dial-In User Service RLP Radio Link Protocol
SGSN Serving GPRS Support Node
SLA Service-level agreement
SMS Short message service
SMSC Short message service center
TCP Transmission Control Protocol
TCH Traffic channel
TE Terminal equipment
TDMA Time Division Multiple Access
TMSI Temporary Mobile Subscriber Index
TS Time slot
Um Interface between the MS and the GPRS fixed network part
UMTS Universal Mobile Telecommunications System
VAS Value-added services
VLR Visitor locations register
VPN Virtual private network
WAP Wireless access Protocol; important protocol stack (Layers 4 through 7
of the OSImodel), used to send simplified Web pages to wireless
devices; uses IP but replaces TCP and Hypertext Transfer Protocol
(HTTP) with UDP and WTP, and requires pages to be written in
WML rather than in HTML
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Reference
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