INPLANT TRAINING REPORT

AT MAHANAGAR TELEPHONE NIGAM LIMITED (BKC)

SUBMITTED BY

ABHISHEK KUMAR PANDEY (6th

ELECTRONICS & COMMUNICATION ENGINEERING

, B.TECH)

NATIONAL INSTITUTE OF TECHNOLOGY, SRINAGAR

FROM 27TH JANUARY 2009 TO 14TH MARCH 2009

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CONTENTS

ACKNOWLEDGEMENT

MTNL HISTORY

MOBILE TECHNOLOGY OVERVIEW

GSM NETWORK ARCHITECTURE

GPRS NETWORK ARCHITECTURE

ROAMING SERVICES IN GSM SYSTEM

CONCLUSION

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ACKNOWLEDGEMENT

The industrial exposure that I have experienced as a trainee in MAHANAGAR

TELEPHONE NIGAM LIMITED (BKC) has helped me a lot not only in improving my

theoretical knowledge but also to understand the working of a large industry.

I am sincerely grateful to the management of MAHANAGAR TELEPHONE NIGAM LIMITED

(BKC) for giving me an opportunity to undergo six weeks Inplant Training in their

organization & for providing homely atmosphere in their organization.

I would like to express my deepest gratitude towards Mr. Sandeep Keshkar (Dy. General

Manager, NSS-1, MS) for associating me in this training. I also express my sincere

gratitude & thanks to my mentor Mr.Vikalp Maurya (Asst Manager) for making timely

guidance and encouraging me at various stages during my training. He also helped me a

lot on my personal front as far as my studies were concerned, by giving me tips to

improve my performance. My experience with him as his subordinate is memorable.

I am also thankful to Mrs. J.Wilson(SDE) and Mr. A.G.Pal(SDE) for their positive support,

coordination & guidance.

And last but not the least I thank all the people of the department, for their kind co-

operation and support.

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MTNL HISTORY

Mahanagar Telephone Nigam Limited is an Indian

Government-owned telephone service provider in

the cities of Mumbai, Thane, New Delhi, and Navi

Mumbai in India. The company was a monopoly

until 2000, when the telecom sector was thrown

open to other service providers.

MTNL provides fixed line telephones, cellular connection of both GSM — Dolphin

(Postpaid) and Trump (prepaid) and WLL (CDMA) — Garuda-FW and Garuda-Mobile and

internet services through dialup and DSL — Broadband internet TriBand. MTNL has also

started Games on demand, video on demand and IPTV services in India through its

Broadband Internet service called Triband. Phone numbers belonging to MTNL start with

the prefix 2 infixed line telephones and WLL & in GSM Mobile services its start from

9869/9969/9868/9968/9757. MTNL also provides other services such as VPN, Internet

Telephony- VOIP and leased lines through BSNL and VSNL.MTNL has been actively

providing connections in both Mumbai and New Delhi areas and the efficiency of the

company has drastically improved from the days when one had to wait years to get a

phone connection to now when one can get a connection in even hours. Pre-activated

Mobile connections are available at many places across both Metros. MTNL has also

unveiled very cost-effective Broadband Internet access plans (TriBand) targeted at

homes and small businesses. At present MTNL enjoys the largest of the market share of

ISP services in Mumbai and Delhi.

With the market opened to competition in 2001, MTNL has been facing rivalry for its

share of the market and declining long-distance call rates. To diversify its revenue base,

the cash rich company has expanded into GSM and CDMA cellular services and is

developing its Internet related services, including ADSL, Intelligent Network services, call

centers and IDCs. The company is expanding beyond its traditional areas to offer

Internet services nationwide, and to provide basic services in Nepal. MTNL is considered

a likely candidate for further divestment by the government.

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MOBILE

TECHNOLOGY OVERVIEW

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Introduction

One of the finest things that happened in 20th century is the use of radio channels for

personal mobile communication systems. Considered to be a revolution of sorts in

telecommunications, mobile communication is the fastest growing market segment and

the field of intense research. Mobile communication today is, perhaps, the most

powerful catalyst for change in lifestyle of the people all over the world. Mobile

communication slowly, but surely is evolving as the backbone for business transactions,

efficiency and success silently taking over the role of the elder cousin PSTN.

Basic to the design of a mobile communication system is the ability of the user to

liberate himself from the confines of a wired line and therefore his freedom to move

anywhere he wants. Mobile communication systems therefore are required to provide

seamless service while the customers are on move transcending geographical and

network borders. Provision of service under such environment throws a number of

challenging issues and the way these issues are addressed and resolved makes each

system different from all others.

The first mobile telephone service started in 1946 in St. Louis, Missouri, USA as a

manually operated system. Between 1950 and 1960, it evolved as an automatic system,

but small subscriber base. Mobile telephony service in its useful form appeared in

1960s.

The 1st generation mobile communication systems appeared in 1970s and remained till

1980s. They used analog transmission techniques for the radio link and confined its

users to their respective system areas for which the mobile phone was designed.

Capacity of the system was very limited and roaming between the coverage areas of the

different systems was impossible. Apart from being very expensive, these systems

provided poor QoS and supported only voice communication.

The 2nd generation mobile communication systems grew out of the limitations of the

1st generation systems. They supported large subscriber base, carried both voice and

data and have capability to design and deliver new value added services (VAS). The radio

link became digital enabling use of versatile signaling capabilities and cross-network

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roaming. However, multiple standards made seamless roaming across all the networks

impossible. GSM and CDMA emerged as the trend setting technologies. The domination

of the 2G systems in the mobile communication market became apparent in second half

of 1990s.

The design objectives of the 3rd generation mobile systems are to provide high

functionality with seamless global roaming. Apart from providing very high data rates,

3G systems seek to integrate the wire lines systems with mobile systems. 3G would

provide users consistent voice, data, graphical, multi-media and video-based

information service regardless of their location in the network (Cordless, Cellular,

Satellite, Fixed/Wire line and so on….). The 3G system is an I.P. based system. 3G

systems would also integrate the Intelligent Network (IN) capabilities into mobile

systems.

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2G

2G (or 2-G) is short for second-generation wireless telephone technology. Second

generation 2G cellular telecom networks were commercially launched on the GSM

standard in Finland by Radiolinja (now part of Elisa Oyj) in 1991. Three primary benefits

of 2G networks over their predecessors were that phone conversations were digitally

encrypted, 2G systems were significantly more efficient on the spectrum allowing for far

greater mobile phone penetration levels; and 2G introduced data services for mobile,

starting with SMS text messages.

After 2G was launched, the previous mobile telephone systems were retrospectively

dubbed 1G. While radio signals on 1G networks are analog, and on 2G networks are

digital, both systems use digital signaling to connect the radio towers (which listen to

the handsets) to the rest of the telephone system.

2G technologies

2G technologies can be divided into TDMA-based and CDMA-based standards depending

on the type of multiplexing used. The main 2G standards are:

GSM (TDMA-based), originally from Europe but used in almost all countries on all six

inhabited continents (Time Division Multiple Access). Today accounts for over 80% of all

subscribers around the world.

IS-95 aka cdmaOne, (CDMA-based, commonly referred as simply CDMA in the US), used

in the Americas and parts of Asia. Today accounts for about 17% of all subscribers

globally. Over a dozen CDMA operators have migrated to GSM including operators in

Mexico, India, Australia and South Korea.

PDC (TDMA-based), used exclusively in Japan

iDEN (TDMA-based), proprietary network used by Nextel in the United States and Telus

Mobility in Canada

IS-136 aka D-AMPS, (TDMA-based, simply TDMA in the US), was once prevalent in the

Americas but most have migrated to GSM.

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Capacity

Using digital signals between the handsets and the towers increases system capacity in

two key ways:

Digital voice data can be compressed and multiplexed much more effectively than

analog voice encodings through the use of various codecs, allowing more calls to be

packed into the same amount of radio bandwidth.

The digital systems were designed to emit less radio power from the handsets. This

meant that cells could be smaller, so more cells could be placed in the same amount

of space. This was also made possible by cell towers and related equipment getting

less expensive.

Advantages

Digital systems were embraced by consumers for several reasons.

The lower powered radio signals require less battery power, so phones last much

longer between charges, and batteries can be smaller.

The digital voice encoding allowed digital error checking which could increase sound

quality by increasing dynamic range and lowering the noise floor.

The lower power emissions helped address health concerns.

Going all-digital allowed introduction of digital data services, such as SMS and

email.

Greatly reduced fraud. With analog systems it was possible to have two or more

"cloned" handsets that had the same phone number.

Enhanced privacy. A key digital advantage not often mentioned is that digital

cellular calls are much harder to eavesdrop on by use of radio scanners. While the

security algorithms used have proved not to be as secure as initially advertised, 2G

phones are immensely more private than 1G phones, which have no protection

against eavesdropping.

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Disadvantages

The downsides of 2G systems, not often well publicized, are:

• In less populous areas, the weaker digital signal may not be sufficient to reach a cell

tower. This tends to be a particular problem on 2G systems deployed on higher

frequencies, but is mostly not a problem on 2G systems deployed on lower

frequencies. National regulations differ greatly among countries which dictate

where 2G can be deployed.

• Analog has a smooth decay curve, digital a jagged steppy one. This can be both an

advantage and a disadvantage. Under good conditions, digital will sound better.

Under slightly worse conditions, analog will experience static, while digital has

occasional dropouts. As conditions worsen, though, digital will start to completely

fail, by dropping calls or being unintelligible, while analog slowly gets worse,

generally holding a call longer and allowing at least a few words to get through.

• While digital calls tend to be free of static and background noise, the lossy

compression used by the codecs takes a toll; the range of sound that they convey is

reduced. You'll hear less of the tonality of someone's voice talking on a digital

cellphone, but you will hear it more clearly.

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GSM

GSM (Global System for Mobile communications:

originally from Groupe Spécial Mobile) is the most

popular standard for mobile phones in the world. Its

promoter, the GSM Association, estimates that 80% of

the global mobile market uses the standard. GSM is used by over 3 billion people across

more than 212 countries and territories. Its ubiquity makes international roaming very

common between mobile phone operators, enabling subscribers to use their phones in

many parts of the world. GSM differs from its predecessors in that both signaling and

speech channels are digital, and thus is considered a second generation (2G) mobile

phone system. This has also meant that data communication was easy to build into the

system.

The ubiquity of the GSM standard has been an advantage to both consumers (who

benefit from the ability to roam and switch carriers without switching phones) and also

to network operators (who can choose equipment from any of the many vendors

implementing GSM). GSM also pioneered a low-cost (to the network carrier) alternative

to voice calls, the Short message service (SMS, also called "text messaging"), which is

now supported on other mobile standards as well. Another advantage is that the

standard includes one worldwide Emergency telephone number, 112. This makes it

easier for international travellers to connect to emergency services without knowing the

local emergency number.

GSM security

GSM was designed with a moderate level of security. The system was designed to

authenticate the subscriber using a pre-shared key and challenge-response.

Communications between the subscriber and the base station can be encrypted. GSM

only authenticates the user to the network (and not vice versa). The security model

therefore offers confidentiality and authentication, but limited authorization

capabilities, and no non-repudiation. GSM uses several cryptographic algorithms for

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security. The A5/1 and A5/2 stream ciphers are used for ensuring over-the-air voice

privacy.

Advantages of GSM

GSM uses radio frequencies efficiently and, because of the digital radio path, the

system tolerates more inter cell disturbances.

The average quality of speech achieved is better than that in existing analogue

systems.

Data transmission is supported throughout the system.

Speech is encrypted and subscriber information security is guaranteed.

Due to ISDN compatibility, new services are offered as compared to the analogue

systems.

International roaming is technically possible within all the countries concerned.

The large market toughens the competition and lowers the prices both for

investments and usage.

GSM Frequencies

GSM networks operate in a number of different frequency ranges (separated into GSM

frequency ranges for 2G and UMTS frequency bands for 3G). Most 2G GSM networks

operate in the 900 MHz or 1800 MHz bands. Some countries in the Americas (including

Canada and the United States) use the 850 MHz and 1900 MHz bands because the 900

and 1800 MHz frequency bands were already allocated. Most 3G GSM networks in

Europe operate in the 2100 MHz frequency band

GSM-900 uses 890–915 MHz to send information from the mobile station to the base

station (uplink) and 935–960 MHz for the other direction (downlink), providing 124 RF

channels (channel numbers 1 to 124) spaced at 200 kHz. Duplex spacing of 45 MHz is

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used. This band of frequencies may be allocated equally for up to 4 operators in a

telecom circle.

To achieve a high spectral efficiency in the cellular network a combination of FDMA

(Frequency Division Multiple Access) and TDMA (Time Division Multiple Access) is used.

The FDMA part involves the division by frequency of the 25 MHz bandwidth into 124

carrier frequencies spaced at 200 KHz for GSM-900. For GSM-18OO the frequency

spectrum of the 75 MHz bandwidth is divided into 374 carrier frequencies spaced at 200

KHz. One or more frequencies are assigned to each BTS. Each of these carrier

frequencies is then divided in time, using a TDMA scheme to increase the number of

channels per carrier. Each carrier frequency channel carries eight time-division

multiplexed physical channels.

FREQUENCY RANGE GSM 900 GSM 1800 GSM 1900

Uplink Freq. 935-960 MHz 1710-1785 MHz 1850-1910 MHz

Downlink Freq. 935-960 MHz 1805-1880 MHz 1930-1990 MHz

Channel Spacing 200 KHz 200 KHz 200 KHz

No. of Channels 124 374 299

Duplex Spacing 45 MHz 95 MHz 80 MHz

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Evolution from 2G to 3G

From 2G to 2.5G (GPRS) The first major step in the evolution to 3G occurred

with the introduction of General Packet Radio Service (GPRS). So the cellular services

combined with GPRS became 2.5G.GPRS could provide data rates from 56 Kbit/s up to

114 Kbit/s. It can be used for services such as Wireless Application Protocol (WAP)

access, Short Message Service (SMS), Multimedia Messaging Service (MMS), and for

Internet communication services such as email and World Wide Web access. GPRS data

transfer is typically charged per megabyte of traffic transferred, while data

communication via traditional circuit switching is billed per minute of connection time,

independent of whether the user actually is utilizing the capacity or is in an idle state.

From 2.5G to 2.75G GPRS networks evolved to EDGE networks with

introduction of 8PSK encoding. Enhanced Data rates for GSM Evolution (EDGE),

Enhanced GPRS (EGPRS), or IMT Single Carrier (IMT-SC) is backward-compatible digital

mobile phone technology that allows improved data transmission rates, as an extension

on top of standard GSM. EDGE can be considered a 3G radio technology and is part of

ITU's 3G definition, but is most frequently referred to as 2.75G.

EDGE is standardized by 3GPP as part of the GSM family, and it is an upgrade that

provides a potential three-fold increase in capacity of GSM/GPRS networks. The

specification achieves higher data-rates by switching to more sophisticated methods of

coding (8PSK), within existing GSM timeslots. EDGE can be used for any packet switched

application, such as an Internet, video and other multimedia.

From 2.75G to 3G From EDGE networks the introduction of UMTS networks

and technology is called pure 3G. 3G Bandwidth 5 MHz

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GSM

NETWORK ARCHITECTURE

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Network structure

The network behind the GSM seen by the customer is large and complicated in order to

provide all of the services which are required. It is divided into a number of sections and

these are each covered in separate articles.

The Base Station Subsystem

The

(the base stations and their controllers).

Network and Switching Subsystem

The

(the part of the network most similar to a

fixed network). This is sometimes also just called the core network.

GPRS Core Network

All of the elements in the system combine to produce many GSM services such as voice

calls and SMS.

(the optional part which allows packet based Internet

connections).

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MOBILE STATION (MS)

The MS consist of two parts, the Mobile Equipment (ME) and an electronic smart card

called as Subscriber Identity Module (SIM).

The ME is the hardware used by the subscriber to access the network. The hardware has

an identity number associated with it, which is unique for that particular device and

permanently stored in it. This identity number is called the International Mobile

Equipment Identity (IMEI) and enables the network operator to identity mobile

equipment which may be causing problems on the system.

The SIM is a card which plugs into the ME. This card identifies the MS subscriber and

also provides other information regarding the service that subscriber should receive.

The subscriber is identified by an identity number called the International Mobile

Subscriber Identity (IMSI).

Mobile Equipment may be purchased from any store but the SIM must be obtained from

the GSM network provider. Without the SIM inserted, the ME will only be able to make

emergency calls. By making a distinction between the subscriber identity, GSM can

route calls and perform billing based on the identity of the subscriber rather than the

equipment or its location.

1. MOBILE EQUIPMENT (ME)

The ME is the only part of the GSM network which the subscribers really see. There are

three main type of ME, these are listed below:

• Vehicle Mounted: These devices are mounted in a vehicle and the antenna is

physically mounted on the outside of the vehicle.

• Portable Mobile Unit: This equipment can be handheld when in operation, but

the antenna is not connected to the handset of the unit.

• Hand portable Unit: This element comprises of a small telephone handset not

much bigger than a calculator. The antenna is connected to the handset.

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The ME is capable of operating at a certain maximum power output dependent on its

type and use. These mobile types have distinct features which must be known by the

network, for example their maximum transmission power and the services they support.

The ME is therefore identified by means of classmark. The classmark is sent by the ME in

its initial message.

2. SUBSCRIBER IDENTITY MODULE (SIM)

The SIM as mentioned previously is a "Smart Card"

which plugs into the ME and contains information

about the MS subscriber hence the name subscriber

Identity Module.

Most of the data contained within the SIM is protected against reading (KI) or

alternations (IMSI). Some of the parameters (LAI) will be continuously updated to reflect

the current location of the subscriber.

The SIM card and the high degree of inbuilt system security provide protection of the

subscriber's information and protection of networks against fraudulent access. SIM

cards are designed to be difficult to duplicate. The SIM can be protected by use of

Personal Identity Number (PIN) password, similar to bank/credit charge cards, to

prevent unauthorized use of the card. The SIM is capable of storing additional such as

accumulated call charges. This information will be accessible to the customer via

handset/keyboard key entry. The SIM also executes the Authentication Algorithm.

The SIM contains several pieces of information:

International Mobile Subscriber Identity (IMSI)

Temporary Mobile Subscriber Identity (TMSI)

Location Area Identity (LAI)

Mobile Station International Services Digital Network (MSISDN)

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Subscriber Authentication Key (Ki)

A3(Authentication Algorithm)

A8 (Cipher Key (Kc)

A5 (Encryption Algorithm)

Functions of MS

The primary functions of MS are to transmit and receive voice and data over the air

interface of the GSM system. MS performs the signal processing function of digitizing,

encoding, error protecting, encrypting, and modulating the transmitted signals. It also

performs the inverse functions on the received signals from the BS.

In order to transmit voice and data signals, the mobile must be in synchronization with

the system so that the messages are the transmitted and received by the mobile at the

correct instant. To achieve this, the MS automatically tunes and synchronizes to the

frequency and TDMA timeslot specified by the BSC. This message is received over a

dedicated timeslot several times within a multi frame period of 51 frames. The exact

synchronization will also include adjusting the timing advance to compensate for varying

distance of the mobile from the BTS.

MS keeps the GSM network informed of its location during both national and

international roaming, even when it is inactive. This enables the System to page in its

present LA.

Finally, the MS can store and display short received alphanumeric messages on the

liquid crystal display (LCD) that is used to show call dialing and status in formation.

These messages are limited to 160 characters in length (varies from mobile to mobile).

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Mobile Station ISDN (MSISDN)

MSISDN Stands for Mobile Station international Subscriber Dialing Number. It is a Logical

Identity. The MS international number must be dialed after the international prefix in

order to obtain a mobile subscriber in another country. The MSISDN numbers is

composed of the country code (CC) followed by the National Destination Code (NDC),

Subscriber Number (SN), which shall not exceed 15 digits. Here too the first two digits of

the SN identify the HLR where the mobile subscriber is administrated. MSISDN must be

registered in the telephone directory. It is used by the calling party for dialing. It is used

to support Call routing to destination terminal or to the MSC/HLR of the called MS.

International Mobile Subscriber Identity (IMSI)

IMSI stands for International Mobile Subscriber Identity. It is the Software Identity. An

IMSI is assigned to each authorized GSM user. It consists of a mobile country code

(MCC), mobile network code (MNC) (to identify the PLMN), and a PLMN unique mobile

subscriber identification number (MSIN) and shall not exceed 15 digits. The IMSI is the

only absolute identity that a subscriber has within the GSM system. It is used in the case

of system-internal signaling transactions in order to identify a subscriber. The first two

digits of the MSIN identify the HLR where the mobile subscriber is administrated.

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International Mobile Equipment Identity (IMEI)

IMEI stands for International Mobile Equipment Identity. It is the Hardware Identity. The

IMEI is the unique identity of the equipment used by a subscriber by each PLMN and is

used to determine authorized (white), unauthorized (black), and malfunctioning (gray)

GSM hardware. In conjunction with the IMSI, it is used to ensure that only authorized

users are granted access to the system.

Temporary Mobile Subscriber Identity (TMSI)

It is used for identification & addressing of the visiting MS. The VLR assigns a TMSI to

each subscriber entering into VLR area. It is assigned only after successful subscriber

authentication. The correlation of a TMSI to an IMSI only occurs during a mobile

subscriber’s initial transaction with an MSC (for example, location updating). TMSI is

stored in MS’s SIM and VLR and is not stored in HLR.

The Mobile Station Roaming Number (MSRN)

The MSRN is allocated on temporary basis when the MS roams into another numbering

area. The MSRN number is used by the HLR for rerouting calls to the MS. It is assigned

upon demand by the HLR on a per-call basis. The MSRN for PSTN/ISDN routing shall have

the same structure as international ISDN numbers in the area in which the MSRN is

allocated. The HLR knows in what MSC/VLR service area the subscriber is located. At the

reception of the MSRN, HLR sends it to the GMSC, which can now route the call to the

MSC/VLR exchange where the called subscriber is currently registered.

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BASE STATION SUBSYSTEM (BSS)

The base station subsystem (BSS) is the section of a traditional cellular telephone

network which is responsible for handling traffic and signaling between a mobile phone

and the network switching subsystem. The BSS carries out transcoding of speech

channels, allocation of radio channels to mobile phones, paging, quality management of

transmission and reception over the air interface and many other tasks related to the

radio network.

Base transceiver station (BTS): The BTS contains the RF components that provide

the air interface for a particular cell. This is the part of the GSM network which

communicates with the MS. The antenna is included as part of the BTS.

Base station controller (BSC): The BSC as its name implies provides the

control for the BSS. The BSC communicates directly with the MSC. The BSC may control

single or multiple BTSs.

Transcoder (XCDR): The Transcoder is used to compact the signals from the MS

so that they are more efficiently sent over the terrestrial interfaces. Although the

transcoder is considered to be a part of the BSS, it is very often located closer to the

MSC. The transcoder is used to reduce the rate at which the traffic (voice/data) is

transmitted over the air interface. Although the transcoder is part of the BSS, it is often

found physically closer to the NSS to allow more efficient use of the terrestrial links.

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CELL PRINCIPLES

Cellular networks have many advantages ewer the

existing land telephones networks. A cellular

telephone system links Mobile Station (MS) subscriber

into the PSTN system on to another MS subscriber. MS

and cellular networks uses radio communication, due to this

MS is able to move around and become fully mobile.

MS within the cellular network are located in "CELLS", these cells are provided by the

BSS. Each BSS can provide one or more cells, dependent on the manufacturer’s

equipment. The cells are normally represented by a hexagon, but in practice they are

irregular in shape. This is as a result of the influence of the surrounding terrain, or of

design by the network planners.

Frequency reuse

The increased capacity in a

cellular network, compared

with a network with a single

transmitter, comes from the

fact that the same radio

frequency can be reused in a

different area for a completely

different transmission. If there

is a single plain transmitter, only one transmission can be used on any given frequency.

Unfortunately, there is inevitably some level of interference from the signal from the

other cells which use the same frequency. This means that, in a standard FDMA system,

there must be at least a one cell gap between cells which reuse the same frequency.

Depending on the size of the city, a taxi system may not have any frequency-reuse in its

own city, but certainly in other nearby cities, the same frequency can be used. In a big

city, on the other hand, frequency-reuse could certainly be in use.

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NETWORK SWITCHING SYSTEM (NSS)

The network switching system

includes the main switching

functions of the GSM network. It

also contains the database

required for subscriber data and

mobility management. It’s main

function is to manage

communication between the GSM

network and other

telecommunication network.

The components of network switching system are listed below:

1.

Mobile Services Switching Centre (MSC)

The MSC is included in the GSM system for call switching. Its overall purpose is the same

as that of any telephone exchange. However, because of the addition complications

involved in the control and security aspects of the GSM cellular system and the wide

range of subscriber facilities that it offers, the MSC has to be capable of fulfilling many

additional functions.

The MSC will carry out several different functions depending upon its position in the

network. When the MSC provides the interface between the PSTN and BSSs in the GSM

network it will be known as a gateway MSC. In this position it will provide the switching

required for all MS originated or terminated traffic.

Each MSC provides service to MSs located within a defined geographic coverage area,

the network typically contains more than one MSC. One MSC is capable of supporting a

regional capital with approximately one million inhabitants. An MSC of this size will be

contained in about half a dozen racks.

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The functions carried out by the MSC are listed below:

• Call Processing

• Operations and Maintenance Support

• Internetwork Interworking

• Billing

2.

• Subscriber ID ( IMSI and MSISDN)

Home Location Registers (HLR)

The HLR is the reference database for subscriber parameters. Various identification

numbers and addresses are stored as well as authentication parameters. Thos

information is entered into the database by the network provider when new subscriber

added to the system. The parameters stored in the HLR are listed opposite:

• Current subscriber VLR (current location)

• Supplementary services subscribed to

• Supplementary service information ( e.g. current forwarding number)

• Subscriber status ( registered/deregistered)

• Authentication key and AUC functionality

• Mobile Subscriber Roaming Number

The HLR database contains the master database of all the subscribers to a GSM PLMN.

The data it contains is remotely accessed by all the MSCs and the VLRs in the network

and although the network may contain more than one HLR, there is only one database

record per subscriber each HLR is therefore handling a portion of the total subscriber

database. The subscriber data may be accessed by either the IMSI or the MSISDN

Number. The data can also be accessed by MSC or a VLR in a different PLMN, to allow

intersystem and inter country roaming.

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3.

• Mobile status (busy. free, no answer etc)

Visitor Locations Register (VLR)

The VLR contains a copy of most of the data stored at the HLR. It is however temporary

data which exists for only as long as the subscriber is “Active” in the particular area

covered by VLR. The VLR database will therefore contain some duplicate data as well as

more precise data relevant to the subscriber remaining within the VLR coverage.

The VLR provides a local database for the subscriber wherever they are physically

located within a PLMN; this may or may not be the home system. This function

eliminates the need for excessive and time consuming reference to the "home" HLR

database.

The additional data stored in the VLR is listed below:

• Location Area Identity (LAI)

• Temporary Mobile Subscriber Identity (TMSI)

• Mobile Station Roaming Number

4.

White list: Contains those IMEIs which are known to have been assigned to valid MS

equipment.

Equipment Identity Registers (EIR)

The EIR contains A centralized database for validity the international mobile equipment

identity (IMEI). This database is concerned solely with MS equipment and not with the

subscriber who is using it to make or receive a call. The EIR database consists of lists of

IMEIs (or ranges of IMEIs) organized as follows:

Black list: Contains IMEIs of MS which have been reported stolen or which are to be

denied service for some other reason.

Grey list: Contains IMEIs of MS which have problems (for example, faulty software).

These are not, however, sufficiently significant to warrant a "black listing".

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The EIR database is remotely accessed by the MSCs in the network and can also be

accessed by an MSC in a different PLMN.As in the case of the HLR; a network may well

contain more than one EIR with each EIR controlling certain blocks of IMIE numbers. The

MSC contains a translation facility, which when given an IMEI, returns the address of the

EIR controlling the appropriate section of the equipment database.

5. Authentication Center

Authentication Procedure

(AUC)

The AUC is a processor system; it performs the "Authentication" function. It will be co-

located with the Home Location Register (HLR) as it will be required to continuously

access and update, as necessary, the system subscriber records. The AUC/HLR center

can be co-located with the MSC or located remote from the MSC. The authentication

process will be usually take place each time the subscriber "initializes" on the system.

When a new subscription is

registered in GSM, the mobile is

given a subscriber authentication

key (Ki) and a telephone number,

or international mobile

subscriber identity (IMSI), which

are used in the network to

identify the mobile. The Ki and IMSI are stored both in the mobile and in a special

network element called AUC. The AUC uses the Ki and IMSI to calculate an identification

parameter called signal response (SRES). SRES is calculated as a function of Ki and a

random number (RAND) generated by the AUC. RAND and SRES are then stored in the

HLR for use in set-up procedures.

Set-up or registration will not be accepted until authentication has been performed.

Using the mobile's IMSI, the MSC fetches the corresponding RAND and SRES from the

HLR. RAND is sent to the mobile, which uses its stored Ki value to calculate SRES. It then

returns the calculated SRES to the MSC, where it is compared with the SRES value

28

received from the HLR. If the values tally, the set-up is accepted; if not, set-up is

rejected.

6.

In many real life implementations, the MSC functionality and the GMSC functionality are

implemented in the same equipment, which is then just called MSC. Many operators use

GMSCs for breakout to external networks such as PSTNs.

Gateway Mobile services Switching Centre (GMSC)

The GMSC is responsible for the same tasks as the MSC, except for paging. It is needed

in case of mobile terminated calls. In fixed networks, a call is established to the local

exchange, to which the telephone is connected. But in GSM, the MSC, which is serving

the MS, changes with the subscriber’s mobility. Therefore, in a mobile terminated call,

the call is set up to a well defined exchange in the subscriber’s home PLMN. This

exchange is called GMSC. The GMSC than interacts with a database called Home

Location Register, which holds the information about the MSC, which is currently serving

the MS. The process of requesting location information from the HLR is called HLR

Interrogation. Given the information about the serving MSC, the GMSC then continues

the call establishment process.

29

GSM TELECOMMUNICATION SERVICES

The ETSI Standards define the telecommunication services. With D900/D1800 the GSM

telecommunication services offered to the GSM subscriber are subdivided as follows:

• Bearer services (for data only)

• Tele-services (for voice and data)

• Supplementary services

Bearer services and tele-services are also called basic telecommunication services. The

use of GSM telecommunication services is subject to subscription. A basic subscription

permits participation in those GSM telecommunication services that are generally

available.

If a GSM subscriber roams out of the entitled area there is no possibility of establishing

communication (roaming not allowed), except the use of the tele-service emergency

call.

Bearer Services

The bearer services are pure transport services for data. Some of the transmission

modes and rates already used in modern data networks are implemented; others are

planned.

The following, already implemented, bearer services provide unrestricted information

transfer between the reference points in the mobile stations.

Bearer services are telecommunication services providing the

capability of transmission of signals between access points. The bearer services describe

what the network can offer (e.g. speech, data and fax).

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• Data CDA (circuit duplex asynchronous) + basic PAD (packet assembler

Disassembler)

• Data CDS (circuit duplex synchronous)

• PAD CDA (dedicated PAD access)

• Alternate speech/data CDA (circuit duplex asynchronous)

• Speech followed by data CDA (circuit duplex asynchronous)

• Data compression on the GSM radio interface

Tele-services Teleservices are telecommunication services including terminal

equipment functions, which provide communication between users according to

protocols established by agreement between network operators. The teleservices are

user end-to-end services (e.g. emergency call and short message service).

Tele-services use both low layer and high layer functions for the control of

communication from terminal to terminal. The following tele- services have already

been realized:

• Telephony

• Emergency call

• Short message service (SMS)

• Short message cell broadcast

• Automatic facsimile (group 3)

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Supplementary Services

• Number Identification Services

Supplementary Services modify or supplement a basic

telecommunication service. Consequently, they cannot be offered to a customer as a

stand-alone service. They must be offered together or in association with a basic

telecommunication service. The same supplementary service may be applicable to a

number of telecommunication services. Most supplementary services are directly

inherited from a fixed network, with minor modifications (when needed) to adapt to

mobility. Supplementary services extend beyond the normal bearer services and tele-

services (basic telecommunication services) and can be subscribed to separately. In the

following a supplementary service is called simply service, in contrast to basic

telecommunication service.

♦ Calling line identification presentation (CLIP)

♦ Calling line identification restriction (CLIR)

• Call Offering Services

♦ Call forwarding unconditional (CFU)

♦ Call forwarding on mobile subscriber busy (CFB)

♦ Call forwarding on no reply (CFNRy)

♦ Call forwarding on mobile subscriber not reachable (CFNRc)

• Call Completion Services

♦ Call hold

♦ Call waiting (CW)

• Multi-Party Service

• Charging Services

♦ Advice of charge (AOC)

• Call Restriction Services

♦ Barring of all outgoing calls (BAOC)

♦ Barring of all outgoing international calls (BOIC)

♦ Barring of all outgoing international calls except to home PLMN country (BOICexHC)

♦ Barring of all incoming calls (BAIC)

♦ Barring of all incoming calls when roaming outside home PLMN country (BIC Roam)

♦ Closed User Group (CUG)

32

ACCESSING A GSM NETWORK

In order to gain access to GSM services, a user needs three things:

A subscription with a mobile phone operator. This is usually either a Pay As You Go

arrangement, where all GSM services are paid for in advance (commercially called

"prepaid"), or a Pay Monthly option where a bill is issued each month for line rental,

normally paid for a month in advance, and for services used in the previous month

(commercially called "postpaid").

A mobile phone which is GSM compliant and operates at the same frequency as the

operator. Most phone companies sell phones from third-party manufacturers.

A SIM ("Subscriber Identity Module") card which is activated by the operator once

the subscription is granted. After activation the card is then programmed with the

subscriber's MSISDN ("Mobile Subscriber Integrated Services Digital Network

Number") (the telephone number). Personal information such as contact numbers

of friends and family can also be stored on the SIM by the subscriber.

After subscribers sign up, information about their identity (telephone number) and what

services they are allowed to access are stored in a "SIM record" in the Home Location

Register (HLR).

Once the SIM card is loaded into the phone and the phone is powered on, it will search

for the nearest mobile phone mast, also called a Base Transceiver Station or BTS. If a

mast can be successfully contacted, then there is said to be coverage in the area.

The key feature of a mobile phone is the ability to receive and make calls in any area

where coverage is available. This is generally called roaming from a customer

perspective, but also called visiting when describing the underlying technical process.

Each geographic area has a database called the Visitor Location Register (VLR) which

contains details of all the mobiles currently in that area. Whenever a phone attaches, or

visits, a new area, the Visitor Location Register must contact the Home Location Register

to obtain the details for that phone. The current cellular location of the phone (i.e.

33

which BTS it is at) is entered into the VLR record and will be used during a process called

paging when the GSM network wishes to locate the mobile phone.

Every SIM card contains a secret key, called the Ki, which is used to provide

authentication and encryption services. This is useful to prevent theft of service, and

also to prevent "over the air" snooping of a users activity. The network does this by

utilizing the Authentication Center and is accomplished without transmitting the key

directly.

Every GSM phone contains a unique identifier (different from the phone number), called

the International Mobile Equipment Identity (IMEI). This can be found by dialing " *#06#

". When a phone contacts the network, its IMEI may be checked against the Equipment

Identity Register to locate stolen phones and facilitate monitoring.

34

VOICE CALLS

How outgoing calls are made from a mobile

Once a mobile phone has successfully attached to a GSM network as described above,

calls may be made from the phone to any other phone on the global Public Switched

Telephone Network.

The users dials the telephone number, presses the send or talk key, and the mobile

phone sends a call setup request message to the mobile phone network via the nearest

mobile phone mast (BTS).

The call setup request message is handled next by the Mobile Switching Center, which

checks the subscriber's record held in the Visitor Location Register to see if the outgoing

call is allowed. If so, the MSC then routes the call in the same way that a telephone

exchange does in a fixed network.

If the subscriber is on a Pay As You Go tariff (sometimes known as Prepaid (for example,

in Australia and India)), then an additional check is made to see if the subscriber has

enough credit to proceed. If not, the call is rejected. If the call is allowed to continue,

then it is continually monitored and the appropriate amount is decremented from the

subscriber's account. When the credit reaches zero, the call is cut off by the network.

The systems that monitor and provide the prepaid services are not part of the GSM

standard services, but instead an example of intelligent network services that a mobile

phone operator may decide to implement in addition to the standard GSM ones.

35

How incoming calls are made to a mobile

Step One: Contact the Gateway MSC

When someone places a call to a mobile phone, they dial the telephone number (also

called a MSISDN) associated with the phone user and the call is routed to the mobile

phone operator's Gateway Mobile Switching Centre. The Gateway MSC, as the name

suggests, acts as the "entrance" from exterior portions of the Public Switched Telephone

Network onto the provider's network.

As noted above, the phone is free to roam anywhere in the operator's network or on the

networks of roaming partners, including in other countries. So the first job of the

Gateway MSC is to determine the current location of the mobile phone in order to

connect the call. It does this by consulting the Home Location Register (HLR), which, as

described above, knows which Visitor Location Register (VLR) the phone is associated

with, if any.

Finally, if the Home Location Register knows that the phone is roaming in a particular

Visited Location Register area, then it will request a temporary number (called an MSRN)

Step Two: Determine how to route the call

When the HLR receives this query message, it determines whether the call should be

routed to another number (called a divert), or if it is to be routed directly to the mobile.

If the owner of the phone has previously requested that all incoming calls be diverted to

another number, known as the Call Forward Unconditional (CFU) Number, then this

number is stored in the Home Location Register. If that is the case, then the CFU number

is returned to the Gateway MSC for immediate routing to that destination.

If the mobile phone is not currently associated with a Visited Location Register (because

the phone has been turned off) then the Home Location Register returns a number

known as the Call Forward Not Reachable (CFNRc) number to the Gateway MSC, and the

call is forwarded there. Many operators may set this value automatically to the phone's

voice mail number, so that callers may leave a message. The mobile phone may

sometimes override the default setting.

36

from that VLR. This number is relayed back to the Gateway MSC, and then used to route

the call to the MSC where the called phone is roaming.

Step Three: Ringing the phone

When the call arrives at the Visiting MSC, the MSRN is used to determine which phone is

being called. The MSC then pages all the mobile phone masts in the area in order to

inform the phone that there is an incoming call for it. If the subscriber answers, a speech

path is created through the Visiting MSC and Gateway MSC back to the network of the

person making the call, and a normal telephone call follows.

It is also possible that the phone call is not answered. If the subscriber is busy on

another call (and call waiting is not being used) the Visited MSC routes the call to a pre-

determined Call Forward Busy (CFB) number. Similarly, if the subscriber does not answer

the call after a period of time (typically 30 seconds) then the Visited MSC routes the call

to a pre-determined Call Forward No Reply (CFNRy) number. Once again, the operator

may decide to set this value by default to the voice mail of the mobile so that callers can

leave a message.

HOW SPEECH IS ENCODED DURING MOBILE PHONE CALLS

During a GSM call, speech is converted from analogue sound waves to digital data by the

phone itself, and transmitted through the mobile phone network by digital means.

(Though older parts of the fixed Public Switched Telephone Network may use analog

transmission.)

The digital algorithm used to encode speech signals is called a codec. The speech codec

used in GSM are called Half-Rate (HR), Full-Rate (FR), Enhanced Full-Rate (EFR) and

Adaptive Multirate (AMR). All codec except AMR operate with a fixed data rate and

error correction level.

37

VOICE CHARGES

Mobile networks in Europe, Asia, Australia & Argentina only charge their subscribers for

outgoing calls. Incoming calls are free to the mobile subscriber; however, callers

typically pay a higher rate when calling mobile phones. Special prefixes are used to

designate mobile numbers so that callers are aware they are calling a mobile phone and

therefore will be charged a higher rate.

In the United States and Canada, callers pay the cost of connecting to the Gateway MSC

of the subscriber's phone company, regardless of the actual location of the phone. As

mobile numbers are given standard geographic numbers according to the North

American Numbering Plan, callers pay the same to reach fixed phones and mobile

phones in a given geographic area. Mobile subscribers pay for the connection time

(typically using in-plan or prepaid minutes) for both incoming and outgoing calls. For

outgoing calls, any long distance charges are billed as if they originate at the GMSC, even

though it is the Visiting MSC which completes the connection to the PSTN. Plans that

include nationwide long distance and/or nationwide roaming at no additional charge

over "local" outgoing calls are popular.

From the caller's point of view, it does not matter where the mobile subscriber is, as the

technical process of connecting the call is the same. If a subscriber is roaming on a

different company's network, the subscriber, instead of the caller, may pay a surcharge

for the connection time. International roaming calls are often quite expensive, and as a

result some companies require subscribers to grant explicit permission to receive calls

while roaming to certain countries.

When a subscriber is roaming internationally and a call is forwarded to his or her voice

mail, such as when his or her phone is off, busy, or not answered, he or she may actually

be charged for two simultaneous international phone calls—the first to get from the

GMSC to the VMSC and the second to get from the VMSC to the Call Forward Busy or

Call Forward No Reply number (typically the voice mailbox) in the subscriber's country.

38

Network Management Subsystem (NMS)

The Network Management Subsystem (NMS) is the third subsystem of the GSM network

in addition to the Network Switching Subsystem (NSS) and Base Station Subsystem

(BSS), which we have already discussed. The purpose of the NMS is to monitor various

functions and elements of the network.

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

• Fault management

• Configuration management

• Performance management

These functions cover the whole of the GSM network elements from the level of

individual BTSs, up to MSCs and HLRs.

39

1. Fault management

The purpose of fault management is to ensure the smooth operation of the network and

rapid correction of any kind of problems that are detected. Fault

management provides the network operator with information about the current status

of alarm events and maintains a history database of alarms.

The alarms are stored in the NMS database and this database can be searched according

to criteria specified by the network operator.

2. Configuration management

The purpose of configuration management is to maintain up-to-date information about

the operation and configuration status of network elements. Specific configuration

functions include the management of the radio network, software and hardware

management of the network elements, time synchronization, and security operations.

3. Performance management

In performance management, the NMS collects measurement data from individual

network elements and stores it in a database. On the basis of these data, the network

operator is able to compare the actual performance of the network with the planned

performance and detect both good and bad performance areas within the network.

40

GPRS NETWORK

ARCHITECTURE

41

INTRODUCTION

The General Packet Radio Service (GPRS) is a packet-switched data transmission

protocol which was incorporated into the GSM standard in 1997. It is backwards-

compatible with systems that use pre-1997 versions of the standard. GPRS does this by

sending packets to the local mobile phone mast (BTS) on channels not being used by

circuit-switched voice calls or data connections. Multiple GPRS users can share a single

unused channel because each of them uses it only for occasional short bursts.

The advantage of packet-switched connections is that bandwidth is only used when

there is actually data to transmit. This type of connection is thus generally billed by the

kilobyte instead of by the second, and is usually a cheaper alternative for applications

that only need to send and receive data sporadically, like instant messaging.

GPRS provides mobile users access to value-added WAP services and different external

packet switched networks. These networks can be, for example, the Internet or

corporate intranets. The GSM-BSS provides the radio interface, and the GPRS core

network handles mobility and access to external packet networks and services.

The GPRS network acts in parallel with the GSM network, providing packet switched

connections to the external networks. The requirements of a GPRS network are the

following:

42

The GPRS network must use as much of the existing GSM infrastructure with the

smallest number of modifications to it.

Since a GPRS user may be on more than one data session, GPRS should be able to

support one or more packet switched connections.

To support the budgets of various GPRS users, it must be able to support different

Quality of Service (QoS) subscriptions of the user.

The GPRS network architecture has to be compatible with future 3rd and 4th

generation mobile communication systems.

Able to support both point-to-point and point-to-multipoint data connections.

It should provide secure access to external networks.

A GPRS network must provide all of the functionality of a GSM network for packet

switched networks and more. The GPRS is expected to perform the functions of a

traditional mobile communication network and a traditional packet switched computer

network.

43

Network elements

The GPRS system brings some new network elements to an existing GSM network. Not

all of the network elements are compulsory for every GPRS network. These elements

are:

Packet Control Unit (PCU)

Serving GPRS Support Node (SGSN): the MSC of the GPRS network

Gateway GPRS Support Node (GGSN): gateway to external networks

Border Gateway (BG): a gateway to other PLMN

Intra-PLMN backbone: an IP based network inter-connecting all the GPRS elements

Charging Gateway (CG)

Legal Interception Gateway (LIG)

Domain Name System (DNS)

Firewalls: used wherever a connection to an external network is required.

44

Packet Control Unit (PCU) The PCU separates the circuit switched and packet

switched traffic from the user and sends them to the GSM and GPRS networks

respectively. It also performs most of the radio resource management functions of the

GPRS network. The PCU can be either located in the BTS, BSC, or some other point

between the MS and the MSC. There will be at least one PCU that serves a cell in which

GPRS services will be available. Frame Relay technology is being used at present to

interconnect the PCU to the GPRS core.

Channel Codec Unit (CCU) The CCU is realized in the BTS to perform the Channel

Coding (including the coding scheme algorithms), power control and timing advance

procedures.

Serving GPRS Support Node (SGSN)

• Ciphering of GPRS data between the MS and SGSN

The SGSN is the most important element of

the GPRS network. The SGSN of the GPRS network is equivalent to the MSC of the GSM

network. There must at least one SGSN in a GPRS network. There is a coverage area

associated with a SGSN. As the network expands and the number of subscribers

increases, there may be more than one SGSN in a network. The SGSN has the following

functions:

• Data compression is used to minimise the size of transmitted data units

• Authentication of GPRS users. Protocol conversion (for example IP to FR)

• Mobility management as the subscriber moves from one area to another, and

possibly one SGSN to another

• Routing of data to the relevant GGSN when a connection to an external network is

required

• Interaction with the NSS (that is, MSC/VLR, HLR, EIR) via the SS7 network in order to

retrieve subscription information

• Collection of charging data pertaining to the use of GPRS users

• Traffic statistics collections for network management purposes.

45

Gateway GPRS Support Node (GGSN)

• Routing mobile-destined packets coming from external networks to the relevant

SGSN

The GGSN is the gateway to external

networks. Every connection to a fixed external data network has to go through a GGSN.

The GGSN acts as the anchor point in a GPRS data connection even when the subscriber

moves to another SGSN during roaming. The GGSN may accept connection request from

SGSN that is in another PLMN. Hence, the concept of coverage area does not apply to

GGSN. There are usually two or more GGSNs in a network for redundancy purposes, and

they back up each other up in case of failure. The functions of a GGSN are given below:

• Routing packets originating from a mobile to the correct external network

• Interfaces to external IP networks and deals with security issues

• Collects charging data and traffic statistics

• Allocates dynamic or static IP addresses to mobiles either by itself or with the help

of a DHCP or a RADIUS server

• Involved in the establishment of tunnels with the SGSN and with other external

networks and VPN.

From the external network's point of view, the GGSN is simply a router to an IP sub-

network. This is shown below. When the GGSN receives data addressed to a specific

user in the mobile network, it first checks if the address is active. If it is, the GGSN

forwards the data to the SGSN serving the mobile. If the address is inactive, the data is

discarded. The GGSN also routes mobile originated packets to the correct external

network.

46

GPRS MS

Different GPRS MS classes were introduced to cope with the different

needs of future subscribers. The mobiles differ in their capabilities.

Domain Name Servers These devices convert IP names into IP addresses, for

example, server.nokia.com to 133.44.15.5. There is a primary DNS server and a

secondary DNS server. In the specifications, the DNS functionality is included in the

SGSN. However, the main vendors have chosen to separate the DNS functions from the

SGSN.

Firewalls A firewall protects an IP network against external attack (for example,

hackers from the mobile users or from the Internet). In the case of GPRS, the firewall

might be configured to reject all packets that are not part of a GPRS subscriber-initiated

connection. The firewall can also include NAT (Network Address Translation), see the

Introduction to TCP/IP module. In the specifications for GPRS, the firewalls are not

47

included. It is however included here due to the fact that operators usually need to

implement firewalls in their GPRS network (for security reasons).

Border Gateway The Border Gateway (BG) is a router that can provide a direct

GPRS tunnel between different operators' GPRS networks. This is referred to as an inter-

PLMN data network. It is more secure to transfer data between two operators' PLMN

networks through a direct connection rather than via the public Internet. The Border

Gateway will commence operation once the GPRS roaming agreements between various

operators have been signed. It will essentially allow a roaming subscriber to connect to

company intranet through the Home

Charging Gateway GPRS users have to be charged for the use of the network. In a

GSM network, charging is based on the destination, duration, and time of call. However,

GPRS offers connectionless service to users, so it not possible to charge subscribers on

the connection duration. Charging has to be based on the volume, destination, QoS, and

other parameters of a connectionless data transfer. These GPRS charging data are

generated by all the SGSNs and GGSNs in the network. This data is referred to as

Charging Data Records or CDRs. One data session may generate a number of CDRs, so

these needs to be collected and processed. The Charging Gateway (CG) collects all of

these records, sorts them, processes it, and passes it on to the Billing System. Here the

GPRS subscriber is billed for the data transaction. All CDRs contain unique subscriber

and connection identifiers to distinguish it. A protocol called GTP' (pronounced GTP

prime) is used for the transfer of data records between GSNs and the Charging Gateway.

48

ROAMING

SERVICES

IN GSM SYSTEM

49

ROAMING

“Roaming is defined as the ability for wireless customers to automatically make and

receive voice calls, send and receive data, or access other services when travelling

outside the geographical coverage area of their own home network, by means of using a

visited network.”

(International) Roaming enables the clients of one network operator to use the services

of another operator where both networks have a commercial agreement in place to

permit this, once all testing and technical implementation are completed.

The roaming process is split into two main phases where different activities are carried

out. In the pre-commercial phase the agreement is negotiated plus the network and IT

elements are implemented and tested. When these activities are successfully

completed, then commercial roaming can begin and customers can use each other’s

networks.

While in most cases roaming involves bi lateral, two-way roaming, in some cases,

unilateral or one way roaming takes place either for technical or commercial reasons.

Roaming Functions

The following functions are common within operators who have launched Roaming.

1. Roaming – Commercial and Operational

Usually you within the Roaming department find a “Roaming Manager” who is in charge

of Agreements, overall coordination between various functions and strategy. The

responsibility of producing the company Inter Operator Tariff (IOT) is most likely to be

placed here. The Roaming Department may also have responsibility for managing

outbound roaming which may include pricing, marketing, and promotion. Increasingly,

companies are recognizing the value of roaming to their business and that roaming is no

Function can be organized in several

ways. In many companies, the functions of Roaming and Interconnection are contained

in the same department.

50

longer simply an implementation and management function. Increasingly, companies

are splitting the work between “operational” roaming and “Commercial” roaming.

Typically one group will look after the implementation and ongoing management whilst

the other will focus on strategy, pricing, commercial inter-operator activities etc.

Sometimes, both are within the same group, other times they are divided between

different departments.

The second role you are most likely to find in this department is the “Roaming

Assistant”. This is the person who has most of the day-to-day contact with the Roaming

partners. As a result this person is the one most likely to collate the IOT information of

the Roaming partners. This information is then published within the company. As the

roaming department often has to interface with every department within the company

and have overall visibility of the status of Roaming, it is often compared to the spider in

the centre of the web.

2. Marketing The role of the Marketing team within Roaming is to design effective

promotional initiatives for your customers travelling outside their home country.

3. Test SIM Card Administrator The person responsible for the test SIM cards is

usually a representative from Customer Services or Network Department; however, it

can often be the responsibility of the Roaming department itself. The role requires

providing all Roaming partners with their requested amount of test SIM (Subscriber

Identity Module) cards, and upon confirmation of receipt of the test SIMs will activate

them accordingly.

4. IREG (Inter-Working, Roaming Expert Group) This function is performing the

actual Roaming tests, and trouble shooting for network problems. They will be

responsible for ordering the signalling links and opening the network to testing, and

later to commercial Roaming. This function also undertakes periodical roaming tests and

troubleshooting after the commercial Roaming is in place.

Signaling is a prerequisite to testing, as it is the basis for the communication between

the two networks. This function is normally an outsourced service provided by a third

party.

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5. TADIG (Transferred Account Data Interchange Group) This function will (on the

basis of the data produced when performing the technical roaming testing) perform

billing tests. They will be responsible for TAP (Transferred Account Procedure) formats,

liaison with Data Clearing House (if used) and managing the TAP file flows between

networks on a daily basis.

6. Finance

• One part is to produce invoices (based on TAP file data) for any traffic generated in

your network by the customer of a Roaming partner.

The functions of the Finance department can be divided into two when it

comes to Roaming.

• The other part is to ensure that you receive invoices from your roaming partners for

any traffic your customers have generated in their network.

The final responsibility will be to ensure payment and collection for all the invoices.

Many operators use the services of a Financial Clearing House for parts or all of this

process.

7. Fraud This function assumes responsibility for the creation and management of

High Usage Reports. They are responsible for supplying data in the event of an actual

fraud case. Many operators contract a Data Clearing House for parts, or all of this

process. All email addresses deployed as part of the High Usage Reports process must be

on company (operator or clearing house) domains. Domains like yahoo.com;

hotmail.com etc may not be used. This email address must be exclusively used for

receiving HURs, to enable automated processing of the incoming HUR emails. This will

ensure that all emails are processed as potential fraud alerts rather than personal

emails.

The Fraud department also supplies IMEIs (International Mobile Equipment Identity) to

either to their own national EIR (Equipment Identity Register) or to the CEIR (Central

Equipment Identity Register), preferably both.

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8. Roaming Customer Care

This function can be divided in two parts, one responsible

for assisting inter operator issues and the second one responsible for assisting in

Roaming Customer Queries.

CAMEL

CAMEL (Customized Application for Mobile network Enhanced Logic) is a network

solution, which allows the functionality of IN services for roamers. It thus compensates

for restrictions met by mobile operators willing to offer IN-based services while roaming.

Emancipation from proprietary solution, real-time call supervision and building operator

specific service for roamers are among the advantages. Moreover, roaming subscribers

using CAMEL based services are offered a Virtual Home Environment enabling service

usage as if they were in their home network.

The importance of CAMEL grew during the last few years, as many operators decided to

offer IN-based Pre-paid services abroad, abandoning the old call-back platform (e.g.

USSD based) and launching a more elegant solution which allows direct connection

towards the home network, with real-time billing. The above described service is just

one component contained in the different features offered with CAMEL phase 1 and 2.

Further CAMEL phases will enable for example services like GPRS Roaming and UMTS

Roaming. CAMEL can also be used to support the above mentioned value added services

to Post-Paid subscribers.

By the implementation of CAMEL phase 1 and 2, many operators encountered major

inter-compatibility problems, mostly due to the matter of fact that vendors enclose

different features in their packages. And we haven’t reached an acceptable quality of

implementation. Further complications are represented by the fact that operators are

using different documents for agreeing commercially about the launch of CAMEL

services. In addition, being no comprehensive information about this topic, it is rather

difficult for non-technical personnel to understand from scratch how to set-up CAMEL

Roaming.

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Services

The main reason to incorporate Camel services within your existing Roaming Portfolio is

indicated below. There are number of key benefits:

Prepaid Roaming Using a CAMEL platform Prepaid customers can roam in a similar

way to postpaid, and via CAMEL the home network can qualify the action the customer

does.

Home Routing Roaming Using Camel it’s possible for Pre-Paid or Post-Paid

customers to set-up a call that is then routed to the home network, and then routed

onwards.

VPN roaming / short codes The Pre-paid or Post-paid customer dials the short code,

and via CAMEL, the home network is requested to tell the long code associated. This can

be as detailed as per IMSI, thus allowing VPN to be used when roaming.

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CONCLUSION

It has been a great opportunity for me to work in one of the most illustrious

telephone company existing in India. This not only help me to bridge the gap between

engineering & industry, but also aids me in having a few of an industry, it's

environment & functioning of various departments for achievements of the company

objective.

Since I was placed in MAHANAGAR TELEPHONE NIGAM LIMITED (BKC), I learned the

importance of teamwork. I also had experience about how to analyze a problem & solve

it.

This training offered an exposure to industrial environment, which cannot be simulated

in engineering college. We understood the scope function job responsibilities of an

engineering organization.

We have to touch the right chords of the people & get the work done without

hurting their feelings. I was able to learn some of these skills during our training.

Thus I can confidentially conclude that this training is memorable and a fruitful one for

me.