A

Report

On

Practical Training

Taken at

“BHARAT SANCHAR NIGAM LIMITED”

Submitted in the partial fulfillment of the requirement for award of the

Degree of Bachelor of Technology

In

Electrical Engineering

From

Rajasthan Technical University

Submitted By: Submitted To:Name: Himanshu Lawania Mr. Ujjwal KallaClass: Electrical (7th Sem) Head of DepartmentScholar No.: 07/03/19 Electrical EngineeringEnroll. No.: 07E1EBEEM10P019

DEPARTMENT OF ELECTRICAL ENGINEERINGEngineering College Bikaner

SESSION 2010-11

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ACKNOWLEDGEMENT

This is my first practical training installment taken at BSNL, Bikaner. I am immensely grateful to Mr. Sudan Singh (SDE) who helped me to grasp the various concepts of GSM, Optical fiber and telecommunication. I am also thankful to Mr. Kalidas Tanwar (JTO) who helped me in my project with full interest. I am also thankful to our respected H.O.D Ujjwal Kalla Sir and to my faculty members and also to my Training and Placement In charge for arranging my training at BSNL, Bikaner. The uphill task of completing this training report would support of all staff member of BSNL, Bikaner.

Himanshu Lawania

IV Year (7th SEM)

Electrical Engineering

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CONTENTS

S.No. Title Page No.

1. Introduction 1

2. The Evolution of Mobile Telephone Systems 2

3. Overview Of GSM Technology 3

4. GSM Architecture 4

5. GSM Network Areas 18

6. GSM Specification 20

7. Subscribers Identity Module 24

8. GSM Subscriber Services 27

9. Supplementary Services 30

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LIST OF FIGURES

1. Cellular Subscriber Growth Worldwide

2. Graphical Explanation of GSM Architecture

3. Network Areas

4. Location Areas

5. MSC\VLR Service Areas

6. PLMN Service Area

7. SIM Card.

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About BSNL

Bharat Sanchar Nigam Ltd. Formed in Oct. 2000 is world’s 7th largest telecommunications

company providing comprehensive range of telecom services in India: wire line, CDMA mobile,

GSM mobile, internet, broadband, carrier services. Within a span it has become the one of the

largest public sector unit in India.

BSNL is the only service provider, making focused efforts and planned initiatives to bridge the

rural –urban digital divide ICT sector. In fact there is no telecom operator in the country to beat

it reach with its wide network giving services I every nook & corner of country and operates

across India except Delhi & Mumbai.

BSNL cellular service cellone has more than 20.7 million cellular customers, garnering 24 % of

all mobile users as its subscribers. That means that almost every fourth mobile user in the

country has a BSNL connection. In basic services, BSNL is miles ahead of its rivals, with 35.1

million Basic Phone Subscribers i.e. 85 % share of the subscribers and 92 % share in revenue

terms.

BSNL has set up a world class multi-gigabit, multi-protocol convergent IP infrastructure that

provides convergent services like voice, data and video through the same Backbone and

broadband access network. At present there are 0.6 million Data one broadband customers.

The turnover, nationwide coverage, reach, comprehensive range of the telecom services and the

desire to excel has made BSNL the no. 1 telecom company of India.

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The Evolution of Mobile Telephone Systems:

Cellular is one of the fastest growing and most demanding telecommunications applications.

Today, it represents a continuously increasing percentage of all new telephone subscriptions

around the world. Currently there are more than 45 million cellular subscribers worldwide, and

nearly 50 percent of those subscribers are located in the United States. It is forecasted that

cellular systems using a digital technology will become the universal method of

telecommunications. By the year 2005, forecasters predict that there will be more than 100

million cellular subscribers worldwide. It has even been estimated that some countries may have

more mobile phones than fixed phones by the year 2000 (see Figure 1).

Figure 1: shows Cellular Subscriber Growth Worldwide

The concept of cellular service is the use of low-power transmitters where frequencies can be

reused within a geographic area. The idea of cell-based mobile radio service was formulated in

the United States at Bell Labs in the early 1970s. However, the Nordic countries were the first to

introduce cellular services for commercial use with the introduction of the Nordic Mobile

Telephone (NMT) in 1981.

Cellular systems began in the United States with the release of the advanced mobile phone

service (AMPS) system in 1983. The AMPS standard was adopted by Asia, Latin America, and

Oceanic countries, creating the largest potential market in the world for cellular.

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In the early 1980s, most mobile telephone systems were analog rather than digital, like today's

newer systems. One challenge facing analog systems was the inability to handle the growing

capacity needs in a cost-efficient manner. As a result, digital technology was welcomed. The

advantages of digital systems over analog systems include ease of signaling, lower levels of

interference, integration of transmission and switching, and increased ability to meet capacity

demands. Table 1 charts the worldwide development of mobile telephone systems.

Year Mobile System

1981 Nordic Mobile Telephone (NMT) 450

1983 American Mobile Phone System (AMPS)

1985 Total Access Communication System (TACS)

1986 Nordic Mobile Telephony (NMT) 900

1991 American Digital Cellular (ADC)

1991 Global System for Mobile Communication (GSM)

1992 Digital Cellular System (DCS) 1800

1994 Personal Digital Cellular (PDC)

1995 PCS 1900—Canada

1996 PCS—United States

Table 1 shows The Development of Mobile Telephone Systems

Throughout the evolution of cellular telecommunications, various systems have been developed

without the benefit of standardized specifications. This presented many problems directly related

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to compatibility, especially with the development of digital radio technology. The GSM standard

is intended to address these problems.

From 1982 to 1985 discussions were held to decide between building an analog or digital system. After multiple field tests, a digital system was adopted for GSM. The next task was to decide between a narrow or broadband solution. In May 1987, the narrowband time division multiple access (TDMA) solution was chosen. A summary of GSM milestones is given in Table 2.

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Year Milestone

1982 GSM formed

1986 field test

1987 TDMA chosen as access method

1988 memorandum of understanding signed

1989 validation of GSM system

1990 Pre operation system

1991 commercial system start-up

1992 coverage of larger cities/airports

1993 coverage of main roads

1995 coverage of rural areas

GLOBALSYSTEM FOR MOBILE COMMUNICATION (GSM):

During the period of Evolution of mobile communication technologies various systems were

introduced and deployed to achieve standardization in mobile industry but all the efforts were

failed. Multiple issues were sustained like incompatibility of systems, development of digital

radio frequency. That is when GSM (Global System for Mobile Communication) Technology

was introduced and problems like standardization, incompatibility etc were overcame. TDMA

solution was chosen in 1987, it is narrowband system and TDMA standards for Time Division

Multiple access.

GSM systems were in market for testing purposes in 1980’s but first commercial lunch of GSM

technology was made in 1991 in Finland. GSM based mobile phones are operated on TDMA

Systems, in TDMA single radio frequency is offered to users with any interference. After all

these years, GSM is now the largest mobile communication technology worldwide, all

manufacturers of Mobile phones develop their products based on GSM, and all mobile

companies provide their subscribers GSM networks. GSM standards for Global System for

Mobile Communication, it is widely used mobile technology worldwide and it adopted by more

than 214 countries around the world.

The GSM logo is used to identify compatible handsets and equipment

Features of GSM Technology

There are many features associated with GSM technology due to which it is by far the most

leading mobile communication technology in the world today. GSM technology facilitates with

high speed integrated data; voice data, fax, mail, voice mail and mostly used SMS feature. GSM

also make sure that all the communication made between networks are secured and protected

from intruders and frauds.

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One of the major advantages of GSM technology which changed the way we looked mobile

phones at the beginning. GSM actually brought the concept of being Mobile way beyond the

limits. It enabled us to communicate across the continents.

GSM supports multiple frequency levels like 900 MHz, 1800 MHz, 1900 MHz 1900MHz

frequency is used in North America where as 1800MHz is used in other parts of the world.

Different frequency bands are used by different mobile phone operators. If you are using Mobile

phone which supports 1800MGz and operators are available on this band, phone can be used the

network, where as if phone is out of the range of the frequency band on mobile operator

frequency than you need to have phone that supports the frequency. To avoid such cases one

should always adopt to have mobile phones that support multiple frequency bands.

Different Frequency Bands

There are three different frequency bands on which mobile phones are usually operates and these

are Dual Band, Tri-Band and Quad Band.

 Dual Band : Dual frequency band operates on 900MHz and 1800 MHz, that means mobile

phone that supports dual band can be operated anywhere in the world where 900 MHz and 1800

MHz frequencies are used. Dual Band GSM networks usually found in all continents Europe,

Asia, Africa, Australia and South America.

Tri-Band: As name is obvious three frequencies are supported in Tri Band, these frequencies are

900 MHz, 1800MHz and 1900 MHz Tri band is also supported all around the world these days.

Quad-Band: Quad Band supports four frequencies which are 850 MHz, 900 MHz, 1800 MHz ,

1900 MHz Quad band also enables GSM phones to road almost anywhere in the world. All

countries support GSM networks hence make communication possible. 

There are over 700 GMS networks available in the world operating in their respective countries

and providing international roaming services courtesy GSM technology. There are over 2 billion

GSM subscribers in the world. Countries which are using GSM networks on larger scales are

Russia, china Pakistan, United States, India. 

GSM phone deliver very good voice quality, support useful services and standards, it is very

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likely that GSM will remain the only mobile communication network technology to be adopted

by each and every country of the world.

Radio interface:

GSM is a cellular network, which means that mobile phones connect to it by searching for cells

in the immediate vicinity. GSM networks operate in four different frequency ranges. Most 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.

The rarer 400 and 450 MHz frequency bands are assigned in some countries, notably

Scandinavia, where these frequencies were previously used for first-generation systems.

In the 900 MHz band the uplink frequency band is 890-915 MHz, and the downlink frequency

band is 935-960 MHz this 25 MHz bandwidth is subdivided into 124 carrier frequency channels,

each spaced 200 kHz apart. Time division multiplexing is used to allow eight full-rate or sixteen

half-rate speech channels per radio frequency channel. There are eight radio timeslots (giving

eight burst periods) grouped into what is called a TDMA frame. Half rate channels use alternate

frames in the same timeslot. The channel data rate is 270.833 Kbit/s, and the frame duration is

4.615 ms.

The transmission power in the handset is limited to a maximum of 2 watts in GSM850/900 and 1

watt in GSM1800/1900.

GSM has used a variety of voice codes to squeeze 3.1 kHz audio into between 6 and 13 Kbit/s.

Originally, two codecs, named after the types of data channel they were allocated, were used,

called "Full Rate" (13 Kbit/s) and "Half Rate" (6 Kbit/s). These used a system based upon linear

predictive coding (LPC). In addition to being efficient with bit rates, these codecs also made it

easier to identify more important parts of the audio, allowing the air interface layer to prioritize

and better protect these parts of the signal.GSM was further enhanced in 1997 with the GSM-

EFR codec, a 12.2 Kbit/s codec that uses a full rate channel. Finally, with the development of

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UMTS, EFR was refectories into a variable-rate codec called AMR-Narrowband, which is high

quality and robust against interference when used on full rate channels, and less robust but still

relatively high quality when used in good radio conditions on half-rate channels.

Multiple Access TDMA/FDMA/FDA

Uplink frequency(mobile to base) 890-915 MHz

Downlink frequency(base to mobile ) 935-960 MHz

Channel Bandwidth 200 KHz

Number of channels 124

Channels/carrier 8(full rate),16(half rate)

Frame duration 4.6ms

Interleaving duration 40ms

Modulation GMSK

Speech coding method RPE-LTE convolution

Speech coder bit rate 13kb/s (full rate)

Associated control channel Extra frame

Handoff scheme Mobile assisted

Mobile station power levels 0.8, 2,58 w

There are four different cell sizes in a GSM network - macro, micro, Pico and umbrella cells. The coverage area of each cell varies according to the implementation environment. Macro cells can be regarded as cells where the base station antenna is installed on a mast or a building above average roof top level. Micro cells are cells whose antenna height is under average roof top level; they are typically used in urban areas. Pico cells are small cells whose coverage diameter is a few dozen meters; they are mainly used indoors. Umbrella cells are used to cover shadowed regions of smaller cells and fill in gaps in coverage between those cells.

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Indoor coverage is also supported by GSM and may be achieved by using an indoor picocell base

station, or an indoor repeater with distributed indoor antennas fed through power splitters, to

deliver the radio signals from an antenna outdoors to the separate indoor distributed antenna

system. These are typically deployed when a lot of call capacity is needed indoors, for example

in shopping centers or airports. However, this is not a prerequisite, since indoor coverage is also

provided by in-building penetration of the radio signals from nearby cells.

The modulation used in GSM is Gaussian minimum-shift keying (GMSK), a kind of continuous-

phase frequency shift keying. In GMSK, the signal to be modulated onto the carrier is first

smoothed with a Gaussian low-pass filter prior to being fed to a frequency modulator, which

greatly reduces the interference to neighboring channels (adjacent channel interference).

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DETAILS:

A nearby GSM handset is usually the source of the "dit dit dit, dit dit dit, dit dit dit" signal that

can be heard from time to time on home stereo systems, televisions, computers, and personal

music devices. When these audio devices are in the near field of the GSM handset, the radio

signal is strong enough that the solid state amplifiers in the audio chain function as a detector.

The clicking noise itself represents the power bursts that carry the TDMA signal. These signals

have been known to interfere with other electronic devices, such as car stereos and portable

audio players. This is a form of RFI, and could be mitigated or eliminated by use of additional

shielding and/or bypass capacitors in these audio devices. However, the increased cost of doing

so is difficult for a designer to justify.

GSM Network Architecture:

 Architecture and Working of GSM Networks

 

We have already read about how GSM technology had taken over mobile communication

technologies and grown over to 214 countries around the world.  Now it is important to learn

how GSM network works and what is the architecture of GSM networks? GSM network is

consist of thee major systems, it can also be considered architecture of GSM networks. These

three systems are SS, which is known to be The Switching System, BSS, it is The Base

Station and the other important system is The operation and support System for GSM networks.

Below all three systems are defined in details with sub systems of each system.

The Switching System:

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The Switching system is very operative system in which many crucial operations are conducted,

SS systems holds five databases with in it which performs different functions. If we talk about

major tasks of SS system it performs call processing and subscriber related functions. These five

databases from SS systems are HLR, MSC, VLR, AUC and EIR. Let’s study each database in

detail and learn what functions this little systems performs.

HLR- Home Location Register:                         

HLR is database, which holds very important information of subscribers. It is mostly known for

storing and managing information of subscribers. It contains subscriber service profile, status of

activities, information about locations and permanent data of all sorts. When new connections

are purchased, these subscribers are registered in HLR of mobile phone companies.

MSC- Mobile Services Switching Center:

MSC is also important part of SS, it handles technical end of telephony. It is build to perform

switching functionality of the entire system. It’s most important task is to control the calls to and

from other telephones, which means it controls calls from same networks and calls from other

networks. Toll ticketing, common channel signaling, network interfacing etc are other tasks

which MSC is responsible for.

 VLR- Visitor Location Register:

VLR performs very dynamic tasks; it is database which stores temporary data regarding

subscribers which is needed by Mobile Services Switching Center-MSC VLR is directly

connected to MSC, when subscribe moves to different MSC location, Visitor location register –

VLR integrates to MSC of current location and requests the data about subscriber or Mobile

station (MS) from the Home Location Register –HLR. When subscriber makes a call the Visitor

location register-VLR will have required information for making call already and it will not

required to connect to Home Register Location - HRL again.

AUC- Authentication Center:

 AUC is small unit which handles the security end of the system. Its major task is to authenticate

and encrypt those parameters which verify user’s identification and hence enables the

confidentiality of each call made by subscriber. Authentication center – AUC makes sure mobile

operators are safe from different frauds most likely to happen when hackers are looking for even

smallest loop wholes in systems.

EIR – Equipment Identity Register:

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EIR is another important database which holds crucial information regarding mobile equipments.

EIR helps in restricting for calls been stolen, mal functioning of any MS, or unauthorized access.

AUC – Authentication center and EIR- Equipment Identity registers are either Stand-alone nodes

or sometimes work together as combined AUC/EIR nodes for optimum performance.

The Base Station System (BSS):

The base station system have very important role in mobile communication. BSS are basically

outdoor units which consist of iron rods and are usually of high length. BSS are responsible for

connecting subscribers (MS) to mobile networks. All the communication is made in Radio

transmission. The Base station System is further divided in two systems. These two systems,

they are BSC, and BTS. Let’s study these two systems in detail.

 

BTS – The Base Transceiver Station:

Subscriber, MS (Mobile Station) or mobile phone connects to mobile network through BTS; it

handles communication using radio transmission with mobile station. As name suggests,

Base transceiver Station is the radio equipment which receive and transmit voice data at the same

time. BSC control group of BTSs.

BSC – The Base Station Controller:

The Base Station normally controls many cells; it registers subscribers, responsible for MS

handovers etc. It creates physical link between subscriber (MS) and BTS, then manage and

controls functions of it. It performs the function of high quality switch by handover over the MS

to next BSC when MS goes out of the current range of BTS, it helps in connecting to next in

range BTS to keep the connection alive within the network. It also performs functions like cell

configuration data, control radio frequency in BTS. Data moves to MSC-Mobile switching center

after BSC done processing it. MSC is switching center which acts as bridge between different

mobile networks.

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Figure 2: Shows the graphical explanation of GSM Architecture and Working of GSM

Networks. 

The Operation and Support System (OSS):

 OMC- Operations and maintenance center is designed to connect to equipment of MSC- Mobile

Switching Center and BSC-Base Station Controller. The implementation of OMC is called OSS-

The Operations and Support System.OSS helps in mobile networks to monitor and control the

complex systems. The basic reason for developing operation and support system is to provide

customers a cost effective support and solutions. It helps in managing, centralizing, local and

regional operational activities required for GMS networks.

Maintaining mobile network organization, provide overview of network, support and

maintenance activities are other important aspects of Operation and Support System.

Additional Functional Elements:

Message center (MXE): The MXE is a node that provides integrated voice, fax, and data

messaging. Specifically, the MXE handles short message service, cell broadcast, voice

mail, fax mail, e-mail, and notification.

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Mobile service node (MSN): The MSN is the node that handles the mobile intelligent

network (IN) services.

Gateway mobile services switching center (GMSC): A gateway is a node used to

interconnect two networks. The gateway is often implemented in an MSC. The MSC is

then referred to as the GMSC.

GSM interworking unit (GIWU): The GIWU consists of both hardware and software that

provides an interface to various networks for data communications. Through the GIWU,

users can alternate between speech and data during the same call. The GIWU hardware

equipment is physically located at the MSC/VLR.

GSM Network Areas:

The GSM network is made up of geographic areas. As shown in Figure 3, these areas include

cells, location areas (LAs), MSC/VLR service areas, and public land mobile network (PLMN)

areas.

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Figure 3: showing Network Areas

The cell is the area given radio coverage by one base transceiver station. The GSM network

identifies each cell via the cell global identity (CGI) number assigned to each cell. The location

area is a group of cells. It is the area in which the subscriber is paged. Each LA is served by one

or more base station controllers, yet only by a single MSC (see Figure 4). Each LA is assigned a

location area identity (LAI) number.

Figure 4: showing location Areas.

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An MSC/VLR service area represents the part of the GSM network that is covered by one MSC

and which is reachable, as it is registered in the VLR of the MSC (see Figure 5).

Figure 5: showing MSC\VLR Service Areas.

The PLMN service area is an area served by one network operator (see Figure 6).

Figure 6: showing PLMN Service Area.

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GSM Specifications:

Before looking at the GSM specifications, it is important to understand the following basic

terms:

Bandwidth: the range of a channel's limits; the broader the bandwidth, the faster data can

be sent

bits per second (bps): a single on-off pulse of data; eight bits are equivalent to one byte

frequency: the number of cycles per unit of time; frequency is measured in hertz (Hz)

Kilo (K): Kilo is the designation for 1,000; the abbreviation kbps represents 1,000 bits

per second

megahertz (MHz): 1,000,000 hertz (cycles per second)

milliseconds (ms): one-thousandth of a second

watt (W): a measure of power of a transmitter

Specifications for different personal communication services (PCS) systems vary among the

different PCS networks. Listed below is a description of the specifications and characteristics for

GSM.

Frequency band: The frequency range specified for GSM is 1,850 to 1,990 MHz (mobile

station to base station).

Duplex distance: The duplex distance is 80 MHz Duplex distance is the distance between

the uplink and downlink frequencies. A channel has two frequencies, 80 MHz apart.

Channel separation: The separation between adjacent carrier frequencies. In GSM, this is

200 kHz.

Modulation: Modulation is the process of sending a signal by changing the characteristics

of a carrier frequency. This is done in GSM via Gaussian minimum shift keying

(GMSK).

Transmission rate: GSM is a digital system with an over-the-air bit rate of 270 kbps.

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Access method: GSM utilizes the time division multiple access (TDMA) concept. TDMA

is a technique in which several different calls may share the same carrier. Each call is

assigned a particular time slot.

Speech coder: GSM uses linear predictive coding (LPC). The purpose of LPC is to

reduce the bit rate. The LPC provides parameters for a filter that mimics the vocal tract.

The signal passes through this filter, leaving behind a residual signal. Speech is encoded

at 13 kbps.

Subscriber identity module:

Figure 7: showing SIM Card

One of the key features of GSM is the Subscriber Identity Module (SIM), commonly known as a

SIM card. The SIM is a detachable smart card containing the user's subscription information and

phonebook. This allows the user to retain his or her information after switching handsets.

Alternatively, the user can also change operators while retaining the handset simply by changing

the SIM. Some operators will block this by allowing the phone to use only a single SIM, or only

a SIM issued by them; this practice is known as SIM locking, and is illegal in some countries.

In Australia, Canada, Europe and the United States many operators lock the mobiles they sell.

This is done because the price of the mobile phone is typically subsidized with revenue from

subscriptions, and operators want to try to avoid subsidizing competitor's mobiles. A subscriber

can usually contact the provider to remove the lock for a fee, utilize private services to remove

the lock, or make use of ample software and websites available on the Internet to unlock the

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handset themselves. While most web sites offer the unlocking for a fee, some do it for free. The

locking applies to the handset, identified by its International Mobile Equipment Identity (IMEI)

number, not to the account (which is identified by the SIM card). It is always possible to switch

to another (non-locked) handset if such a handset is available.

Some providers will unlock the phone for free if the customer has held an account for a certain

time period. Third party unlocking services exist that are often quicker and lower cost than that

of the operator. In most countries, removing the lock is legal. Cingular and T-Mobile provide

free unlocking services to their customers after 3 months of subscription

In countries like Belgium, India, Indonesia and Pakistan, etc., all phones are sold unlocked.

However, in Belgium, it is unlawful for operators there to offer any form of subsidy on the

phone's price. This was also the case in Finland until April 1, 2006, when selling subsidized

combinations of handsets and accounts became legal, though operators have to unlock phones

free of charge after a certain period (at most 24 months).

GSM Subscriber Services:

There are two basic types of services offered through GSM: telephony (also referred to as tele-

services) and data (also referred to as bearer services). Telephony services are mainly voice

services that provide subscribers with the complete capability (including necessary terminal

equipment) to communicate with other subscribers. Data services provide the capacity necessary

to transmit appropriate data signals between two access points creating an interface to the

network. In addition to normal telephony and emergency calling, the following subscriber

services are supported by GSM:

Dual-tone multi frequency (DTMF): DTMF is a tone signaling scheme often used for

various control purposes via the telephone network, such as remote control of an

answering machine. GSM supports full-originating DTMF.

Facsimile group III: GSM supports CCITT Group 3 facsimile. As standard fax machines

are designed to be connected to a telephone using analog signals, a special fax converter

connected to the exchange is used in the GSM system. This enables a GSM–connected

fax to communicate with any analog fax in the network.

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Short message services: A convenient facility of the GSM network is the short message

service. A message consisting of a maximum of 160 alphanumeric characters can be sent

to or from a mobile station. This service can be viewed as an advanced form of

alphanumeric paging with a number of advantages. If the subscriber's mobile unit is

powered off or has left the coverage area, the message is stored and offered back to the

subscriber when the mobile is powered on or has reentered the coverage area of the

network. This function ensures that the message will be received.

Cell broadcast: A variation of the short message service is the cell broadcast facility. A

message of a maximum of 93 characters can be broadcast to all mobile subscribers in a

certain geographic area. Typical applications include traffic congestion warnings and

reports on accidents.

Voice mail: This service is actually an answering machine within the network, which is

controlled by the subscriber. Calls can be forwarded to the subscriber's voice-mail box

and the subscriber checks for messages via a personal security code.

Fax mail: With this service, the subscriber can receive fax messages at any fax machine.

The messages are stored in a service center from which they can be retrieved by the

subscriber via a personal security code to the desired fax number.

Supplementary Services:

GSM supports a comprehensive set of supplementary services that can complement and support

both telephony and data services. Supplementary services are defined by GSM and are

characterized as revenue-generating features. A partial listing of supplementary services follows.

Call forwarding: This service gives the subscriber the ability to forward incoming calls to

another number if the called mobile unit is not reachable, if it is busy, if there is no reply,

or if call forwarding is allowed unconditionally.

Barring of outgoing calls: This service makes it possible for a mobile subscriber to

prevent all outgoing calls.

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Barring of incoming calls: This function allows the subscriber to prevent incoming calls.

The following two conditions for incoming call barring exist: baring of all incoming calls

and barring of incoming calls when roaming outside the home PLMN.

Advice of charge (AOC): The AOC service provides the mobile subscriber with an

estimate of the call charges. There are two types of AoC information: one that provides

the subscriber with an estimate of the bill and one that can be used for immediate

charging purposes. AOC for data calls is provided on the basis of time measurements.

Call hold: This service enables the subscriber to interrupt an ongoing call and then

subsequently reestablish the call. The call hold service is only applicable to normal

telephony.

Call waiting: This service enables the mobile subscriber to be notified of an incoming call

during a conversation. The subscriber can answer, reject, or ignore the incoming call.

Call waiting is applicable to all GSM telecommunications services using a circuit-

switched connection.

Multiparty service: The multiparty service enables a mobile subscriber to establish a

multiparty conversation—that is, a simultaneous conversation between three and six

subscribers. This service is only applicable to normal telephony.

Calling line identification presentation/restriction: These services supply the called party

with the integrated services digital network (ISDN) number of the calling party. The

restriction service enables the calling party to restrict the presentation. The restriction

overrides the presentation.

Closed user groups (CUGs): CUGs are generally comparable to a PBX. They are a group

of subscribers who are capable of only calling themselves and certain numbers.

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