bharat sanchar nigam limited report

7/31/2019 Bharat Sanchar Nigam Limited Report

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INDUTRIAL REPORT

RTTC, LUCKNOW

Submited By:

NAME: Smriti Ladia

ROLL NO: 0803313056

COURSE: B.TECH

BRANCH: C.S.E

COLLEGE: R.K.G.I.T(GHAZIABAD)


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ACKNOWLEDGEMENT

It gives us a great sense of pleasure to present the report of the Industrial Training undertaken

during Summer Vacation. We owe a special debt of gratitude to Mr. Arvind Gaur, Divisional

Engineer, BSNL RTTC, LUCKNOW for his constant support and guidance throughout the course

of our work. His sincerity, thoroughness and perseverance have been a constant source of

inspiration for us. It is only his cognizant efforts that our endeavors have seen light of the day.

We would also not like to miss the opportunity to acknowledge the contribution of all staff

members of the department for their kind assistance and cooperation during the training.


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BHARAT SANCHAR NIGAM LIMITED (BSNL)

An Introduction:-

Today, BSNL is the No. 1 telecommunication company and the largest public sector undertaking

of India and its responsibilities includes improvement of the already impeccable quality oftelecom services, expansion of telecom services in all villages and instilling confidence among

its customers.

Apart from vast network expansions, especial emphasis has given for introducing latest

technologies and new services like I-NET, INTERNET, ISDN (INTEGRATED SERVICES DIGITAL

NETWORK), IN (INTELLIGENT NETWORK), GSM and WLL (WIRELESS IN LOCAL LOOP) services

etc. Now BSNL has also entered in mobile communication. BSNL has all the new services send

technological advantages, which are available with any well, developed Telecom network

anywhere else in the country.

Full credit for all above achievement goes to the officers and staff of the BSNL. The

administration is fully aware of the challenges lying ahead and quite committed to provide the

latest and best telecom services by their continued support and active co-operation.

BSNL Services:-

When it comes connecting the four corners of the country , and much beyond , one solitary

name lies embedded at the pinnacle- BSNL, a company that has gone past the number game

and the quest to attain the position of the leader. It is working round the clock to take India in

to the future by providing excellent telecom services for people of India.

Driven by the very best of telecom technology from global leaders, it connects each inch of

India to the infinite corners of the globe, to enable you to step in to tomorrow.The telecom services have been recognized the world over as an important tool for socio-

economic development for a nation and hence telecom infrastructure is treated a crucial factor

to realize the socio-economic objectives in India. Accordingly the Department of Telecom has

been formulating developmental policies for the accelerated growth of the telecommunication

services in various cities. The department is also responsible for frequency management in the

field of radio connection in close coordination with the international bodies.

MAKING A TELEPHONE CALL

A telephone call starts when the caller lifts the handsets of the base. Once the dial tone is

heard, the caller uses a rotary or a push button dial mounted either on the handset or on the

base to enter a sequence of digits, the telephone number of called party. The switching

equipment from the exchange removes the dial tone from the line after the first digit is

received and after receiving the last digit, determines the called party is in the same exchange

or a different ones. If the called is in the same exchange, burst of ringing current is applied to


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the called partys line. Each telephone contains a ringer that responds to specific electric

frequency. When the called party answers the telephone by pocking up the handset, steady

start to flow in the called partys line and is detected by the exchange. The exchange than stops

applying ringing and sets up the connection between the caller and the called party. If the

called party is in different exchange from the caller, the caller exchange set up the connection

over the telephone network to the called partys exchange. The called party then handles theprocess of ringing, detecting an answer, and notifying the calling and billing machinery when

the call is completed. When conversation is over, one or both parties hang up by replacing their

handset on the base, stopping the flow of current. The exchange when initiates the process of

taking down the connection, including notifying billing equipment of the duration of the call if

appropriate.

ABOUT THE EXCHANGE

All telephone subscribers are served by automatic exchanges, which perform the functions the

human operator. The number being dialed is stored and then passed to the exchanges central

computer, which in turns operates the switching to complete the call or routes it a higher level

switch for further processing. Todays automatic exchanges uses a pair of computers, one

running the program that provides services and the second monitoring the operation of the

first, ready to take over in a few seconds in the event of equipment failure.

Various exchanges present in BSNL are:

1. E-10B

2. OCB 283

3. EWSD

All exchange has some purposes and some basic structural units, which are:

1. subscribers connection unit

2. switching network (CX)

3. control unit

4. OMC

For smooth working of an exchange following unit are very important:-

1. Computer Unit: - it deals with additional services of the exchange to the customers with thehelp of computers.

2. Power Plant:- to feed proper power supply to exchange

3. AC Plant: - to maintain the continuous temperature + or 2 degree Celsius to the digital

switch (exchange).

4. MDF: - to connect switch (exchange) with the external environment (subscriber) i.e. it is the

interface between subscribers and exchange.


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Computer unit

As the name specified it is the main part of the exchange that deals with the all services

provided by the exchange to the customers with the help of computer. It also provides the

updated data to all other part of the exchange.

The customers are using the services of the exchange by using the internet also gets connectedto the main server present this room via an internet room.

It mainly consists of the servers that are providing the different services. The main servers of

this room are:-

IVRS is used for the change number services provided by the exchange.

CERS are provided by the exchange to avoid the problems that the users are facing the

repairing of telephone. In this system when the user enters its complained it gets directly

entered to the server and user is allotted with an id number.

LOCAL DIRECTORY ENQUIRY is another services provided by the exchange, by using this;

subscribers calls the particular number and gets the directory enquiry. The server present in the

main computer room provides this service.

INTERNET DIRECTORY ENQUIRY is the latest service by the exchange. In this type of service

makes it enquiry using the internet, which gets connected to the main server at the internet

room in the exchange and further to the main server in the computer room.

POWERPLANT

As we know that, the power is the main source or any organization. It is the case of E-10B

exchange. That is the first requirement of any organization is the input.

The main source of this exchange is AC supply. However, as soon as the power supply is gone

off, then what is source? No one think on this that the telephone is always plays its role in the

human life. Even if the power supply gone off. Thus there must be adjustment source of power.

The main parts of the power room are:

Batteries: - these are the instant sources of the power as soon as power is gone off.

UPS (Uninterrupted Power Supply):- the UPS must give supply to the computer. As we know

there is some equipment which can withstand any type of power supply, but there are also

some instruments which cannot withstand with this type of power supply, even a microsecond

delay will cause the loss of data.

Charging- Discharging Unit: - the batteries we are using in the power room need timely

charging. As soon as the AC power supply is on, we make use of the charging unit present in the


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power room. The slowly charging of the batteries is known as the trickle charging. But

sometimes we need the BOOSTER charging. In this type of charging awe take of the batteries

from the load and charge separately, until it gets fully charged.

The main work of the discharging unit is to control the discharging of the batteries.

Inverter and Converter Unit: - the main use of this system is to change AC mains to DC and viceversa as required by the parts of exchange.

Engine Room:-we know that the batteries are the instant source of supply but we cannot use it

for much larger time, thus for this, we have an engine to generate the power supply. They are

of 885 KVA. Thus, this room controls the supply of the engine.

CENTRAL AIR CONDITIONER

For the function of electrical equipment, cooling system is basic requirement. The basic

advantages of cooling systems are following-

It provides the thermal stability so that the temperature does not reach the tolerance limit of

electronic equipment

It saves equipment from dust so to avoid malfunction of equipments.

It protects equipment from excess humidity which can caused rusting of equipment.

The basic unit of measurement used in the industry is known as ton of refrigeration (TR)

which is equivalent to the heat extracted in 24 hours for converting thousands kg of liquid to ice

at zero degree.

The compressor is the heart of the AC system and the costliest. It increases the pressure and

temperature of the refrigerant gas coming from the evaporator coils by compressing it.Compressor comes in various types. The most widely used is simple reciprocal type a cylinder

and piston arrangement. For capacity more than 120 TR, centrifugal compressors are used. The

condenser liquefies the refrigerant gas by a heat exchange process. The capillary tube or the

expansion valve pressurizes liquid refrigerant and meters it flows to the evaporator.

The refrigerant then passes trough the evaporator coils, which extract heat out of the

ambience.

MAIN DISTRIBUTION FRAME

The primary function of MDF is:

The fault of telephone number is removed in the MDF; it is called as Fault Remove Section.

For removing the fault of telephone number, we use the testing

These testing are T.T.Y. testing, Group testing, etc.


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For any type of testing firstly we need the vertical no. or the live tester, printer and computer

test N.E. number of that particular telephone number.

The telephone numbers are also disconnected in the MDF because of some specific reason.

ORGANISATION OF THE MDF:

PARTS OF THE MDF

1. Horizontal side

2. Vertical side

HORIZONTAL SIDE:

It is again subdivided in to two parts

1. Exchange side

2. Line side

Description of the horizontal side:-

RACK: - On the rack, the tags are situated. One rack is having eight tags. The courting is done

from up (0) to down (7).

TAG: - Each rack consists of eight tags.

1 tag = 4 core

1 core = 4 bunch

1 bunch = 2 line

N.E.:- The word NE stands for the NUMBER OF EQUIPMENT.It is a 128 pair cable. The EWSD and MDF connected by NE.

WEDGE:-If we want to disconnect any two numbers then we insert a wedge between subscriber

side and exchange side. Here wedge works as insulator made of plastic.

VERTICAL SIDE:

The vertical aside connected to the underground cable. This cable is having 100 pairs.

These pair is distributed when we allot the telephone number to the subscriber.

Vertical side is again subdivided in two parts:

One part is connected with the horizontal side and another with the subscriber line by using

100 pair underground cable.

This is how the present day telephone system works. Different exchanges have different

architectures of switching call routing and other features.


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Now let us see how BSNL has kept up with the changing world and provided the subscribers

with the latest facilities technologies, which include the WLL (wireless in local loop) and the

GSM mobile.

FIXED ASSIGNMENT TIME DIVISION MULTIPLE ACCESS (F-TDMA)

In a fixed assignment TDMA, each frame is divided in to slots of fixed time durations among

stations of network. The assignment of stations to slots is permanent similar to TDMA system

carrying digitalized voice except FTDMA does not have synchronization. Packets are sent

asynchronously, with no frame sync signals.

FEATURES

No inter modulation problems.

Transport utilization is better.

Burst from different stations must arrive at satellite exactly in allocated slots.

Throughput is 70% to 80%

Delay medium is too high.

Complexity -medium.

RANDOM ACCESS

With TDMA schemes, signals are transmitted by earth stations in a burst mode. If no scheduling

is provided b/w the transmitting station, this type of access is called time random multiple

access. This simplest method for the stations to transmit burst without regard for other station.

CODE DIVISION MULTIPLE ACCESS (CDMA)

With CDMA transmission from earth station are spread over the time frequency plane by a

code transformation. These techniques are referred to as Spread Spectrum Systems. In addition

to their multiple access capabilities, they are useful in combating jamming, and are for this

reason principally used in military systems.

Features

All stations operate on the same transponder frequency using a large bandwidth than needed

for the data rate.Network needs no time for frequency coordination.

Provide anti jam capabilities or protection against interference.

Provide for a graceful degradation of network performance as the number of simultaneous

users increases.

Low spectral density compared to conventional emissions.

It yields same capacity as FDMA.


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Limitations of CDMA

Requires a large transponder ratio.

Due to imperfect code orthogonalities, expected simultaneous users may be limited.

Requires a highly central earth station called HUB using star configuration.

VSAT technology using SSMA is presently available only for low bit rate application.

VSAT NETWORK IN DOT

Department of telecommunication entered the VSAT era in 1991 by commissioning its first

satellite based low bit rate network known as REMOTE AREA BUSINESS MESSAGE NETWORK

(RABMN).

This has been engineered for users located in remote areas for stable and reliable data

communication.

This service envisages installation of very small aperture terminals (VSAT) to work with satellite

based pocket switched network.

It has 3 main components:-

A large master earth station (hub)

A satellite transponder located in geo stationary orbit

A small micro earth station located at users premises

Frequency division multiple access (FDMA):-

Bandwidth is split in to narrow frequency bands with multiple users each allocated a frequencyrange within the larger bandwidth.

Time division multiple access (TDMA):-

Each terminal is allotted a short time slot in which to transmit on a sequential basis. This time

slot is usually a fraction of a second.

Code division multiple access (CDMA)

Each terminal is allotted a unique encryption code. The transmitted signals are encoded andonly the terminal intended to receive it, can decode it. This is also known as Spread Spectrum

Multiple Access.

WIRELESS IN LOCAL LOOP (WLL) MOBILE

WLL is a communication system that connects customers to the Public Switch Telephone


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Network (PSTN) using radio frequency signals as substitutes of conventional wires for all part of

connection between the subscribers and the telephone exchange. It works on CDMA technique.

The local loop is access part of telecommunication network i.e. the part between PSTN switch

and subscribers. WLL network application involves uses of radio to replace of the wire link

between PSTN switch and subscriber. The radio technology is able to provide same quality of

services as that provided by the wires line. Application of wireless loop technology has justbeen started in the worldwide. There is no standard for this so far. However, a number of

national and international air interface standards for digital cellular mobile telephone system

are available.

TECHNICAL ASPECTS:

WLL is based on CDMA technique and is entirely different from GSM. The system for WLL

services can be divided in to following parts:-

BSC (Base Switching Centre):- It provides links between BTS & BSM; it consists of different

processors, in BSNL it is of SUN Polaris of LG Company. In LG 1 BSC can have 48 BTS? In BSNL we

have two types of BSC:-

V-5.2:- This type of BSC cannot switch by itself so it is dependent on local exchange / PSTN for

switching and keeping records of billing etc. BSNL uses this type of BSC for rural areas.

CCS-7 / R2:- These types of BSC are totally automatic it doesnt depend on local exchange for its

functions, it is complete in itself. BSNL uses this type of BSC for urban areas.

BTS (Base Transreceiver System):- As it is clear from its name it transmits as well as receive

signal, it works as an amplifier (router) to overcome the loss in signal in transmission.

BSM (Base Station Management):- It controls and manages the WLL services. It can

troubleshoot the problem; add new users as well as capable to block service given to user. It is

basically a computer system, which manages the whole process of WLL service. In BSNL BSM

are two UNIX based computer system.

CODE DIVISION MULTIPLE ACCESS (CDMA):

CONCEPT OF MULTIPLE ACCESSES: - Multiple access system allows a large number of users to

share a common pool of radio telephone circuits, like sharing of trunked radio facility. Multiple

access radio has similarity to the LAN in which the common channel is available to all users. The

circuits are demands assigned i.e. assigned on demand first-cum-first-served basis. The


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provision of access to the radio circuits methods of multiple accesses are:

CDMA: - Where large number of transmission are combined on the same channel at the same

time and separated by the codes.

FDMA (Frequency Division Multiple Access):- Where individual transmission separated by each

other by the time.

WHAT IS CDMA?

CDMA, a cellular technology originally known as IS-95, competes with GSM technology for

dominance in the cellular world.

There are now different variations, but the original CDMA is known as CdmaOne.

Latest CDMA global subscriber & operators numbers

As of December 2002, there were 120 millions users worldwide, with 55 million of these in the

USA.

See other cellular technology in the world.

We now have CDMA2000 and its variant like 1X EV, 1XEV-DO and MC 3X. The refer of variant of

usage of a 1.25 MHz channel. 3X uses a 5 MHz channel. Wide band CDMA forms that the basis

of UMTS 3G networks, developed originally by Qualcomm, high capacity and small cell radius,

employing spread-spectrum technology and special coding scheme characterized by CDMA.

The Telecommunication Industry Association (TIA) in 1993 adopted CDMA. May 2001 there

were 35 million subscribers on cdmaOne system worldwide. Over 35 countries have eithercommercial or trial activity ongoing. There were already 43 WLL systems in 22 countries using

cdmaOne technology.

Enhancing todays data capabilities is the 1XRTT CDMA standard this next evolutionary step for

cdmaOne operators will provide data rates up to 300 kbps, significant capacity increases as well

as extended batteries life for handsets.

Worldwide resources are being devoted to roll out third generation CDMA technology,

including multi-carrier (cdmaOne2000 1xMC and HDR in 1.25 MHz bandwidth and 3xMC in 5

MHz bandwidth) and direct spread (WCDMA in 5 MHz bandwidth).

This first phase of cdmaOne2000 variously called 1XRTT, 3G1X or just plain 1X is designed to

double current voce capacity and support always on data transmission speed 10 times fasterthan typically available today, some 153.6 kbps on both the forward and reverse links.

ADVANTAGES OF WLL:

Country wide induction of WLL underway of areas than are non-feasible for the normal network


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Helping relieves congestion of connections in the normal cable / wire based network in urban

areas

Limited the mobility without any airtime charges

It has improved signal and reducing the interference

Greater capacity than mobile

Provides ease of operation, administration & maintenance at lower cost.The telecommunication is the biggest factor in influencing the speed of life in the modern age.

Today we can get connection with any corner of world through the push button of computer;

with the small mobile phone we can send not only the messages but also the secret document.

As we know that there is positive view behind any mention that it should be helpful in the

development of society. But humans have diverted mentality some of them of positive view

and some of them of negative view. Where use any invention for the welfare of society but

some uses for the satisfaction their disturbed mentality and to earn more and more money

whether it may be harmful for the society. They infringe the norms of society and their

behavior is condemned as antisocial, immoral and sinful.

CELLULAR MOBILE SERVICES:

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

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

around the world. Currently there are more than 45 million subscribers in worldwide and nearly

50% of those subscribers are located in USA. It is forecasted that cellular system 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.


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CELLULAR CONCEPT

Traditional mobile service was structured similar to television broadcasting: One very powerful

transmitter located at the highest spot in an area would broadcast in a radius of up to fi ftykilometers. The Cellular concept structured the mobile telephone network in a different way.

Instead of using one powerful transmitter many low-powered transmitter were placed through

out a coverage area. For example, by dividing metropolitan region into one hundred different

areas (cells) with low power transmitters using twelve conversation (channels) each, the system

capacity could theoretically be increased from twelve conversations using one hundred low

power transmitters.

The cellular concept employs variable low power levels, which allows cells to be sized according

to subscriber density and demand of a given area. As the populations grows, cells can be added

to accommodate that growth. Frequencies used in one cell cluster can be reused in other cells.

Conversations can be handed over from cell to cell to maintain constant phone service as the

user moves between cells.

The cellular system design was pioneered by during70s by Bell Laboratories in the United

States, and the initial realization was known as AMPS (Advanced Mobile Phone Service). The

AMPS cellular service was available in United States in 1983. AMPS is essentially generation 1

analog cellular system in contrast to generation 2 digital cellular systems of GSM and CDMA

(1S-95).

CELLS :

A cell is the basic geographic unit of cellular system. The term cellular comes from the

honeycomb areas into which a coverage region is divided. Cells are base stations transmitting

over small geographic areas that are represented as hexagons. Each cell size varies depending

upon landscape. Because of constraint imposed by natural terrain and man-made structures,

the true shape of cell is not a perfect hexagon.

A group of cells is called a cluster. No frequencies are reused in a cluster.

Features of Digital Cellular Systems:

Small cells Frequency reuse Small, battery-powered handsets Performance of handovers


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CELLULAR SYSTEM CHARACTERISTICS

General Cellular radio systems allow the subscriber to place and

receive telephone calls over the wire-line telephone network whereever cellular coverage is provided. Roaming capabilities extend service

to users traveling outside their outside home service areas.

characteristics of

digital

cellular systems

The distinguishing features of digital cellular systems compared

to other mobile radio systems are:

Small cellsA cellular system uses many base stations with relatively

small coverage radii (on the order of a 100 m to 30 km).

Frequency reuseThe spectrum allocated for a cellular network is limited. As

a result there is a limit to the number of channels or frequencies

that can be used. For this reason each frequency is used

simultaneously by multiple base-mobile pairs. This frequency

reuse allows a much higher subscriber density per MHz of

spectrum than other systems. System capacity can be further

increased by reducing the cell size (the coverage area of a single

base station), down to radii as small as 200 m.

Small, battery-powered handsets In addition to supporting muchhigher densities than previous systems, this approach enables the

use of small, battery-powered handsets with a radio frequency

that is lower than the large mobile units used in earlier systems.

Performance of handoversIn cellular systems, continuous coverage is achieved by executing a

handover (the seamless transfer of the call from one base station to

another) as the mobile unit crosses cell boundaries. This requires the

mobile to change frequencies under control of the cellular network.

FREQUENCY REUSE :

Why frequency

reuse

The spectrum allocated for a cellular network is limited. As a

result there is a limit to the number of frequencies or channels that

can be used. A cellular network can only provide service to a large

number of subscribers, if the channels allocated to it can be reused.

Channel reuse is implemented by using the same channels within cells


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located at different positions in the cellular network service area.

Radio channels can be reused provided the separation between

cells containing the same channel set is far enough apart so that co-

channel interference can be kept below acceptable levels most of the

time. Cells using the same channel set are called co-channel cells.

Cell clustering The figure on the opposite page shows an example. Within the

service area (PLMN), specific channel sets are reused at a different

location (another cell). In the example, there are 7 channel sets: A

through G. Neighboring cells are not allowed to use the same

frequencies. For this reason all channel sets are used in a cluster of

neighboring cells. As there are 7 channel sets, the PLMN can be divided

into clusters of 7 cells each. The figure shows three clusters.

The number of channel sets is called K. K is also called the reusefactor. In the figure, K=7. Valid values of K can be found using equation

(where i and j are integers):

K=i+j+I*j

Explaining this equation is beyond the scope of this course.

Some constraints to K are provided later in this chapter. Note that in

the example: Cells are shaped ideally (hexagons). The distance

between cells using the same channel set is always the same.

Other cell clusters The figure on the opposite page shows some examples of

possible clusters. The more cells in a cluster, the greater the separation

between co-channel cells when Other clusters are deployed. The idea

is to keep co-channel cell separation the same throughout the system

area for cells of the same size. Some valid cluster sizes that allow this

are: 1, 3, 4, 7, 9 and 12.

Procedure for

locating co-

channel cells

It is always possible to find cells using the same channel set, if

only the value of K is known. The following procedure is used.

In the figure on the opposite page an example is shown with K

= 19.

Signal attenuation

With distance

Frequencies can be reused throughout a service area because

radio signals typically attenuate with distance to the base station (or

mobile station). When the distance between cells using the same

frequencies becomes too small, co-channel

Interference might occur and lead to service interruption or


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unacceptable quality of service.

Step Action

1 Use the integer values i and j from the equation, and start

With the upper left cell. Through this cell, draw the j-axis.

2 Draw the i-axis. To find the starting point for the i-axis, count j cells down the

j-axis. In the example, one has to count 2 cells down (j=2). The positive

direction of the i-axis is always two cell faces (120 degrees) relative to the

positive direction of the j-axis.

3 Find the first co-channel cell. It is found by counting i cells in the positive i-axis

direction. In the example, i = 3.

4 Find the other co-locating cells by repeating the previous steps. The

Starting point is again at the upper left cell, but now choose another

Direction for the j-axis (e.g. rotate the j-axis with 60 degrees, which is one cell

face). As each cell has 6 faces, one will find 6 co-channel cells around the

starting cells. These are the nearest located co-channel cells.

Capacity/Performance Trade-offs :

n If K increases, then performance increases

n If K increases, then call capacity decreases per cell

The number of sites to cover a given area with a given high traffic density, and hence the cost of

the infrastructure, is determined directly by the reuse factor and the number of traffic channels

that can be extracted from the available spectrum. These two factors are compounded in what

is called spectral efficiency of the system. Not all systems allow the same performance in this

domain: they depend in particular on the robustness of the radio transmission scheme against

interference, but also on the use of a number of technical tricks, such as reducing transmission


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during the silences of a speech communication. The spectral efficiency, together with the

constraints on the cell size, determines also the possible compromises between the capacity

and the cost of the infrastructure. All this explains the importance given to spectral efficiency.

Many technical tricks to improve spectral efficiency were conceived during the system design

and have been introduced in GSM. They increase the complexity, but this is balanced by the

economical advantages of a better efficiency. The major points are the following:

The control of the transmitted power on the radio path aims at minimizing the average power

broadcast by mobile stations as well as by base stations, whilst keeping transmission quality

above a given threshold. This reduces the level of interference caused to the other

communications;

Frequency hopping improves transmission quality at slow speeds through frequency diversity,

and improves spectral efficiency through interferer diversity;

Discontinuous transmission, where by transmission is suppressed when possible, allows a

reduction in the interference level of other communications. Depending on the type of user

information transmitted, it is possible to derive the need for effective transmission. In the case

of speech, the mechanism called VAD (Voice Activity Detection) allows transmission

requirements to be reduced by an important factor (typically, reduced by half);

The mobile assisted handover, whereby the mobile station provides measurements concerning

neighboring cells, enables efficient handover decision algorithms aimed at minimizing the

interference generated by the cell (whilst keeping the transmission quality above some

threshold).


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GSM ARCHITECTURE

INTRODUCTION

A GSM system is basically designed as a combination of three major subsystems: the network

subsystem, the radio subsystem, and the operation support subsystem. In order to ensure that

network operators will have several sources of cellular infrastructure equipment, GSM decided

to specify not only the air interface, but also the main interfaces that identify different parts.

There are three dominant interfaces, namely, an interface between MSC and the base

Transceiver Station (BTS), and an Um interface between the BTS and MS.

GSM NETWORK STRUCTURE

Every telephone network needs a well-designed structure in order to route incoming called to

the correct exchange and finally to the called subscriber. In a mobile network, this structure is

of great importance because of the mobility of all its subscribers [1-4]. In the GSM system, the

network is divided into the following partitioned areas.

GSM service area; PLMN service area; MSC service area; Location area; Cells.

The GSM service is the total area served by the combination of all member countries where a

mobile can be serviced. The next level is the PLMN service area. There can be several within a

country, based on its size. The links between a GSM/PLMN network and other PSTN, ISDN, or

PLMN network will be on the level of international or national transit exchange. All incoming

calls for a GSM/PLMN network will be routed to a gateway MSC. A gateway MSC works as an

incoming transit exchange for the GSM/PLMN. In a GSM/PLMN network, all mobile-terminated

calls will be routed to a gateway MSC. Call connections between PLMNs, or to fixed networks,

must be routed through certain designated MSCs called a gateway MSC. The gateway MSC

contains the interworking functions to make these connections. They also route incoming calls

to the proper MSC within the network. The next level of division is the MSC/VLR service area. In

one PLMN there can be several MSC/VLR service area. MSC/VLR is a role controller of calls

within its jurisdiction. In order to route a call to a mobile subscriber, the path through links to

the MSC in the MSC area where the subscriber is currently located. The mobile location can be

uniquely identified since the MS is registered in a VLR, which is generally associated with an

MSC.

The next division level is that of the LAs within a MSC/VLR combination. There are several LAs

within one MSC/VLR combination. A LA is a part of the MSC/VLR service area in which a MS may


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move freely without updating location information to the MSC/VLR exchange that control the

LA. Within a LA a paging message is broadcast in order to find the called mobile subscriber. The

LA can be identified by the system using the Location Area Identity (LAI). The LA is used by the

GSM system to search for a subscriber in a active state. Lastly, a LA is divided into many cells. A

cell is an identity served by one BTS. The MS distinguishes between cells using the Base StationIdentification code (BSIC) that the cell site broadcast over the air.

MOBILE STATION

The MS includes radio equipment and the man machine interface (MMI) that a

subscribe needs in order to access the services provided by the GSM PLMN. MS can be installed

in Vehicles or can be portable or handheld stations. The MS may include provisions for data

communication as well as voice. A mobile transmits and receives message to and from the GSM

system over the air interface to establish and continue connections through the system .

Different type of MSs can provide different type of data interfaces. To provide a

common model for describing these different MS configuration, reference configuration forMS, similar to those defined for ISDN land stations, has been defined.

Each MS is identified by an IMEI that is permanently stored in the mobile unit. Upon

request, the MS sends this number over the signaling channel to the MSC. The IMEI can be used

to identify mobile units that are reported stolen or operating incorrectly.

Just as the IMEI identities the mobile equipment, other numbers are used to identity the

mobile subscriber. Different subscriber identities are used in different phases of call setup. The

Mobile Subscriber ISDN Number (MSISDN) is the number that the calling party dials in order to

reach the subscriber. It is used by the land network to route calls toward an appropriate MSC.

The international mobile subscribe identity (IMSI) is the primary function of the subscriber

within the mobile network and is permanently assigned to him. The GSM system can also assign

a Temporary Mobile Subscriber Identity (TMSI) to identity a mobile. This number can be

periodically changed by the system and protect the subscriber from being identified by those

attempting to monitor the radio channel.

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 withthe 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 multiframe period of 51 frames. We shall discuss the details of this in the next

chapter. The exact synchronization will also include adjusting the timing advance to

compensate for varying distance of the mobile from the BTS.


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The MS monitors the power level and signal quality, determined by the BER for known

receiver bit sequences (synchronization sequence), from both its current BTS and up to six

surrounding BTSs. This data is received on the downlink broadcast control channel. The MS

determines and send to the current BTS a list of the six best-received BTS signals. The

measurement results from MS on downlink quality and surrounding BTS signal levels are sent to

BSC and processed within the BSC. The system then uses this list for best cell handoverdecisions.

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.

The MS includes an equalizer that compensates for multi-path distortion on the

received signal. This reduces inter-symbol interface that would otherwise degrade the BER.

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 information. These

messages are limited to 160 characters in length.Power Levels

These are five different categories of mobile telephone units specified by the European

GSM system: 20W, 8W, 5W, 2W, and 0.8W. These correspond to 43-dBm, 39-dBm, 37-dBm, 33-

dBm, and 29-dBm power levels. The 20-W and 8-W units (peak power) are either for vehicle-

mounted or portable station use.

The MS power is adjustable in 2-dB steps from its nominal value down to 20mW (13

dBm). This is done automatically under remote control from the BTS, which monitors the

received power and adjusts the MS transmitter to the minimum power setting necessary for

reliable transmission.SIM Card

As described in the first chapter, GSM subscribers are provided with a SIM card with its

unique identification at the very beginning of the service. By divorcing the subscriber ID from

the equipment ID, the subscriber may never own the GSM mobile equipment set. The

subscriber is identified in the system when he inserts the SIM card in the mobile equipment.

This provides an enormous amount of flexibility to the subscribers since they can now use any

GSM-specified mobile equipment. Thus with a SIM card the idea of Personalize the

equipment currently in use and the respective information used by the network (location

information) needs to be updated. The smart card SIM is portable between Mobile Equipment

(ME) units. The user only needs to take his smart card on a trip. He can then rent a ME unit atthe destination, even in another country, and insert his own SIM. Any calls he makes will be

charged to his home GSM account. Also, the GSM system will be able to reach him at the ME

unit he is currently using.

The SIM is a removable SC, the size of a credit card, and contains an integrated circuit

chip with a microprocessor, random access memory (RAM), and read only memory (ROM). It is

inserted in the MS unit by the subscriber when he or she wants to use the MS to make or


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receive a call. As stated, a SIM also comes in a modular from that can be mounted in the

subscribers equipment.

When a mobile subscriber wants to use the system, he or she mounts their SIM card and

provide their Personal Identification Number(PIN), which is compared with a PIN stored within

the SIM. If the user enters three incorrect PIN codes, the SIM is disabled. The PIN can also be

permanently bypassed by the service provider if requested by the subscriber. Disabling the PIN

code simplifies the call setup but reduces the protection of the users account in the event of a

stolen SIM.

International Mobile Subscriber Identity.

An IMSI is assigned to each authorized GSM user. It consists of a mobile country code (MSC),

mobile network code (MNC), and a PLMN unique mobile subscriber identification number

(MSIN). The IMSI is not hardware-specific. Instead, it is maintained on a SC by an authorized

subscriber and is the only absolute identity that a subscriber has within the GSM system. The

IMSI consists of the MCC followed by the NMSI and shall not exceed 15 digits.

TEMPORARY MOBILE SUBSCRIBER IDENTITY

A TMSI is a MSC-VLR specific alias that is designed to maintain user confidentiality. It is assigned

only after successful subscriber authentication. The correlation of a TMSI to an IMSI only occurs

during a mobile subscribers initial transaction with an MSC (for example, location updating).

Under certain condition (such as traffic system disruption and malfunctioning of the system),

the MSC can direct individual TMSIs to provide the MSC with their IMSI.

MOBILE STATION ISDN NUMBER

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 Significant Number (N(S)N), which shall not exceed 15 digits.

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.

INTERNATIONAL MOBILE EQUIPMENT 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


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

granted access to the system. An IMEI is never sent in cipher mode by MS.

BASE STATION SYSTEM

The BSS is a set of BS equipment (such as transceivers and controllers) that is in view by the

MSC through a single A interface as being the entity responsible for communicating with MSs in

a certain area. The radio equipment of a BSS may be composed of one or more cells. A BSS may

consist of one or more BS. The interface between BSC and BTS is designed as an A-bis interface.

The BSS includes two types of machines: the BTS in contact with the MSs through the radio

interface and the BSC, the latter being in contact with the MSC. The function split is basically

between transmission equipment, the BTS, and managing equipment at the BSC. A BTS

compares radio transmission and reception devices, up to and including the antennas, and also

all the signal processing specific to the radio interface. A single transceiver within BTS supports

eight basic radio channels of the same TDM frame. A BSC is a network component in the PLMN

that function for control of one or more BTS. It is a functional entity that handles common

control functions within a BTS.

A BTS is a network component that serves one cell and is controlled by a BSC. BTS is typically

able to handle three to five radio carries, carrying between 24 and 40 simultaneous

communication. Reducing the BTS volume is important to keeping down the cost of the cell

sites.

An important component of the BSS that is considered in the GSM architecture as a part of the

BTS is the Transcoder/Rate Adapter Unit (TRAU). The TRAU is the equipment in which coding

and decoding is carried out as well as rate adoption in case of data. Although the specifications

consider the TRAU as a subpart of the BTS, it can be sited away from the BTS (at MSC), and even

between the BSC and the MSC.

The interface between the MSC and the BSS is a standardized SS7 interface (A-interface) that,

as stated before, is fully defined in the GSM recommendations. This allows the system operator

to purchase switching equipment from one supplier and radio equipment and the controller

from another. The interface between the BSC and a remote BTS likewise is a standard the A-bis.

In splitting the BSS functions between BTS and BSC, the main principle was that only such

functions that had to reside close to the radio transmitters/receivers should be placed in BTS.This will also help reduce the complexity of the BTS.

Functions of BTS


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As stated, the primary responsibility of the BTS is to transmit and receive radio signals from a

mobile unit over an air interface. To perform this function completely, the signals are encoded,

encrypted, multiplexed, modulated, and then fed to the antenna system at the cell site. Trans-

coding to bring 13-kbps speech to a standard data rate of 16 kbps and then combining four of

these signals to 64 kbps is essentially a part of BTS, though, it can be done at BSC or at MSC.The voice communication can be either at a full or half rate over logical speech channel. In

order to keep the mobile synchronized, BTS transmits frequency and time synchronization

signals over frequency correction channel (FCCH and BCCH logical channels. The received signal

from the mobile is decoded, decrypted, and equalized for channel impairments.

Random access detection is made by BTS, which then sends the message to BSC. The

channel subsequent assignment is made by BSC. Timing advance is determined by BTS. BTS

signals the mobile for proper timing adjustment. Uplink radio channel measurement

corresponding to the downlink measurements made by MS has to be made by BTS.

BTS-BSC CONFIGURATIONS

There are several BTS-BSC configurations: single site; single cell; single site; multicell; and

multisite, multicell. These configurations are chosen based on the rular or urban application.

These configurations make the GSM system economical since the operation has options to

adapt the best layout based on the traffic requirement. Thus, in some sense, system

optimization is possible by the proper choice of the configuration. These include omni

directional rural configuration where the BSC and BTS are on the same site; chain and

multidrop loop configuration in which several BTSs are controlled by a single remote BSC with a

chain or ring connection topology; rural star configuration in which several BTSs are connectedby individual lines to the same BSC; and sectorized urban configuration in which three BTSs

share the same site amd are controlled by either a collocated or remote BSC.

In rural areas, most BSs are installed to provide maximum coverage rather then maximum

capacity.

Transcoder

Depending on the relative costs of a transmission plant for a particular cellular operator, there

may be some benefit, for larger cells and certain network topologies, in having the transcoder

either at the BTS, BSC or MSC location. If the trascoder is located at MSC, they are still

considered functionally a part of the BSS. This approach allows for the maximum of flexibility

and innovation in optimizing the transmission between MSC and BTS.

The transcoder is the device that takes 13-Kbps speech or 3.6/6/12-Kbps data multiplexes and

four of them to convert into standard 64-Kbps data. First, the 13 Kbps or the data at 3.6/6/12


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Kbps are brought up to the level of 16 Kpbs by inserting additional synchronizing data to make

up the difference between a 13-Kbps speech or lower rate data, and then four of them are

combined in the transcoder to provide 64 Kpbs channel within the BSS. Four traffic channel can

then be multiplexed on one 64-Kpbs circuit. Thus, the TRAU output data rate is 64 Kpbs. Then,

up to 30 such 64-Kpbs channels are multiplexed onto a 2.048 Mpbs if a CEPT1 channel isprovided on the A-bis interface. This channel can carry up to 120-(16x 120) traffic and control

signals. Since the data rate to the PSTN is normally at 2 Mbps, which is the result of combining

30-Kbps by 64-Kbph channels, or 120- Kbps by 16-Kpbs channels.

BSC

The BSC, as discussed, is connected to the MSC on one side and to the BTS on the other. The

BSC performs the Radio Resource (RR) management for the cells under its control. It assigns

and release frequencies and timeslots for all MSs in its own area. The BSC performs the intercell

handover for MSs moving between BTS in its control. It also reallocates frequencies to the BTSs

in its area to meet locally heavy demands during peak hours or on special events. The BSC

controls the power transmission of both BSSs and MSs in its area. The minimum power level for

a mobile unit is broadcast over the BCCH. The BSC provides the time and frequency

synchronization reference signals broadcast by its BTSs. The BSC also measures the time delay

of received MS signals relative to the BTS clock. If the received MS signal is not centered in its

assigned timeslot at the BTS, The BSC can direct the BTS to notify the MS to advance the timing

such that proper synchronization takes place. The functions of BSC are as follows.

The BSC may also perform traffic concentration to reduce the number of transmission

lines from the BSC to its BTSs, as discussed in the last section.

SWITCHING SUBSYSTEMS: MOBILE SWITCHING CENTER AND GATEWAY SWITCHING CENTER

The network and the switching subsystem together include the main switching functions of

GSM as well as the databases needed for subscriber data and mobility management (VLR). The

main role of the MSC is to manage the communications between the GSM users and other

telecommunication network users. The basic switching function of performed by the MSC,

whose main function is to coordinate setting up calls to and from GSM users. The MSC has

interface with the BSS on one side (through which MSC VLR is in contact with GSM users) and

the external networks on the other (ISDN/PSTN/PSPDN). The main difference between a MSCand an exchange in a fixed network is that the MSC has to take into account the impact of the

allocation of RRs and the mobile nature of the subscribers and has to perform, in addition, at

least, activities required for the location registration and handover.

The MSC is a telephony switch that performs all the switching functions for MSs located in a

geographical area as the MSC area. The MSC must also handle different types of numbers and


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identities related to the same MS and contained in different registers: IMSI, TMSI,ISDN number,

and MSRN. In general identities are used in the interface between the MSC and the MS, while

numbers are used in the fixed part of the network, such as, for routing.

FUNCTIONS OF MSC

As stated, the main function of the MSC is to coordinate the set up of calls between GSM

mobile and PSTN users. Specifically, it performs functions such as paging, resource

allocation, location registration, and encryption.

Specifically, the call-handling function of paging is controlled by MSC. MSC coordinates the set

up of call to and from all GSM subscribers operating in its areas. The dynamics allocation of

access resources is done in coordination with the BSS. More specifically, the MSC decides when

and which types of channels should be assigned to which MS. The channel identity and related

radio parameters are the responsibility of the BSS, The MSC provides the control of

interworking with different networks. It is transparent for the subscriber authenticationprocedure. The MSC supervises the connection transfer between different BSSs for MSs, with

an active call, moving from one call to another. This is ensured if the two BSSs are connected to

the same MSC but also when they are not . In this latter case the procedure is more complex,

since more then one MSC in involved. The MSC performs billing on calls for all subscribers

based in its areas. When the subscriber is roaming elsewhere, the MSC obtains data for the call

billing from the visited MSC. Encryption parameters transfers from VLR to BSS to facilitate

ciphering on the radio interface are done by MSC. The exchange of signaling information on

the various interface toward the other network elements and the management of the interface

themselves are all controlled by the MSC. Finally, the MSC serves as a SMS gateway to forwardSMS messages from Short Message Service Centers (SMSC) to the subscribers and from the

subscribers to the SMSCs. It thus acts as a message mailbox and delivery system.

VLR

The VLR is collocated with an MSC. A MS roaming in an MSC area is controlled by the VLR

responsible for that area. When a MS appears in a LA, it starts a registration procedure. The

MSC for that area notices this registration and transfers to the VLR the identify of the LA where

the MS is situated. A VLR may be in charge of one or several MSC LAs. The VLR constitutes the

databases that support the MSC in the storage and retrieval of the data of subscribers presentin its area. When an MS enters the MSC area borders, it signals its arrival to the MSC that stores

its identify in the VLR. The information necessary to manage the MS is contained in the HLR and

is transferred to the VLR so that they can be easily retrieved if so required.


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DATA STORED IN VLR

The data contained in the VLR and in the HLR are more or less the same. Nevertheless the data

are present in the VLR only as long as the MS is registered in the area related to that VLR. Data

associated with the movement of mobile are IMSI, MSISDN, MSRN, and TMSI. The terms

permanent and temporary, in this case, are meaningful only during that time interval. Somedata are mandatory, others are optional.

HOME LOCATION REGISTER

The HLR is a database that permanently stores data related to a given set of subscribers. The

HLR is the reference database for subscriber parameters. Various identification numbers and

addresses as well as authentication parameters, services subscribed, and special routing

information are stored. Current subscriber status including a subscribers temporary roaming

number and associated VLR if the mobile is roaming, are maintained.

The HLR provides data needed to route calls to all MS-SIMs home based in its MSC area, even

when they are roaming out of area or in other GSM networks. The HLR provides the current

location data needed to support searching for and paging the MS-SIM for incoming calls,

wherever the MS-SIM may be. The HLR is responsible for storage and provision of SIM

authentication and encryption parameters needed by the MSC where the MS-SIM is operating.

It obtains these parameters from the AUC.

The HLR maintains record of which supplementary service each user has subscribed to and

provides permission control in granting services. The HLR stores the identification of SMS

gateways that have messages for the subscriber under the SMS until they can be transmitted tothe subscriber and receipt is knowledge.

Some data are mandatory, other data are optional. Both the HLR and the VLR can be

implemented in the same equipment in an MSC (collocated). A PLMN may contain one or

several HLRs.

AUTHENTICATION CENTER

The AUC stores information that is necessary to protect communication through the air

interface against intrusions, to which the mobile is vulnerable. The legitimacy of the subscriber

is established through authentication and ciphering, which protects the user informationagainst unwanted disclosure. Authentication information and ciphering keys are stored in a

database within the AUC, which protects the user information against unwanted disclosure and

access.


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In the authentication procedure, the key Ki is never transmitted to the mobile over the air path,

only a random number is sent. In order to gain access to the system, the mobile must provide

the correct Signed Response (SRES) in answer to a random number (RAND) generated by AUC.

Also, Ki and the cipher key Kc are never transmitted across the air interface between the BTS

and the MS. Only the random challenge and the calculated response are transmitted. Thus, the

value of Ki and Kc are kept secure. The cipher key, on the other hand, is transmitted on the SS7

link between the home HLR/AUC and the visited MSC, which is a point of potential vulnerability.

On the other hand, the random number and cipher key is supposed to change with each phone

call, so finding them on one call will not benefit using them on the next call.

The HLR is also responsible for the authentication of the subscriber each time he makes or

receives a call. The AUC, which actually performs this function, is a separate GSM entity that

will often be physically included with the HLR. Being separate, it will use separate processing

equipment for the AUC database functions.

EQUIPMENT IDENTIFY REGISTER

EIR is a database that stores the IMEI numbers for all registered ME units. The IMEI uniquely

identifies all registered ME. There is generally one EIR per PLMN. It interfaces to the various

HLR in the PLMN. The EIR keeps track of all ME units in the PLMN. It maintains various lists of

message. The database stores the ME identification and has nothing do with subscriber who is

receiving or originating call. There are three classes of ME that are stored in the database, and

each group has different characteristics.

White List: contains those IMEIs that are known to have been assigned to valid MSs.This is the category of genuine equipment.

Black List: contains IMEIs of mobiles that have been reported stolen. Gray List: contains IMEIs of mobiles that have problems (for example, faulty

software, wrong make of the equipment). This list contains all MEs with faults not

important enough for barring.

INTERWORKING FUNCTION

GSM provided a wide range of data services to its subscribers. The GSM systeminterface with the various forms of public and private data networks currently

available. It is the job of the IWF to provide this interfacing capability.The IWF, which in essence is a part of MSC, provides the subscriber with access to data rate and

protocol conversion facilities so that data can be transmitted between GSM Data Terminal

Equipment (DTE) and a land-line DTE.


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ECHO CANCELER

EC is used on the PSTN side of the MSC for all voice circuits. The EC is required at the MSC PSTN

interface to reduce the effect of GSM delay when the mobile is connected to the PSTN circuit.

The total round-trip delay introduced by the GSM system, which is the result of speech

encoding, decoding and signal processing, is of the order of 180 ms. Normally this delay wouldnot be an annoying factor to the mobile, except when communicating to PSTN as it requires a

two-wire to four-wire hybrid transformer in the circuit. This hybrid is required at the local

switching office because the standard local loop is a two-wire circuit. Due to the presence of

this hybrid, some of the energy at its four-wire receive side from the mobile is coupled to the

four-wire transmit side and thus retransmitted to the mobile. This causes the echo, which does

not effect the land subscriber but is an annoying factor to the mobile. The standard EC cancels

about 70 ms of delay.

During a normal PSTN (land-to-land call), no echo is apparent because the delay is too short and

the land user is unable to distinguish between the echo and the normal telephone side tones

However, with the GSM round-trip delay added and without the EC, the effect would be

irritating to the MS subscriber.

OPERATION AND MAINTENANCE CENTER

The OMC provides alarm-handling functions to report and log alarms generated by the

other network entities. The maintenance personnel at the OMC can define that criticality of the

alarm. Maintenance cover both technical and administrative actions to maintain and correct

the system operation, or to restore normal operations after a breakdown, in the shortest

possible time.

The fault management functions of the OMC allow network devices to be manually or

automatically removed from or restored to service. The status of network devices can be

checked, and tests and diagnostics on various devices can be invoked. For example, diagnostics

may be initiated remotely by the OMC. A mobile call trace facility can also be invoked. The

performance management functions included collecting traffic statistics from the GSM network

entities and archiving them in disk files or displaying them for analysis. Because a potential to

collect large amounts of data exists, maintenance personal can select which of the detailed

statistics to be collected based on personal interests and past experience. As a result of

performance analysis, if necessary, an alarm can be set remotely.

The OMC provides system change control for the software revisions and configuration data

bases in the network entities or uploaded to the OMC. The OMC also keeps track of the

different software versions running on different subsystem of the GSM.


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GSM SERVICES

It is important to note that all the GSM services were not introduced since the appearance of

GSM but they have been introduced in a regular way. The GSM Memorandum of Understanding(MoU) defined four classes for the introduction of the different GSM services:

E1: introduced at the start of the service. E2: introduced at the end of 1991. Eh: introduced on availability of half-rate channels. A: these services are optional.Three categories of services can be distinguished:

Teleservices. Bearer services. Supplementary Services.Teleservices

- Telephony (E1 Eh).

- Facsimile group 3 (E1).

- Emergency calls (E1 Eh).

- Teletex.

Short Message Services (E1, E2, A) Using these services, a message of a maximum of 160

alphanumeric characters can be sent to or from a mobile station. If the mobile is powered off,

the message is stored. With the SMS Cell Broadcast (SMS-CB), a message of a maximum of 93

characters can be broadcast to all mobiles in a certain geographical area.

- Fax mail. Thanks to this service, the subscriber can receive fax messages at any fax

machine.

- Voice mail. This service corresponds to an answering machine.

Bearer services

A bearer service is used for transporting user data. Some of the bearer services are

listed below:

Asynchronous and synchronous data, 300-9600 bps (E1). Alternate speech and data, 300-9600 bps (E1).


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Asynchronous PAD (packet-switched, packet assembler/dissembler) access, 300-9600 bps(E1).

Synchronous dedicated packet data access, 2400-9600 bps (E2).Supplementary Services

- Call Forwarding (E1). The subscriber can forward incoming calls to another number ifthe called mobile is busy (CFB), unreachable (CFNRc) or if there is no reply (CFNRy). Call

forwarding can also be applied unconditionally (CFU).

- Call Barring. There are different types of call barring' services:

Barring of All Outgoing Calls, BAOC (E1). Barring of Outgoing International Calls, BOIC (E1). Barring of Outgoing International Calls except those directed toward the Home PLMN

Country, BOIC-exHC (E1).

Barring of All Incoming Calls, BAIC (E1)

Barring of incoming calls when roaming (A).- Call holds (E2) puts an active call on hold.- Call Waiting, CW (E2) informs the user, during a conversation, about another incoming call.

The user can answer, reject or ignore this incoming call.

- Advice of Charge, AoC (E2) provides the user with online charge information.

- Multiparty service (E2) Possibility of establishing a multiparty conversation.

- Closed User Group, CUG (A). It corresponds to a group of users with limited possibilities ofcalling (only the people of the group and certain numbers).

- Calling Line Identification Presentation, CLIP (A). It supplies the called user with the ISDN of

the calling user.

- Calling Line Identification Restriction, CLIR (A). It enables the calling user to restrict the

presentation.

- Connected Line identification Presentation, CoLP (A). It supplies the calling user with the

directory number he gets if his call is forwarded.

- Connected Line identification Restriction, CoLR (A). It enables the called user to restrict the

presentation.

- Operator determined barring (A). Restriction of different services and call types by the

operator.

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