training report bsnl

7/31/2019 Training Report Bsnl

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TRAINING REPORT

On

TELECOMMUNICATION

At

Bharat Sanchar Nigam Limited (BSNL)

CIRCLE TELECOM TRAINING CENTRE, PATNA

DURATION: 05/12/2011 to 30/12/2011

Under guidance of:-

Anand Prakash Singh

SDE (Admn)

SUBMITTED BY:-

Om Prakash Jha

COURSE: B.TECH (ELECTRICAL & ELECTRONICS ENGINEERING)

VIT University, Vellore

Year: 3rd

year (5th

semester)

Reg. No.: 09BEE165


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ACKNOWLEDGEMENT

This report is on vocational training which was undertaken

under Bharat Sanchar Nigam Limited (BSNL) in partial

fulfilment of the requirement for the B.TECH in

(ELECTRICAL AND ELECTRONICS ENGG.) from VIT

UNIVERSITY, VELLORE, Tamil Nadu. The main purpose of

this training was to acquaint myself with practical experienceof actual work condition. I learnt a lot from the practical

experience of the engineering & other personals under

whom i was placed for training. This helped me to develop

the habit of analysing critically various aspects of problem at

the time of decision making.

Submitted By:

Om Prakash Jha


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CERTIFICATE

This is to certify that the project entitled

TELECOMMUNICATION & submitted by Om

Prakash Jha

for the partial fulfilment of electrical & electronics

engineering from VIT UNIVERSITY ,VELLORE

embodies the project done by him under my

supervision.

Anand Prakash Singh

SDE (Admn)


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COMPANY PROFILE

Bharat Sanchar Nigam Limited (abbreviated BSNL) is an Indian state-ownedtelecommunications company headquartered in New Delhi, India. It is the largest

provider of fixed telephony and fourth largest mobile telephony provider in India, and isalso a provider of broadband services. However, in recent years the company's revenueand market share plunged into heavy losses due to intense competition in Indiantelecommunications sector.

BSNL is India's oldest and largest communication service provider (CSP). It had acustomer base of 95 million as of June 2011. It has footprints throughout India exceptfor the metropolitan cities of Mumbai and New Delhi, which are managed by MahanagarTelephone Nigam (MTNL).

Type State-owned enterprise

Industry Telecommunications

Founded 19th century, incorporated 2000

HeadquartersNew Delhi, India

Key peopleR.K. Upadhyay

(Chairman & MD)

Products

Fixed line and mobile telephony,

Internet services, digital television,

IPTV

Revenue27,933 crore (US$5.28 billion)

(2011-12)

Employees 276,306 (August 2011)


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ABSTRACT

Telecommunication networks carry information signals among entities, which are

geographically far apart. An entity may be a computer or human being, a facsimile machine, a

teleprinter, a data terminal and so on. The entities are involved in the process of information

transfer that may be in the form of a telephone conversation (telephony) or a file transfer between

two computers or message transfer between two terminals etc.

With the rapidly growing traffic and untargeted growth of cyberspace, telecommunication

becomes a fabric of our life. The future challenges are enormous as we anticipate rapid growth items

of new services and number of users. What comes with the challenge is a genuine need for more

advanced methodology supporting analysis and design of telecommunication architectures.

Telecommunication has evaluated and growth at an explosive rate in recent years and will

undoubtedly continue to do so.

The communication switching system enables the universal connectivity. The universal

connectivity is realized when any entity in one part of the world can communicate with any other

entity in another part of the world. In many ways telecommunication will acts as a substitute for the

increasingly expensive physical transportation.

The telecommunication links and switching were mainly designed for voice communication.

With the appropriate attachments/equipments, they can be used to transmit data. A modern

society, therefore needs new facilities including very high bandwidth switched data networks, and

large communication satellites with small, cheap earth antennas.

In all my modesty, i wish to record here that a sincere attempt has been made for

the presentation of this project report. I also trust that this study will not only prove to be of

academic interest but also will be able to insight into the area of technical management.


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CONTENT

S No. Description

1. OVERVIEW OF TELECOMMUNICATION NETWORKS

2. BATTERY & POWER PLANT

3. OFC & OFS CONCEPTS

4. OVERVIEW OF BROADBAND

5. TECHNICAL AWARENESS OF GSM MOBILE

6. CDMA TECHNOLOGY


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OVERVIEW OF TELECOMMUNICATION NETWORKS

Introduction

The telephone is a telecommunication device that is used to transmit and receive

electronically or digitally encoded speech between two or more people conversing. It is one of the

most common household appliances in the world today. Most telephones operate through transmission

of electric signals over a complex telephone network which allows almost any phone user to

communicate with almost any other user.

Telecommunication networks carry information signals among entities, which are

geographically far apart. An entity may be a computer or human being, a facsimile machine, a

teleprinter, a data terminal and so on. The entities are involved in the process of information transferthat may be in the form of a telephone conversation (telephony) or a file transfer between two

computers or message transfer between two terminals etc.

With the rapidly growing traffic and untargeted growth of cyberspace, telecommunication

becomes a fabric of our life. The future challenges are enormous as we anticipate rapid growth items

of new services and number of users. What comes with the challenge is a genuine need for more

advanced methodology supporting analysis and design of telecommunication architectures.

Telecommunication has evaluated and growth at an explosive rate in recent years and will

undoubtedly continue to do so.

The communication switching system enables the universal connectivity. The universalconnectivity is realized when any entity in one part of the world can communicate with any other

entity in another part of the world. In many ways telecommunication will acts as a substitute for the

increasingly expensive physical transportation.

The telecommunication links and switching were mainly designed for voice communication.

With the appropriate attachments/equipments, they can be used to transmit data. A modern society,

therefore needs new facilities including very high bandwidth switched data networks, and large

communication satellites with small, cheap earth antennas.

Voice Signal Characteristics

Telecommunication is mainly concerned with the transmission of messages between two

distant points. The signal that contains the messages is usually converted into electrical waves before

transmission. Our voice is an analog signal, which has amplitude and frequency characteristics.

Voice frequencies: - The range of frequencies used by a communication device determines the

communication channel, communicating devices, and bandwidth or information carrying capacity.

The most commonly used parameter that characterizes an electrical signal is its bandwidth of analog


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signal or bit rate if it is a digital signal. In telephone system, the frequencies it passes are restricted

to between 300 to 3400 Hz.

In the field oftelecommunications, a Telephone exchange or a Telephone switch is a system

of electronic components that connects telephone calls. A central office is the physical building used

to house inside plant equipment including telephone switches, which make telephone calls "work" in

the sense of making connections and relaying the speech information.

Switching system fundamentals

Telecommunications switching systems generally perform three basic functions: they

transmit signals over the connection or over separate channels to convey the identity of the called

(and sometimes the calling) address (for example, the telephone number), and alert (ring) the calledstation; they establish connections through a switching network for conversational use during the

entire call; and they process the signal information to control and supervise the establishment and

disconnection of the switching network connection.

In some data or message switching when real-time communication is not needed, the

switching network is replaced by a temporary memory for the storage of messages. This type of

switching is known as store-and-forward switching.

Signaling and control

The control of circuit switching systems is accomplished remotely by a specific form of data

communication known as signaling. Switching systems are connected with one another by

telecommunication channels known as trunks. They are connected with the served stations or

terminals by lines.

In some switching systems the signals for a call directly control the switching devices over

the same path for which transmission is established. For most modern switching systems the signals

for identifying or addressing the called station are received by a central control that processes callson a time-shared basis. Central controls receive and interpret signals, select and establish

communication paths, and prepare signals for transmission. These signals include addresses for use

at succeeding nodes or for alerting (ringing) the called station.

Most electronic controls are designed to process calls not only by complex logic but also by logic

tables or a program of instructions stored in bulk electronic memory. The tabular technique is

known as translator. The electronic memory is now the most accepted technique and is known as

stored program control (SPC). Either type of control may be distributed among the switching devices

rather than residing centrally. Microprocessors on integrated circuit chips are a popular form of

distributed stored program control.
http://en.wikipedia.org/wiki/Telecommunicationshttp://en.wikipedia.org/wiki/Inside_planthttp://en.wikipedia.org/wiki/Telephone_callhttp://www.answers.com/topic/spc-abbreviationhttp://www.answers.com/topic/spc-abbreviationhttp://en.wikipedia.org/wiki/Telephone_callhttp://en.wikipedia.org/wiki/Inside_planthttp://en.wikipedia.org/wiki/Telecommunications


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Development of exchanges

Digital Switching Systems

A Digital switching system, in general, is one in which signals are switched in digital form. These

signals may represent speech or data. The digital signals of several speech samples are time

multiplexed on a common media before being switched through the system.

To connect any two subscribers, it is necessary to interconnect the time-slots of the two speech

samples, which may be on same or different PCM highways. The digitalized speech samples are

switched in two modes, viz., Time Switching and Space Switching. This Time Division Multiplex Digital

Switching System is popularly known as Digital Switching System.The ESS No.1 system was the first fully electronic switching system but not digital. But later came ESS

No.4 system which was digital for trunk portion only. When designed, the cost of A/D conversion

(CODEC) on each subscriber line was seen as prohibitive. So the ESS No.4 system was acting as aTrunk/Tandem exchange but not as a local exchange. So the main difficulty for implementing a

digital local exchange was the implementation of the subscriber line interface. This was solved by

the introduction of Integrated Circuits, which made the digital local exchange economically feasible.

This implementation handles the following functions:

B-Battery feedO-Over-voltage protection (from lightning and accidental power line contact)

R-Ringing

S-Supervisory Signaling

C-Coding (A/D inter conversion & low pass filtering)

H-Hybrid (2W to 4W conversion)

T-Testing the connectivity of SubscriberExamples of digital exchanges (switching systems) include CDOT, OCB, AXE, EWSD, 5ESS etc.


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Secondary Cell ( Conventional )

The Primary requirement of any Telephone System is that service shall be available to the subscriber

at all times. The electrical energy required for signaling, switching, speech transmission etc. in

telephone exchange is derived either directly or indirectly from the public supply. In order to provide

uninterrupted service, the exchange power supply system is designed to give continuous energy to

the system. So provision is also made for alternate source of supply in the event of mains failure or

public supply failure. This emergency energy is derived from

1) Batteries of Secondary Cells.

2) A Combination of battery and prime mover Generator sets.

POWER STACK - VRLA BATTERY

When a conventional flooded battery becomes fully charged, it evolves oxygen and hydrogen gases,

and water is lost from the cell. In Power Stack cells, the oxygen gas generated at the positive plate, is

transported in the gas phase through a highly absorbent and porous glass mat separator to the

negative plate. The microporous glass separator is not completely saturated with electrolyte and the

void space thus available allows an unimpeded access of oxygen to the negative plate. The oxygen

gas gets reduced at the negative plate surface, thereby effectively suppressing the evolution of

hydrogen. Consequently, Power Stack cells do not lose any water under normal operation and

therefore, no topping-up is required.

Voltage:

Power stack cells are 2V units which are assembled in modular racks to get 2V, 6V and 12V modules.

These racks are mounted horizontally and can be stacked one above the other. For maximum service

life, the recommended float voltage is 2.25 Volts per cell. Power Stack cells are normally rated to an

end cell voltage of 1.75 Volts per cell. Where it is necessary to terminate discharge at higher end cell

voltage due to reasons of equipment compatibility, that can be done by providing higher rated

capacities.

Chargers:

Power Stack cells should be charged with constant potential Chargers. The charging current should

be limited to a maximum of 0.2.C10. The widely accepted charging methods use a current of O.1C10.

Float charging is at 2.25 VPC and the recommended boost charge voltage is 2.30 VPC. If the charger

does not have a float-cum-boost mode, it is important to switch over to float after boost not later

than 24 hours under steady current conditions.

Applications: Power Stack cells are designed specially for stand-by applications. The deep discharge

cycle performance combined with excellent float characteristics applications like Telecom. Power

generating stations and sub-stations, uninterrupted Power Supplies and Solar Photovoltaic.


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FRESHENING CHARGE

General Batteries lose some charge during the period to installation. A battery should be

installed and given a freshening charge after receipt as soon as possible. Battery positive (+) terminal

should be connected to charger positive (+) terminal and battery negative (-) terminal to charger

negative (-) terminal.

Constant Voltage Method

Constant voltage is the only charging method recommended. Most modern chargers are of the

constant voltage type.

Determine the maximum voltage that may be applied to the system equipment. This voltage,

divided by the number of cells connected in series, will established the maximum volts per cell (VPC)

that may be used.

SMPS POWER PLANT (SWITCH MODE POWER SUPPLY)

Introduction:-SMPS power plants have the major advantages of extremely small size, weight and

floor space requirement when compared to their thyristorised counterparts. They operate at very

high switching frequencies (20 KHz to 200 KHz), thus having very little audible noise because mains

frequency magnetics is not used.

The disadvantages of such power supplies are mainly with regard to the complexity of both

the power and control circuit, making trouble shooting and repair extremely difficult by ordinarily

trained personnel. However, due to the possibility of modular design in this case, repair can be

carried out by replacement of modules within the power supply. Another major problem with SMPS

power supplies is that they generate very large amount of radio frequency interference as well as

disturbance on its output bus, due to the high switching frequency used at the various internal

stages. This problem can be reduced through the use of properly designed additional RFI filters at

both its input and output.

GENERAL FEATURES OF POWER PLANT

RECTIFIER: - The input diode bridge rectifier converts the supply sinusoidal AC voltage waveform to

unidirectional pulses of rectified sine wave. The bridge consists of four diodes in case of single phase

and six diodes in case of three phase.

FILTER:-The bridge rectifier is followed by a filter capacitor bank to make the DC as smooth as

possible. Filter inductors are not used to reduce the size and weight of the system. This DC bus

voltage will be high corresponding almost to the peak of the input supply voltage. Thus the DC

voltage varies accordingly to the input supply variation.

SWITCHING CONVERTER:-The high voltage DC bus is fed to the switching converter stage which is

the heart of the system. The fundamental concept is to covert the DC bus to either a chopped train

of unidirectional flat topped pulses or to an alternating wave form with flat-topped pulses. In either


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case the pulse repetitive frequency is very high and the widths of the pulses are presentable while

the pulse magnitudes are equal to that of the DC bus.

FERRITE CORE OR METAGLASS X-FORMER:-The unidirectional or alternating pulses generated by the

converter stage is fed to a specially designed transformer that can handle these waveform and

transform them at the secondary winding to a different magnitude in voltage. Thus the high voltage

pulses are reduced to a smaller magnitude while the transformer size is very small due to the

involvement of very high frequencies. However high frequency has its own disadvantages in that.

The core loss will increase exorbitantly in a normal CARGO transformer while the copper loss will

also increase significantly due to the increase in effective resistance because of skin effect. Thus the

core material is special - usually Ferrite Metaglass, which is ceramic type of magnetic material that

exhibits very low losses at high frequencies To reduce the copper loss multi strand conductors are

required with the size of individual conductors restricted so that its full section effectively carries the

current even at high frequency.

RFI &EMI RECTIFIER FILTER DC TO DCSUPPRESSOR CAPACITOR CONVERTER

(AC FILTER) BANK

AC I/P

FERRITE CORE HIGH SPEED FILTER EMI & RFI

OR METAGLASS RECTIFIER SUPPRESSORTRANSFORMER

50V

DC

FUNCTIONAL BLOCK DIAGRAM OF S.M.P.S. SUB-ASSEMBLY

EARTHING IN TELEPHONE EXCHANGES

EARTH ELECTRODE SYSTEMS ARE INSTALLED AT TELEPHONE EXCHANGES(a) To provide an earth connection to the battery circuit, to stabilize the potential of the

lines and equipment with respect to earth, thus reducing the risk of talk. This is due to lines and

equipment assuming an indefinite voltage with respect to earth, and enabling single pole switching

to be used on the exchange power plant. This also reduces the number of fuses required in the

circuit and avoids the need of insulating the earthed conductor i.e. positive bus bar.

(b) To provide a direct to person and plant against leakage from station apparatus.

(c) To provide protection to persons and plant against leakage from station power

wiring to metallic apparatus, frames etc.

(d) To provide means of earthing electrostatic screen on apparatus and of earthing lead

sheaths of cables.

(e) To complete the circuit of telephone systems employing a common path forsignaling purposes.


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Fiber-Optic Applications

FIBRE OPTICS: The use and demand for optical fiber has grown tremendously and

optical-fiber applications are numerous. Telecommunication applications are widespread,

ranging from global networks to desktop computers. These involve the transmission of voice,

data, or video over distances of less than a meter to hundreds of kilometers, using one of a

few standard fiber designs in one of several cable designs.

Carriers use optical fiber to carry plain old telephone service (POTS) across their

nationwide networks. Local exchange carriers (LECs) use fiber to carry this same service

between central office switches at local levels, and sometimes as far as the neighborhood or

individual home (fiber to the home [FTTH]).

Optical fiber is also used extensively for transmission of data. Multinational firms

need secure, reliable systems to transfer data and financial information between buildings to

the desktop terminals or computers and to transfer data around the world. Cable televisioncompanies also use fiber for delivery of digital video and data services. The high bandwidth

provided by fiber makes it the perfect choice for transmitting broadband signals, such as

high-definition television (HDTV) telecasts. Intelligent transportation systems, such as smart

highways with intelligent traffic lights, automated tollbooths, and changeable message signs,

also use fiber-optic-based telemetry systems.

Another important application for optical fiber is the biomedical industry. Fiber-optic systems

are used in most modern telemedicine devices for transmission of digital diagnostic images.

Other applications for optical fiber include space, military, automotive, and the industrial

sector.

ADVANTAGES OF FIBRE OPTICS:Fibre Optics has the following advantages:

SPEED: Fiber optic networks operate at high speeds - up into the gigabits

BANDWIDTH: large carrying capacity

DISTANCE: Signals can be transmitted further without needing to be "refreshed" or

strengthened.

RESISTANCE: Greater resistance to electromagnetic noise such as radios, motors or other

nearby cables.

MAINTENANCE: Fiber optic cables costs much less to maintain.

Fiber Optic System:

Optical Fibre is new medium, in which information (voice, Data or Video) is transmitted through a

glass or plastic fibre, in the form of light, following the transmission sequence give below:

(1) Information is Encoded into Electrical Signals.

(2) Electrical Signals are Coverted into light Signals.

(3) Light Travels Down the Fiber.

(4) A Detector Changes the Light Signals into Electrical Signals.

(5) Electrical Signals are Decoded into Information.


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OF TRANSMISSION SYSTEMS & THEIR FEATURES

SDH is an ITU-T standard for a high capacity telecom network. SDH is a synchronous digital

transport system, aim to provide a simple, economical and flexible telecom infrastructure. The basis

of Synchronous Digital Hierarchy (SDH) is synchronous multiplexing - data from multiple tributary

sources is byte interleaved.

SDH brings the following advantages to network providers:

High transmission rates

Transmission rates of up to 40 Gbit/s can be achieved in modern SDH systems. SDH is therefore themost suitable technology for backbones, which can be considered as being the super highways in

today's telecommunications networks.

Simplified add & drop function

Compared with the older PDH system, it is much easier to extract and insert low-bit rate channels

from or into the high-speed bit streams in SDH. It is no longer necessary to demultiplex and then

remultiplex the plesiochronous structure.

High availability and capacity matching

With SDH, network providers can react quickly and easily to the requirements of their customers. For

example, leased lines can be switched in a matter of minutes. The network provider can use

standardized network elements that can be controlled and monitored from a central location by meansof a telecommunications network management (TMN) system.

Reliability

Modern SDH networks include various automatic back-up and repair mechanisms to cope with

system faults. Failure of a link or a network element does not lead to failure of the entire network

which could be a financial disaster for the network provider. These back-up circuits are also

monitored by a management system.

Future-proof platform for new services

Right now, SDH is the ideal platform for services ranging from POTS, ISDN and mobile radio

through to data communications (LAN, WAN, etc.), and it is able to handle the very latest services,

such as video on demand and digital video broadcasting via ATM that are gradually becomingestablished.


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Interconnection SDH makes it much easier to set up gateways between different network providers

and to SONET systems. The SDH interfaces are globally standardized, making it possible to combine

network elements from different manufacturers into a network. The result is a reduction in equipment

costs as compared with PDH.

Network Elements of SDH

Figure given below is a schematic diagram of a SDH ring structure with various tributaries. The

mixture of different applications is typical of the data transported by SDH. Synchronous networks

must be able to transmit plesiochronous signals and at the same time be capable of handling future

services such as ATM.

Current SDH networks are basically made up from four different types of network element. The

topology (i.e. ring or mesh structure) is governed by the requirements of the network provider.

Regenerators

Regenerators as the name implies, have the job of regenerating the clock and amplitude relationships

of the incoming data signals that have been attenuated and distorted by dispersion. They derive their

clock signals from the incoming data stream. Messages are received by extracting various 64 kbit/s

channels (e.g. service channels E1, F1) in the RSOH (regenerator section overhead). Messages can

also be output using these channels.

Terminal Multiplexer

Terminal multiplexers Terminal multiplexers are used to combine plesiochronous and synchronous

input signals into higher bit rate STM-N signals.

Schematic diagram of hybrid communications networks

Add/drop Multiplexers (ADM)

Add/drop multiplexers (ADM) Plesiochronous and lower bit rate synchronous signals can be

extracted from or inserted into high speed SDH bit streams by means of ADMs. This feature makes it

possible to set up ring structures, which have the advantage that automatic back-up path switching is

possible using elements in the ring in the event of a fault.

Digital Cross-connect

Digital cross-connects (DXC) This network element has the widest range of functions. It allows

mapping of PDH tributary signals into virtual containers as well as switching of various containers up

to and including VC-4.


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OVERVIEW OF BROAD BAND

Definition of Broad Band

Broadband is often called high-speed Internet, because it usually has a high rate of data

transmission. In general, any connection to the customer of 256 kbit/s or more is considered

broadband.

HOW IS BROADBAND DIFFERENT FROM DIAL-UP SERVICE?

Broadband service provides higher speed of data transmissionAllows more contentto be carried through the transmission pipeline.

Broadband provides access to the highest quality Internet servicesstreamingmedia, VoIP (Internet phone), gaming and interactive services. Many of these current

and newly developing services require the transfer of large amounts of data whichmay not be technically feasible with dial-up service. Therefore, broadband servicemay be increasingly necessary to access the full range of services and opportunitiesthat the Internet can offer.

Broadband is always ondoes not block phone lines and no need to reconnect tonetwork after logging off.

Less delay in transmission of content when using broadband.

WHY IS BROADBAND IMPORTANT?

Broadband can provide you with the technical capability to access a wide range of

resources, services and products that can enhance your life in a variety of ways. These

resources, services and products include,

Education, Culture, & Entertainmento Broadband can overcome geographical and financial barriers to provideaccess to a wide range of educational, cultural and recreational opportunities andresources.

Tele-health & Telemedicineo Broadband can facilitate provision of medical care to unserved and underservedpopulations through remote diagnosis, treatment, monitoring and consultations withspecialists.

Economic Development/E-CommerceoBroadband can promote economic development and revitalization through electroniccommerce (e-commerce) by:

Creating new jobs and attracting new industries. Providing access to regional, national and worldwide markets.

Electronic Government (E-Government)

oElectronic government can help streamline peoples interaction with governmentagencies and provide information about government policies, procedures, benefits andprograms.

Public Safety and Homeland Security

oBroadband can help protect the public by facilitating and promoting public safetyinformation and procedures, including, but not limited to:


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Early warning/public alert systems and disaster preparation programs. Remote security monitoring and real time security background checks. Backup systems for public safety communications networks.

Broadband Communications ServicesoBroadband provides access to new telecommunications technologies such as VoiceOver Internet Protocol (VoIP) allowing voice communication using the Internet.

Communications Services for People With DisabilitiesoBroadband permits users of Telecommunications Relay Services (TRS) to use VideoRelay Services (VRS) to communicate more easily, quickly and expressively with voicetelephone users.

TYPES OF BROADBAND CONNECTIONS

Broadband includes several high-speed transmission technologies such as:

Digital Subscriber Line (DSL) Cable Modem Fiber Wireless Satellite Broadband over Power lines (BPL)

The broadband technology you choose will depend on a number of factors. These may

include whether you are located in an urban or rural area, how broadband Internet access is

packaged with other services (like voice telephone and home entertainment), price and

availability.

What is Broadband Service?

Broadband refers to a connection that has capacity to transmit large amount of data at high

speed. Presently a connection having download speeds of 256 kbps or more is classified as

broadband. When connected to the Internet broadband connection allows surfing or

downloading much faster than a dial-up or any other narrowband connections. BSNL offers 2

Mbps minimum download speed for its Broadband connections.

Requirement for providing Broad Band connection

1. Personal Computer2. ADSL Modem

3. Land Line Connection4. Splitter for separating telephone from Personal computer.

What is ADSL?

ADSL stands for Asymmetric Digital Subscriber Line. It is a technology that allows copper

telephone pairs to be used to provide a broadband connection. It provides always-on

Internet connection that is automatically established once the PC and ADSL modem are

switched on.


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Modem Connections

The following shows the switch and various connectors that are equipped on the rear panel

of the ADSL modem

1. Power Port This is where you will connect the power adapter.

2. Console Port Reserved for future development.

3. LAN Port This LAN (Local Area Network) port connects to your PC with network cable included

in your kit. You can also connect network devices, such as hubs and switches with a straight- through

RJ-45 cable or use a cross-over RJ-45 cable to connect a router (cross-over cable not supplied).

4. Line Port Connects your modem to your telephone line.

INSTALLATION

ADSL Installation Kit Contents

1 -ADSL Modem

1 - Ethernet cable

1 - Telephone cable

1 - ADSL Filter

1 - Phone jack splitter

1 - DC power adapter


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TECHNICAL AWARENESS OF GSM MOBILE

Principle of Mobile Communication

Multiple Access methodologyThe technique of dynamically sharing the finite limited radio spectrum by multiple users is called

Multiple Access Technique.

Generally there are three different types of multiple access technologies. They are

Frequency Division Multiple Access (FDMA)

Time Division Multiple Access (TDMA)

Code Division multiple Access (CDMA)

Frequency Division Multiple Access (FDMA):

FDMA is a familiar method of allocating bandwidth, where a base station is allowed to transmit on

one or more number of preassigned carrier frequencies and a mobile unit transmits on

corresponding reverse channels.

Time Division Multiple Access (TDMA)

In a TDMA system each channel is split up into time segments, and a transmitter

is given exclusive use of one or more channels only during a particular time

period.

Duplexing and Multiple Access Techniques in use:

No Name of System Multiple Access Duplexing1 GSM FDMA-TDMA FDD

2 CDMA CDMA FDD

FREQUENCY ALLOCATION

Two frequency bands have been allocated for the GSM system:

The band 890-915 MHz and 1710-1785 MHz has been allocated for the uplink direction

(transmitting from the mobile station to the base station).

The band 935-960 MHz and 1805-1880 MHz has been allocated for the downlink direction

(transmitting from the base station to the mobile station).

ARCHITECTURE OF THE GSM NETWORK


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Subsystems and network elements in GSM

The GSM network is called Public Land Mobile Network (PLMN). It is organised in three subsystems:

Base Station Subsystem (BSS)

Network Switching Subsystem (NSS) Network Management Subsystem (NMS)

The three subsystems, different network elements, and their respective tasks are presented in the

following.

1. Network Switching Subsystem (NSS)

The Network Switching Subsystem (NSS) contains the network elements MSC, GMSC, VLR, HLR, AC

and EIR.

The main functions of NSS are:

Call control

This identifies the subscriber, establishes a call, and clears the connection after the conversation is

over.

Charging

This collects the charging information about a call (the numbers of the caller and the called

subscriber, the time and type of the transaction, etc.) and transfers it to the Billing Centre.

Mobility management

This maintains information about the subscriber's location.

Signalling

This applies to interfaces with the BSS and PSTN.

Subscriber data handling

This is the permanent data storage in the HLR and temporary storage of relevant data in the VLR.

Mobile services Switching Centre (MSC)

Mobile-services Switching Center (MSC) performs the switching functions for all mobile stations

located in the geographic area covered by its assigned BSSs. Functions performed include interfacing

with the Public Switched Telephone Network (PSTN) as well as with the other MSCs and other

system entities, such as the HLR, in the PLMN.

Home Location Register (HLR)

The Home Location Register (HLR) contains the identities of mobile subscribers (called International

Mobile Subscriber Identities or IMSIs), their service parameters, and their location information.

In summary, the HLR contains:

Identity of mobile subscriber

ISDN directory number of mobile station

Subscription information on teleservices and bearer services

Service restrictions (if any)


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Supplementary services

Location information for call routing

Visitor Location Register (VLR)

The Visitor Location Register (VLR) contains the subscriber parameters and location information for

all mobile subscribers currently located in the geographical area (i.e., cells) controlled by that VLR.

In summary, the VLR contains:

Identity of mobile subscriber

Any temporary mobile subscriber identity

ISDN directory number of mobile

A directory number to route calls to a roaming station

Location area where the mobile station is registered

Copy of (part of) the subscriber data from the HLR

Equipment Identity Register (EIR)

The Equipment Identity Register (EIR) is accessed during the equipment validation procedure when a

mobile station accesses the system. It contains the identity of mobile station equipment (called

International Mobile Station Equipment Identity or IMEI) which may be valid, suspect, or known to

be fraudulent.

This contains:

White or Valid list - List of valid MS equipment identities

Grey or Monitored list - List of suspected mobiles under observation

Black or prohibited list - List of mobiles for which service is barred.

Authentication Center (AUC)

The Authentication Center (AUC):

Contains subscriber authentication data called Authentication Keys (Ki)

Generates security related parameters needed to authorize service using Ki

Generates unique data pattern called a Cipher Key (Kc) needed for encrypting userspeech and data

2. Base Station Subsystem (BSS)

The Base Station Subsystem is responsible for managing the radio network, and it is controlled by an

MSC. Typically, one MSC contains several BSSs. A BSS itself may cover a considerably largegeographical area consisting of many cells (a cell refers to an area covered by one or more frequency

resources). The BSS consists of the following elements:

BSC Base Station Controller

BTS Base Transceiver Station

TRAU Transcoder and Rate Adaptation Unit (often referred to as TC (Transcoder))

Radio path control

In the GSM network, the Base Station Subsystem (BSS) is the part of the network taking care of radio

resources, that is, radio channel allocation and quality of the radio connection.

3. OPERATION AND MAINTENANCE CENTER (OMC)

The Operations and Maintenance Center (OMC) is the centralized maintenance and diagnostic heart

of the Base Station System (BSS). It allows the network provider to operate, administer, and monitorthe functioning of the BSS.


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CDMA ACCESS A CONCEPT

On the receive side only the signal energy with the selected binary sequence code is accepted and

original information content (data) is recovered. The other users signals, whose codes do not match

contribute only to the noise and are not despread back in bandwidth. This transmission and

reception of signals differentiated by codes using the same frequency simultaneously by a number

of users is known as Code Division Multiple Access (CDMA) Technique as opposed to conventional

method of Frequency Division Multiple Access and Time Division Multiple Access.

The salient features of a typical CDMA system are as follows:

Frequency of operation: 824-849 MHz and 869-894 MHz

Duplexing Method: Frequency Division Duplexing (FDD)

Access Channel per carrier: Maximum 61 Channels

RF Spacing: 1.25 MHz

Coverage: 5 Km with hand held telephones and approx.

20 Km with fixed units

Advantages: CDMA wireless access provides the following unique advantages.

Larger Capacity:

Let us discuss this issue with the help of Shannons Theorem. It states that the channel capacity is

related to product of available band width and S/N ratio.

C = W log 2 (1+S/N)

Where C = channel capacity

W = Band width available

S/N = Signal to noise ratio.

It is clear that even if we improve S/N to a great extent the advantage that we are expected to get in

terms of channel capacity will not be proportionally increased. But instead if we increase the

bandwidth (W), we can achieve more channel capacity even at a lower S/N. That forms the basis of

CDMA approach, wherein increased channel capacity is obtained by increasing both W & S/N. The

S/N can be increased by devising proper power control methods.

Vocoder and variable data rates:

As the telephone quality speech is band limited to 4 KHz when it is digitized with PCM its bit rate

rises to 64Kb/s vocoding compress it to a lower bit rate to reduce bandwidth. The transmitting

vocoder takes voice samples and generates an encoded speech/packet for transmission to the

receiving vocoder. The receiving vocoder decodes the received speech packet into voice samples.

One of the important feature of the variable rate vocoder is the use of adaptive threshold to

determine the required data rate. Vocoders are variable rate vocoders. By operating the vocoder at

half rate on some of the frames the capacity of the system can be enhanced without noticeable

degradation in the quality of the speech. This phenomenon helps to absorb the occasional heavy

requirement of traffic apart from suppression of background noise. Thus the capacity advantagemakes spread spectrum an ideal choice for use in areas where the frequency spectrum is congested.


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Less (Optimum) Power per cell:

Power Control Methods: As we have already seen that in CDMA the entire bandwidth of 1.25 MHz is

used by all the subscribers served in that area. Hence they all will be transmitting on the same

frequency using the entire bandwidth but separated by different codes. At the receiving end the

noise contributed by all the subscribers is added up. To minimize the level of interfering signals in

CDMA, very powerful power control methods have been devised and are listed below:

1. Reserve link open loop power control

2. Reserve link closed loop power control

3. Forward link power control

The objective of open loop power control in the reverse link (Mobile to Base) is that the mobile

station should adjust its transmit power according to the changes in its received power from the

base. Open loop power control attempts to ensure that the received signal strength at the base

station from different mobile stations, irrespective of their distances from the base site, should be

same.

In Closed loop power control in reverse link, the base station provides rapid corrections to the

mobile stations open loop estimates to maintain optimum transmit power by the mobile stations.

The base station measures the received signal strength from the mobile connected to it and

compares it with a threshold value and a decision is taken by the base every 1.25 ms to either

increase or decrease the power of the mobile.

In forward link power control (Base to Mobile) the cell (base) adjusts its power in the forward link

for each subscriber, in response to measurements provided by the mobile station so as to provide

more power to the mobile who is relatively far away from the base or is in a location experiencing

more difficult environment.

These power control methods attempt to have an environment which permits high quality

communication (good S/N) and at the same time the interference to other mobile stations sharing

the same CDMA channel is minimum. Thus more numbers of mobile station are able to use the

system without degradation in the performance. Apart from the capacity advantage thus gained

power control extends the life of the battery used in portables and minimizes the concern of ill

effects of RF radiation on the human body.

Seamless Hand-off:

CDMA provides soft hand-off feature for the mobile crossing from one cell to another cell by

combining the signals from both the cells in the transition areas. This improves the performance of

the network at the boundaries of the cells, virtually eliminating the dropped calls.

No Frequency Planning:

A CDMA system requires no frequency planning as the adjacent cells use the same common

frequency. A typical cellular system (with a repetition rate of 7) and a CDMA system is shown in the

following figures which clearly indicates that in a CDMA network no frequency planning is required.

CDMA Frequency


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Frequency Reuse of 7 in GSM

High Tolerance to Interference:

The primary advantage of spread spectrum is its ability to tolerate a fair amount of interfering

signals as compared to other conventional systems. This factor provides a considerable advantage

from a system point of view.

Multiple Diversity:

Diversity techniques are often employed to counter the effect of fading. The greater the number ofdiversity techniques employed, the better the performance of the system in a difficult propagation

environment.

CDMA has a vastly improved performance as it employs all the three diversity techniques in the form

of the following:

A .Frequency Diversity: A wide band RF signal of 1.25 MHz being used.

B. Space Diversity: Employed by way of multipath rake receiver.

C. Time Diversity: Employed by way of symbol interleaving error detection and correction coding.

Capacity Considerations

Let us discuss a typical CDMA wireless in local loop system consisting of a single base station located

at the telephone exchange itself, serving a single cell. In order to increase the number of

subscribers served the cell is further divided into sectors. These sectors are served by directional

antennas.

The capacity of a cellular system is claimed to be 20-40 active lines per sector per 1.25 MHz for a

single CDMA Radio Channel. In WLL environment assuming an average busy hour traffic of 0.1

Erlang, 400 subscribers can be served per sector over a single 1.25 MHz channel.

Assuming typically six sectors in a cell the total capacity of a CDMA network consisting of 1.25 MHz

duplex channels is 2400 (400x6) subscribers.

Conclusion

Hence we see that use of common frequency, multipath rake receiver, power control & variable bit

rate vocoding and soft hand-off features of CDMA give us the benefits of no frequency planning,

larger capacity, flexibility alongwith high performance quality.


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References:-

Overview of Telecommunication Networks

Compiled by MC Faculty ALTTC, Ghaziabad

Training material

From CIRCLE TELECOM TRAINING CENTRE, PATNA


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CONCLUSION

The opportunity of being able to be in BSNL and getting

to know the actual working condition has really been a

privilege. The operations of each unit and the detailed

explanation by our instructor has proved quite fruitful.

We sincerely hope that this training has left us brighter

than before and will help in times to come. We also like

to take the opportunity to thank our chief instructor

Mr.Anand Prakash Singhand other staff members for

their excellent support and care for us.

Yours sincerely

Om Prakash Jha

training report bsnl

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