Internship Report

1. COMPANY PROFILE

Bharat Sanchar Nigam Limited is a state-owned telecommunications company headquartered in New Delhi, India. BSNL is one of the largest Indian cellular service providers, with over 87.1 million subscribers as of April 2011, and the largest land line telephone provider in India.

BSNL is India's oldest and largest communication service provider (CSP). It had a customer base of 90 million as of June 2008. It has footprints throughout India except for the metropolitan cities of Mumbai and New Delhi, which are managed by Mahanagar Telephone Nigam Limited (MTNL). As of June 30, 2010, BSNL had a customer base of 27.45 million wireline and 72.69 million wireless subscribers.

BSNL is the only service provider, making focused efforts and planned initiatives to bridge the Rural-Urban Digital Divide ICT sector. In fact there is no telecom operator in the country to beat its reach with its wide network giving services in every nook & corner of country and operates across India except Delhi & Mumbai. Whether it is inaccessible areas of Siachen glacier and North-eastern region of the country. BSNL serves its customers with its wide bouquet of telecom services.

BSNL is numero uno operator of India in all services in its license area. The company offers vide ranging & most transparent tariff schemes designed to suite every customer.BSNL cellular service, CellOne, has 55,140,282 2G cellular customers and 88,493 3Gcustomers as on 30.11.2009. In basic services, BSNL is miles ahead, with 85 per cent share of the subscriber base and 92 percent share in revenue terms. BSNL has more than 2.5 million WLL subscribers and 2.5 million Internet Customers who access Internet through various modes. BSNL has been adjudged as the NUMBER ONE ISP in the country. 

BSNL has set up a world class multi-gigabit, multi-protocol convergent IP infrastructure that provides convergent services like voice, data and video through the same Backbone and Broadband Access Network. At present there are 0.6 million DataOne broadband customers. The company has vast experience in Planning, Installation, network integration and Maintenance

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of Switching & Transmission Networks and also has a world class ISO 9000 certified Telecom Training Institute.

2. TELECOM NETWORK

We can broadly classify any telecom network as three parts.

1) Access Network: It is the one which connects the CPE (Customer premises Equipment) to the Switching Location.

Example: Copper wire, Microwave, OFC.

2) Switching network: It is the location of the switching station.

Example: Telephone Exchange, MSC etc.

3) Core Network: Different switching networks will be combined to form a Core network.

Layout of a WIRED TELECOM NETWORK -

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Fig 1 : Wired Telecom Network

MDF (Main Distribution Frame) –

A Main Distribution Frame (MDF or main frame) is a signal distribution frame for connecting equipment (inside plant) to cables and subscriber carrier equipment (outside plant).

The MDF is a termination point within the local telephone exchange where exchange equipment and terminations of local loops are connected by jumper wires at the MDF. All cable copper pairs supplying services through user telephone lines are terminated at the MDF and distributed through the MDF to equipment within the local exchange e.g. repeaters and DSLAM. Cables to intermediate distribution frames terminate at the MDF. Trunk cables may terminate on the same MDF or on a separate trunk main distribution frame (TMDF).

Pillars –

PILLARs are the intermediate testing boxes where the primary and distribution cable terminates. Underground cables that connect the MDF and pillars are called as Primary cables. U/G cables that connect the pillar and the DPs (Distribution Point) in that pillar area are called as Distribution cables.

DP (Distribution Point) –

A Distribution Point is the point from where the connection wires are extended to the customers. A DP’s capacity can be 5, 10, 20 or 50 pairs. Each DP is given with a 4 digit number, in which the first 2 digits indicate the pillar number, in which that DP is working. Through a Drop wire, the connection is extended into customer premises from the distribution point.

2.1 HOW A TELECOM EXCHANGE WORKS –

A telephone exchange or 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.

The basic block diagram for a telecom exchange is as follows –

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Fig 2: Block diagram of telephone exchange

Engine and Alternator: It provides AC output in the event of commercial power supply failure. The diesel engine provides the prime mover to the alternator so that the alternating current is generated to support the exchange systems.

Battery and Power Plant: Batteries provides continuous DC voltage for uninterrupted exchange operation. The power plant keeps the batteries on float so as to give out the dc output in the event of commercial power supply failure. The rectifiers in the power plant convert sc into dc.

OMC (Operation and Maintenance Control): It contains input-output processor terminals, visual display units, printers, catridges, etc. It controls the entire operation of exchange data and billing data. The new connections, adding and removing of facilities to the subscriber is done in the OMC room.

Main Distribution Frame: It provides the physical connectivity from the exchange side to the line side. All the primary cables are terminated at the MDF line side and all the switching cables are terminated at the exchange side on the MDF crone modules.

Switch: It provides the switching facility and connection to the outside of the exchange. The switch room contains actual telephone switching hardware such as cabinets, racks, slots and cards. Switching is the most important part of the exchange process.

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Battery-A

Battery-B

Eng/Alt

Power Plant

Switch RoomOM

C

MDF

Extnl.plant

1. SWITCHING

A switch is defined as establishing a temporary connection from the calling subscriber to the called subscriber. Switch is a device that makes the connection and breaks the connection. It is a device that channels incoming data from any of the multiple input ports to the specific input that will take the data toward its intended destination.

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.

Fig 3: General Diagram of a Digital Switch

AU: Subscriber rack for feeding current and other functionalities

Interface: Interface between main exchange and subscribers/Trunks

Switch: Main switching network and other exchange equipment

MDD: Magnetic Disk Drive for storing data

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AU

SWITCH

interface

interface

control

MDD MTD OMT

subs

trunks

MTD: Magnetic Tape Drive for backup and regeneration of the exchange

OMT: Operation and Maintenance terminal to issue various commands.

Control: Processor to control peripherals and interfacing Main Exchange.

Printer: To get hard copy for all the reports

3.1 TYPES OF DSS -

There are two types of Digital Switching Systems.-

1) Space Division Switching System2) Time Division Switching System

Generally, a digital switching system has several time division multiplexed (PCM) samples. These PCM samples are conveyed on PCM highways (the common path over which many channels can pass with separation achieved by time division). Switching of calls in this environment , requires placing digital samples from one time-slot of a PCM multiplex in the same or different time-slot of another PCM multiplex.

In the space-switching mode, corresponding time-slots of I/C and O/G PCM highways are interconnected. As a sample, in a given time-slot, TSi of an I/C HWY, say HWY1, is switched to same time-slot, TSi of an O/G HWY, SAY HWY2. Obviously there is no delay in switching of the sample from one highway to another highway since the sample transfer takes place in the same time-slot of the PCM frame.

Time Switching, on the other hand, involves the interconnection of different time-slots on the incoming and outgoing highways by re-assigning the channel sequence. For example, a time-slot TSx of an I/C Highway can be connected to a different time-slot., TSy, of the outgoing highway. In other words, a time switch is, basically, a time-slot changer.

Different types of Electronic Switches are –

(1) C-DOT : Indian Made

(2) E10B : France Made

(3) OCB : France Made

(4) EWSD : Germany Made

(5) 5ESS : USA Made

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Of these, the most important ones include C-DOT and EWSD.

3.2 C-DOT –

C-DOT DSS MAX is a universal digital switch which can be configured for different applications as local, transit, or integrated local and transit switch. High traffic/load handling capacity up to 8,00,000 BHCA with termination capacity of 40,000 Lines as Local Exchange or 15,000 trunks as Trunk Automatic Exchange, the C-DOT DSS family is ideally placed to meet the different requirements of any integrated digital network.

C-DOT DSS MAX exchanges can be configured using four basic modules

• Base Module - The Base Module (BM) is the basic growth unit of the system. It interfaces the external world to the switch. The interfaces may be subscriber lines, analog and digital trunks, CCM and PBX lines. Each Base Module can interface upto 2024 terminations.

• Central Module - Central Module (CM) consists of a message switch and a space switch to provide inter-module communication and perform voice and data switching between Base Modules. It provides control message communication between any two Base Modules, and between Base Modules and Administrative Module for operation and maintenance functions. It also provides clock and synchronization on a centralized basis.

• Administrative Module - Administrative Module (AM) performs system-level resource allocation and processing function on a centralized basis. It performs all the memory and time intensive call processing support functions and also administration and maintenance functions. It communicates with the Base Module via the Central Module. It supports the Input Output Module for providing man-machine interface. It also supports the Alarm Display Panel for the audiovisual indication of faults in the system.

• Input Output Module - Input, Output Module (IOM) consists of duplicated Input Output Processor (IOP). The Input Output Processor (IOP) is a general-purpose computer with UNIX Operating System. It is used as the front-end processor in C-DOT DSS. It handles all the input and output functions in C-DOT DSS. The IOP is connected to AP/BP via HDLC links.

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3.3 EWSD –

EWSD (Electronic Digital Switching System/Electronic World Switch Digital in English) is one of the most widely installed telephone exchange systems in the world. EWSD can work as a local or tandem switch or combined local/tandem, and for landline or mobile phones. It is manufactured by Siemens AG, who claims that EWSD switches perform switching for over 160 million subscriber lines in more than 100 countries.

Main subsystems are:

CP (Central Processor)

MB (Message Buffer)

CCNC (Common Channel Network Control)

LINE (Analog Line Group)

LTG (Line Trunk Group)

DLU (Digital Line Unit)

SN (Switching Network)

PA (ISDN Primary Access) 

All system units are redundant so the inactive side can take over immediately in case of an error.

DLU handles analog and ISDN lines and includes codecs for analog lines, one of

the BORSCHT functions for subscriber lines. Digital signals are assigned a time slot. The

Switching Network consists of 4 space division stages of 16x16 switches, and a time division

section with 16 stages of 4x4 switches. Control is provided by the CP Co-ordination Processor.

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2. MOBILE COMMUNICATION

A mobile phone, cell phone or hand phone is an electronic device used to make mobile

telephone calls across a wide geographic area, served by many public cells, allowing the user to

be mobile. By contrast, a cordless telephone is used only within the range of a single, private

base station, for example within a home or an office.

A mobile phone can make and receive telephone calls to and from the public telephone

network which includes other mobiles and fixed-line phones across the world. It does this by

connecting to a cellular network provided by a mobile network operator.

In addition to telephony, modern mobile phones also support a wide variety of

other services such as text messaging, MMS, email, Internet access, short-range wireless

communications (infrared, Bluetooth), business applications, gaming and photography. Mobile

phones that offer these more general computing capabilities are referred to as smart phones.

Generation Gap:

Generation #1 – Analog [routines for sending voice]

• All systems are incompatible

• No international roaming

Generation #2 – digital [voice encoding]

• Increased capacity

• More security

• Compatibility

• Can use TDMA or CDMA for increasing capacity

Generation #2.5 – packet-switching

• Connection to the internet is paid by packets and not by connection time.

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• Connection to internet is cheaper and faster [up to 56KBps]

• The service name is GPRS – General Packet Radio Services

Generation #3- The present future

• Permanent web connection at 2Mbps

• Internet, phone and media: 3 in 1

• The standard based on GSM is called UMTS.

• The EDGE standard is the development of GSM towards 3G.

The genius of the cellular system is the division of a city into small  cells. This allows extensive frequency reuse across a city, so that millions of people can use cell phones simultaneously. In a typical analog cell-phone system, the cell-phone carrier receives about 800 frequencies to use across the city. The carrier chops up the city into cells. Each cell is typically sized at about 10 square miles(26 square kilometers). Cells are normally thought of as hexagons on a big hexagonal grid, like this:

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Fig 4: Because cell phones and base stations use low-power transmitters, the same frequencies can be reused in non-adjacent cells.

4.1 HOW A CALL IS CONNECTED -

When you first power up the phone, it listens for an SID on the control channel. The control channel is a special frequency that the phone and base station use to talk to one another about things like call set-up and channel changing. If the phone cannot find any control channels to listen to, it knows it is out of range and displays a "no service" message.

When it receives the SID, the phone compares It to the SID programmed into the phone. If the SIDs match, the phone knows that the cell it is communicating with is part of its home system.

Along with the SID, the phone also transmits a registration request, and the MTSO keeps track of your phone's location in a database -- this way, the MTSO knows which cell you are in when it wants to ring your phone.

The MTSO gets the call, and it tries to find you. It looks in its database to see which cell you are in.

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4

5

6

7

2

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The MTSO picks a frequency pair that your phone will use in that cell to take the call.

The MTSO communicates with your phone over the control channel to tell it which frequencies to use, and once your phone and the tower switch on those frequencies, the call is connected. Now, you are talking by two-way radio to a friend.

As you move toward the edge of your cell, your cell's base station notes that your signal strength is diminishing. Meanwhile, the base station in the cell you are moving toward (which is listening and measuring signal strength on all frequencies, not just its own one-seventh) sees your phone's signal strength increasing. The two base stations coordinate with each other through the MTSO, and at some point, your phone gets a signal on a control channel telling it to change frequencies. This hand off switches your phone to the new cell.

Let's say you're on the phone and you move from one cell to another -- but the cell you move into is covered by another service provider, not yours. Instead of dropping the call, it'll actually be handed off to the other service provider.

If the SID on the control channel does not match the SID programmed into your phone, then the phone knows it is roaming. The MTSO of the cell that you are roaming in contacts the MTSO of your home system, which then checks its database to confirm that the SID of the phone you are using is valid. Your home system verifies your phone to the local MTSO, which then tracks your phone as you move through its cells. And the amazing thing is that all of this happens within seconds.

4.2 CDMA –

One of the basic concepts in data communication is the idea of allowing several transmitters to send information simultaneously over a single communication channel. This allows several users to share a band of frequencies. This concept is called multiple access. 

  CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same physical channel. By contrast, time division multiple access (TDMA) divides access by time, while frequency-division multiple access(FDMA) divides it by frequency. CDMA is a form of spread-spectrum signalling, since the modulated coded signal has a much higher data bandwidth than the data being communicated.

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Fig 5 : Differences b/w FDMA, TDMA and CDMA

FDMA---Different users use different frequency

TDMA---Different user use different time slot of one frequency

CDMA---Different user use same frequency at the same time, but with different spreading code

CDMA is a spread spectrum multiple access[1] technique. A spread spectrum technique spreading the bandwidth of the data uniformly for the same transmitted power. Spreading code is a pseudo-random code that has a narrow Ambiguity function, unlike other narrow pulse codes. In CDMA a locally generated code runs at a much higher rate than the data to be transmitted. Data for transmission is combined via bitwise XOR(exclusive OR) with the faster code. 

Each user in a CDMA system uses a different code to modulate their signal. Choosing the codes used to modulate the signal is very important in the performance of CDMA systems. The best performance will occur when there is good separation between the signal of a desired user and the signals of other users. The separation of the signals is made by correlating the received signal with the locally generated code of the desired user. If the signal matches the desired user's code then the correlation function will be high and the system can extract that signal. If the desired user's code has nothing in common with the signal the correlation should be as close to zero as possible (thus eliminating the signal); this is referred to as cross correlation. If the code is correlated with the signal at any time offset other than zero, the correlation should be

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Power

Power

Power

FDMA

TDMA

CDMA

as close to zero as possible. This is referred to as auto-correlation and is used to reject multi-path interference.

Advantages of CDMA -

Frequency reuse factor is 1. Network design and expanding become much easier.

Large Coverage, almost 2 times than GSM, saves money for operators.

High spectrum capacity，8--10 times than AMPS, 4—6 times than GSM.

High privacy, hard to wiretapping.

Perfect Power Control and voice activation make the MS power low, healthy for body—green mobile phone.

Use soft handoff, decreases call-drop rate.

CDMA ”： make before break”---soft handoff

Other systems: “make after break”---hard handoff

Fig 6: Differences b/w CDMA and other systems

4.3 GSM –

GSM (Global System for Mobile Communications), is a standard set developed by the European Telecommunications Standards Institute (ETSI) to describe technologies for second generation (or "2G") digital cellular networks. Developed as a replacement for first generation analog cellular networks, the GSM standard originally described a digital, circuit switched network optimized for full duplex voice telephony. The standard was expanded over time to include first circuit switched data transport, then packet data transport via GPRS. Packet data transmission speeds were later increased via EDGE. The GSM standard is succeeded by the third generation (or "3G")UMTS standard developed by the 3GPP. GSM networks will evolve

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further as they begin to incorporate fourth generation (or "4G") LTE Advanced standards. "GSM" is a trademark owned by the GSM Association.

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

for cells in the immediate vicinity. There are five different cell sizes in a GSM network—

macro, micro, pico, femto and umbrella cells. The coverage area of each cell varies according to

the implementation environment. Macro cells can be regarded as cells where the base

station antenna is installed on a mast or a building above average roof top level. Micro cells are

cells whose antenna height is under average roof top level; they are typically used in urban areas.

Picocells are small cells whose coverage diameter is a few dozen metres; they are mainly used

indoors. Femtocells are cells designed for use in residential or small business environments and

connect to the service provider’s network via a broadband internet connection. Umbrella cells

are used to cover shadowed regions of smaller cells and fill in gaps in coverage between those

cells.

Cell horizontal radius varies depending on antenna height, antenna gain and propagation

conditions from a couple of hundred meters to several tens of kilometres. The longest distance

the GSM specification supports in practical use is 35 kilometres (22 mi). There are also several

implementations of the concept of an extended cell,[7] where the cell radius could be double or

even more, depending on the antenna system, the type of terrain and the timing advance.

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

picocell base station, or an indoor repeater with distributed indoor antennas fed through power

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

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

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

coverage is also provided by in-building penetration of the radio signals from any nearby cell.

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

continuous-phase frequency shift keying. In GMSK, the signal to be modulated onto the carrier

is first smoothened with a Gaussian low-pass filter prior to being fed to a frequency modulator,

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

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GSM subsystems:

1. Network Subsystem: includes the equipments and functions related to end-to-end call.

2. Radio Subsystem: includes the equipments and functions related to the management of the connections on the radio path.

3. Operations and Maintenance subsystem: includes the operation and maintenance of GSM equipment for the radio and network interface.

GSM Network Architecture -

Fig 7: Network architecture of GSM

GSM Evolution –

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Fig 8: Evolution of GSM

Advantages for Operators:

• More Revenue :

By providing more than a mobile connection.

Also operator can charge on the basis of type and amount of content accessed.

• Huge Potential Market for Data Sevices :

Mobile Phone and Internet, both are fastest growing technologies and GPRS is the merger of two.

• Fast Roll-out and Continuous Network Expansion :

GPRS is an integral part of GSM.

• GPRS uses excess voice capacity for data :

GPRS Packets are transmitted in short, free periods between busy hour calls.

3. BROADBAND

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“An ‘always-on’ data connection that is able to support interactive services including Internet access and has the capability of the minimum download speed of 256 kilo bits per second (kbps) to an individual subscriber from the Point Of Presence (POP) of the service provider is called Broadband.

Data rates are defined in terms of maximum download because network and server

conditions significantly affect the maximum speeds that can be achieved and because common

consumer broadband technologies such as ADSL are "asymmetric"—supporting much lower

maximum upload data rate than download. In practice, the advertised maximum bandwidth is

not always reliably available to the customer; physical link quality can vary, and ISPs usually

allow a greater number of subscribers than their backbone connection or neighbourhood access

network can handle, under the assumption that most users will not be using their full connection

capacity very frequently. This aggregation strategy (known as a contended service) works more

often than not, so users can typically burst to their full bandwidth most of the time;

however, peer-to-peer (P2P) file sharing systems, often requiring extended durations of high

bandwidth usage, violate these assumptions, and can cause major problems for ISPs. In some

cases the contention ratio, or a download cap, is agreed in the contract, and businesses and other

customers, who need a lower contention ratio or even an uncontended service, are typically

charged more. When traffic is particularly heavy, the ISP can deliberately throttle back users

traffic, or just some kinds of traffic. This is known as traffic shaping. Careful use of traffic

shaping by the network provider can ensure quality of service for time critical services even on

extremely busy networks, but overuse can lead to concerns about network neutrality if certain

types of traffic are severely or completely blocked.

5.1 FEATURES OF BROADBAND

Fast connection to the Internet

Access to the services which would otherwise be impossible on a slower dial up

connection. These include facilities such as downloading music or video footage, listening to

your favourite radio station or downloading (or sending) large attached files with emails.

“Always-on” connection

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Means that you are permanently connected to the internet;hence no need to dial up a

connection every time you want to surf the web, send email, etc.

Flat-rate billing

If you choose an uncapped rate there will be no additional charges for the time you are

online. You can use it as much or as little as you would like, for a fixed fee. Some connections

are available at a lower cost, but limit you to the amount of data being downloaded (known as

'capped rate').

Dedicated connection

Simultaneous use of both telephone & data line.

5.2 WIRELINE BROADBAND TECHNOLOGIES -

ADSL (Asymmetric Digital Subscriber Line) –

ADSL exploits the copper wires which have a much greater bandwidth or range of

frequencies than that demanded for voice without disturbing the line's ability to carry phone

conversations. The A stands for asymmetric, meaning that data transmission rate is not the same

in both directions ie.,more bandwidth, or data-carrying capacity, is devoted to data traveling

downstream-from the Internet to your PC-than to upstream data traveling from your PC to the

Internet. The reason for the imbalance is that, generally upstream traffic is very limited to a few

words at a time, like for example –an URL request and downstream traffic, carrying graphics,

multimedia, and shareware program downloads needs the extra capacity. An ADSL circuit

connects an ADSL modem on each end of a twisted pair telephone line, creating three

information channels

1. A high speed downstream channel

2. A medium speed duplex channel

3. A basic telephone service channel

The basic telephone service channel is split off from the digital modem by filters, thus

guaranteeing uninterrupted basic telephone service, even if ADSL fails.

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Splitter ADSL

STB

RJ 11 RJ 11RJ 11 RJ 45 RJ 45

RJ 45

AV Port

Single User withVoice, Data and Video

Line RJ 11

Features of ADSL

Allows simultaneous access to the line by the telephone and the computer

In case of power/ADSL failure, data transmission is lost but basic telephone service

will be operational

ADSL Provides 16-1000 kbps upstream and 1.5-24 Mbps downstream. It can work

up to a distance of 3.7 to 5.5 kms depending upon the speed required.

Advantages of ADSL –

You can leave your Internet connection open and still use the phone line for voice

calls.

The speed is much higher than a regular modem

DSL doesn't necessarily require new wiring; it can use the phone line you already

have.

In BSNL, Broadband Access Network, there has to be an ADSL modem on either end of

the telephone line. One end of the line, terminated at Subscriber’s premises is first connected to

the splitter which filters out the low frequency voice to be connected to the telephone instrument.

The higher frequency, which carries the data is connected to the modem. The connectivity is

shown in the figure 1 given below.

\

Fig 9 : Broadband Connections

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The other end is terminated at service provider’s end which also has similar arrangement.

But at service provider’s point, numerous ADSL lines are terminated and there has to be equal

number of splitters and ADSL modems. So instead of separate splitters & modems, it is

aggregated into single nit called Digital Subscriber Line Access Multiplexer (DSLAM). So one

side of the DSLAM interfaces the subscriber lines and the other side interfaces to the core

network through several LAN switches. Before being given access to the subscriber, subscriber

is authenticated based on username and password by the BRAS. After authentication

(verification of username & password), subscriber is authorised to access the Provider’s core

network and in turn is connected to whatever service or content the subscriber demands and

accounting is initiated based on either time based or volume based billing. The LAN Switch co

located with the Core router is termed as Tier – 1 Switch and all other LAN switches which

aggregate the DSLAM are called Tier -2 switch. DSLAM’s can also be aggregated to Tier -1

switch.

The various components in the Broadband Access Network are

Customer Premises Equipment(CPE) (ADSL Modem & Splitter)

Digital Subscriber Line Access Multiplexer (DSLAM)

LAN Switches: for aggregating DSLAM (Tier -1 & Tier -2 Switch)

Broadband Remote Access Server (BRAS)

DSL –

DSL is a family of technologies that provides digital data transmission over the wires of a local

telephone network. DSL originally stood for digital subscriber loop. In telecommunications

marketing, the term Digital Subscriber Line is widely understood to mean Asymmetric Digital

Subscriber Line (ADSL), the most commonly installed technical variety of DSL. DSL service is

delivered simultaneously with regular telephone on the same telephone line. This is possible

because DSL uses a higher frequency. These frequency bands are subsequently separated by

filtering.

The data throughput of consumer DSL services typically ranges from 256 Kb/s to 20 Mbit/s in

the direction to the customer (downstream), depending on DSL technology, line conditions, and

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service-level implementation. In ADSL, the data throughput in the upstream direction, (i.e. in

the direction to the service provider) is lower, hence the designation of asymmetric service. In

Symmetric Digital Subscriber Line (SDSL) service, the downstream and upstream data rates are

equal.

ISDN –

Integrated Service Digital Network (ISDN) is one of the oldest broadband digital access methods for consumers and businesses to connect to the Internet. It is a telephone data service standard. A basic rate ISDN line (known as ISDN-BRI) is an ISDN line with 2 data "bearer" channels (DS0 - 64 kbit/s each). Using ISDN terminal adapters (erroneously called modems), it is possible to bond together 2 or more separate ISDN-BRI lines to reach bandwidths of 256 kbit/s or more. The ISDN channel bonding technology has been used for video conference applications and broadband data transmission.

Advantages:

1. Constant data rate at 64 kbit/s for each DS0 channel.

2. Two way broadband symmetric data transmission, unlike ADSL.

3. One of the data channels can be used for phone conversation without disturbing the data

transmission through the other data channel. When a phone call is ended, the bearer

channel can immediately dial and re-connect itself to the data call.

4. Call setup is very quick.

5. Low latency

6. ISDN Voice clarity is unmatched by other phone services.

7. Caller ID is almost always available for no additional fee.

8. Maximum distance from the central office is much greater than it is for DSL.

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BPL –

Broadband over power lines (BPL), also known as power-line Internet or powerband, is the use

of PLC technology to provide broadband Internet access through ordinary power lines. A

computer (or any other device) would need only to plug a BPL "modem" into any outlet in an

equipped building to have high-speed Internet access.

BPL may offer benefits over regular cable or DSL connections: the extensive infrastructure

already available appears to allow people in remote locations to access the Internet with

relatively little equipment investment by the utility. Also, such ubiquitous availability would

make it much easier for other electronics, such as televisions or sound systems, to hook up. Cost

of running wires such as ethernet in many buildings can be prohibitive; Relying on wireless has

a number of predictable problems including security, limited maximum throughput and inability

to power devices efficiently.

5.3 APPLICATIONS OF BROADBAND

Basic WWW browsing and Email access

Run Servers (Web / FTP)

Business tariff, can depend on company

Some technologies are asymmetric (cable, ADSL)

Video On Demand (VOD)

Audio Streams (Internet Radio)

Fast File Transfers (Possibility of downloading large files in short period of time)

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Comparative study for various applications using different technologies .

Application Dialup Modem ISDN Broadband

Download Webpage 14secs 6 secs 1.6 secs

Download 30 sec Video Clip 3.5 mins 1.5 mins 0.4 mins

Download Single mp3 file 12 mins 5 mins 1.3 mins

Download 10mb File 24 mins 10 mins 2.5 mins

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4. CONCLUSION

Bharat Sanchar Nigam Ltd. Formed in October 2000 is the world’s 7 th largest Telecommunications company providing comprehensive range of telecom services in India: Wired-line, CDMA mobile, GSM mobile, Internet, Broadband, Carrier Service, MPLS-VPN, VSAT, VoIP services, IN services, etc. Presently it is one of the largest and leading public sector unit in India.

The training was aimed at providing the students with basic knowledge about telecommunications and the working of telecom exchanges. The various aspects regarding the working of telecommunications, the various modules in the telecom exchange and their importance in the exchange process was explained. Both wired and wireless (mobile) communication aspects were dealed with. Mobile communication – both CDMA and GSM – was extensively covered. Also, information about broadband internet and its requirements was provided.

Along with technical lecture sessions, practical sessions were also conducted where the telecom exchanges and their equipment were shown and explained.

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5. REFERENCES

BSNL In-plant training material

www.wikipedia.com

www.encarta.msn.com

Telecommunication system engineering by Roger L Freeman

www.dataone.com

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