Page | 1

SUMMER INTERNSHIP

Project Report

Broadband Technology used in BSNL

Under the Guidance of: Industry Guide:

Submitted by:-

Amity Institute of Information Technology

AMITY University, Uttar Pradesh, Noida.

Mr. Himanshu Gupta

Senior Faculty Member

AIIT

Syed Adil Gilani

Junior Telecom Officer

BSNL Srinagar

Syed Arafat Ahmad

MSC NT & M – III(2012-14)

Enrolment No : A1000812011

Page | 2

PLAGIARISM CERTIFICATE

This is to certify that the Project Report titled Broadband Technology used in

BSNL, is scanned, of Syed Arfat Ahmad . Enrollment No.: A1000812011

I found that 64 (%) of the report is having Unique content and original.

Signature: _______________________

Date: ____________________________

Page | 3

ACKNOWLEDGEMENT

It is my esteemed pleasure to present the training report. I had a golden

opportunity of getting industrial training at Bharat Sanchar Nigam Ltd. (Govt. Of

India Ent.) Srinagar. I express my deep gratitude to Mr. SYED ADIL GEELANI and

Ms HINA ,who gave me the chance to know about the Broadband technology used

in BSNL . The other employees also deserve thanks for helping me in completion of

my report. It indeed was an enriching experience to study the many technology used

in Bharat Sanchar Nigham Ltd. This acknowledgement will hardly be sufficient

in expressing our deep sense of gratitude to our respected professors and

individuals in the preparation of this object. Last but not least we are highly

grateful to our parents for helping us round the clock and for their

encouragement and love.

Page | 4

ABSTRACT

It is not viable to expand the telecom network in India substantially at the prevalent

level of per-line investment. However, systems based on new technologies, many developed

in India, promise to more than halve the investment required.

This article looks at the telecom scenario, the new technologies, the Indian products

based on these technologies, and the cost reductions they promise. The provision of

widespread Internet service with low access tariff is an important aspect of the new approach.

In the era of Modernization and Globalization communication became the part and

parcel of human life, whereas BSNL is one of its kinds in such a communication.

The term broadband refers to a telecommunications signal or device of

greater bandwidth, in some sense, than another standard or usual signal or device (and the

broader the band, the greater the capacity for traffic).

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 (such as voice telephone and home entertainment), price, and

availability.

Broadband communications technology can be divided broadly into wire line

technologies and wireless technologies.

Advantages of Broadband are Always on (Not on shared media), Fast (speed ranging

from 256 kbps), No disconnection, No additional access charge, Telephone and Data

simultaneously

Page | 5

DECLARATION

I, Syed Arafat Ahmad, student of Msc network and Management from Amity Institute of Information

Technology, Amity University Uttar Pradesh. Hereby declare that I have completed Summer

Internship Project on “Broadband Technology used in BSNL” at Bharat Sanchar Nigham Ltd

Srinagar (J&K)

I further declare that the information presented in this project is true and original to the best of my

knowledge.

Date: 20/08/2013 Syed Arafat Ahmad

Place: New Delhi Enrollment No A1000812011.

Msc. NT&M (2012-2014)

Page | 6

List of contents

1. About the organization…………………………………………….9

2. Introduction………………………………………………………..10

2.1 Bsnl Services……………………………………… ………13

2.2 Architecture Priciples……………………………………...20

2.3 Modern Backbone…………………………………...…….22

2.4 Techonology used in BSNL……………………………….23

2.5 DSL………………………………………………… ……...25

2.6 Network Connectivity……………………………………..26

3. Customer Site: ADSL Modem…………………………………....30

4. SDSL/VHDSL/HDBSL………………………………………..….31

5. DSLAM………………………………………………………...….33

6. XDSL Connectivity Diagram………………………………….…34

7. Tier Networks………………………………………………..……35

8. Fiber-Optic Communication……………………………………...36

9. Routing Concepts………………………………………………....45

10. Wi-fi/Wi-Max……………………………………………………..51

11. Advantages & Disadvantages of Broadband………………...…52

12. Frequency Model………………………………………………...55

13. BSC(Base Station Controller)…………………………………..58

14. Hand-Off Strategies……………………………………………..59

15. Interference……………………………………………………...60

16. Conclusion………………………………………………….……61

Page | 7

About the Organization

BHARAT SANCHAR NIGAM LIMITED

Bharat Sanchar Nigam Limited (abbreviated as BSNL) is a state owned telecommunications.

Company head quartered in New Delhi, India. BSNL is one of the largest Indian cellular service providers in

india, with over 88.1 million subscribers as of April 2011, and the largest land line and wll telephone provider

in India. However, in recent years the company's revenue and market share plunged into losses due to intense

competition in Indian telecommunications sector.

Bharat Sanchar Nigam Limited 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 wire line and

72.69million wireless subscriber

It is India’s largest telecommunication company with 24% market share as on March

31st2008.Its headquarters are at Bharat Sanchar Bhawan, Harish Chandra Mathura Lane, New Delhi. It

has the status of MINI RATNA, a status assigned to public sector companies in India.

BSNL has set up a world class multi-Gigabit(GB), multi-Protocol convergent IP

infrastructure that provides convergent services like Data, Voice and video through the same

Backbone and Broadband Access Network. At present there are 0.61 million DataOne

broadband customers.

The BSNL has vast experience in Planning, Installation, Network integration and

Maintenance of Switching & Transmission Networks and also has a world class ISO 9000

certified Telecom Training Institute.

Page | 8

Introduction :-

The term broadband refers to the wide bandwidth characteristics of a transmission medium

and its ability to transport multiple signals and traffic types simultaneously. The medium can

be coax, optical fiber, twisted pair or wireless. In contrast, baseband describes a

communication system in which information is transported across a single channel.

Prior to the invention of home broadband, dial-up Internet access was the only means by

which one could access the Internet and download files such as songs, movies, e-mails, etc. It

would take anywhere from 10–30 minutes to download one song (3.5 MB) and over 28 hours

to download a movie (700 MB). Dial-up Internet was also considered very inconvenient as it

would impair the use of the home telephone line, and users would contemplate whether or not

to get a second line, and if doing so was worth the cost.

In 1997, the cable modem was introduced, although the common use of broadband didn't

begin rising until 2001. Having a broadband connection enabled one to download

significantly faster than on dial-up. As with many new technologies, most consumers were

unable to afford the cost of faster Internet service. However, high costs weren't a factor for

long as by 2004, most average American households considered home broadband service to

be affordable. Since its inception, broadband has continually strengthened and available

connection speeds continue to rise.

Different criteria for "broad" have been applied in different contexts and at different times. Its

origin is in physics, acoustics and radio systems engineering, where it had been used with a

meaning similar to wideband. However, the term became popularized through the 1990s as a

vague marketing term for Internet access

2007 was declared as "Year of Broadband" in India and BSNL announced plans for

providing 5 million broadband connectivity by the end of 2007. BSNL upgraded Dataone

connections for a speed of up to 2 Mbit/s without any extra cost. This 2 Mbit/s broadband

service was provided by BSNL at a cost of just US$ 11.7 per month (as of 21 July 2008 and

at a limit of 2.5GB monthly limit with 0200-0800 hrs as no charge period). Further, BSNL is

rolling out new broadband services such as triple play. BSNL planned to increase its

customer base to 108 million customers by 2010. With the frantic activity in the

communication sector in India the target appears achievable.

Page | 9

BSNL is a pioneer of rural telephony in India. BSNL has recently bagged 80% of US$ 580 m

(INR 25 billion) Rural Telephony project of Government of India.

On 20 March 2009 BSNL advertised the launch of BlackBerry services across its Telecom

circles in India. The corporation has also launched 3G services in select cities across the

country. Presently, BSNL and MTNL are the only players to provide 3G services, as the

Government of India has completed auction of 3G services for private players. BSNL shall

get 3G bandwidth at lowest bidder prices of Rs 185 billion, which includes Rs 101.86 billion

for 3G and Rs 83.13 billion for BWA.

As of December 2011, many other private operators have started rolling out their 3rd

Generation (aka 3G) services alongside and are enjoying some success in their campaigns to

get market share. While BSNL still maintains its connectivity standard and expands to many

more areas including rural areas with their 3G services. Also the network infrastructure has

been upgraded from to provide 3.6 Mbit/s to 7.2 MBits/sec. It is enjoying a slow but

somewhat steady success in gaining market share in this regard.

The introduction of MNP(Mobile Number Portability) which is an service that lets the

consumer change wireless service providers while retaining their actual mobile number,

BSNL has seen many customers opting for this service to move away from the services to

other operators. Despite this as the Indian Wireless market grows BSNL still has a loyal base

of subscribers and many more subscribers being added to it every day. This provides

customer services for 95 million as of June 2011.

BSNL announced the discontinuation of its telegram services from 15 July 2013, after 160

years in service. It was opened to the public in February 1855; in 2010 it was upgraded to a

web-based messaging system in 2010, through 182 telegraph offices across India

Page | 10

External/internal infrastructure:

External infrastructure: Lines and cables

(U/G include)

Internal infrastructure:

Battery, Power

Plant E/A, A/C plant, MDF,

Switches (C-DOT, OCB 283, EWSD, AXE etc),

Leased Lines (MLLN), Broad Band, MPLS VPN.

Interesting Facts about BSNL:

Page | 11

BSNL Services:-

01) BSNL LANDLINE

Though varrious of latest telecom services are introduced, still then (bharat sanchar nigham

limted) BSNL landline was much in demand. Its speech clarity, steady service, availability of

a number of value of added services has kept it popular. We have introduced a number of

new tariff plans to suit the customers.

· Introduction of Free SIM (Pyari Jodi) against each Land Line

Connection in india.

· Landline connection bundled with Broadband available at

cheep rate.

· Unlimited calls to Landline Subscriber having different plans.

02) BSNL MOBILE

BSNL Mobile is a mobile phone service provider provided by the Indian public enterprise

BSNL. It provides both pre-paid and post-paid mobile services as well as many value added

services

POST - PAID

P R E - PA I D

UNIFIED MESSAGING

GPRS/WAP/MMS

DEMOs

TARIFF

SMS & BULK SMS

Page | 12

03) BSNL WLL

This is a communication system that connects customers to the Public

Switched Telephone Network (PSTN) using radio frequency signals as

a substitute for conventional wires for all or part of the connection

between the subscribers and the telephone exchange.Countrywide

WLL is being offered in areas that are non-feasible for the normal

network.Helping relieve congestion of connections in the normal

cable/wire based network in urban areas.Connecting the remote and

scattered rural areas.Limited mobility without any air-time charge.

Services are available through out UP East circle even where Land line

is not there.

04) BSNL BROADBAND

The best high speed internet access service provider and India's No:1 Largest Broadband

Subscriber base Telecom Operator Bharat Sanchar Nigham Limited (BSNL) provides

Unlimited Broadband Internet Home Plans and Tariff.

BSNL Offers Limited and Unlimited Broadband Plans, which are more attractive to the

home users as well as Combo Plans for business users. BSNL offers many unlimited Internet

Broadband plans like HOME ULD 525, HOME COMBO 650, HOME COMBO ULD 800,

HOME COMBO ULD 950 for home users and combo plans like COMBO ULD 900,

COMBO ULD 1425, COMBO ULD 1800, COMBO ULD 2250, COMBO ULD 3500,

COMBO ULD 6300, for both Home and Business (Commercial) users.

BSNL offers these Broadband Plans with a high speed bandwidth from 512 Kbps to 4 Mbps

Page | 13

DL speed according to choice of the customer opts. The Voice of the Customer about BSNL

Broadband is "BSNL IS THE BEST INTERNET BROADBAND SERVICE PROVIDER IN

INDIA" and the plans are "MORE POCKET FRIENDLY PLANS".

REGISTER ONLINE

TARIFF

CHECK USAGE

FAQ

05) ISDN

Integrated Services Digital Network (ISDN) is a set of communication standards for

simultaneous digital transmission of voice, video, data, and other network services over the

traditional circuits of the public switched telephone network. It was first defined in 1988 in

the CCITT red book. Prior to ISDN, the telephone system was viewed as a way to transport

voice, with some special services available for data. The key feature of ISDN is that it

integrates speech and data on the same lines, adding features that were not available in the

classic telephone system. There are several kinds of access interfaces to ISDN defined as

Basic Rate Interface (BRI), Primary Rate Interface (PRI), Narrowband ISDN (N-ISDN), and

Broadband ISDN (B-ISDN).

ISDN is a circuit-switched telephone network system, which also provides access to packet

switched networks designed to allow digital transmission of voice and data over ordinary

telephone copper wires, resulting in potentially better voice quality than an analog phone can

Page | 14

provide. It offers circuit-switched connections (for either voice or data), and packet-switched

connections (for data), in increments of 64 kilobit/s. A major market application for ISDN in

some countries is Internet access, where ISDN typically provides a maximum of 128 kbit/s in

both upstream and downstream directions. Channel bonding can achieve a greater data rate;

typically the ISDN B-channels of three or four BRIs (six to eight 64 kbit/s channels) are

bonded.

ISDN should not be mistaken for its use with a specific protocol, such as Q.931 whereby

ISDN is employed as the network, data-link and physical layers in the context of the OSI

model. In a broad sense ISDN can be considered a suite of digital services existing on layers

1, 2, and 3 of the OSI model. ISDN is designed to provide access to voice and data services

simultaneously.

06) VIDEO CONFERRENCING

Videoconferencing is the conduct of a videoconference (also known as a video conference

or videoteleconference) by a set of telecommunication technologies which allow two or

more locations to communicate by simultaneous two-way video and audio transmissions. It

has also been called 'visual collaboration' and is a type of groupware.

Videoconferencing differs from videophone calls in that it's designed to serve a conference or

multiple locations rather than individuals. It is an intermediate form of videotelephony, first

Page | 15

deployed commercially in the United States by AT&T Corporation during the early 1970s as

part of their development of Picturephone technology.

With the introduction of relatively low cost, high capacity broadband telecommunication

services in the late 1990s, coupled with powerful computing processors and video

compression techniques, videoconferencing has made significant inroads in business,

education, medicine and media. Like all long distance communications technologies (such as

phone and Internet), by reducing the need to travel to bring people together the technology

also contributes to reductions in carbon emissions, thereby helping to reduce global warming

07) AUDIO CONFERRENCING

A conference call is a telephone call in which the calling party wishes to have more than one

called party listen in to the audio portion of the call. The conference calls may be designed to

allow the called party to participate during the call, or the call may be set up so that the called

party merely listens into the call and cannot speak. It is sometimes called ATC (Audio Tele-

Conference).

Conference calls can be designed so that the calling party calls the other participants and adds

them to the call; however, participants are usually able to call into the conference call

themselves by dialing a telephone number that connects to a "conference bridge" (a

specialized type of equipment that links telephone lines).

Companies commonly use a specialized service provider who maintains the conference

bridge, or who provides the phone numbers and PIN codes that participants dial to access the

meeting or conference call.

Page | 16

The more limited Three-way calling is available (usually at an extra charge) on home or

office phone lines. For a three-way call, the first called party is dialed. Then the Hook flash

button (or recall button) is pressed and the other called party's phone number is dialed. While

it is ringing, flash / recall is pressed again to connect the three people together. This option

allows callers to add a second outgoing call to an already connected call.

08) TELEX/TELEGRAPH

Telegraphy is the long-distance transmission of textual (as opposed to verbal or audio)

messages without the physical exchange of an object bearing the message. Thus semaphore is

a method of telegraphy whereas pigeon post is not.

Telegraphy requires that the method used for encoding the message be known to both sender

and receiver. Such methods are designed according to the limits of the signalling medium

used. The use of smoke signals, beacons, reflected light signals, and flag semaphore signals

are early examples. In the 19th century, the harnessing of electricity brought about the means

to transmit signals via electrical telegraph. The advent of radio in the early 1900s brought

about radiotelegraphy and other forms of wireless telegraphy. In the Internet age, telegraphic

means developed greatly in sophistication and ease of use, with natural language interfaces

that hide the underlying code, allowing such technologies as electronic mail and instant

messaging.

09) INET

Inet India is a web service company offering wide variety of solutions ranging from

conceptualizing and designing a website to development of online applications. We work on

all platforms and technologies. We have the right solution for companies of all sizes and

nature.

Inet India is based at Jaipur and has an office at Princeton, New Jersey USA. The company

has come a long way since its inception 14 yrs back. We have many prestigious clients in our

kitty like palacetours.com (Palace tours), uniquebuilders.com (Unique Builders, Jaipur),

jaipurdentalhospital.com (Jaipur Dental Hospital, Jaipur). Our relationship with our clients

can be gauged by the fact that they have stayed with us ever since they came to us for the first

time.

Page | 17

We have experience in developing websites with web 2.0 technologies which facilitate

information sharing, creating communities, interactive features and is user friendly. These

sites are therefore becoming more and more popular with the online community.

The amount of business which is happening electronically has grown by leaps and bounds

with the popularity of the Internet. We can boast of some state of the art ecommerce websites

which make the clients business easier, it is easier for them to reach the audience and get

business online.

We are ready to meet any challenges and aim to provide quality web design and development

services. We are looking at becoming the one stop shop for all online development related

requirement for any and every company.

10) EPABX

BSNL permits telephone subscribers to use their own PABX/EPABX connected to the BSNL

network under certain commercial/technical conditions :

The type of Subscriber owned EPABX should be approved by BSNL

External extensions outside subscriber's premises will be permitted only on the

specific approval of the concerned authority and charged as per departmental tariff. In

cases where external extensions from subscriber owned EPABX are provided within

the premises of the subscribers using their own cables and wires without crossing any

public road, no charge will be levied.

Subscriber is free to use the existing internal wiring of the internal extensions left at

the premises after the closure of the EPABX.

External extensions from subscriber owned PABX may be provided by the

department and charged. Underground cables and lines may continue to be maintained

by the department since the same may be required for provision of various telecom

services the subscriber may require.

In cases where BSNL feels that the existing cables/overhead wires are not be

used/likely to be used by the company the same can be made over to the user after

recovering the depreciated value of assets.

Where subscribers themselves provide and maintain external extensions from the

EPABX, applicable license fee would be charged if the extensions are crossing a

public road.

Page | 18

Cases where PBX/PABX facilities are surrendered before the expiry of the guarantee

period will be regulated as per Company rules.

National Internet Backbone (NIB):

The Internet backbone refers to the principal data routes between large, strategically interconnected

networks and core routers in the Internet. These data routes are hosted by commercial, government,

academic and other high capacity network centers, the Internet exchange points and network that interchange

Internet traffic between the countries, continents and across the oceans of the world.

Architectural Principles:-

The Internet, and consequently its backbone networks, does not rely on central control or coordinating

facilities, nor do they implement any global network policies. The resilience of the Internet results from its

principal architectural features, most notably the idea of placing as few network state and control functions as

possible in the network elements, but instead relying on the endpoints of communication to handle most of the

processing to ensure data integrity, reliability ,and authentication. In addition to this, the high degree

of redundancy of today's network links and sophisticated real-time routing protocols provide alternate paths of

communications for load balancing and congestion avoidance.

Infrastructure:

The internet backbone is a conglomeration of multiple, redundant networks owned by numerous

companies. It is typically a fiber optic trunk line. The trunk line consists of many fiber optic cables bundled

together to increase the capacity. The backbone is able to re route traffic in case of a failure. The data speeds of

backbone lines have changed with the times. In 1998, all of the United States backbone networks had utilized

Page | 19

the slowest data rate of 45 Mbps. However the changing technologies allowed for 41 percent of backbones to

have data rates of 2,488 Mbps or faster by the mid 2000's. The FCC currently defines "high speed" as any

connection with data speeds that exceed 200 kilobits per second. An Azerbaijani based telecommunication

company, Delta Telecom, has recently developed a very efficient trunk line with possible speeds of to

1.6terabits per second.

Internet traffic from this line goes through the countries of Iran, Iraq and Georgia. Fiber-

optic cables are the medium of choice for internet backbone providers for many reasons. Fiber-optics allows

for fast data speeds and large bandwidth; they suffer relatively little attenuation, allowing them to cover long

distances with few repeaters; they are also immune to crosstalk and other forms of EM interference which

plague electrical transmission.

Page | 20

Modern Backbone:

Because of the enormous overlap between long distance telephone networks and the internet

backbone networks, the largest long distance voice carriers such as AT&T, MCI, Sprint and west also own

some of the largest internet backbone networks. These backbone providers will then sell their service to ISPs.

Each ISP has its own contingency backbone network, and at the very least, is equipped with an outsourced

backup. These networks are intertwined and criss-crossed to create a redundant network. Many companies

operate their own backbones that are all interconnected at various NAPs around the world.

In order for data to navigate through this diverse web that the backbone creates, backbone routers are

desperately needed. These backbone routers are routers that are powerful enough to handle information on the

internet backbone, and they direct data to other routers in order to send it to its final destination. Without these

backbone routers, information would be lost since data would not know how to locate its end destination. The

very largest providers, known as Tier 1 providers, have such comprehensive networks that they never need to

purchase transit agreements from other providers. As of 2000 there were only five internet backbone providers

at the Tier 1 level in the telecommunications industry.

NIB in India :-

India's backbone is very extensive due to a very large population. This country alone has nearly 250 million

internet users as of 2009. Four of India's top Internet Service Providers are Tata Communications, BSNL,

MTNL, and Reliance Communications. Tata Communications is a Tier-1 IP network, with connectivity to

more than 200 countries across 400 Pops and nearly 1,000,000square feet (93,000 m2) of data center and

collocation space worldwide. It is India's largest provider in data center services and also operates India's

largest data center in Pune. The backbone structure keeps on getting stronger because of the huge number of

new emerging mobile operators which leads to decrease in prices due to competition in the market.

Economy of the Backbone:

Peering agreements: Backbone providers of roughly equivalent market share regularly create

agreements called peering agreements. These agreements allow the use of another's network to hand off

traffic where is ultimately delivered. They usually do not charge each other for this use as they all get revenue

from their customers regardless.

Transit agreements: Backbone providers of unequal market share usually create agreements called transit

agreements, and usually contain some type of monetary agreement.

Page | 21

Regulation: Anti trust authorities have acted to ensure that no provider grows large enough to dominate the

backbone market. The FCC has also decided not to monitor the competitive aspects of the Internet Backbone

interconnection relationships, as long as the market continues to function well without regulation

Technology used in BSNL :-

The standard broadband technologies in most areas are asymmetric digital line subscriber line(ADSL )and

cable internet. Newer technologies in use include very high bit rate digital subscriber line( VDSL) and pushing

optical fiber connections closer to the subscriber in both telephone and cable plants. Fiber-optic

communication, while only recently being used in fiber to the premises and fiber to the curb schemes , has

played a crucial role in enabling Broadband Internet access by making transmission of information over larger

distances much more cost-effective than copper wire technology.

In a few areas not served by cable or ADSL, community organizations have begun to install Wi-Fi networks,

and in some cities and towns local governments are installing municipal Wi-Fi networks. The newest

technology being deployed for mobile and stationary broadband access is Wi -MAX.

Broadband in DSL:

The various forms of digital subscriber line (DSL) services are broadband in the sense that digital

information is sent over a high-bandwidth channel. This channel is located above (i.e., at higher frequency

than) the baseband voice channel on a single pair of wires.

Digital Subscriber Line or DSL:-

.Digital subscriber line (DSL) is one of the most promising technology for supporting high speed digital

communication over the existing local loops. DSL technology is a set of technologies which is used to

provide higher speed access to the internet. In telecommunications marketing, the term Digital

Subscriber Line is widely used 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.

Page | 22

Brief Functions of DSL Components :-

DSL CPEs:It is also called digital subscriber line customer premises equipment . On one end it

connects telephone cable coming from exchange. At the other end, it connects to PC through Ethernet

and Telephone through RJ-45 connector.

DSLAM: It is also called as digital subscriber line Access Multiplexer (DSLAM). It has a built in splitter

which splits voice and data. While voice follows the normal conventional path through exchange, data is

aggregated and up linked through Ethernet Port (Gigabit Ethernet for 480 port and Fast Ethernet for

lower DSLAM).

LAN Switch: It is used for aggregating multiple digital subscriber line access multiplexer

(DSLAM).LAN switching is a technology that promises to increase the efficiency of local area networks

and solve the current bandwidth problems. It is a form of packet switching used in local area networks.

BRAS: It is called as Broadband Remote Access Server. It is the First intelligent device in the whole

chain. It terminates the customer session, authenticates, a lot IP addresses and keeps track of user session

for billing along with RADIUS.

SSSS: - It is called as Subscriber Service Selection System. When customer logs in it , he will be

welcomed with this customized screen from where he can select various range of service. This provides

on demand service without manual intervention.

RADIUS: - It is known as remote authentication dial in user service. This is in conjunction with

broadband remote access server (BRAS) and it authenticates customer, uploads customer profile in the

SSSS and keeps track of billing.

LDAP: - It is also called as light weight directory access protocol. It is an application protocol for

accessing and maintaining distributed directory information services over an internet protocol network. It

stores customer database viz username, password and the default services that it can subscribe to.

Provisioning: - This is the most critical components for ensuring quick delivery of service.It ensures

end-to-end provisioning of service right from DSL CPE’s to DSLAM to Switch to BRAS to LDAP.

Basic technology:

The basic technology of DSL uses telephones. Telephones are connected to the telephone exchange

via a local loop, which is a physical pair of wires. It was not considered in the digital age that the use of

the local loop for anything other than the transmission of speech, encompasses an audio frequency range

Page | 23

of 300 to 3400 Hertz (voice band or commercial bandwidth) . The long distance trunks were gradually

converted from analog to digital operation, through the local loop when the idea of data pass through . In

current practice, speech is digitized by using an analog-to-digital converter sampling at a rate of 8000

samples per second, capturing eight-bit values and producing a 64 kilobit per second data stream.

According to the Nyquist Shannon sampling theorem’’if an input audio signal injected into such an

analog-to-digital converter contains frequency components higher than half of the sampling frequency,

then such high frequency components will be aliased by the system, and so must be blocked at the input

by an appropriate low-pass filter in order to prevent such effects. Due to the presence of the low-pass

filter, input frequencies above four kilohertz (KHz)will be blocked, preventing the passage of arbitrarily

high frequencies through the normal telephone voice path.

The local loop connecting the telephone exchange to most subscribers has the capability of carrying

frequencies well beyond the 3.4 kHz upper limit of plain old telephone service( POTS). Depending on

the length and quality of the loop, the upper limit can be tens of megahertz. DSL takes advantage of this

unused bandwidth of the local loop by creating 4312.5 Hz wide channels starting between 10 and100

kHz, depending on how the system is configured. Allocation of channels continues at higher and higher

frequencies (up to 1.1 MHz for ADSL) until new channels are deemed unusable. Each channel is

evaluated for usability in much the same way an analog modem would on a Plain old telephone

service(POTS) connection. More usable channels equates to more available bandwidth, which is why

distance and line quality are a factor (the higher frequencies used by DSL travel only short distances). The

pool of usable channels is then split into two different frequency band for upstream and downstream

traffic , based on a preconfigured ratio. This segregation reduces interference. Once the channel groups

have been established, the individual channels are bonded into a pair of virtual circuits, one in each

direction. Like analog modems, DSL transceivers constantly monitor the quality of each channel and will

add or remove them from service depending on whether they are usable.

Page | 24

Network Connectivity Diagram:-

Typical setup and connection procedures:-

Physical connection must come first. On the customer side, the DSL Transceiver, or ATU-R, are more

commonly known as a DSL modem, is hooked up to a phone line. The telephone company (telco)

connects the other end of the line to a digital subscriber line access multiplexer( DSLAM), which

concentrates a large number of individual digital subscriber line(DSL )connections into a single box. The

location of the DSLAM depends on the telco, but it cannot be located too far from the user because of

attenuation, the loss of data due to the large amount of electrical resistance encountered as the data moves

between the DSLAM and the user's DSL modem. It is common for a few residential blocks to be

connected to one DSLAM.

When the DSL modem powers up it goes through a sync procedure. The actual process varies from

modem to modem but generally involves the following steps:

1. The DSL transceiver performs a self-test.

2. The DSL transceiver checks the connection between the DSL transceiver and the computer. For

residential variations of DSL, this is usually the Ethernet (RJ-45) port or a USB port; in

Page | 25

rare models, a FireWire port is used. Older DSL modems sported a native ATM interface (usually, a 25

M bit serial interface). Also, some variations of DSL (such as SDSL) use synchronous serial connections.

3. The DSL transceiver then attempts to synchronize with the DSLAM. Data can only come into the

computer when the DSLAM and the modem are synchronized. The synchronization process is relatively

quick (in the range of seconds) but is very complex, involving extensive tests that allow both sides of the

connection to optimize the performance according to the characteristics of the line in use. External or

stand-alone modem units have an indicator labeled "CD", "DSL", or "LINK", which can be used to tell if

the modem is synchronized. During synchronization the light flashes; when synchronized, the light stays

lit, usually with a green color.

The accompanying figure is a schematic of a simple DSL connection (in blue). The right side the shows a

DSLAM residing in the telephone company's central office. The left side shows the customer premises

equipment with an optional router. This router manages a local area network (LAN) off of which are

connected some number of PCs. With many service providers, the customer may opt for a modem which

contains a wireless router. This option (within the dashed bubble) often simplifies the connection

DSL Connection schematic :-

Page | 26

Equipment:-

The customer end of the connection consists of a terminal adaptor or in layman's terms" DSL modem".

This converts data between the digital signals used by computers and the voltage signal of a suitable

frequency range which is then applied to the phone line.

In some DSL variations (for example, HDSL), the terminal adapter connects directly to the

computer via a serial interface, using protocols such as Ethernet or V.35. In other cases (particularly

ADSL), it is common for the customer equipment to be integrated with higher level functionality, such as

routing, firewalling, or other application-specific hardware and software. In this case, the equipment is

referred to as a gateway.

Some kinds of DSL technology require installation of appropriate filters to separate, or "split", the DSL

signal from the low frequency voice signal. The separation can take place either at the demarcation

point, or with filters installed at the telephone outlets inside the customer premises. Either way has its

practical and economical limitations.

DSL TYPES:

1: ASYMMETRIC DIGITAL SUBSCRIBER LINE(ADSL) :-

The first technology in the set is asymmetric digital subscriber line(ADSL). It provides higher speed bit

rate in the down stream direction from the internet to the resident and in upstream direction it provides bit

rate from the resident to the internet. That is why it is called asymmetric. The designers of ADSL

specifically divides the available bandwidth of the local loop unevenly for the residential customer. This

service is not suitable for business customers who need a large bandwidth in both directions.

Page | 27

In other words we can define ADSL as “it is an asymmetric communication technology designed for

residential users,not suitable for businesses”.

Asymmetric digital subscriber line(ADSL) uses the existing local loops. The existing local loops can

handle bandwidths upto 1.1Mhz. Here the question arises how does ADSL reach a data rate that was

never achieved with traditional modems? The answer is that the twisted pair local loop is actually

capable of handling bandwidths upto 1.1Mhz,but the filter installed at the end office of the telephone

company where each local loop terminates limits the bandwidth to 4Khz which is sufficient for voice

communication. If the filter is removed, the entire 1.1 Mhz is available for data and voice

communication.

ADSL is an adaptive technology. The system uses a data rate based on the condition of the local loop

line. The modulation technique that has become standard for ADSL is called the discrete multitone

technique which combines Quadrature amplitude (QAM) and Frequency division multiplexing (FDM).

There is no set way that the bandwidth of the system is divided. Each system can decide on its

bandwidth division. Typically an available bandwidth of 1.104Mhz is divided into 256 channels. Each

channel uses a bandwidth of 4.312khz.Each bandwidth is divided into:

1.Voice: Channel 0 is reserved for voice communication.

2.Idle: Channels 1 to 5 are not used and provide a gap between voice and data communication.

3.Upstream data and control: Channels 6 to 30 are used for upstream data transfer and control. One

channel is for control and 24 channels are for data transfer. Data rate is normally below 500kbps because

some of the carriers are deleted at frequencies where the noise level is large. In other words some of the

channels may be unused.

4.Downstream data and control: Channels 31 to 255 are used for down stream data transfer and control.

One channel is for control, and 224 channels are for data. Data rate is normally below 8mbps because

some of the carriers are deleted at frequencies where the noise level is large. In other words some of the

channels may be unused.

.Customer site: ADSL Modem :-

ADSL modem is installed at a customer’s site. The local loop connects to a splitter which seperates voice

and data communications. The ADSL modem modulates and demodulates the data using DMT and

creates downstream and upstream channels. Here the splitter needs to b installed at the customers

Page | 28

premises ,normally by a technician from the telephone company. The voice line can use the existing

telephone wiring in the house,but the data lines needs to b installed by a professional. All this makes the

ADSL lines expensive.

ADSL LITE:- The installation of splitters at the border of the premises and the new wiring for the

data line can be expensive and impractical enough to dissuade most subscribers.A new version of ADSL

technology called ADSL LITE or UNIVERSAL ADSL OR SPLITTERLESS ADSL is available for

these subscribers. This technology allows an ADSL LITE modem to be plugged directly into a telephone

jack and connected to the computer. The splitting is done at telephone company. ADSL LITE uses 256

DMT carriers with 8 bit modulation. However some of the carriers may not b available because errors

created by the voice signal might mingle with them. It can provide a maximum downstream data rate of

1.5mbps and an upstream data rate of 512kbps.

HIGH BIT RATE DIGITAL SUBSCRIBER LINE (HDSL):-

It was designed as an alternative to the T-1line(1.544mbps).This line uses alternative mark

inversion(AMI) encoding which is very susceptible to attenuation at high frequiences. This limits the

length of a T-1 Line to 1km.for longer distances a repeater is necessary which means increased costs.

HDSL uses two twisted pairs to achieve full duplex transmission.

SYMMETRIC DIGITAL SUBSCRIBER LINE(SDSL):-

It is one twisted pair version of HDSL.It provides full duplex symmetric communication supporting upto

768kbps in each direction .SDSL,which provides symmetric communication can be considered as

alternative to ADSL.ADSL provides asymmetric communication with a downstream bit rate that is

much higher than the upstream bit rate. Although this feature meets the needs of most residential

subscribers ,it is not suitable for businesses that send and receive data in large volumes in both directions.

VERY HIGH BIT RATE DIGITAL SUBSCRIBER LINE(VDSL):-

It is an alternative approach that is similar to ADSL .It uses coaxial ,fiber optic or twisted pair cable for

short distances. The modulating technique is DMT. It provides a range of bit rates for upstream

communications at distances of 3000 to 10000ft.The downstream rate is normally 3.2mbps .It is a DSL

technology providing faster data transmission . Second-generation VDSL2 systems (ITU-T G.993.2

Approved in February2006) utilize bandwidth of up to 30 MHz to provide data rates exceeding 100 M

Page | 29

bits simultaneously in both the upstream and downstream directions. The maximum available bit rate is

achieved at a range of about 300 meters; performance degrades as the loop attenuation increases.

Currently, the standard VDSL uses up to 7 different frequency bands.

Digital Subscriber Line Access Multiplexer:-

A Digital Subscriber Line Access Multiplexer(DSLAM, often pronounced dee-slam)

delivers exceptionally high speed data transmission over existing copper telephone lines. A

DSLAM seperates the voice frequency signals from the high speed data traffic and controls

and routes digital subscriber line traffic between the subscriber’s end user equipment and the

network service providers network. It allows telephone lines to make faster connections to the

Internet. It is a network device, located in the telephone exchanges of the internet service providers, that

connects multiple customer Digital Subscriber Lines (DSLs) to a high-speed Internet backbone line using

multiplexing techniques. By placing additional remote DSLAMs at locations remote to the telephone

exchange, telephone companies provide DSL service to locations previously beyond effective range.

Path taken by data to DSLAM:-

1.Customer premises: DSL modem terminating the ADSL, SHDSL or VDSL circuit and providing

LAN interface to single computer or LAN segment

2. Local loop: The telephone company wires from a customer to the telephone company' s central office

or to a Serving area interface, often called the "last mile" (LM).

3. Central Office(CO):

a) Main Distribution Frame (MDF): a wiring rack that connects outside subscriber lines with internal

lines. It is used to connect public or private lines coming into the building to internal networks. At the

telco, the MDF is generally in proximity to the cable vault and not far from the telephone switch.

b) XDSL filters: DSL filters are used in the Central Office (CO) to split voice from data signals. The

voice signal can be routed to a POTS provider or left unused whilst the data signal is routed to the ISP

DSLAM via the HDF (see next entry)

c). Handover Distribution Frame (HDF): a distribution frame that connects the last mile provider with the

service provider's DSLAM.

Page | 30

d) DSLAM : A device for DSL service. The DSLAM port where the subscriber local loop is connected

converts analog electrical signals to data traffic (upstream traffic for data upload) and data traffic to analog

electrical signals (downstream for data download).

Role of DSLAM:-

The DSLAM equipment collects the data from its many modem ports and aggregates their voice and

data traffic into one complex composite "signal" via multiplexing.

Depending on its device architecture and setup a DSLAM aggregates the DSL lines over its

asynchronous transfer mode(ATM),frame relay, and internet protocol network. The aggregated traffic is

then directed to a telco's backbone switch, via an access network (AN) also called a Network Service

Provider (NSP) at up to 10 G bit/s data rates.

The DSLAM acts like a network switch since its functionality is at Layer 2 of the OSI model. Therefore

it cannot re-route traffic between multiple IP networks, only between ISP devices and end-

user connection points.

The DSLAM traffic is switched to a Broadband Remote Access Server where the end user traffic is then

routed across the ISP network to the Internet. Customer Premises Equipment that interfaces well with the

DSLAM to which it is connected may take advantage of enhanced telephone voice and data line

signaling features and the bandwidth monitoring and compensation capabilities it supports.

DSLAMs are also used by hotels, lodges, residential neighborhoods, and other businesses operating their

own private telephone exchange .In addition to being a data switch and multiplexer, a DSLAM is also a

large collection of modems. Each modem on the aggregation card communicates with a single

subscriber's DSL modem. This modem functionality is integrated into the DSLAM itself instead of being

done via an external device like a traditional computer modem. Like traditional voice-band modems, a

DSLAM's integrated DSL modems usually have the ability to probe the line and to adjust themselves to

electronically or digitally compensate for forward echoes and other bandwidth-limiting factors in order to

move data at the maximum connection rate capability of the subscriber's physical line. This compensation

capability also takes advantage of the better performance of "balanced line" DSL connections, providing

capabilities for LAN segments longer than physically similar unshielded twisted pair (UTP) Ethernet

connections, since the balanced line type is generally required for its hardware to function correctly. This

is due to the nominal line impedance (measured in Ohms but comprising both resistance and inductance)

of balanced lines being somewhat lower than that of UTP, thus supporting 'weaker' signals (however the

solid-state electronics required to construct such digital interfaces is more costly).

Page | 31

XDSL Connectivity diagram:-

Tier 1 Network: A tier 1 network is an internet protocol network that participates in the

internet solely via settlement free interconnection also known as settlement free peering.

Although there is no authority that defines tiers of networks participating in the Internet, the most

common definition of a tier 1 network is one that can reach every other network on the Internet without

purchasing IP transit or paying settlements.

By this definition, a tier 1 network is a transit-free network that peers with every other tier-1 network. But

not all transit-free networks are tier 1 networks. It is possible to become transit-free by paying for peering

or agreeing to settlements. It is difficult to determine whether a network is paying settlements if the

business agreements are not public information, or covered under a non-disclosure agreement. The

Internet "peering community" is roughly the set of peering coordinators present at Internet exchanges on

more than one continent. The subset representing "tier 1"networks is collectively understood, but not

published as such. Strictly observing this definition of "tier 1" would exclude every network. For instance,

many large telephone companies are tier 1 networks, but they buy, sell, or swap fiber amongst

themselves. Payments between companies are not all known, nor whether they cover peering

connections.

As a result, the term "tier 1 network" is used in the industry to mean a network with no overt settlements.

An overt settlement would be a monetary charge for the amount, direction, or type of traffic sent between

networks.

Page | 32

TIER 2 NETWORK:-

It is an internet service provider who engages in the practice of peering with other networks.

TIER 2 providers are the most common providers on the internet as it is much easier to purchase transit

from a tier 1 network than it is to peer with them and then attempt to push into becoming a tier 1 carrier.

We can also define it as “a network that peers with some networks,but still purchases IP transit or pays

settlements to reach atleast some portion of the internet”

Lower tier ISPs and their customers may be unaffected by these partitions because they may have

redundant interconnections with more than one tier-1 provider. Frequent misconceptions of the tier

hierarchy include:

Internet traffic between any two tier 1 networks is critically dependent on the peering relationship of the

partners, because a tier 1 network does not have any alternate transit paths. If two tier 1 networks arrive at

an impasse and discontinue peering with each other (usually in auni lateral decision), single-

homed customers of each network will not be able to reach the customers of other networks. This

effectively partitions the Internet and traffic between certain parts of the Internet is interrupted. This has

happened several times during the history of the Internet. Those portions of the Internet typically remain

Page | 33

partitioned until one side purchases transit, or until the collective pain of the outage or threat of litigation

motivates the two networks to resume voluntary peering.

Tier 1 networks are closer to the backbone of the Internet.

In reality, tier 1 networks usually have only a small number of peers (typically only other tier 1

networks and very large tier 2 networks), while tier 2 networks are motivated to peer with many

other tier 2 and end-user networks. Thus a tier 2 network with good peering is frequently much

closer to most end users than a tier 1.

Tier 1 networks by definition offer better quality Internet connectivity.

By definition, there are networks which tier 1 networks have only one path to, and if they lose

that path, they have no backup transit which preserves their continuous connectivity.

Some tier 2 networks are significantly larger than some tier 1 networks, and are often a let

provide more or better connectivity

Fiber-optic communication;-

is a method of transmitting information from one place to another by sending pulses of light

through an optical fiber. The light forms an electromagnetic carrier wave that is modulated to

carry information. First developed in the 1970s, fiber-optic communication systems have

revolutionized the telecommunications industry and have played a major role in the advent of

the Information Age. Because of its advantages over electrical transmission, optical fibers

have largely replaced copper wire communications in core networks in the developed world.

The process of communicating using fiber-optics involves the following basic steps:

Creating the optical signal involving the use of a transmitter, relaying the signal along the

fiber, ensuring that the signal does not become too distorted or weak, receiving the optical

signal, and converting it into an electrical signal.

Page | 34

Applications

Optical fiber is used by many telecommunications companies to transmit telephone signals,

Internet communication, and cable television signals. Due to much lower attenuation and

interference, optical fiber has large advantages over existing copper wire in long-distance and

high-demand applications. However, infrastructure development within cities was relatively

difficult and time-consuming, and fiber-optic systems were complex and expensive to install

and operate. Due to these difficulties, fiber-optic communication systems have primarily been

installed in long-distance applications, where they can be used to their full transmission

capacity, offsetting the increased cost. Since 2000, the prices for fiber-optic communications

have dropped considerably. The price for rolling out fiber to the home has currently become

more cost-effective than that of rolling out a copper based network. Prices have dropped to

$850 per subscriber in the US and lower in countries like The Netherlands, where digging

costs are low.

Since 1990, when optical-amplification systems became commercially available, the

telecommunications industry has laid a vast network of intercity and transoceanic fiber

communication lines. By 2002, an intercontinental network of 250,000 km of submarine

communications cable with a capacity of 2.56 Tb/s was completed, and although specific

network capacities are privileged information, telecommunications investment reports

indicate that network capacity has increased dramatically since 2004.

Technology

Modern fiber-optic communication systems generally include an optical transmitter to

convert an electrical signal into an optical signal to send into the optical fiber, a cable

containing bundles of multiple optical fibers that is routed through underground conduits and

buildings, multiple kinds of amplifiers, and an optical receiver to recover the signal as an

electrical signal. The information transmitted is typically digital information generated by

computers, telephone systems, and cable television companies.

Page | 35

Transmitters

A GBIC module (shown here with its cover removed), is an optical and electrical transceiver.

The electrical connector is at top right, and the optical connectors are at bottom left

The most commonly used optical transmitters are semiconductor devices such as light-

emitting diodes (LEDs) and laser diodes. The difference between LEDs and laser diodes is

that LEDs produce incoherent light, while laser diodes produce coherent light. For use in

optical communications, semiconductor optical transmitters must be designed to be compact,

efficient, and reliable, while operating in an optimal wavelength range, and directly

modulated at high frequencies.

In its simplest form, an LED is a forward-biased p-n junction, emitting light through

spontaneous emission, a phenomenon referred to as electroluminescence. The emitted light is

incoherent with a relatively wide spectral width of 30-60 nm. LED light transmission is also

inefficient, with only about 1%[citation needed]

of input power, or about 100 microwatts,

eventually converted into launched power which has been coupled into the optical fiber.

However, due to their relatively simple design, LEDs are very useful for low-cost

applications.

Communications LEDs are most commonly made from Indium gallium arsenide phosphide

(InGaAsP) or gallium arsenide (GaAs). Because InGaAsP LEDs operate at a longer

wavelength than GaAs LEDs (1.3 micrometers vs. 0.81-0.87 micrometers), their output

spectrum, while equivalent in energy is wider in wavelength terms by a factor of about 1.7.

The large spectrum width of LEDs is subject to higher fiber dispersion, considerably limiting

their bit rate-distance product (a common measure of usefulness). LEDs are suitable

Page | 36

primarily for local-area-network applications with bit rates of 10-100 Mbit/s and transmission

distances of a few kilometers. LEDs have also been developed that use several quantum wells

to emit light at different wavelengths over a broad spectrum, and are currently in use for

local-area WDM networks.

Today, LEDs have been largely superseded by VCSEL (Vertical Cavity Surface Emitting

Laser) devices, which offer improved speed, power and spectral properties, at a similar cost.

Common VCSEL devices couple well to multi mode fiber.

A semiconductor laser emits light through stimulated emission rather than spontaneous

emission, which results in high output power (~100 mW) as well as other benefits related to

the nature of coherent light. The output of a laser is relatively directional, allowing high

coupling efficiency (~50 %) into single-mode fiber. The narrow spectral width also allows for

high bit rates since it reduces the effect of chromatic dispersion. Furthermore, semiconductor

lasers can be modulated directly at high frequencies because of short recombination time.

Commonly used classes of semiconductor laser transmitters used in fiber optics include

VCSEL (Vertical Cavity Surface Emitting Laser), Fabry–Pérot and DFB (Distributed Feed

Back).

Laser diodes are often directly modulated, that is the light output is controlled by a current

applied directly to the device. For very high data rates or very long distance links, a laser

source may be operated continuous wave, and the light modulated by an external device such

as an electro-absorption modulator or Mach–Zehnder interferometer. External modulation

increases the achievable link distance by eliminating laser chirp, which broadens the

linewidth of directly modulated lasers, increasing the chromatic dispersion in the fiber.

A transceiver is a device combining a transmitter and a receiver in a single housing (see

picture on right).

Receivers

The main component of an optical receiver is a photodetector, which converts light into

electricity using the photoelectric effect. The primary photodetectors for telecommunications

are made from Indium gallium arsenide The photodetector is typically a semiconductor-based

photodiode. Several types of photodiodes include p-n photodiodes, p-i-n photodiodes, and

Page | 37

avalanche photodiodes. Metal-semiconductor-metal (MSM) photodetectors are also used due

to their suitability for circuit integration in regenerators and wavelength-division

multiplexers.

Optical-electrical converters are typically coupled with a transimpedance amplifier and a

limiting amplifier to produce a digital signal in the electrical domain from the incoming

optical signal, which may be attenuated and distorted while passing through the channel.

Further signal processing such as clock recovery from data (CDR) performed by a phase-

locked loop may also be applied before the data is passed on.

Fiber cable types

A cable reel trailer with conduit that can carry optical fiber.

Single-mode optical fiber in an underground service pit

Main articles: Optical fiber and Optical fiber cable

Page | 38

An optical fiber consists of a core, cladding, and a buffer (a protective outer coating), in

which the cladding guides the light along the core by using the method of total internal

reflection. The core and the cladding (which has a lower-refractive-index) are usually made

of high-quality silica glass, although they can both be made of plastic as well. Connecting

two optical fibers is done by fusion splicing or mechanical splicing and requires special skills

and interconnection technology due to the microscopic precision required to align the fiber

cores.

Two main types of optical fiber used in optic communications include multi-mode optical

fibers and single-mode optical fibers. A multi-mode optical fiber has a larger core (≥ 50

micrometers), allowing less precise, cheaper transmitters and receivers to connect to it as well

as cheaper connectors. However, a multi-mode fiber introduces multimode distortion, which

often limits the bandwidth and length of the link. Furthermore, because of its higher dopant

content, multi-mode fibers are usually expensive and exhibit higher attenuation. The core of a

single-mode fiber is smaller (<10 micrometers) and requires more expensive components and

interconnection methods, but allows much longer, higher-performance links.

In order to package fiber into a commercially viable product, it typically is protectively

coated by using ultraviolet (UV), light-cured acrylate polymers, then terminated with optical

fiber connectors, and finally assembled into a cable. After that, it can be laid in the ground

and then run through the walls of a building and deployed aerially in a manner similar to

copper cables. These fibers require less maintenance than common twisted pair wires, once

they are deployed.

Specialized cables are used for long distance subsea data transmission, e.g. transatlantic

communications cable. New (2011–2013) cables operated by commercial enterprises

(Emerald Atlantis, Hibernia Atlantic) typically have four strands of fiber and cross the

Atlantic (NYC-London) in 60-70ms. Cost of each such cable was about $300M in 2011..

Another common practice is to bundle many fiber optic strands within long-distance power

transmission cable. This exploits power transmission rights of way effectively, ensures a

power company can own and control the fiber required to monitor its own devices and lines,

is effectively immune to tampering, and simplifies the deployment of smart grid technology.

Page | 39

Optical amplifier

The transmission distance of a fiber-optic communication system has traditionally been

limited by fiber attenuation and by fiber distortion. By using opto-electronic repeaters, these

problems have been eliminated. These repeaters convert the signal into an electrical signal,

and then use a transmitter to send the signal again at a higher intensity than it was before.

Because of the high complexity with modern wavelength-division multiplexed signals

(including the fact that they had to be installed about once every 20 km), the cost of these

repeaters is very high.

An alternative approach is to use an optical amplifier, which amplifies the optical signal

directly without having to convert the signal into the electrical domain. It is made by doping a

length of fiber with the rare-earth mineral erbium, and pumping it with light from a laser with

a shorter wavelength than the communications signal (typically 980 nm). Amplifiers have

largely replaced repeaters in new installations.

Parameters

Bandwidth–distance product

Because the effect of dispersion increases with the length of the fiber, a fiber transmission

system is often characterized by its bandwidth–distance product, usually expressed in units of

MHz·km. This value is a product of bandwidth and distance because there is a trade off

between the bandwidth of the signal and the distance it can be carried. For example, a

common multi-mode fiber with bandwidth–distance product of 500 MHz·km could carry a

500 MHz signal for 1 km or a 1000 MHz signal for 0.5 km.

Engineers are always looking at current limitations in order to improve fiber-optic

communication, and several of these restrictions are currently being researched.

Record speeds

Each fiber can carry many independent channels, each using a different wavelength of light

(wavelength-division multiplexing). The net data rate (data rate without overhead bytes) per

fiber is the per-channel data rate reduced by the FEC overhead, multiplied by the number of

channels (usually up to eighty in commercial dense WDM systems as of 2008).

Page | 40

Year Organization Effective speed WDM channels Per channel speed Distance

2009 Alcatel-Lucent 15 Tbit/s 155 100 Gbit/s 90 km

2010 NTT 69.1 Tbit/s 432 171 Gbit/s 240 km

2011 KIT 26 Tbit/s 1 26 Tbit/s 50 km

2011 NEC 101 Tbit/s 370 273 Gbit/s 165 km

2012 NEC, Corning 1.05 Petabit/s 12 core fiber

52.4 km

Dispersion

For modern glass optical fiber, the maximum transmission distance is limited not by direct

material absorption but by several types of dispersion, or spreading of optical pulses as they

travel along the fiber. Dispersion in optical fibers is caused by a variety of factors. Intermodal

dispersion, caused by the different axial speeds of different transverse modes, limits the

performance of multi-mode fiber. Because single-mode fiber supports only one transverse

mode, intermodal dispersion is eliminated.

In single-mode fiber performance is primarily limited by chromatic dispersion (also called

group velocity dispersion), which occurs because the index of the glass varies slightly

depending on the wavelength of the light, and light from real optical transmitters necessarily

has nonzero spectral width (due to modulation). Polarization mode dispersion, another source

of limitation, occurs because although the single-mode fiber can sustain only one transverse

mode, it can carry this mode with two different polarizations, and slight imperfections or

distortions in a fiber can alter the propagation velocities for the two polarizations. This

phenomenon is called fiber birefringence and can be counteracted by polarization-

maintaining optical fiber. Dispersion limits the bandwidth of the fiber because the spreading

optical pulse limits the rate that pulses can follow one another on the fiber and still be

distinguishable at the receiver.

Page | 41

Some dispersion, notably chromatic dispersion, can be removed by a 'dispersion

compensator'. This works by using a specially prepared length of fiber that has the opposite

dispersion to that induced by the transmission fiber, and this sharpens the pulse so that it can

be correctly decoded by the electronics.

Attenuation

Fiber attenuation, which necessitates the use of amplification systems, is caused by a

combination of material absorption, Rayleigh scattering, Mie scattering, and connection

losses. Although material absorption for pure silica is only around 0.03 dB/km (modern fiber

has attenuation around 0.3 dB/km), impurities in the original optical fibers caused attenuation

of about 1000 dB/km. Other forms of attenuation are caused by physical stresses to the fiber,

microscopic fluctuations in density, and imperfect splicing techniques.

Transmission windows

Each effect that contributes to attenuation and dispersion depends on the optical wavelength.

The wavelength bands (or windows) that exist where these effects are weakest are the most

favorable for transmission. These windows have been standardized, and the currently defined

bands are the following:

Band Description Wavelength Range

O band original 1260 to 1360 nm

E band extended 1360 to 1460 nm

S band short wavelengths 1460 to 1530 nm

C band conventional ("erbium window") 1530 to 1565 nm

L band long wavelengths 1565 to 1625 nm

U band Ultra long wavelengths 1625 to 1675 nm

Note that this table shows that current technology has managed to bridge the second and third

windows that were originally disjoint.

Page | 42

Historically, there was a window used below the O band, called the first window, at 800-

900 nm; however, losses are high in this region so this window is used primarily for short-

distance communications. The current lower windows (O and E) around 1300 nm have much

lower losses. This region has zero dispersion. The middle windows (S and C) around

1500 nm are the most widely used. This region has the lowest attenuation losses and achieves

the longest range. It does have some dispersion, so dispersion compensator devices are used

to remove this.

Regeneration

When a communications link must span a larger distance than existing fiber-optic technology

is capable of, the signal must be regenerated at intermediate points in the link by repeaters.

Repeaters add substantial cost to a communication system, and so system designers attempt

to minimize their use.

Recent advances in fiber and optical communications technology have reduced signal

degradation so far that regeneration of the optical signal is only needed over distances of

hundreds of kilometers. This has greatly reduced the cost of optical networking, particularly

over undersea spans where the cost and reliability of repeaters is one of the key factors

determining the performance of the whole cable system. The main advances contributing to

these performance improvements are dispersion management, which seeks to balance the

effects of dispersion against non-linearity; and solitons, which use nonlinear effects in the

fiber to enable dispersion-free propagation over long distances.

Routing concepts:

Routing means finding route or the next hop for a packet .A device called router does the

routing function. It uses a table called routing table to find the rout to the packet’s final

destination. Routing tables contain information about the potential paths that a data packet

should take to travel through the internetwork and reach its destination.

ROUTING METHODS:

There are two methods of routing.

1: Static routing

Page | 43

2: Dynamic routing

STATIC ROUTING:In static routing method, routing tables are manually configured by the

network administrator. Static routing is used in smaller networks that contain only a smaller

number of routers or where security is a major concern. Routers that use static routing are

called static routers. Each static router must be configured and maintained separately because

static routers do not exchange routing information with each other.

DYNAMIC ROUTING: It is a routing mechanism which is handled by a routing protocols

such as routing information protocol, open shortest first protocol. These protocols

dynamically exchange routing information among routers on an internetwork. Routers that

use these methods are called dynamic routers. A routing protocol is installed on each

dynamic router. The router s periodically exchange their routing information so that if the

internetwork is reconfigured or a router goes down,the routing tables of each router are

modified accordingly.

Dynamic routers are less secure because routing tables can be hampered by hackers. Routing

protocols also create additional network traffic.

Internet Router:

A router is a device that forwards data packets across computer networks. Routers perform the data

"traffic directing" functions on the Internet. A router is connected to two or more data lines from different

networks. When data comes in on one of the lines, the router reads the address information in the packet

to determine its ultimate destination. Then, using information in its routing table, it directs the packet to

the next network on its journey or drops the packet. A data packet is typically passed from router to router

through the networks of the Internet until it gets to its destination computer unless the source IP is on a

private network.

The most familiar type of routers are home and small office routers that simply pass data, such as web

pages and email, between the home computers and the owner's cable or DSL modem, which connects to

the Internet (ISP).In enterprises, a core router may provide a "collapsed backbone" interconnecting the

distribution tier routers from multiple buildings of a campus, or large enterprise locations. They tend to be

optimized for high bandwidth

Page | 44

A typical home or small office router showing the ADSL telephone line and

ETHERNET network cable connections.

Broadband Remote Access Server (BRAS):

A broadband remote access server(BRAS,B-RAS or BBRAS) routes traffic to and

from broadband remote access devices such as digital subscriber line access multiplexers (DSLAM) on

an Internet service provider's (ISP) network. BRAS can also be referred to as broad network gateway

(BNG).

The BRAS sits at the core of an ISP's network, and aggregates user sessions from the access network. It is

at the BRAS that an ISP can inject policy management and IP Quality of Service (QoS).

The specific tasks include:

Aggregates the circuits from one or more link access devices such as DSLAM’s

Provides layer 2 connectivity through either transparent bridging or PPP sessions over Ethernet

or ATM sessions

Enforces quality of service (QoS) policies

Provides layer 3 connectivity and routes IP traffic through an Internet service provider’s Back

bone network to the Internet

A DSLAM collects data traffic from multiple subscribers into a centralized point so that it can be

transported to a switch or router over a Frame Relay, ATM, or Ethernet connection.

Page | 45

The router provides the logical network termination. The BRAS is also the interface to authentication,

authorization and accounting systems

ROUTING IN BRAS:

The main purpose of a router is to connect multiple networks and forward packets destined either for its

own networks or other networks. A router is considered a Layer 3 device because its primary forwarding

decision is based on the information in the Layer 3 IP packet, specifically the destination IP address. This

process is known as routing. When each router receives a packet, it searches its routing table to find the

best match between the destination IP address of the packet and one of the network addresses in the

routing table. Once a match is found, the packet is encapsulated in the Layer 2 data link frame for that

outgoing interface. A router does not look into the actual data contents that the packet carries, but only at

the layer 3 addresses to make a forwarding decision, plus optionally other information in the header for

hint on, for example, QoS. Once a packet is forwarded, the router does not retain any historical

information about the packet, but the forwarding action can be collected into the statistical data, if so

configured.

Forwarding decisions can involve decisions at layers other than layer 3. A function that forwards based

on layer 2 information, is properly called a bridge. This function is referred to as layer 2 bridging, as the

addresses it uses to forward the traffic are layer 2 addresses (e.g. MAC addresses on Ethernet).

Besides making decision as which interface a packet is forwarded to, which is handled primarily via the

routing table, a router also has to manage congestion, when packets arrive at a rate higher than the router

can process. Three policies commonly used in the Internet are tail drop, random early detection (RED),

and weighted random early detection (WRED). Tail drop is the simplest and most easily implemented;

the router simply drops packets once the length of the queue exceeds the size of the buffers in the router.

RED probabilistically drops data grams early when the queue exceeds a pre-configured portion of the

buffer, until a pre-determined max, when it becomes tail drop. WRED requires a weight on the average

queue size to act upon when the traffic is about to exceed the pre-configured size, so that short bursts will

not trigger random drops.

Another function a router performs is to decide which packet should be processed first when multiple

queues exist. This is managed through quality of service (QoS), which is critical when Voice over IP is

deployed, so that delays between packets do not exceed 150ms to maintain the quality of voice

conversations. Yet another function a router performs is called policy-based routing where special rules

Page | 46

are constructed to override the rules derived from the routing table when a packet forwarding decision is

made. These functions may be performed through the same internal paths that the packets travel inside

the router. Some of the functions may be performed through an application-specific integrated circuit

(ASIC) to avoid overhead caused by multiple CPU cycles, and others may have to be performed through

the CPU as these packets need special attention that cannot be handled by an ASIC.

Router:

A router is a device that forwards data packets between computer networks, creating an

overlay internetwork. A router is connected to two or more data lines from different

networks. When a data packet comes in one of the lines, the router reads the address

information in the packet to determine its ultimate destination. Then, using information in its

routing table or routing policy, it directs the packet to the next network on its journey.

Routers perform the "traffic directing" functions on the Internet. A data packet is typically

forwarded from one router to another through the networks that constitute the internetwork

until it reaches its destination node.

The most familiar type of routers are home and small office routers that simply pass data,

such as web pages, email, IM, and videos between the home computers and the Internet. An

example of a router would be the owner's cable or DSL modem, which connects to the

Internet through an ISP. More sophisticated routers, such as enterprise routers, connect large

business or ISP networks up to the powerful core routers that forward data at high speed

along the optical fiber lines of the Internet backbone. Though routers are typically dedicated

hardware devices, use of software-based routers has grown increasingly common.

Page | 47

Forwarding :-

The main purpose of a router is to connect multiple networks and forward packets

destined either for its own networks or other networks. A router is considered a Layer 3 device because

its primary forwarding decision is based on the information in the Layer 3 IP packet, specifically the

destination IP address. This process is known as routing. When each router receives a packet, it searches

its routing table to find the best match between the destination IP address of the packet and one of the

network addresses in the routing table. Once a match is found, the packet is encapsulated in the Layer 2

data link frame for that outgoing interface. A router does not look into the actual data contents that the

packet carries, but only at the layer 3 addresses to make a forwarding decision, plus optionally other

information in the header for hint on, for example, QoS. Once a packet is forwarded, the router does not

retain any historical information about the packet, but the forwarding action can be collected into the

statistical data, if so configured.

Forwarding decisions can involve decisions at layers other than layer 3. A function that

forwards based on layer 2 information, is properly called a bridge. This function is referred to as layer 2

bridging, as the addresses it uses to forward the traffic are layer 2 addresses (e.g. MAC addresses on

Ethernet).

Besides making decision as which interface a packet is forwarded to, which is

handled primarily via the routing table, a router also has to manage congestion, when packets arrive at ar

ate higher than the router can process. Three policies commonly used in the Internet are tail drop, random

early detection (RED), and weighted random early detection (WRED). Tail drop is the simplest and most

easily implemented; the router simply drops packets once the length of the queue exceeds the size of the

buffers in the router. RED probabilistically drops data grams early when the queue exceeds a pre-

configured portion of the buffer, until a pre-determined max, when it becomes tail drop. WRED requires

a weight on the average queue size to act upon when the traffic is about to exceed the pre-configured size,

so that short bursts will not trigger random drops.

Another function a router performs is to decide which packet should be processed

first when multiple queues exist. This is managed through quality of service (QoS), which is critical when

Voice over IP is deployed, so that delays between packets do not exceed 150ms to maintain the quality of

voice conversations. Yet another function a router performs is called policy-based routing where special

rules are constructed to override the rules derived from the routing table when a packet forwarding

decision is made. These functions may be performed through the same internal paths that the packets

travel inside the router. Some of the functions may be performed through an application-specific

Page | 48

integrated circuit (ASIC) to avoid overhead caused by multiple CPU cycles, and others may have to be

performed through the CPU as these packets need special attention that cannot be handled by an ASIC.

Service control module:-

It is responsible for authentication and management of user access requests. It identifies

legal users. It can extract and record the statistics of user data packets and online duration for

implementing the traffic based or duration based accounting function.

MA5200G sends the user’s accounting information to the RADIUS server. BRAS

allocates IP address through DHCP. It supports 4k to 96k IP addresses.MA5200G adopts packet

binding technology. After user passes authentication It checks the binding relation of the IP address,

MAC address, logical port and PPPoE session ID in each packet of this user and the packets that do not

match will be discarded.

Wi-Fi:-

Wireless Technology is an alternative to wired Technology for connecting the devices in wireless mode.

Wi-Fi refers to the IEEE 802.11 communication standard for wireless LAN. Wi-Fi network connect

computers to each other to the internet and to the other wired networks. Wi-Fi networks use Radio

Technologies to transmit & receive date at high speeds.

Wi MAX:-

Wi MAX (Worldwide Interoperability for Microwave Access) is a

telecommunications protocol that provides fixed and mobile Internet access. The current Wi MAX

revision provides up to 40 M bit/s with the IEEE 802.16m update expected to offer up to 1 G bit/s fixed

speeds. The name "Wi-MAX" was created by the Wi MAX Forum, which was formed in June 2001to

promote conformity and interoperability of the standard. The forum describes Wi MAX as "a standards-

based technology enabling the delivery of last mile wireless broadband access as an alternative to cable.

Comparison between Wi-Fi and Wi-MAX:-

Comparisons and confusion between Wi MAX and Wi-Fi are frequent because both are related

to wireless connectivity and Internet access.

Page | 49

Wi MAX is a long range system, covering many kilometers that uses licensed or unlicensed

spectrum to deliver connection to a network, in most cases the Internet whereas Wi-Fi uses

unlicensed spectrum to provide access to a local network.

Wi-Fi runs on the Media Access Control's CSMA/CA protocol, which is connectionless and

contention based, whereas Wi MAX runs a connection-oriented MAC.

Wi MAX and Wi-Fi have quite different quality of service (QoS) mechanisms. WiMAX uses a

QoS mechanism based on connections between the base station and the user device. Each

connection is based on specific scheduling algorithms

Advantages of Broadband:-

Connection speed is up to 100 times faster than dialup connection. You can download pictures

files, software in seconds or minutes instead of hours. Online gaming is only possible using

a broadband internet access. It does not affect the phone line. For DSL internet access, you can

use the same phone line for both voice/fax and data transmission. For cable internet access,

you are connected to the internet via the cable network. In either case, your phone line is not

occupied while you are connected to the internet

It is convenient because the internet connection is always on.

You don't need to dial an access number and risk getting a busy signal.

Broadband internet offers unlimited access and you won't be charged based on the connection

duration.

Broadband internet not only gives you high speed internet access, it can also provide cheap

phone services via VoIP technology.

Disadvantages of Broadband:-

High monthly fee compared to dialup internet access.

Higher security risk than dialup connection. A personal firewall is needed to protect your

computer.

Page | 50

Not all phone wires are equipped for DSL service.

Not all cable TV networks are equipped for cable internet access.

May not be available in rural or remote areas.

Applications:-

In telecommunication:-

Broadband in telecommunications refers to a signaling method that includes or handles a

relatively wide range (or band) of frequencies, which may be divided into channels or frequency

bins. The wider the bandwidth of a channel, the greater the information-carrying capacity.

Telemedicine :-

enables health care professionals and patients to take advantage of digital communications to

save money, time, and travel and most importantly, improve the quality of care.

Teleworking or telecommuting :-

is working from home or outside the traditional office or workplace using a digital device

and an Internet connection. Telework benefits employers who see savings in

Information Gathering:-

More and more people are using the Internet to gather information for anything from

medical information to job searching and news and information and shopping.

Page | 51

Tourism:-

Broadband and community content allow people to find out what is available in tourist

destinations and also helps people to see events or exhibits they might otherwise never be able to visit in

person.

Entertainment:-

Many people use the Internet for fun, to play games, gamble, download movies, music,

TV shows, books or information and services. As technology advances the applications and opportunities

for e-commerce and entertainment expand exponentially Office overhead costs as well as increased

productivity and motivation of their employees.

E-Government:-

Refers to the increasing push for government at all levels to make more services

available online. Local governments use e-Government to deliver services and information to their

residents and customers 24 hours a day, seven days a week.

Public Safety:-

Broadband networks can assist police, fire and other law enforcement personnel in

many crisis situations.

National Security:-

Broadband can be used by national, state and local authorities for surveillance,

videoconferencing, data mining, pattern matching and other applications to assist law enforcement and

medical services.

How a cellular telephone call is made:-

Cellular telephony is designed to provide communication between two moving units called

mobile stations or between one mobile unit and one stationary unit,often called a land unit. A

service provider must be able to locate and track a caller,assign a channel t the call and

transfer the channel from base station to base station as the caller moves out of range.

Page | 52

To make this tracking call possible,each cellular service area is divided into small regions

called cells. Each cell contains an antenna and is controlled by a solar or AC powered

network station called the base station. Each base station in turn is controlled by a switching

office called a mobile switching center(MSC).The MSC coordinates communication

between all the base stations and the telephone central office. It is a computerized center that

is responsible for connecting calls, recording call information and billing.

Cell size is not fixed and can be increased or decreased depending on the population of the

area. The typical radius of the cell is 1 to 12mi.Once determined ,cell size is optimized to

prevent the interference of the adjacent cell signals. The transmission power of each cell is

kept low to prevent its signal from interfering with those of other cells

When we place a cellular phone call, we dial the number and press the send button. A number

of steps then follow:

1. Our cell scans for the nearest base station in order to provide it with the strongest signal

and, in turn, the best possible connection. It checks 21 different control channels to determine

thestrongest available signal.

2. Our cell phone then selects the strongest signal for its use.

3. An origination message (a very short message of about ¼ second in length) is then sent

by the cellular phone, which includes its MIN (Mobile Identification Number, that is, your

cellular phone number), as well as the ESN (Electronic Serial Number).

4. Once the cellular service provider verifies that we are among its customers - based on the

sent-out MIN and ESN - the base station sends a channel assignment message to the cellular

phone (another ¼ of a second in length), telling the phone where the conversation will be.

5. The cell phone then tunes into that assigned channel and the call begins.

Frequency reuse:

A frequency reuse pattern is a configuration of N cells,N being the reuse factor,in which each

cell uses a unique set of frequencies. When the pattern is repeated, the frequencies can be

reused.The key characteristic of a cellular network is the ability to re-use frequencies to

Page | 53

increase both coverage and capacity. The numbers in a cell define the pattern.the cells with

the same number in a pattern can use the same set of frequiences.we call these cells as

reusing cells. adjacent cells must use different frequencies however there is no problem with

two cells sufficiently far apart operating on the same frequency.

The elements that determine frequency reuse are the reuse distance and the reuse factor.

The reuse distance, D is calculated as

where R is the cell radius and N is the number of cells per cluster. Cells may vary in radius in

the ranges (1 km to 30 km). The boundaries of the cells can also overlap between adjacent

cells and large cells can be divided into smaller cells.

The frequency reuse factor is the rate at which the same frequency can be used in the

network. It is 1/K (or K ) where K is the number of cells which cannot use the same

frequencies for transmission. Common values for the frequency reuse factor are 1/3, 1/4, 1/7,

1/9 and 1/12 (or 3, 4, 7, 9 and 12 depending on notation)

In case of N sector antennas on the same base station site, each with different direction, the

base station site can serve N different sectors. N is typically 3. A reuse pattern of N/K

denotes a further division in frequency among N sector antennas per site. Some current and

historical reuse patterns are 3/7 (North American AMPS), 6/4 (Motorola NAMPS), and 3/4

(GSM).

Page | 54

If the total available bandwidth is B, each cell can only use a number of frequency channels

corresponding to a bandwidth of B/K, and each sector can use a bandwidth of B/NK.

Code division multiple access based systems use a wider frequency band to achieve the same

rate of transmission as FDMA, but this is compensated for by the ability to use a frequency

reuse factor of 1, for example using a reuse pattern of 1/1.

In other words, adjacent base station sites use the same frequencies, and the different base

stations and users are separated by codes rather than frequencies. While N is shown as 1 in

this example, that does not mean the CDMA cell has only one sector, but rather that the entire

cell bandwidth is also available to each sector individually.

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

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

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

Recently also orthogonal frequency-division multiple access based systems such as LTE are

being deployed with a frequency reuse of 1. Since such systems do not spread the signal

across the frequency band, inter-cell radio resource management is important to coordinate

resource allocation between different cell sites and to limit the inter-cell interference. There

are various means of Inter-cell Interference Coordination (ICIC) . Coordinated scheduling,

multi-site MIMO or multi-site beam forming are other examples for inter-cell radio resource

management .

In addition to this we can define it as”Frequency reuse is a technique of reusing frequencies

and channels within a communications system to improve capacity and spectral efficiency”.

Frequency reuse is one of the fundamental concepts on which commercial wireless systems

are based that involves the partitioning of an RF radiating area (cell) into segments of a cell.

One segment of the cell uses a frequency that is far enough away from the frequency in the

bordering segment that it does not provide interference problems. Frequency re-use in mobile

cellular systems means that each cell has a frequency that is far enough away from the

frequency in the bordering cell that it does not provide interference problems. The same

frequency is used at least two cells apart from each other

Page | 55

BASE STATION CONTROLLER (BSC):

The BSC basically manages the base transceiver station ( BTSs). It reserves radio

frequencies, handles the handover from one BTS to another within the base station system(

BSS) and performs paging of the mobile station(MS).The base station controller(BSC) also

multiplexes the radio channels onto the fixed network connections at the “A” interface .

The base station controller (BSC) provides the intelligence behind the BTSs. Typically a BSC

has tens or even hundreds of BTSs under its control. The BSC handles allocation of radio

channels, receives measurements from the mobile phones, and controls handovers from BTS

to BTS (except in the case of an inter-BSC handover in which case control is in part the

responsibility of the anchor MSC). A key function of the BSC is to act as a concentrator

where many different low capacity connections to BTSs (with relatively low utilisation)

become reduced to a smaller number of connections towards the mobile switching center

(MSC) (with a high level of utilisation). Therefore it means that networks are often structured

to have many BSCs distributed into regions near their BTSs which are then connected to

large centralised MSC sites.

Page | 56

The BSC is undoubtedly the most robust element in the BSS as it is not only a BTS controller

but, for some vendors, a full switching center, as well as an SS7 node with connections to the

MSC and serving GPRS support node (SGSN) (when using GPRS). It also provides all the

required data to the operation support subsystem (OSS) as well as to the performance

measuring centers.

A BSC is often based on a distributed computing architecture, with redundancy applied to

critical functional units to ensure availability in the event of fault conditions. Redundancy

often extends beyond the BSC equipment itself and is commonly used in the power supplies

and in the transmission equipment .

The databases for all the sites, including information such as carrier frequencies, frequency

hopping lists, power reduction levels, receiving levels for cell border calculation, are stored in

the BSC. This data is obtained directly from radio planning engineering which involves

modelling of the signal propagation as well as traffic projections.

Ater is the interface used in base station controller. It is the interface between the BSC and

transcoder. It is a proprietary interface whose name depends on the vendor (for example Ater

by Nokia), it carries the A interface information from the BSC leaving it untouched.

Handoff strategies:

In cellular telecommunications, the term handover or handoff refers to the process of

transferring an ongoing call or data session from one channel connected to the core network

to another. In satellite communications it is the process of transferring satellite control

responsibility from one earth station to another without loss or interruption of service.

Page | 57

When a mobile moves into a different cell while a conversation is in progress, the MSC

automatically transfers the call to a new channel belonging to the new base station. This

handoff operation not only involves identifying a new base station, but also requires that the

voice and control signals be allocated to channels associated with the new base station.

Processing handoffs is an important task in any cellular radio system. Many handoff

strategies prioritize handoff requests over call initiation requests when allocating unused

channels in a cell site. Handoffs must be performed successfully and as infrequently as

possible, and be imperceptible to the users. In order to meet these requirements, system

designers must specify an optimum signal level at which to initiate a handoff. Once a

particular signal level is specified as the minimum usable signal for acceptable voice quality

at the base station receiver (normally taken as between –90 dBm and –100 dBm), a slightly

stronger signal level is used as a threshold at which a handoff is made. This margin, given by

Δ = Pr handoff – Pr minimum usable, cannot be too large or too small. If Δ is too large, unnecessary

handoffs which burden the MSC may occur, and if Δ is too small, there may be insufficient

time to complete a handoff before a call is lost due to weak signal conditions. Therefore, Δ is

chosen carefully to meet these conflicting requirements.

HANDOFF can be either hard handoff or soft handoff.

Hard handoff is used by early systems.in a hard handoff,a mobile station only communicates

with one base station.when the MS moves from one cell to another,communication must first

be broken with the previous base station before communication can be established with the

new one. This may create a rough transition.

Soft handoff is used by new systems. In this case a mobile station can communicate with two

base stations at the same time. This means that during handoff ,a mobile station may continue

with the new base station before breaking off from the old one.

INTERFERENCE:

Interference is the major limiting factor in the performance of cellular radio systems. Sources

of interference include another mobile in the same cell, a call in progress in a neighboring

cell, other base stations operating in the same frequency band, or any non cellular system

which inadvertently leaks energy into the cellular frequency band. Interference on voice

channels causes cross talk, where the subscriber hears interference in the background due to

Page | 58

an undesired transmission. On control channels, interference leads to missed and blocked

calls due to errors in the digital signaling. Interference is more severe in urban areas, due to

the greater RF noise floor and the large number of base stations and mobiles. Interference has

been recognized as a major bottleneck in increasing capacity and is often responsible for

dropped calls.

The two major types of system-generated cellular interference are co-channel interference

and adjacent channel interference. Even though interfering signals are often generated within

the cellular system, they are difficult to control in practice (due to random propagation

effects). Even more difficult to control is interference due to out-of-band users, which arises

without warning due to front end overload of subscriber equipment or intermittent

intermodulation products.The transmitters from competing cellular carriers are often a

significant source of out-of-band interference, since competitors often locate their base

stations in close proximity to one another in order to provide comparable coverage to

customers.

COCHANNEL INTERFERENCE:

Frequency reuse implies that in a given coverage area there are several cells that use the same

set of frequencies. These cells are called co-channel cells, and the interference between

signals from these cells is called co-channel interference. Unlike thermal noise which can be

overcome by increasing the signal-to-noise ratio (SNR), co-channel interference cannot be

combated by simply increasing the carrier power of a transmitter.

Page | 59

This is because an increase in carrier transmit power increases the interference to neighboring

co-channel cells. To reduce co-channel interference, co-channel cells must be physically

separated by a minimum distance to provide sufficient isolation due to propagation

Adjacent channel interference: It is an interference caused by extraneous power from a signal

in an adjacent channel. It may be caused by inadequate filtering,improper tuning or poor

frequency control.

Adjacent Channel Interference :-

Interference resulting from signals which are adjacent in frequency to the desired signal is

called adjacent channel interference. Adjacent channel interference results from imperfect

receiver filters.which allow nearby frequencies to leak into the passband. The problem can be

particularly serious if an adjacent channel user is transmitting in very close range to a

subscriber’s receiver, while the receiver attempts to receive a base station on the desired

channel. This is referred to as the near–far effect, where a nearby transmitter (which may or

may not be of the same type as that used by the cellular system) captures the receiver of the

subscriber. Alternatively, the near–far effect occurs when a mobile close to a base station

transmits on a channel close to one beingused by a weak mobile. The base station may have

difficulty in discriminating the desired mobile user from the “bleedover” caused by the close

adjacent channel mobile.

Adjacent channel interference can be minimized through careful filtering and channel

assignments. Since each cell is given only a fraction of the available channels, a cell need not

be assigned channels which are all adjacent in frequency. By keeping the frequency

separation between each channel in a given cell as large as possible, the adjacent channel

interference may be reduced considerably. Thus instead of assigning channels which form a

contiguous band of frequencies within a particular cell, channels are allocated such that the

frequency separation between channels in a given cell is maximized. By sequentially

assigning successive channels in the frequency band to different cells, many channel

allocation schemes are able to separate adjacent channels in a cell by as many as N channel

bandwidths, where N is the cluster size. Some channel allocation schemes also prevent a

secondary source of adjacent channel interference by avoiding the use of adjacent channels in

neighboring cell sites.

Page | 60

Conclusion/ Goal

I have learned about the broadband internet connectivity using the dsl connections,

wifi connectivity and internet through landline phones, Problems persisting while

connecting the internet, new technologies about wi-max ,routers, mobile switching

center and remote access servicing at Bharat Sanchar Nigham Ltd.