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Broadband Technology used in BSNL
Under the Guidance of: Industry Guide:
Amity Institute of Information Technology
AMITY University, Uttar Pradesh, Noida.
Mr. Himanshu Gupta
Senior Faculty Member
Syed Adil Gilani
Junior Telecom Officer
Syed Arafat Ahmad
MSC NT & M – III(2012-14)
Enrolment No : A1000812011
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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.
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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.
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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
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
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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
I further declare that the information presented in this project is true and original to the best of my
Date: 20/08/2013 Syed Arafat Ahmad
Place: New Delhi Enrollment No A1000812011.
Msc. NT&M (2012-2014)
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List of contents
1. About the organization…………………………………………….9
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
6. XDSL Connectivity Diagram………………………………….…34
7. Tier Networks………………………………………………..……35
8. Fiber-Optic Communication……………………………………...36
9. Routing Concepts………………………………………………....45
11. Advantages & Disadvantages of Broadband………………...…52
12. Frequency Model………………………………………………...55
13. BSC(Base Station Controller)…………………………………..58
14. Hand-Off Strategies……………………………………………..59
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About the Organization
BHARAT SANCHARNIGAM LIMITED
Bharat Sanchar Nigam Limited (abbreviatedasBSNL)isastateowned telecommunications.
Company head quarteredinNewDelhi, India. BSNL is one of the largest Indiancellularserviceproviders in
india, withover 88.1 millionsubscribers as ofApril2011, and the largest land line and wlltelephone provider
inIndia. However, inrecent yearsthecompany'srevenueand market shareplunged into lossesdueto intense
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 MumbaiandNewDelhi, whicharemanaged byMahanagar Telephone
NigamLimited (MTNL). As of June 30, 2010, BSNL had a customer base of 27.45 million wire line and
It is India’s largest telecommunication company with 24% market share as on March
2008.Its headquarters are at Bharat Sanchar Bhawan, HarishChandra Mathura Lane, New Delhi. It
hasthestatusofMINIRATNA, astatusassignedtopublicsectorcompanies inIndia.
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
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.
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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.
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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
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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
· 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
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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
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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".
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
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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
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
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
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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 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.
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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.
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
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
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
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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
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.
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
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Cases where PBX/PABX facilities are surrendered before the expiry of the guarantee
period will be regulated as per Company rules.
National InternetBackbone (NIB):
The Internet backbone refers tothe principaldata routes between large, strategically interconnected
networks and core routersintheInternet. These data routes are hosted by commercial, government,
academic and other high capacitynetworkcenters,theInternet exchangepointsandnetworkthat interchange
facilities, nor do they implement any global network policies. The resilience of the Internet results from its
principalarchitectural features, most notably the idea ofplacing as few network state and control functions as
possible inthe networkelements,but insteadrelyingonthe endpointsofcommunicationto handle most ofthe
processing to ensure data integrity, reliability ,and authentication. In addition to this,the highdegree
ofredundancyof today's networklinks and sophisticatedreal-timeroutingprotocolsprovidealternatepathsof
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
togetherto increasethecapacity.The backbone is ableto reroutetraffic incaseofa failure. Thedataspeedsof
backbone lines have changed withthe times. In 1998, allofthe United States backbone networks had utilized
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the slowest data rateof45 Mbps. Howeverthe changing technologies allowed for 41 percent ofbackbones 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
Internet traffic from this line goes through the countries of Iran, Iraq and Georgia. Fiber-
opticcablesare the mediumof choice for internetbackboneproviders 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
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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 ofthe largest internet backbone networks. These backbone providers will thenselltheir service toISPs.
EachISPhas its owncontingency 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
Inorder for datato navigate throughthis diverse webthat the backbone creates, backbone routers are
desperatelyneeded.These backboneroutersareroutersthatarepowerfulenoughto handle informationonthe
internet backbone, and theydirect datato otherrouters inorderto send it to its finaldestination. Without these
backbone routers, informationwould be lost since data would not know howto locate itsend destination. The
verylargest providers, knownas Tier 1providers,have suchcomprehensive networksthat theynever need to
purchasetransit agreementsfromotherproviders.Asof2000therewereonlyfive internet backboneproviders
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
Economy of theBackbone:
Peering agreements: Backbone providers of roughly equivalent market share regularly create
agreementscalledpeering agreements.These agreements allow theuseofanother's network to hand off
traffic where is ultimatelydelivered. Theyusuallydo not charge eachother forthis use as theyall get revenue
Transit agreements: Backboneprovidersofunequalmarketshareusuallycreateagreementscalled transit
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Regulation: Antitrust authorities haveactedto ensurethat no providergrowslargeenoughto dominatethe
backbone market. The FCC has also decided not to monitor the competitive aspects ofthe Internet Backbone
interconnectionrelationships, as longasthemarket continuesto functionwellwithoutregulation
Technology used in BSNL :-
The standard broadband technologies in most areas are asymmetric digital line subscriber line(ADSL )and
optical fiber connections closer to the subscriber in both telephone andcable plants. Fiber-optic
communication, while only recently being used in fiber tothe premisesand fibertothe curbschemes , has
playeda crucialrole inenabling Broadband Internet accessbymaking transmissionofinformationover larger
Ina few areas not served bycable or ADSL, communityorganizations have begunto install Wi-Fi networks,
and in some cities and towns local governments are installing municipal Wi-Fi networks. The newest
technologybeingdeployed formobileandstationarybroadbandaccess 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
Digital Subscriber Line or DSL:-
.Digitalsubscriber line (DSL) is one ofthe 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
frequencybands are subsequentlyseparated byfiltering.
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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 digitalsubscriber line Access Multiplexer (DSLAM). It has a built insplitter
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
LAN Switch: It is used for aggregating multiple digital subscriber line access multiplexer
(DSLAM).LAN switching is a technology that promises to increase the efficiencyof localarea networks
and solve the current bandwidth problems. It is a formofpacket switching used in localarea 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 trackof 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
ondemand 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 keepstrackofbilling.
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 andthe 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 ofservice right fromDSLCPE’s to DSLAM to Switchto BRAS to LDAP.
The basic technology of DSL uses telephones. Telephones are connected to thetelephone 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 transmissionof speech, encompasses an audio frequency range
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of300 to 3400 Hertz (voice band or commercial bandwidth) . The long distance trunks were gradually
converted fromanalog to digitaloperation, throughthe local loop when the idea ofdata 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 throughthe normaltelephone voice path.
The local loop connecting the telephone exchange to most subscribers has the capability ofcarrying
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 qualityare a factor(the higher frequencies used byDSLtravelonlyshort distances). The
pool of usable channels is then split into two different frequency band for upstream and downstream
traffic , based ona 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 qualityofeach channel and will
add orremove themfromservice depending onwhether theyare usable.
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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 individualdigital 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 ofdata due to the large amount ofelectricalresistance encountered as the data moves
between the DSLAM and the user's DSL modem. It is common for a few residential blocks to be
connectedto one DSLAM.
When the DSL modem powers up it goes through a sync procedure. The actual process varies from
modemto modembut generally involves the following steps:
1. The DSLtransceiver 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
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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 ofDSL(such as SDSL) use synchronous serialconnections.
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 modemunits 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, usuallywith a greencolor.
The accompanying figure is a schematic ofa simple DSLconnection(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 ofPCs. With manyservice providers, the customer mayopt for a modemwhich
contains a wireless router. This option(within the dashed bubble) often simplifies the connection
DSL Connection schematic :-
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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
frequencyrange 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 serialinterface, using protocols such asEthernet or V.35. Inother 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
referredto 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
practicaland economical limitations.
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 downstreamdirection fromthe internet to theresident and in upstreamdirection 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 alarge bandwidth in bothdirections.
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In other words we can define ADSL as “it is an asymmetric communication technology designed for
residentialusers,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
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
channeluses a bandwidthof4.312khz.Each bandwidth is divided into:
1.Voice: Channel0 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 controland 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
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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 impracticalenough 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 technologyallows an ADSL LITE modemto 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 upstreamdatarate of512kbps.
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.
HDSLuses two twisted pairs to achieve fullduplextransmission.
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 andreceive 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
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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 VDSLuses upto 7different frequencybands.
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 DigitalSubscriber Lines (DSLs) to a high-speed Internet backbone line using
multiplexing techniques. By placing additional remote DSLAMs at locations remote to thetelephone
exchange, telephone companies provide DSL service to locations previously beyond effective range.
Path taken by data to DSLAM:-
1.Customer premises: DSLmodemterminating the ADSL, SHDSLor VDSL circuit and providing
LAN interface to single computer or LAN segment
2. Local loop: The telephone company wires froma customer to the telephone company' s centraloffice
orto aServing 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 proximityto the cable vault and not far fromthe 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 withthe
service provider's DSLAM.
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d) DSLAM : A device for DSLservice. The DSLAM port wherethe subscriber local loop is connected
converts analog electricalsignals to datatraffic (upstreamtraffic for data upload) and datatraffic to analog
electricalsignals (downstreamfor data download).
Role of DSLAM:-
The DSLAM equipment collects the data from its many modem ports and aggregates their voice and
datatraffic 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 atelco's backbone switch, via an access network (AN) also called a Network Service
Provider (NSP) at upto 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 usertraffic 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 andthe 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 ofbeing
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 maximumconnectionrate capabilityofthe 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 requiredto construct suchdigital interfaces is more costly).
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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 IPtransit or paying settlements.
Bythis definition, a tier 1 network is a transit-free network that peers with everyother 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. Strictlyobserving this definitionof"tier 1" would exclude everynetwork. 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
As a result, the term"tier 1 network" is used in the industryto mean a network with no overt settlements.
An overt settlement would be a monetarycharge for the amount, direction, ortype oftraffic sent between
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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 portionofthe 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
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 anyalternate 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
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partitioned until one side purchases transit, or until the collective pain of the outage or threat of litigation
motivates thetwo networks to resume voluntarypeering.
Tier 1 networks are closer to the backbone ofthe 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 atier 1.
Tier 1 networks bydefinitionoffer betterqualityInternet connectivity.
By definition, there are networks which tier 1 networks have only one path to, and if they lose
that path, theyhave no backuptransit 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
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.
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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.
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.
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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%
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
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
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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
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).
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
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avalanche photodiodes. Metal-semiconductor-metal (MSM) photodetectors are also used due
to their suitability for circuit integration in regenerators and wavelength-division
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
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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
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.
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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.
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.
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).
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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
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.
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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.
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.
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.
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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.
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 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.
There are two methods of routing.
1: Static routing
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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
Dynamic routers are less secure because routing tables can be hampered by hackers. Routing
protocols also create additional network traffic.
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 fromdifferent
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 onits journeyor dropsthe packet. A data packet is typically passed fromrouter to router
through the networks of the Internet until it gets to its destination computer unless the source IP is on a
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
distributiontier routers from multiple buildings ofa campus, or large enterprise locations. Theytend to be
optimized for high bandwidth
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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
frombroadband remote access devices such as digitalsubscriber line access multiplexers (DSLAM) on
an Internet service provider's (ISP) network. BRAS can also be referred to as broad network gateway
The BRAS sits at the coreofan ISP's network, and aggregates user sessions fromthe access network. It is
at the BRAS that anISP can inject policy management and IP Qualityof Service (QoS).
The specifictasks include:
Aggregatesthe circuits fromone or more link access devices such as DSLAM’s
Provides layer 2 connectivitythrough eithertransparent bridging orPPP sessions over Ethernet
or ATM sessions
Enforces qualityofservice (QoS) policies
Provides layer 3 connectivityand routes IPtraffic through an Internet service provider’s Back
bone networkto theInternet
A DSLAM collects datatraffic from multiple subscribers into a centralized point so that it can be
transportedto a switchorrouter over a Frame Relay, ATM, orEthernet connection.
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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
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 thetraffic are layer 2 addresses (e.g. MAC addressesonEthernet).
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 randomdrops.
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
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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 ofthe 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 asthese packets need specialattentionthat cannot be handled byan ASIC.
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.
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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
statisticaldata, ifso 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
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 aretaildrop, random
earlydetection (RED), and weighted randomearlydetection (WRED). Taildrop 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 onthe average queue size to act upon whenthe traffic is about to exceed the pre-configured size,
so that short bursts willnot trigger randomdrops.
Another function a router performs is to decide which packet should be processed
first when multiple queues exist.This is managed throughqualityofservice (QoS), which is criticalwhen
Voice over IP is deployed, so that delays between packets do not exceed 150ms to maintain the qualityof
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 ofthe 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 throughthe CPU as these packets need special attentionthat cannot be handled byan 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 willbe discarded.
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 (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 technologyenabling the deliveryoflast 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 connectivityand Internet access.
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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 spectrumto provide access to a localnetwork.
Wi-Fi runs on the Media Access Control's CSMA/CA protocol, which is connectionless and
contention based, whereas WiMAX 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 connectedto the internet
It is convenient becausethe internet connection is always on.
You don't needto dialan access number and risk getting a busysignal.
Broadband internet offers unlimited access and you won't be charged based on the connection
Broadband internet not only gives you high speed internet access, it can also provide cheap
phone services via VoIPtechnology.
Disadvantages of Broadband:-
High monthly fee comparedto dialup internet access.
Higher security risk than dialup connection. A personal firewall is needed to protect your
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Not allphone wires are equipped for DSLservice.
Not allcable TV networks are equipped for cable internet access.
May not be available in ruralorremote areas.
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 bandwidthofa channel, the greaterthe information-carrying capacity.
enables health care professionals and patients to take advantage ofdigitalcommunications to
save money, time, and traveland most importantly, improve the qualityofcare.
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
More and more people are using the Internet to gather information for anything from
medical informationto job searching and news and information and shopping.
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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
Many people use the Internet for fun, to playgames, gamble, download movies, music,
TV shows, books or information and services. As technologyadvances the applications and opportunities
for e-commerce and entertainment expand exponentially Office overhead costs as well as increased
productivityand motivationoftheir employees.
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.
Broadband networks can assist police, fire and other law enforcement personnel in
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
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.
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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 Â¼ 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 Â¼ 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.
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
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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
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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
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
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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.
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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
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.
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.
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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 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
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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
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
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.
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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
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.
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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.