16453913 reliance training report by chirag mohanty 123

8/6/2019 16453913 Reliance Training Report by Chirag Mohanty 123

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APROJECT REPORTON TRAININGATRELIANCE COMMUNICATIONS

Submitted by:

CHIRAG MOHANTY

Roll no.: 604045

B.Tech, 6th Semester

Department of Electronics and Telecommunications

Kalinga Institute of Industrial Technology

KIIT UNIVERSITY

Bhubaneshwar



CERTIFICATION

This is to certify that Mr. Chirag Mohanty, Roll no. 604045, of 3rd year,Electronics and Telecommunication Engineering, underwent PracticalTraining from 1st May 2009 to 15th June 2009 at our firm; for the course

requirement at Kalinga Institute of Industrial Technology, KIITUNIVERSITY, Bhubaneshwar.

He has completed his training with utmost dedication and sincerity.

We wish him all the best for his future endeavours.

Signature Signature

Jugal P. Satapathy Sarthak Dash

H.R. Engineer Incharge of

Orissa Circle TrainingReliance Communications Limited



Company Profile

Reliance Anil Dhirubhai Ambani Group, an offshoot of the Reliance Group foundedby ShriDhirubhai H Ambani (1932-2002), ranks among Indias top three private sector business houses

in terms of net worth. The group has business interests that range from telecommunications(Reliance Communications Limited) to financial services (Reliance Capital Ltd) and thegeneration and distribution of power (Reliance Infrastructure Limited).

Reliance ADA Groups flagship company, Reliance Communications, is India's largestprivatesector information and communications company, with over 77 million subscribers.It has beenlisted on the National Stock Exchange and the Bombay Stock Exchange. It has established a pan-

India, high-capacity, integrated (wireless and wireline), convergent (voice, data and video) digitalnetwork, to offer services spanning the entire infocomm value chain.

Other major group companies Reliance Capital and Reliance Infrastructure are widelyacknowledged as the market leaders in their respective areas of operation.

The Late Dhirubhai Ambani dreamt of a digital India -an India where the common man wouldhave access to affordable means of information and communication. Dhirubhai, whosinglehandedlybuilt Indias largest private sector company virtually from scratch, had stated as

early as1999: Make the tools of information and communication available to people at an affordablecost. They will overcome the handicaps of illiteracy and lack of mobility. It was one of Dhirubhais great dreams in life to see ordinary Indians enjoy the enormouseconomic benefits of being able to access affordable yet world class telecommunicationsinfrastructure. He wanted Reliance to spearhead a communications revolution thatwoulddramatically cut down the cost of connectivity, and propel India into the digital age. His ultimate

ambition: To make the cost of a phone call cheaper than that of a post card. Itwas thereforeentirely logical for Reliance to enter the telecommunications space when the sector was openedup for private participation in the 1990s.The rest, as they say, is history.Today, Reliance Communications is Indias largest information and communications servicesprovider offering the full range of integrated telecom servicesat prices that are, by far, thelowest anywhere in the world.

It was with this belief in mind that Reliance Communications (formerly RelianceInfocomm)

started laying 60,000 route kilometres of a pan-India fibre optic backbone. Thisbackbone wascommissioned on 28 December 2002, the auspicious occasion of Dhirubhais 70th birt



hday,though sadly after his unexpected demise on 6 July 2002.

Our business encompasses a complete range of telecom services covering mobile and fixed linetelephony. It includes broadband, national and international long distance services and data

services along with an exhaustive range of value-added services and applications. Our constantendeavour is to achieve customer delight by enhancing the productivity of the enterprises andindividuals we serve.

Reliance Mobile (formerly Reliance India Mobile), launched on 28 December 2002,coincidingwith the joyous occasion of the late Dhirubhai Ambanis 70th birthday, was among the initial



initiatives of Reliance Communications. It marked the auspicious beginning of Dhirubhais dreamof ushering in a digital revolution in India. Today, we can proudly claim that we wereinstrumental in harnessing the true power of information and communication, by bestowing it in

the hands of the common man at affordable rates.

Reliance Communications has a reliable, high-capacity, integrated (both wirelessand wireline)and convergent (voice, data and video) digital network. It is capable of delivering a range ofservices spanning the entire infocomm (information and communication) value chain, includinginfrastructure and services - for enterprises as well as individuals, applications, and consulting.

Today, Reliance Communications is revolutionizing the way India communicates and

networks,truly bringing about a new way of life.

History of Telecommunications



Radio has been around only for the last 100 years (out of ~6000 years of writtenhuman history).

.1680s: Isaac Newtons idea of the spectrum.

1830s: Basic Electricity.1890s: First demos of radio by experimenters

Telegraphy:

Early electronic communication was carried only by wires and used only crude on-off signalingto laboriously spell out the message.

.1837: Samuel Morse patented his telegraph.1844: First commercial telegraph systems operational.1857: First trans-atlantic cable put in service



Telephony:

In 1876, Alexander Graham Bell patented his telephone, a device for carrying actual voices overwires. Initial telephone demonstrations sparked intense public interest and by the late 1890s,

telephone service was available in most towns and cities across the USA.Thus, the telecommunications industry, as we know it today, originated in 1876 when AlexanderGraham Bell developed the telephone in an attempt to communicate with his motherand wife,who were both deaf. Bell filed his patent for the telephone on February 14, 1876, just four hoursbefore Elisha Grey applied for the same patent. But for that timing, we might have had the GreyTelephone System instead of the Bell Telephone System. Through legal maneuveringBellspatent was upheld and the Bell Telephone Company, which was formed in 1877, bega

n to expandacross the United States of America and emerged as a near monopoly supplier of telephone

services. In 1880 the company was renamed American Bell.Radio Milestones:

.1888: Heinrich Hertz, German physicist, gives lab demo of existance of electromagneticwaves at radio frequencies



.1895: Guglielmo Marconi demonstrates a wireless radio telegraph over a 3-km pathnearhis home it Italy

.

1897: the British fund Marconis development of reliable radio telegraphy over ranges of100 kM

.1902: Marconis successful trans-Atlantic demonstration

.1902: Nathan Stubblefield demonstrates voice over radio

.1906: Lee De Forest invents audion, triode vacuum tube (feasible now to make stead

y

carriers, and to amplify signals)

.1914: Radio became valuable military tool in World War I

.1920s: Radio used for commercial broadcasting

.1940s: first application of RADAR -English detection of incoming German planes

during WW-II

.1950s: first public marriage of radio and telephony - MTS, Mobile Telephone System

.1961: transistor developed: portable radio now practical

.1961: IMTS - Improved Mobile Telephone Service

.1970s: Integrated circuit progress: MSI, LSI, VLSI, ASICs

.1979, 1983: AMPS cellular demo, commercial deployment

Frequencies Used by Wireless Systems:

Overview of the Radio Spectrum



Structure of a Typical Wireless System



Wireless Base Stations:

.It provides the radio connection between mobile users and the switch..One wireless system in a large metropolitan area may require hundreds of base st

ations todeliver unbroken coverage and provide sufficient capacity to handle all potential users.

The Switch:



.The HLR (Home Location Register) is the official database of all customers on awirelesssystem.It can be part of the switch, or held in a server at a central location where mu

ltipleswitches can interrogate it

Information held in the HLR:

current account status/validity phones technical parameters whether the phone is presently turned on, and if so, the identity of switch which is presentlyserving the phone secret keys for authentication to avoid fraudulent use/cloningDelivering an Incoming Wireless Call:

.Someone dials a mobile subscribers number

1.System checks database for current location of mobile, and pages this area.Database is kept up-to-date by a process called registration2.Mobile recognizes page and sends back acknowledgment to the strongest cell3.System assigns a voice channel to the mobile.

System sends voice channel assignment to mobile on control channel.mobile acknowledges and jumps to the assigned voice channel4.Phone rings and mobile subscriber answers call.Conversation beginsAn illustration of the above is given on the following page.



Managing Handoffs:

.As a mobile travels through the service area, it passes from the coverage zone of one basestation into the coverage of another

.Signal strength measurements by the mobile or the base station trigger the BSC andswitch to hand off the call from base station to base station, avoiding dropped calls andinterference

.Each wireless technology uses its own methods to implement the handoffs. CDMA caneven simulcast to the mobile from multiple base stations to reduce fading effects

(this iscalled soft handoff)

What is Multiple Access?



.Multiple Access is the simultaneous use of a communications system bymore than one user

.Each users signal must be kept uniquely distinguishable from other users signals,

toallow private communications on demand

.Users can be separated in many ways:

physically: on separate wires by arbitrarily defined channels established in frequency, time, or any other variableimaginableWireless Multiple Access MethodsFrequency Division Multiple Access

A users channel is a private frequencyTime Division Multiple Access

A users channel is a specific frequency, but it only belongs to the user during certain timeslots in a repeating sequenceCode Division Multiple Access

Each users signal is a continuous unique code pattern buried within a shared signal, mingledwith other users code patterns. If a users code pattern is known, the presence orabsence of their

signal can be detected, thus conveying information.



TDMA: Time Division Multiple Access

Each user has a specific frequency but only during an assigned time slot. The frequencyis used by other users during other time slots, like a condominium at a beach resort

UNITED STATES VERSIONS:

.IS-54: The original TDMA format, intended for use within existing AMPS systems.IS-136: Enhanced TDMA with special control channels to allow short message service,battery life extension, other features.6 timeslots, three users occupy in rotation

INTERNATIONAL VERSION

.GSM: Groupe Special Mobile.Developed in Europe, used in roughly 50% of all wireless systems worldwide.8 timeslots, 7 or 8 users occupy in rotation

CDMA: Code Division Multiple Access

.

Each users signal is a continuous unique code pattern buried within a shared signal,mingled with other users code patterns. If a users code pattern is known, the presence orabsence of their signal can be detected, thus conveying information.

.All CDMA users occupy the same frequency at the same time! Time and frequency are

not used as discriminators.

CDMA interference comes mainly from nearby users.CDMA operates by using CODING to discriminate between users.Each user is a small voice in a roaring crowd - but with a uniquely recoverablecode



Third Generation Wireless Systems

2G to 3G Migration Paths:

A Game of Avoiding Extremes



The traffic engineer must walk a fine line between two problems:

.Overdimensioning.too much cost

.insufficient resources to construct.traffic revenue is too low to support costs.very poor economic efficiency!

.Underdimensioning.Blocking

.Poor technical performance(interference)

.Capacity for billable revenue is low.very poor economic efficiency!.revenue is low due to poor quality.users unhappy, cancel service.very poor economic efficiency

Principles of Traffic Engineering:

Blocking Probability / Grade of Service

.Blocking is inability to get a circuit when one is needed.Probability of Blocking is the likelihood that blocking will happen.In principle, blocking can occur anywhere in a wireless system:

not enough radios, the cell is full not enough paths between cell site and switch not enough paths through the switching complex not enough trunks from switch to PSTN.Blocking probability is usually expressed as a percentage using a shorthand notation: P.02 is 2% probability, etc. Blocking probability sometimes is called Grade Of Service .Most blocking in cellular systems occurs at the radio level. P.02 is a common goal at the radio level in a system



Wireless System Performance Optimization

.Key Performance Indicators and Objectives

Dropped Calls, Access Failures, system BER, FER

Handoff Activity Levels Capacity and Blocking.Success comes from managing resources

Handoff Thresholds properly set Neighbor lists well-optimized RF Coverage: holes vs. excessive overlap PN or Frequency Planning Hardware defects: watch statistics for cluesANALOG AND DIGITAL SIGNALS



ANALOG:

Historically, telephone systems were entirely analog circuits. When voice is converted to anelectrical signal through the microphone in a telephone, it provides a continuously varying

electrical wave. The wave matches the pressure pattern of the sound that createdit and conveysloudness which is measured as amplitude, and pitch which is measured as frequency. Because thetone (pitch) and loudness (amplitude) of voice is unpredictable, the analog signal is alsounpredictable.

The basic shape of an electrical wave used to transmit telecommunications signals is representedby the sine wave. The rate at which the electrical current alternates is measured in hertz, which

means cycles per second. A voice telephone circuit is designed to handle frequencies from 300 to4,000 hertz (4 Khz).

As an analog signal travels through a wire, the signal loses strength over distance (attenuation)and has to be amplified. Unfortunately, when the voice signal is amplified, anynoise on the lineis also amplified. After much amplification the line noise component may be larger than theactual voice signal. Circuit noise can make the conversion unintelligible.

DIGITAL:

Unlike the analog signal, a digital signal is predictable. A digital signal is aseries of discrete,discontinuous voltage pulses. The analog voice signal is sampled at the rate of8,000 samples persecond, and each sample is transmitted as a binary code. The binary states of 0and 1 arerepresented as discrete levels of voltage.

Digital transmission has higher quality than analog. Like analog signals, digital signals lose

strength over distance. However, with digital transmission, regenerators detectthe incoming bitstream of 0s and 1s and create a new signal that is identical to the original signal.

What is a Transmission Network?



.Area of Telecom Network dealing with transport of data, voice, video and other signalsover long distances is referred to as Transport (Tpt) or Transmission (Tx) Network.

e.g. -Intercity connectivity between local trunk and tandem exchanges within a cityalso falls in the category of Tpt NW e.g. Intracity also called Backhaul NW.Tpt NW - Physically consists of MW, OFC or satellites as a medium (criterion ofselection

-Tx rate, distance, protection, cost, reliability, environmental conditions).Figurative Rep of a Tpt NW.NW design -STAR, TREE, RING or MESH topologies (main criterion -connectivity,

protection and cost)

Transport Systems required to carry large data

.2.5 Gbps (1Gb=109b) - 30,000 voice channels, 10 Gbps, 40 Gbps.Terabits per sec (1 Tb=1012b) -Lucent recently tried 2 Tbps data rate usingDWDM over a single fibre.Future Data Rates in terms of Petabits per sec (1 Pb=1015b) and Exabits per second(1 Eb = 1018b)

Transmission systems, since they carry large data rates, must have

.Min Down Time (0.003%).Low Bit Error Rates (BER < 10-9).High MTBF (5 years).Self Healing Ring Structure

Transmission links used are primarily of two types these days:

.Microwave Link.Optical Fiber Cable (OFC) Link.Coaxial cable.VSAT



What is Microwave Radio?

Microwave radio is a point to point fixed link that operates in duplex mode I.e.each radiofrequency channel consists of a pair of frequencies for the transmit and receivedirections



respectively. The base band signal which contains the user information occupiesa limitedbandwidth depending upon the modulation scheme used. The signal is modulated over an RFcarrier and is transmitted over the air as an electromagnetic waveform. The Microwave Radio

links cover the frequency spectrum from 150 MHz to 60 GHz.

Characteristics of a Radio Link System:

.Signal follows a straight line or line of sight (LOS) path.

.Beam traverses through the Troposphere.

.

Microwaves are electromagnetic waves similar to light.

.Propagation is affected by Free Space Attenuation, Reflection, Precipitation, Refraction,

Diffraction, Scattering and Polarization.

.Uses frequencies above 150 MHz.

.Uses angle modulation I.e. Frequency Modulation or Phase Modulation

Advantages of Microwave Radio:

.Microwave radios are cheaper than Satellite or Leased Line Service..Do not involve ROW (Right Of Way) Permissions..Radios have a stepped cost profile where as fibre has a linear cost profile.



.Radio systems are easy to install..Installation of Radios does not impact the intervening terrain since no diggingis involved..

Fast Roll out..Better overall reliability.

Stages in installation of a Microwave System:

Microwave links are set up for connecting two distinctly located points for establishingtelecommunications circuits. This is similar to laying multi-core cables betweenthe two points;

but in quality and overall economics this is far superior to the cable system. Various sub-activitiesare briefly explained below:



1)Survey -The first job to be undertaken before establishing a microwave link is survey ofthe terrain between the two locations intended to be connected. The survey consists of twoparts: theoretical survey using survey maps and actual survey by visiting variou

s sites.

Survey of India publishes maps which clearly indicate the height of various points above mean

sea level (MSL) for theoretical survey. But in different terrain and in city areas it will be difficult

to complete the survey without actual visits to the sites. For this purpose a accurate device, GPS

(Global Positioning System) is extensively used by engineers for more accurate &

reliable results.2) Assessment of height -Once all the physical obstructions have been identified, distancefrom one of the point to be connected is plotted against the obstruction heightat thatpoint. However for assessment of the actual height of the obstruction it is notsufficient toconsider the height of physical structure above MSL alone. For this purpose airfilledballoons are used to estimate height.

For the purpose of economy following policies are followed:a) Existing structures if available are used so that structures height at the end

it isavailable is used to check required tower height at the other end.b) Since ground space is costly at a location, lower tower height are used at that end.c) If any existing tall building is available at any end, choose the biggest tower height thatthe building can support.d) If transportation of the material is difficult or if soil condition is bad atone end, use oflower tower height at this end is going to be cheaper.

3)Construction of Equipment room -The equipment room is constructed keeping in viewthe size of the equipment as well as the capacity of the equipment to be installed in theroom. Proper layout is made well in advance and should be approved from the owner/user.Care should be taken to keep elbow space i.e. space for future expansion. If the installation is to be done on the ground floor it should be ensured that water logging doesnot take place.If the room in which the equipment is to be installed is on the top floor of the

building, itis to be made sure that the position chosen for installing the equipment is freefrom any



water drips.

4)Erection of Tower -The erection of tower involves selection of proper tower design,fabrication of tower members, and design of the tower, provision of tower foundations

and fitting of tower members. The tower design must ensure that the twist and sway of thetower is within the beam width of the microwave beam. Typical twist and sway isrequiredto be restricted within about 0. 5 Degrees for antenna gains of about 40 dB.

5)Fitting Of Antenna -After erecting the tower and also the antenna-mounting arrangement,it is possible to install the antennas. For this purpose the antennas to be installed arebrought below the tower structure and ropes tied at suitable anchoring points of

theantennas. Once the antenna is lifted to the top is bolted onto the antenna mounting pipesthrough suitable fittings which normally come with the antenna. After that, other fittingssuch as the feed horn and wave-guide have to be done.

6)Waveguides & Flexible cable -Waveguides or coaxial cables are used for connectingantenna feed horns to radio transceivers. Normally the main waveguides/coaxial cablesare very rigid and the ends connections are made by small lengths of flexible co

axialcables. These cables are flexible but cannot be used in lengths more than one metre.

7)Radio Transceivers -The installation of the radio transceiver does not involve much effort,as the present-day equipment are lightweight and modular in structure. Most of the



Objects closer to the headlights appear brighter than objects further away.

Transmitting source (car head light)

pointA

pointB

The loss between the transmitting and the receiving antenna with transmission medium asvacuum is termed as free space loss. The antenna at each side is isotropic having a gain of 1 or 0dB.

FSL = 96.6 + 20 log D + 20 log F

Where F = frequency in GHzD = distance in miles

Receiver Sensitivity Threshold:

The Receiver Sensitivity Threshold (Rx) defines the minimum signal strength required inorder for a radio to successfully receive a signal. A radio can not receive or interpret a signalthat is weaker than the receiver sensitivity threshold.

Receive Signal Level:

The Receive Signal Level (RSL) is the expected strength of a signal when it reaches thereceiving radio. The following formula defines the Receive Signal Level:

O - Lctx + Gatx Lcrx + Gatx FSL = RSLWhere,Po is the output power of the transmitter (in dBm)Lctx is the cable loss between the transmitter and its antenna (in dB)Gatx is the gain of the transmitters antenna (in dBi)



Lcrx is the cable loss between the receiver and its antenna (in dB)

Gatx is the gain of the receivers antenna (in dBi)

FSL is free space loss (in dB)

Link Feasibility Formula

To determine if a link is feasible, we have to compare the calculated Receive SignalLevel with the Receiver Sensitivity Threshold. The link is theoretically feasible if

RSL > = Rx

If the Receive Signal Level is greater than or equal to the Receiver Sensitivity Threshold, then the link may be feasible since the signal should be strong enoug

h to besuccessfully interpreted by the receiver.The link is not feasible since RSL is less than Rx (-80.5 dB <- 77 dB).

Note: This formula is not a guarantee that a link is viable. It should be used for proof-ofconceptpurpose only. The Receiver Signal Level does account for path fading phenomenathat may add addition loss to the radio signal and cause the strength of received signal to fallbelow the receiver sensitivity threshold.

Fade Margin and link availability

Fade margin is the difference between the unfaded received signal level and thereceivesensitivity threshold. Each link must have sufficient fade margin to protect against pathfading that weakens the radio signals. Fade margin is directly related to Link Availability,which is the percentage of time that the link is functional. The percentage of time that link isavailable increases as the fade margin increases. A link will experience fewer system outageswith greater Fade Margin. A link with little or no Fade Margin may experience pe

riodicoutages due to path fading phenomena.

Climate condition and path fading

Path fading occurs more frequently in flat, humid environments (like south easternU.S.) than in rough, dry location (like Rocky Mountain States). Therefore link in flat andhumid area requires a greater Fade Margin to achieve the same level of Link Availability as alink in a rocky and dry location.

Path profile

A path profile is a graphical representation of the path traveled by the radio w



aves betweenthe two ends of a link. The path profile determines the location and height of the antenna ateach end of the link, and it insures that the link is the link of obstructions,such as hills, andnot subject to propagation losses from radio phenomena, such as multipath reflections.



In addition to terrain elevation ,a Path Profile must consider the effects of severalradio phenomena , including multipath reflections and refraction, and provide adequateFresnel Zone clearance.

Fresnel Zone clearance

The endpoints of a radio link must have unobstructed radio line-of-sight. Radioline-of-sightis not the same optical line-of-sight (that is, the ability to see one end of alink from theother). Microwaves have a lower frequency than visible light and , therefore, behavedifferently in response to environmental conditions. Radio line-of-sight requires moreclearance than optical line-of-sight to accommodate the characteristics of microwave signals.

Figure illustrates a case where a path has optical line-of- sight but not radioline-of-sight.An electromagnetic wave does not travel in a straight line: the wave spreads outas itpropagates. Also, the individual waves that make up a radio signal do not travelat the samephase velocity. A French physicist, Augustine Fresnel, defined the propagation of a radiowave as a three-dimensional elliptical path between the transmitter and receiver.Fresnel divide the path into several zones based on the phase and speed of thepropagating waves ,as shown in the figure.

The size of each Fresnel Zone varies based on the frequency of the radio signaland thelength of the path. As frequency decreases, the size of the Fresnel Zone increases. As thelength of the path increases, the size of the Fresnel Zone also increases. A Fresnel Zonesradius is greatest at the mid point of the path. Therefore, the midpoint requires the mostclearance of any point in the path.

Multipath Reflections

As described earlier in the discussion of Fresnel Zones, a radio signal is composed ofindividual waves that travel in different directions as the signal propagates. When a radiowave hits a physical object, it may penetrate the object, be reflected by the object, or beabsorbed by the object.

A reflected wave causes a phenomenon known as multipath. Multipath means that the radiosignal can travel multiple paths to reach the receiver. Typically, multipath occurs when areflected wave reaches the receiver at the same as the direct wave that travels

in a straightline from the transmitter. If the two signals reach the receiver in-phase (thatis, both signals



are at the same point in the wave cycle when they reach the receiver), then thesignal isamplified. This is known as an upfade. If the two waves reach the receiver out-of-phase(that is, the two signals are at opposite points in the wave cycle when they reach thereceiver), they weaken the overall received signal. If the two waves are 180° apar

t whenthey reach the receiver, they can completely cancel each other out so that a radio does not



receive a signal at all. A location where a signal is canceled out by multipathis called anull or downfade.

Smooth surfaces , such as a body of water, a flat stretch of earth, or a metal roof, reflect

radio signals. In figure below, the body of water reflects a wave that cancels out the directsignals and brings down the radio link.

To avoid system failures, one should design a path so that the reflected signalis dispersed byan uneven surface before it reaches the receiver and cancels out the direct wave. In otherwords, one should design the path so its reflection point does not fall on a reflective surface.An RF engineer is to be consulted or use a path profile software program to identify the

location of a paths reflection point.

Transmitter Receiver

Reflected Signal Cancels Out Direct Signal

If necessary, one can adjust the height or change the position of one or both antennas to move thereflection point so that it is blocked by an obstruction or strikes an uneven surface. In figureabove, the height of the transmitting antenna has been reduced so that the reflected signal is

dispersed by rocky terrain.

A Change in the Antenna Height Moves the Reflection Point

Refraction



Radio waves move slower through substances of greater densities. This causes a wave tobend or refract as it travels through substances of different densities. For example, lightbends when it hits water. Since the density of the earths atmosphere decreases as

altitude increases, the bottom of a radio wave travels through a denser atmosphereand moves more slowly than the top of the wave . This causes the radio signal to refract or bend towards to earths surface following the curvature of the earth.Refraction varies with environment conditions, such as humidity, temperature, barometricpressure, and air density. For example, a radio signal bends closer to the earthat night thanduring the day due to the increased moisture in the lower atmosphere that resultsfrom condensation. In fact, most path fading caused by refraction occurs between

midnightand 7:00 am.

The refraction index, or K Factor, describes how a radio wave bends in relationto theearths surface. In general, a Path Profile will use K = 4/3 to determine the effects ofrefraction on a proposed radio link.

Commonly Used Capacity Configurations in MW Radio.4 x 2 Mbps or 4 x E1.

8 x 2 Mbps or 8 x E1.16 x 2 Mbps or 16 x E1.155 Mbps or STM1

In microwave link there are mainly two types of transmission (Tx) technologies:

.Plesiochronous Digital Hierarchy (PDH).Synchronous Digital Hierarchy (SDH)

Q. What is meant by "Plesiochronous"?If two digital signals are Plesiochronous, their transitions occur at "almost" the same rate,with any variation being constrained within tight limits. These limits are set down in ITUTrecommendation G.811. For example, if two networks need to interwork, their clocksmay be derived from two different PRCs. Although these clocks are extremely accurate,there's a small frequency difference between one clock and the other. This is known as a

plesiochronous difference.

Q. What is meant by "Synchronous"?



In a set of Synchronous signals, the digital transitions in the signals occur atexactly thesame rate. There may however be a phase difference between the transitions of the twosignals, and this would lie within specified limits. These phase differences maybe due topropagation time delays, or low-frequency wander introduced in the transmission



network. In a synchronous network, all the clocks are traceable to one Stratum 1PrimaryReference Clock (PRC).

Plesiochronous Digital Hierarchy (PDH)

There are three separate standards for PDH:

.CEPT Standards (Committee of European Posts and Telegraph).Min packet size is 2Mbps (30 voice channels or 32´64kbps -2 channels reserved forsignaling and related Tx info) also called E1

.Further multiples such as 8Mbps (120 channels), 34Mbps (480 channels),140Mbps(1920 channels) were standardised by ITU-T. These different Tx capacities

are called Tx hierarchies. Each step, apart from data capacity, also contains some infofor handling the data e.g. destination addresses. Higher value systems working at565Mbps are also available as proprietary equipment

.USA Standards.Basic packet capacity - 1.5Mbps corresponding to 24 voice calls (also called T1) .Later extended to 6Mbps (96 channels) and 45Mbps(672 channels)

.Japans Standards.Basic packet capacity - 1.5Mbps (like USA).Later expanded to 32Mbps (480 channels), 100Mbps (1,440 channels) and 400Mbps

(5,760 channels) & 1.6Gbps (23,040 channels)

Comparison of Multiplexing Hierarchies



.CEPT & USA Standards are most popular

This multiplexing hierarchy appears simple enough in principle but there are complications.When multiplexing a number of 2 Mbit/s channels they are likely to have been cre

ated bydifferent pieces of equipment, each generating a slightly different bit rate. Thus, before these 2Mbit/s channels can be bit interleaved they must all be brought up to the same bit rate adding'dummy' information bits, or 'justification bits'. The justification bits are recognize as such whendemultiplexing occurs, and discarded, leaving the original signal. This processis known asplesiochronous operation, from Greek, meaning "almost synchronous". The same problems withsynchronization, as described above, occur at every level of the multipexing hie

rarchy, sojustification bits are added at each stage. The use of plesiochronous operationthroughout thehierarchy has led to adoption of the term "plesiochronous digital hierarchy", orPDH.

Details of PDH Signals:

Signal Digital Bit RateChannels

E0 64 kbit/sOne 64 kbit/s

E1 2.048 Mbit/s32 E0

E2 8.448 Mbit/s128 E0

E3 34.368 Mbit/s16 E1

E4 139.264 Mbit/s64 E1

The main limitations of PDH are:

.Inability to identify individual channels in a higher-order bit stream.

.Insufficient capacity for network management

.Most PDH network management is proprietary

.

There's no standardised definition of PDH bit rates greater than 140 Mbit/s

.



There are different hierarchies in use around the world. Specialized interface equipment isrequired to interwork the two hierarchies

Synchronous Digital Hierarchy (SDH)

SDH stands for Synchronous Digital Hierarchy & is an international Standard for

a high capacityoptical telecommunications network. It is a synchronous digital transport systemaimed atproviding a more simple, economical and flexible telecommunication infrastructure.



Q. What led to SDH development ?Before SDH, the first generations of fibre-optic systems in the public telephonenetwork usedproprietary architectures, equipment line codes, multiplexing formats, and maintenanceprocedures. The users of this equipment wanted standards so they could mix and m

atchequipment from different suppliers

The primary reason for the creation of SDH was to provide a long-term solution for an opticalmid-span meet between operators; that is, to allow equipment from different vendors tocommunicate with each other. This ability is referred to as multi-vendor interworking and allowsone SDH-compatible network element to communicate with another, and to replace severalnetwork elements, which may have previously existed solely for interface purpose

s.

Traditionally, digital transmission systems and hierarchies have been based on multiplexingsignals which are plesiochronous (running at almost the same speed). Also, various parts of theworld use different hierarchies which lead to problems of international interworking; for example,between those countries using 1.544 Mbit/s systems (U.S.A. and Japan) and thoseusing the 2.048Mbit/s system.

Details of SDH Signals:

Bit Rate Abbreviated SDH SDH Capacity

51.84 Mbit/s 51 Mbit/s STM-0 21 E1155.52 Mbit/s 155 Mbit/s STM-1 63 E1 or 1 E4622.08 Mbit/s 622 Mbit/s STM-4 252 E1 or 4 E42488.32 Mbit/s 2.4 Gbit/s STM-16 1008 E1 or 16 E49953.28 Mbit/s 10 Gbit/s STM-64 4032 E1 or 64 E439813.12 Mbit/s 40 Gbit/s STM-256 16128 E1 or 256 E4STM = Synchronous Transport Module

Q. What are the advantages of SDH over PDH?

The increased configuration flexibility and bandwidth availability of SDH provides significantadvantages over the older telecommunications system.



points in the multiplexing hierarchy, this space capacity is filled with "fixedstuffing" bits thatcarry no information, but are required to fill up the particular frame.

1+1 protection:

In 1+1 protection switching, there is a protection facility (backup line) for each working facilityAt the near end the optical signal is bridged permanently (split into two signals) and sent overboth the working and the protection facilities simultaneously, producing a working signal and aprotection signal that are identical. At the Far End of the section, both signals are monitoredindependently for failures. The receiving equipment selects either the working or the protectionsignal. This selection is based on the switch initiation criteria which are either a signal fail (hard

failure such as the loss of frame (LOF) within an optical signal), or a signal degrade (soft failurecaused by the error rate exceeding some pre-defined value).

1:N protection:In 1:N protection switching, there is one protection facility for several working facilities (therange is from 1 to 14). In 1:N protection architecture, all communication from the Near End to theFar End is carried out over the APS channel, using the K1 and K2 bytes. All switching isrevertive; that is, the traffic reverts to the working facility as soon as the failure has been

corrected. In 1:N protection switching, optical signals are normally sent only over the workingfacilities, with the protection facility being kept free until a working facility fails.

Standard Network Topologies

.Star

Advantages:

.Optimised cost of paths

.Simple NMS

Disadvantages:

oNo Protection PathoCentre determines the performance of the whole NWo

No optimised BW.Tree



Advantages:

.Clear Hierarchies

.

Simple NMS

Disadvantages:

oNo Protection PathoFailure of one branch separates whole NW parts.Ring

Advantages:



.High Availability.Simple NMS

Disadvantages:

oNo. of elements depends on ring capacity and traffic relationsoConnected rings increase complexity.Mesh

Advantages:.High Availability

.High Flexibility

.Optimised paths.Optimised BW

Diadvantages:

oComplex NMSCommon Network Architectures

.For N Stations N-1 Links are required.Nth station depends on N-1 Links



For N Stations N-1 Links are required Each Station depends on Only 1 Link.For N Stations N Links are required.Route Diversity is available for all stations

.Each Station is Connected to Every Other.Full Proof Route Protection



.Typical Network Consist of Rings and Spurs

Network Routes and Route Capacities

.

Inter- City routes Backbone

· Backbone routes are planned at Lower Frequency Bands· 2, 6 and 7 GHz Frequency Bands are used· Backbone routes are normally high capacity routes· Nominal Hop Distances 25 40 Km.Intra City routes Access

· Access routes are planned at Higher Frequency Bands· 15,18 and 23 GHz Frequency Bands are used· Nominal Hop Distance 1 10 Km

Few well known MW Radio Manufacturers:



.ABB Nera.NEC.Siemens

.Digital Microwave Corporation.Fujitsu.Ericsson.Alcatel.Lucent.Hariss

SDH BackBone Rings

At the National level Reliance Communications has established 7 very high bandwidth TransportRings, called National BackBone/ Long Distance Rings. Practically there are 11 rings as Ring 1and 3 comprise 3 rings each (1A, 1B, 1C & 3A, 3B, 3C). These Rings are so designed that allmajor cities get enough bandwidth and not too many cities come on the same ring.Also havingthese 11 rings provide enough alternative routes in case of failure in one secti

on. These ringstraverse all the 18 circles, touch all major cities and cover about 90% of Indian population.Established (read utilized) Bandwidth of these rings is at 10 GBps, but thats just tip of theiceberg compared to what we can achieve. What gives these rings such gargantuanbandwidth OFC - which I will discuss later in this report.These rings connect 22 Core MCNs. From these rings, at these 22 MCNs, emerges severalMetro Access Rings, which connect other small cities and towns to the NBB.



Network Elements

1. Optical Fiber Cable- Siemens, Corning2. OTDR- Tectorinx

3. Fiber Management System Agilent4. SDH Equipment- Nortel, Fibcom5. DWDM Equipment- Nortel6. Sync Equipment- Datum7. Router - STM -256- Cisco Juniper8. Transport TN1C at BTS STM -1- NortelTN1X STM- 1

TN-4XSTM 4X & TN 16 X / STM-16XSmall mux equivalent to TN1C) N6110 STM-1

- TejasN6130 - STM - 16N 5200 STM N6500 10 Gg / STM 64

9. Cross Connect - Dx -140 Gb/ STM-64- NortelHDx -1280 Gb / STM-64 / 80 .Huawei T- 6040 16. & 6130 40 .OMS 1684 / 64 / 54 / 40 Marconi - - - STM 64 to STM 4 (16 port STM- 1) &

4 port STM-16 card Single port STM -64

Cross Connect - Dx -140 Gb/ STM-64



Cross connect is connected with more then one links each link having capacity STM-64 i.e.cross connect Equipment must be capable of controlling all of them simultaneously & thatcapacity is 140 GB (e.g. A train may be having capacity to carry 1000 passengersbut the station

should have capacity -much more than that train -to control many trains at a time). Thebackbone transport provides for connectivity between different LDCAs, SDCAs andcities. Inaddition interconnect is extended for other NLD, CSP and FSP networks. The corenetworkcomprises fully meshed, 7 primary and 14 secondary nodes. Physical architectureof the CoreNetwork comprises of two-tier ring network Express Ring & Collector Ring. Traffic betweenmajor metros and all major node cities is transported on the high capacity transport path The

Express Ring. Traffic from the other LDCAs (Long Distance Charging Areas) is transported on

The Collector Ring. The ring topology provides necessary protection to traffic in terms ofalternate path in case of breakage of the optical fibre or equipment failure thus ensuring smoothundisrupted operation of the network.

The functions of the Core-Backbone Network are as follows:

.Provide connections, either on permanent basis or temporary basis for the transfer of

information in a cost effective, reliable and speedy manner

.Routing which way to send the information

.Transport how the information is carried

Ring Elements and Terminologies

In a Ring each node is called an Add-Drop Multiplexer (ADM).An ADM has grossly three parts:



.Tributary - Interfaces with the non-ring nodes to bring in Traffic

.Payload Manager - Manages multiplexing & de-multiplexing activities

.Aggregate - Interfaces with the OFC Ring

From MCNs on the NBB, we get Metro Access Rings - like state highways emerging from thenational highways. These MAR carry the traffic to over 1100 cities and town of the country.Bandwidth of these MAR are in the range of 625 Mbps 2.5 GBps and upgradeable further withlittle change in the infrastructure. Nodes on MAR are known as MAN (e.g. SRM (Parel), AndheriMIDC, Chembur). From MAN (Metro Access Nodes) on Metro Access Rings, we get Buil

dingAccess Rings (like Main Roads inside a City or Town.) These BAR connect variousBuildingAccess Nodes. At the BAN, we have the Central Terminals (CTs) or the Base TransceiverStation (BTS). The CTs connect several (14 as of today) Remote Terminal Units (RTUs) whichin turn provide Fixed Access. The BTS covers all the Mobile Stations (MS) withinits radius ofcoverage, thus providing Wireless Access. Connection right up to the RTU is -through OFC (thisis therefore called Fiber To The Building), thus providing enormous bandwidth. These networks

are capable of providing both Narrow Band & Broadband services.Transport element on MAN & BAN is known as ADM.

Ring capacity FTTB STM-1, BAR - STM 1 to STM 4MAR - STM 4 to STM 16 NBB - STM - 64

Optical Fiber Cable (OFC) Link

Advantages of Optical Fiber



Distance:

The extremely low losses of modern telecom grade fiber enable distances of 50-100Km betweenrepeaters to be routinely achieved.

Capacity/Bandwidth:

The information carrying capacity of optical fiber can be enormous. G-652 has capacity2.5Gbps/fiber/wave length. It can provide the equivalent of 30,000 individual telephone signals of64kbit/sec and G-655 has capacity 10Gbps/fiber/wavelength (1000GB/sec is now very close tobeing achieved).

Security:

Optical fiber systems do not radiate any signal, and hence have almost total immunity to wiretapping. It can be done but is very difficult unless access to splices or connectors is possible.

Immunity to Noise:

The glass optical fiber is a dielectric rather than a metal and thus does not act as an antenna in theway metal conducting elements do. The fiber will not, therefore suffer from inductive interferencesuch as Radio Interference (RFI), Electromagnetic Interference (EMI), Electromagnetic Pulse

(EMP). This effective immunity to interference makes it possible to use fibers alongside or evenon power lines.

Long Life:

Fiber does not corrode like metal conductors.

Light Weight:

Optical fiber is remarkably light in weight. A 10Km stand of telecom grade fiberon a shipping

spool weighs less than 2kg whereas a 500m reel of co-ax copper cable weighs 30kg.

Environmentally Friendly:

Manufactured from the most abundant material in the earths crust. Comparativelysmall amountsof raw material are required therefore energy, transport and process costs are reduced. By usingfiber for communications the worlds copper reserves are saved for other purposes.

Future Proof:

Maybe yes - maybe no. It is impossible to know, however the signs are encouraging. It lasts a



long time we only use a small amount of its theoretical capacityas a result it isprobably fair tosay that fiber provides our most future proof transmission medium.



Disadvantages:

1. OFC is costlier than Cu-wire.2. OFC is fragile.3. OFC are difficult to join.4. OFC has its own set of losses dispersion, absorption, etc.

An optical fiber is made of three sections:.The core that carries the light signals i.e. optic pulse travels in core only.The cladding that keeps the light in the core serves the purpose of Compound wall.The coating that protects the glass

Fiber dimensions are measured in µm.

· 1 µm = 0.000001 meters (10-6)

· 1 human hair ~ 50 µmRefractive Index (n)

· n = c / v· n ~ 1.468· n (core) > n (cladding)· c = 3 x 108 Meter/secondFiber Geometry

Core:

The core of an optical fiber is a glass rod - denotes the central part of the fiber where the majorityof the light propagates.



Cladding:

The cladding of an optical fiber surrounds the core and has a Refractive Index lower than that ofcore. This difference in refractive index allows total internal reflection to occur within the fiber

core and avoids the entry into the Cladding. Total internal reflection is the phenomenon by whichlight propagates in optical fiber.

Coating is made up of PVC material-available in different colours as per ITU code.

If we get an optical tunnel where once a light pulse enters at one end can onlycome out at theother end, would serve our purpose. An OFC is just that. Transmission through anOFC is like a

light ball traveling down a tunnel. It reflects several times on thewall

before reaching the end

of the tunnel.

Snell's law is defined as: n1 sinA1 = n2 sinA2,

Where

n is the refractive index and A the corresponding angles as shown. The refractive index is the ratio of the speed of light in a vacuum to the speedof light in a

given medium. n1 = C / V C = Velocity of light in Vacuum i.e. 3 x 108 metres per second. V = Velocity of light in a given mediumSo, if the top part of the diagram is CORE & n1 is Refractive Index of the Corematerial and ifthe bottom part is Cladding, n2 is Refractive Index of the Cladding material. When light passesfrom one medium to another, the angles & refractive indexes of the media determined the path

that light took. The relationship is a function of the sine of the angles, alsoknown as the Law ofSines (by Descartes).



The phenomenon of total internal reflection was discovered by John Tendel in 1854, when hefilled a can with water, which had a hole at the lowest level. Obviously water started flowing outof the hole forming a curved projectile path. As Tendell lit a torch at the topof the Can, a portion

of that light would come out of the hole at the bottom. These light rays then experience totalinternal reflection because Refractive Index (n) of water is greater than air. Thus these rays wouldbend along with the watery projectile path giving rise to the idea that light could travel in acurved path if the phenomenon of TIR is repeated many times.

Optical Fibre Specifications



Optical Spectrum

The Optical Spectrum can be divided into three regions:

Ultra Violet:



That portion of the electromagnetic spectrum in which the longest wavelength isjust below thevisible spectrum, extending from approximately 4 nm to 400 nm.

Visible Light:

Electromagnetic radiation visible to the human eye; wavelengths of 400-700 nm.

Infrared (IR):

The region of the electromagnetic spectrum bounded by the long wavelength, extreme of thevisible spectrum (about 0.7 µm) and the shortest microwaves (about 0.1 µm).

Nowadays to generate different wavelengths pluggable lasers of different Frequency areavailable. In the old days different cards were available for different frequency.

Attenuation

.Attenuation is the measure of the reduction in signal magnitude, or loss, alonga length of

fiber.

.Attenuation is one factor which determines the power loss.

.

Attenuation in fiber optic cabling is usually expressed in decibels per unit length of cable

(i.e. dB/km) at a specified wavelength..Attenuation describes how energy is lost or dissipated.Loss is the cost of moving something, like charges or particles or light pulses.

Attenuation in fiber optic cabling is usually expressed in decibels per unit length of cable (i.e.dB/km) at a specified wavelength.

Attenuation = 10 log10 (Iout / Iin)

Where,Iout = outgoing intensity (intensity is measured in Watt/m-2)Iin = incoming intensity (Watt/m-2)

Sources of Attenuation in Fibers

Absorption (proportional to 1 / .)



Caused by impurities in the glass, and any atomic defects in the glass increasesdramaticallyabove 1700 nm. The peak absorption occurs at approximately 1400nm..

Scattering (proportional to 1 / .4)

Scattering is caused by small variations in the density of glass. Loss of optical energy due toimperfections / in homogeneities (localized density variations). And therefore act as scattering

objects.Geometric Effects (proportional to .)

Bending losses increases with increase in wavelength. Effects of 2 cm radius bend at three

wavelengths.Scattering and Absorption decides suitability of optical fiber for transmissionat specificfrequencies only. If a graph of Loss in dB/km is plotted against the wavelengththen we observethat, Attenuation varies with the wave length of light. The fiber exhibits minimumattenuation atwavelength slots, 1310nm, and 1550nm. These are called, second window and thirdwindow.



The second and the third windows are in practical use today, i.e. we don't use the 850 nm anymore except for some restricted applications. The 850 nm was in use in the pastwhen the LaserDiodes available were of 850 nm only.

Bending Losses

Wavelength Multiplexing

Large increase in Bandwidth can be achieved by using a technique called Dense Wave DivisionMultiplexing (DWDM). Suppose we had a one lane HW, only one vehicle can run at atime. If weneeded more vehicles to run simultaneously we will have to add more lanes, say 4

or 6 lane or wecan construct multistory Highway.



In the above sketch, each lane is equated with different colour of light (violet, blue, green, yellow,orange, red, etc.) .When seven colours are passed through a triangular prism ,itbecomes one(Multiplexer theory) and when it will come out it becomes 7 colours again. DWDMuses the

above phenomenon, but uses Laser and IR light instead of visible light. The result is the same,only that we can multiplex many more wavelengths and demultiplex them at the receiving end.Normally we can achieve BW 10 GBps with one wavelength, As per DWDM technology,we cango up to 800 GBps by using 80 Wave length, that too in a single fiber of OFC. And we have 48cores in one cable and 6 such cables that can be laid in our NBB.

DWDM - 1530. to 1563 . = C band = Conventional1570 . to 1620 . = L band = Long

DWDM Capacity with G 652 & G 655

G 652

.1550 nm can support up to 32 Lambda wave lengths for DWDM

.The bandwidth per lambda are limited to 2.5Gbps.

.Total bit rate for 32 Lambdas is 2.5 X 32Gbps. = 80 Gbps.

.Good for Short haul applications up to 350 - 400Km and Metro regions.

.This fiber is used for - City network Access / SDCA routes

G 655

.10 Gbps can be supported per wave length.

.For DWDM total number of wave length supported is 80 Lambda.

.Total capacity = 10Gbps x 80 . = 800Gbps

.Good for Long haul applications - on NBB / NLD routes.



This is our Reliance India Roadmap. Its a mega network of 80.000 km of OFC highwayconnecting 12 rings, 227 LDCA, 565 SDCA, covering 18 telecom circles, extendingwirelineconnectivity to 138 cities and wireless connectivity in 578 cities. Business conducted in these

cities constitutes 80% of Indias GDP. It is necessary to monitor the health of such a hugenetwork. This is done by monitoring the health of Dark Fibers by means of FiberMonitoringSystem.To the user it means how much competitive rates she/ he pays for a Local or STDcall or oninternet how fast is the download of an interesting article or favorite song. The core rings connect22 Core MCNs with 17 ILTs at this moment. These are our Life-lines. The subtendedringsinterconnect some of these MCNs and function like the Bypasses. Like how healthy

you are inindicated by how well your heart is functioning and how good is your blood circulation, similarlythe health of a telecom network can be measured by how is the reliability of these transportnetwork is & how much bandwidth these transport network can handle .Like multiple lanes of Highways, Transport network provide bandwidth which decides how muchtraffic (read how many calls) can be carried. To the user it translates into howmuch she/ he paysfor a short distance or long distance call or how fast is the download of an interesting article orfavorite song. This module we will see how we live up to that challenge.

Reliance Optical Network International



FLAG Telecom develops and operates advanced fibre-optic global cable systems over which itoffers a growing range of value-added network services. It operates a global network andprovides customers with connectivity to most of the major business centres around the world.

FLAG Europe-Asia is the world's longest privately funded undersea fibre-optic cable systemstretching more than 28,000km from the UK to Japan with landing sites in 13 countries.

FLAG Atlantic-1 is the world's first multi-terabit transoceanic dual cable system providing a fullyprotected city-to-city service between London, Paris and New York.

FLAG North Asian Loop has been designed to support the strong growth in intra-Asia internet

traffic and provides intra-regional, city-to-city connectivity between Hong Kong, Seoul, Tokyoand Taipei.

Network Detail RIC Nodes / Plants

Inter city NLD - NBB



Backbone Network : 55,000 km. (Inter city)Total Network : 80,000 kmMCN : 260 out of which 198 are Maintenance Point

( MSC = 90 + 6 , ILT Switches = 22 )IS : 206

Preside Server : At Mumbai & Hyderabad

Intra - city

Interconnection Network : 25,000 km. (Intra city)BTS : 7713MANS : 45BANS : 670Wireless : 565 CitiesWireline : 184 Cities

.

No. of Ducts in National Backbone: 4/6 HDPE ducts.Laying of ducts (20 meters from road center) taking care of all future rearrangements

(eg. Road widening, bridge replacement, etc.).Cable marker stones placed along the route at every 200 m.Warning tape placed below 0.5m from the finished grade.Tracer wire for ease of detection of fibre placed above duct.

Buried at 1.65m below the ground along the route (Protection against Rodent).Standardized location of manholes and hand holes.Man holes are spaced 4 km apart.Hand holes are spaced 1 km apart ..Cable slacks have been kept in every manhole (15 meters) and hand hole (10 meters) from

maintenance point of view

Switching



Switch not only reduces transmission cost but also reduces the complexity of connectingsubscribers. Here subscribers have complete control on information flow to a subscriber. Similarconcept is further extended to route subscribers traffic to long distance exchanges by taking calls

through exchanges arranged in tandem. R2MFC Registered & Registered Multi FrequencyChannel.

STP - Signal Transferring point - All switches are connected to STPSCP - Switch Control Panel - available at STP for Database-passes data / information (details ofcaller & Receiver party) as & when required by STP.

CCS7 Common Channel Signaling version-7

In Dx connections are made for longer time.In switches connections change from call to call.

Switches are intra-network devices designed to increase performance in client/server networks byfacilitating LAN segmentation. Because switches can be implemented without changing adapters,cabling, hubs, etc., network investments are preserved. In addition, switches facilitate the creationand management of virtual LANs, a logical grouping of users, independent of their physical

location. With switches, ad hoc workgroups can be created, managed, and changedby softwarerather than hardwiring. Essentially, a LAN switch is a low-latency, multiport bridge that createsseparate segments. Switches are used to provide dedicated bandwidth to specificusers or server-based groups of users in Ethernet and Token Ring and/or to transition to higher-speedtechnologies, such as FDDI, Fast Ethernet, Gigabit Ethernet, and/or ATM.

Switches can be used to:

Interconnect elements of a distributed computing system;



Provide high-speed connections to campus backbones and servers; and Scale network bandwidth by adding more switched ports.Switching technology has three principal advantages: scalable bandwidth, flexibility, and highperformance. For all these reasons, switches have emerged as the industrys hottest solution for

increasing network bandwidth, providing higher levels of performance, and reducing overall costof ownership. The common force driving the need for switching is network growthin clients,servers, and applications.

There are no hard and fast rules on where to switch and what technologies to use, but there aresome generally accepted guidelines to consider. Switched Ethernet and Token Ring, since theyare 10, 4, and 16 Mbps technologies respectively, are best suited for workgroupand departmental

deployment. They are also the easiest to implement and most cost effective. FastEthernet, whichis 100 Mbps, is ideal for connecting servers in workgroups and linking departments to buildingbackbones. Gigabit Ethernet, with its 1000 Mbps speed, will provide even fasterconnectivity atthis level and support super-user workgroups. Fast Ethernet is relatively easy to install and iscost-effective, since its based on existing technology and cabling.However, Fast Ethernet does have distance limitations and lower utilization rates, so its not idealfor backbone implementation. This backbone is for relatively shorter distances.

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