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  • 1. IMPLANT TRAINING AT BSNL,PATNA BY: ABHAY ANAND (9910005002) ABHISHEK PRASAD (9910005003) ARGHA DAS (9910005012) ECE-A ,2ND YEAR
  • 2. Implant Training Report Submitted By ABHAY ANAND (9910005002) ABHISHEK PRASAD (9910005003) ARGHA DAS (9910005012) In partial fulfillment of Bachelor of Technology in Electronics and Communication Engineering From 5/12/2011 to 30/12/2011 Kalasalingam University(Kalasalingam Academy of Research and Education) Krishnankoil-626190
  • 3. ACKNOWLEDGEMENTIt gives us immense pleasure to express ours profound gratitude to ours bonafideUniversity, Kalasalingam University to encourage students to undergo summer training togain valuable practical experiences from various industries and companies. We extend mythanks to SDE in charge of training Mr.j mandal, who encouraged us to undergo thisimplant training at BSNL’s Advanced Training Centre, Patna.We also extend my thanks to all the faculties and teaching staff at BSNL for theirinvaluable support and assistance.Lastly we would like to thank all the employees/respondents of BSNL, Patna.Abhay Anand.Abhishek Prasad.Argha Das.
  • 4. CONTENTCOMPANY PROFILEINTRODUCTIONABOUT THE EXCHANGELOCAL AND TRUNK LINEPCMFIBRE OPTICS COMMUNICATIONOVERVIEW OF MOBILE COMMUNICATIONGSM TECHNOLOGYCDMA TECHNOLOGYINTRODUCTION TO INTERNET AND BROADBANDCONCLUSION
  • 5. COMPANY PROFILEEvery day we make phone calls from our telephone sets quite easily but are unaware of thetechnology used behind it. The technologies used in telecommunication is a bit complicated butat the same time interesting too.Here it has been tried to give an idea of the different technologies used for telecommunication byone of the biggest service provides to India, i.e., BHARAT SANCHAR NIGAM LTD.The service provided by BSNL to its customers is:-Basic local telephonyNational and International call serviceMobile CommunicationInternet ServiceThe basic telephony i.e., the local call facility provided to the consumers by BSNL comprises ofthe following:-ExchangeMain Distribution FrameLine ConnectionPower PlantThe exchange is the basic part of telecommunication system. It is through this exchange that asubscriber gets connected to different parts of the world by means of a telephone. There aredifferent types of exchanges depending upon the technology used.
  • 6. INTRODUCTIONAll industries operate in a specific environment which keeps changing and the firms in thebusiness need to understand it to dynamically adjust their actions for best results. Like mindedfirms get together to form associations in order to protect their common interests. Other stakeholders also develop a system to take care of their issues. Governments also need to intervene forensuring fair competition and the best value for money for its citizens. This handout givesexposure on the Telecom Environment in India and also dwells on the role of internationalbodies in standardizing and promoting Telecom Growth in the world.The Indian postal and telecom sectors saw a slow and uneasy start. In 1850, the firstexperimental electric telegraph line was started between and . In 1851, it was opened for the useof. The Posts and Telegraphs department occupied a small corner of the Public WorksDepartment, at that time.Subsequently, the construction of 4,000 miles (6,400 km) of telegraph lines connecting Kolkata(then Calcutta) and Peshawar in the north along with Agra, (then Bombay) through SindwaGhats, and well as and was started in November 1853. , who pioneered the and in India,belonged to the Public Works Department, and worked towards the development of telecomthroughout this period. A separate department was opened in 1854 when telegraph facilities wereopened to the public.In 1880, two namely The Ltd. and The Anglo-Indian Telephone Company Ltd. approached toestablish the permission was refused on the grounds that the establishment of telephones was aGovernment monopoly and that the Government itself would undertake the work. In 1881, theGovernment later reversed its earlier decision and a licence was granted to the Limited of foropening telephone exchanges at ,and and the first formal telephone service was established in thecountry. On the 28th January 1882, Major E. Baring, Member of the s Council declared open theTelephone Exchanges in Calcutta, Bombay and Madras. The exchange in Calcutta named the"Central Exchange", was opened at third floor of the building at 7, Council House Street, with atotal of 93 subscribers. Later that year, Bombay also witnessed the opening of a telephoneexchange.Further milestones and developments 1907 - First Central Battery of telephones introduced in 1913-1914 - First Automatic Exchange installed in kanpur. 1927 - Radio-telegraph system between the and India, with beam stations at khadki and dhundh.. 1933 - system inaugurated between the UK and India. 1953 - 12 channel carrier systemoduced. 1960 - First route commissioned between delhi and kanpur 1975 - First system commissioned between Mumbai city and andheri telephone exchanges. 1979 - First optical fibre system for local junction commissioned at pune
  • 7.  1980 - First satellite earth station for domestic communications established at scikandarabad. 1983 - First analog signal Stored Program Control exchange for trunk line commissioned at Mumbai. 1984 – c-dot exchange established for indigenous development and production of digital exchanges. 1995 - First mobile telephone service started on non-commercial basis on 15 August 1995 in delhi 1995 - Internet Introduced in India starting with Delhi, Bombay, Calcutta, Chennai and Pune on 15 August 1995Modern policies All villages shall receive telecom facilities by the end of 2002. A Communication Convergence Bill introduced in the Parliament on August 31, 2001 is presently before the Standing Committee of Parliament on Telecom and IT. National Long Distance Service (NLD) is opened for unrestricted entry. The International Long Distance Services (ILDS) have been opened to competition. The basic services are open to competition. In addition to the existing three, a fourth cellular operator, one each in four metros and thirteen circles, has been permitted. Cellular operators have been permitted to provide all types of mobile services including voice and non-voice messages, data services and public call office utilizing any type of network equipment, including circuit and/or package switches that meet certain required standards. Policies allowing private participation have been announced as per the New Telecom Policy (NTP), 1999 in several new services, which include Global Mobile Personal Communication by Satellite (GMPCS) Service, digital Public Mobile Radio Trunked Service (PMRTS) and Voice Mail/ Audiotex/ Unified Messaging Services. Wireless Local Loop has been introduced to provide telephone connections in urban, semi- urban and rural areas promptly. Two telecom PSUs, VSNL and HTL have been disinvested. Steps are being taken to fulfill Universal Service Obligation (USO), funding, and administration. A decision to permit Community Phone Service has been announced. Multiple Fixed Service Providers (FSPs) licensing guidelines were announced. Internet Service Providers (ISPs) have been allowed to set up International Internet Gateways, both Satellite and Landing stations for submarine optical fiber cables. Two categories of infrastructure providers have been allowed to provide end-to-end bandwidth and dark fiber, right of way, towers, duct space etc. Guidelines have been issued by the Government to open up Internet telephony (IP).
  • 8. ABOUT THE EXCHANGEIn the field of , a telephone exchange or telephone switch is a system of electroniccomponents that connects telephone calls. A central office is the physical building usedto house equipment including telephone switches, which make "work" in the sense ofmaking connections and relaying the speech information.TYPE’S OF EXCHANGE  Manual exchange  Strowger exchange  Cross bar exchange  Electronics exchange (analog and digital exchange)MANUAL EXCAHNGEWith manual service, the customer lifts the receiver off-hook and asks the operator to connect thecall to a requested number. Provided that the number is in the same central office, the operatorconnects the call by plugging into the jack on the switchboard corresponding to the calledcustomers line. If the call is to another central office, the operator plugs into the trunk for theother office and asks the operator answering (known as the "inward" operator) to connect thecall.STROWGER EXCHANGEStrowger developed a system of automatic switching using an electromechanical switch basedaround electromagnets and pawls. With the help of his nephew (Walter S. Strowger) he produceda working model in 1888 .selector starts in the home position and with each impulse the wipercontacts would progress round the output bank to the next position. Each output would beconnected to a different subscriber, thus the caller could connect to any other subscriber who wasconnected to that bank, without any manual assistance from an operator.Diagram of a simple Selector
  • 9. In Figure 2 (above), the selector has 10 outputs, so a caller can choose to connect to any of 10different subscribers by dialing any digit from 1 to 0 (0=10). This sort of automatic selector isknown as a Uni-selector, as it moves in just one plane (rotary).By mounting several arcs of outlets on top of each other, the number of outlets can be increasedsignificantly but the wipers are then required to move both horizontally to select a bank and thenvertically to move around that bank to the required outlet. Such a selector is known as a Two-Motion Selector. Two-motion selectors typically have 10 rows of 10 outlets, thus 100 possibleoutlets altogether. A two-motion selector can therefore accept two dialed digits from a subscriberand route the call to any of 100 numbers. The selector wipers always start in their resting homeposition. The first digit moves the selector vertically up to the corresponding level and then thesecond digit moves the wipers around the contacts of that level. This is shown in figure 3, below. A Two-Motion "Final" SelectorThe type of selector shown above is known as a Final Selector as it takes the final two digits ofthe number dialed. Most numbers dialed are several digits longer, and therefore pass through achain of selectors. Selectors previous to the Final Selectors are different; they are called GroupSelectors. Group selectors take only ONE digit from the caller, and step up the number of levelsaccording to the digit dialed. The rotary movement is then automatic; the wipers search aroundthat level to find a free outlet - i.e. the next free selector in the chain. This is covered in moredepth later.CROSS BAR EXCAHNGEIn , a crossbar switch (also known as cross-point switch, crosspoint switch, or matrix switch) isa connecting multiple inputs to multiple outputs in a matrix manner. Originally the term wasused literally, for a matrix switch controlled by a grid of crossing . A crossbar switch is anassembly of individual switches between multiple inputs and multiple outputs. The switches arearranged in a matrix. If the crossbar switch has M inputs and N outputs, then a crossbar has amatrix with M x N cross-points or places where the "bars" cross. At each crosspoint is a switch;when closed, it connects one of M inputs to one of N outputs. A given crossbar is a single layer,non-blocking switch. Collections of crossbars can be used to implement multiple layer and/orblocking switches. A crossbar switching system is also called a co-ordinate switching system.
  • 10. ELECTRONICS EXCHANGEIt is based on the automatic control by stored programmed in computer linked to it. It cover allthe main drawbacks of above mentioned exchange. It may be digital or analog but mostly digitalelectronics exchanges are now common. It base on the principal time division switching or spacedivision switching. Space division switching is used for analog electronics exchange and timedivision switching is used for digital exchange.Space Division switching SystemIn a space Division Switching system, a continuous physical path is set up between input andoutput terminations. This path is separate for each connection and is held for the entire durationof the call. Path for different connections is independent of each other. Once a continuous pathhas been established., Signals are interchanged between the two terminations. Such a switchingnetwork can employ either metallic or electronic cross points. Previously, usage of metalliccross-points using reed relays and all were favored. They have the advantage of compatibilitywith the existing line and trunk signaling conditions in the network.Time Division Switching SystemIn Time Division Switching, a number of calls share the same path on time division sharingbasis. The path is not separate for each connection, rather, is shared sequentially for a fraction ofa time by different calls. This process is repeated periodically at a suitable high rate. Therepetition rate is 8 KHz, i.e. once every 125 microseconds for transmitting speech on telephonenetwork, without any appreciable distortion. These samples are time multiplexed with staggeredsamples of other speech channels, to enable sharing of one path by many calls. The TimeDivision Switching was initially accomplished by Pulse Amplitude.
  • 11. DIGITAL CARDIt is programmed data card which is used for automatic control of call set up and call terminationas well as providing various services to the customer. There are three types of digital card whichare as follow 1) TERMINATION CARD 2) SERVICE CARD 3) CONTROL CARDTermination card: its main aim to connect the customer on trunk line .otherfeatures of terminating card is battery feed, over voltage protection,check weathercall is STD or LOCAL or ISDService card: the service like dial tone ,call waiting ,call confrencing etc is givenby this card.Control card: it is there to see whether the call has been established or not. Ifestablished then requisite unit has been established or not.Local and trunk NetworkTrunk LinesThe term Trunk Line in telecommunications refers to the high-speed connection betweentelephone central offices in the. Trunk lines are always digital. The wiring between centraloffices was originally just pairs of twisted copper wire (the twists in the wiring prevented thingsknown as crosstalk and noise). Because it is expensive to string up (or lay trenches for buriedcables), the phone company researched ways in which to carry more data over the existingcopper lines. This was achieved by using. Later, when fiber-optic technology became available,phone companies upgraded their trunk lines to fiber optics and used statistical time-divisionmultiplexing, , coarse or dense wave division multiplexing and optical switching to furtherimprove transmission speeds.The signaling information exchanged between different exchanges via inter exchange trunks forthe routing of calls is termed as Inter exchange Signaling. Earlier in band /out of bandfrequencies were used for transmitting signaling information. Later on, with the emergence ofPCM systems, it was possible to segregate the signaling from the speech channel. A trunk line isa connecting (or other switching equipment), as distinguished from local loop circuit whichextends from telephone exchange switching equipment to individual or informationorigination/termination equipment. When dealing with a private branch exchange (PBX), trunklines are the phone lines coming into the PBX from the telephone provider. This differentiates
  • 12. these incoming lines from extension telephone lines that connect the PBX to (usually) individualphone sets. Trunking saves cost, because there are usually fewer trunk lines than extension lines,since it is unusual in most offices to have all extension lines in use for external calls at once.Trunk lines transmit voice and data in formats such as analog, digital signal 1, ISDN or primaryrate interface. The dial tone lines for outgoing calls are called DDCO (Direct Dial CentralOffice) trunks.A travelling over a trunk line is not actually flowing any faster. The electrical signal on a voiceline takes the same amount of time to traverse the wire as a similar length trunk line. Whatmakes trunk lines faster is that the has been altered to carry more data in less time using moreadvanced multiplexing and techniques. If you compared a voice line and a trunk line and putthem side by side and observed them, the first pieces of information arrive simultaneously onboth the voice and trunk line. However, the last piece of information would arrive sooner on thetrunk line. No matter what, you cant break the laws of physics. Electricity over copper or laserlight over fiber optics, you cannot break the speed of light--though that has rarely stoppeduneducated IT or IS managers from demanding that cabling perform faster instead of upgradingequipment.Trunk lines can contain thousands of simultaneous calls that have been combined using. Thesethousands of calls are carried from one central office to another where they can be connected to ade-multiplexing device and switched through digital access cross connecting switches to reachthe proper exchange and local phone number.What is Trunking?In telecommunications systems, trunking is the aggregation of multiple user circuits into a singlechannel. The aggregation is achieved using some form of multiplexing.PCMA long distance or local telephone conversation between two persons could be providedby using a pair of open wire lines or underground cable as early as mid of 19 thcentury. However, due to fast industrial development and an increased telephoneawareness, demand for trunk and local traffic went on increasing at a rapid rate. Tocater to the increased demand of traffic between two stations or between two subscribersat the same station we resorted to the use of an increased number of pairs on either theopen wire alignment, or in underground cable. This could solve the problem for sometime only as there is a limit to the number of open wire pairs that can be installed onone alignment due to headway consideration and maintenance problems. Similarly
  • 13. increasing the number of open wire pairs that can be installed on one alignment due toheadway consideration and maintenance problems. Similarly increasing the number ofpairs to the underground cable is uneconomical and leads to maintenance problems.It, therefore became imperative to think of new technical innovations which could exploit theavailable bandwidth of transmission media such as open wire lines or underground cables toprovide more number of circuits on one pair. The technique used to provide a number of circuitsusing a single transmission link is called Multiplexing.Basic Requirements for PCM System:To develop a PCM signal from several analogue signals, the following processing steps arerequired: 1. Filtering 2. Sampling 3. Quantisation 4. Encoding 5. Line CodingDuplexing Methodology:Duplexing is the technique by which the send and receive paths are separated over the medium,since transmission entities (modulator, amplifiers, demodulators) are involved.There are two types of Duplexing: 1. Frequency Division Duplexing (FDD) 2. Time Division Duplexing (TDD)
  • 14. Frequency Division Duplexing (FDD): Different frequencies are used for send and receive pathsand hence there will be a forward band and reverse band. Duplexer is needed if simultaneoustransmission (send) and reception (receive) methodology is adopted. Frequency separationbetween forward band and reverse band is constant.Time Division Duplexing (TDD): TDD uses different time slots for transmission and receptionpaths. Single radio frequency can be used in both the directions instead of two as in FDD. Noduplexer is required. Only a fast switching synthesizer, RF filter path and fast antenna switch areneeded. It increases the battery life of mobile phones.FIBER-OPTICS COMMUNICATIONFIBER OPTICS: The use and demand for optical fiber has grown tremendously and optical-fiberapplications are numerous. Telecommunication applications are widespread, ranging from globalnetworks to desktop computers. These involve the transmission of voice, data, or video overdistances of less than a meter to hundreds of kilometers, using one of a few standard fiberdesigns in one of several cable designs.Carriers use optical fiber to carry plain old telephone service (POTS) across their nationwidenetworks. Local exchange carriers (LECs) use fiber to carry this same service between centraloffice switches at local levels, and sometimes as far as the neighborhood or individual home(fiber to the home [FTTH]).Optical fiber is also used extensively for transmission of data. Multinational firms need secure,reliable systems to transfer data and financial information between buildings to the desktopterminals or computers and to transfer data around the world. Cable television companies alsouse fiber for delivery of digital video and data services. The high bandwidth provided by fibermakes it the perfect choice for transmitting broadband signals, such as high-definition television(HDTV) telecasts. Intelligent transportation systems, such as smart highways with intelligenttraffic lights, automated tollbooths, and changeable message signs, also use fiber-optic-basedtelemetry systems.Another important application for optical fiber is the biomedical industry. Fiber-optic systemsare used in most modern telemedicine devices for transmission of digital diagnostic images.Other applications for optical fiber include space, military, automotive, and the industrial sector.ADVANTAGES OF FIBRE OPTICS :Fiber Optics has the following advantages :• SPEED: Fiber optic networks operate at high speeds - up into the gigabits• BANDWIDTH: large carrying capacity• DISTANCE: Signals can be transmitted further without needing to be "refreshed" orstrengthened.
  • 15. • RESISTANCE: Greater resistance to electromagnetic noise such as radios, motors or othernearby cables.• MAINTENANCE: Fiber optic cables costs much less to maintain.Fiber Optic System :Optical Fibre is new medium, in which information (voice, Data or Video) is transmitted througha glass or plastic fibre, in the form of light, following the transmission sequence give below :(1) Information is Encoded into Electrical Signals.(2) Electrical Signals are Coverted into light Signals.(3) Light Travels Down the Fiber.(4) A Detector Changes the Light Signals into Electrical Signals.(5) Electrical Signals are Decoded into Information.- Inexpensive light sources available. - Repeater spacing increases along with operating speeds because low loss fibres are used at high data rates.Principle of Operation - Theory Total Internal Reflection - The Reflection that Occurs when a Ligh Ray Travelling in One Material Hits a Different Material and Reflects Back into the Original Material without any Loss of Light.
  • 16. PROPAGATION OF LIGHT THROUGH FIBERThe optical fiber has two concentric layers called the core and the cladding. The inner core is thelight carrying part. The surrounding cladding provides the difference refractive index that allowstotal internal reflection of light through the core. The index of the cladding is less than 1%, lowerthan that of the core. Typical values for example are a core refractive index of 1.47 and acladding index of 1.46. Fiber manufacturers control this difference to obtain desired optical fibercharacteristics. Most fibers have an additional coating around the cladding. This buffer coatingis a shock absorber and has no optical properties affecting the propagation of light within thefiber. Figure shows the idea of light travelling through a fiber. Light injected into the fiber andstriking core to cladding interface at greater than the critical angle, reflects back into core, sincethe angle of incidence and reflection are equal, the reflected light will again be reflected. Thelight will continue zigzagging down the length of the fiber. Light striking the interface at lessthan the critical angle passes into the cladding, where it is lost over distance. The cladding isusually inefficient as a light carrier, and light in the cladding becomes attenuated fairly.Propagation of light through fiber is governed by the indices of the core and cladding by Snellslaw.Such total internal reflection forms the basis of light propagation through a optical fiber. Thisanalysis consider only meridional rays- those that pass through the fiber axis each time, they arereflected. Other rays called Skew rays travel down the fiber without passing through the axis.The path of a skew ray is typically helical wrapping around and around the central axis.Fortunately skew rays are ignored in most fiber optics analysis. The specific characteristics of light propagation through a fiber depends on many factors,including- The size of the fiber.- The composition of the fiber. - The light injected into the fiber. Jacket Jacket Cladding Core Cladding (n2) Cladding Core (n2) Jacket Light at less than Angle of Angle of critical angle is incidence reflection absorbed in jacket Light is propagated by total internal reflection Fig. Total Internal Reflection in an optical Fibre50 m and a cladding diameter of 125 m.
  • 17. FIBER TYPESThe refractive Index profile describes the relation between the indices of the core and cladding.Two main relationship exists :(I) Step Index(II) Graded IndexThe step index fiber has a core with uniform index throughout. The profile shows a sharp step atthe junction of the core and cladding. In contrast, the graded index has a non-uniform core. TheIndex is highest at the center and gradually decreases until it matches with that of the cladding.There is no sharp break in indices between the core and the cladding.By this classification there are three types of fibers :(I) Multimode Step Index fiber (Step Index fiber)(II) Multimode graded Index fiber (Graded Index fiber)(III) Single- Mode Step Index fiber (Single Mode Fiber) STEP-INDEX MULTIMODE FIBER has a large core, up to 100 microns in diameter. As aresult, some of the light rays that make up the digital pulse may travel a direct route, whereasothers zigzag as they bounce off the cladding. These alternative pathways cause the differentgroupings of light rays, referred to as modes, to arrive separately at a receiving point. The pulse,an aggregate of different modes, begins to spread out, losing its well-defined shape. The need toleave spacing between pulses to prevent overlapping limits bandwidth that is, the amount ofinformation that can be sent. Consequently, this type of fiber is best suited for transmission overshort distances, in an endoscope, for instance. STEP-INDEX MULTIMODE FIBER GRADED-INDEX MULTIMODE FIBER contains a core in which the refractive indexdiminishes gradually from the center axis out toward the cladding. The higher refractive index atthe center makes the light rays moving down the axis advance more slowly than those near thecladding. GRADED-INDEX MULTIMODE FIBER Also, rather than zigzagging off the cladding, light in the core curves helically because ofthe graded index, reducing its travel distance. The shortened path and the higher speed allowlight at the periphery to arrive at a receiver at about the same time as the slow but straight rays inthe core axis. The result: a digital pulse suffers less dispersion.
  • 18. SINGLE-MODE FIBER has a narrow core (eight microns or less), and the index of refractionbetween the core and the cladding changes less than it does for multimode fibers. Light thustravels parallel to the axis, creating little pulse dispersion. Telephone and cable televisionnetworks install millions of kilometers of this fiber every year. SINGLE-MODE FIBEROPTICAL FIBRE PARAMETERSOptical fiber systems have the following parameters.(I) Wavelength.(II) Frequency.(III) Window.(IV) Attenuation.(V) Dispersion.(VI) Bandwidth.9.1 WAVELENGTHIt is a characteristic of light that is emitted from the light source and is measures in nanometers(nm). In the visible spectrum, wavelength can be described as the colour of the light.For example, Red Light has longer wavelength than Blue Light, Typical wavelength for fibre useare 850nm, 1300nm and 1550nm all of which are invisible.FREQUENCYIt is number of pulse per second emitted from a light source. Frequency is measured in units ofhertz (Hz). In terms of optical pulse 1Hz = 1 pulse/ sec.WINDOWA narrow window is defined as the range of wavelengths at which a fibre best operates.ATTENUATIONAttenuation is defined as the loss of optical power over a set distance, a fibre with lowerattenuation will allow more power to reach a receiver than fibre with higher attenuation.Attenuation may be categorized as intrinsic or extrinsic.INTRINSIC ATTENUATIONIt is loss due to inherent or within the fibre. Intrinsic attenuation may occur as(1) Absorption - Natural Impurities in the glass absorb light energy. Light Ray
  • 19. (2) Scattering - Light Rays Travelling in the Core Reflect from small Imperfections into aNew Pathway that may be Lost through the cladding. Light is lost Light Ray Fig. 10 ScatteringEXTRINSIC ATTENUATIONIt is loss due to external sources. Extrinsic attenuation may occur as – (I) Macrobending - The fibre is sharply bent so that the light travelling down the fibre cannot make the turn & is lost in the cladding. Micro and Macro bending (II) Micro bending - Micro bending or small bends in the fibre caused by crushing contraction etc. These bends may not be visible with the naked eye.Attenuation is measured in decibels (dB). A dB represents the comparison between thetransmitted and received power in a system.BANDWIDTHIt is defined as the amount of information that a system can carry such that each pulse of light isdistinguishable by the receiver.System bandwidth is measured in MHz or GHz. In general, when we say that a system hasbandwidth of 20 MHz, means that 20 million pulses of light per second will travel down the fibreand each will be distinguishable by the receiver.NUMBERICAL APERTURENumerical aperture (NA) is the "light - gathering ability" of a fibre. Light injected into the fibreat angles greater than the critical angle will be propagated. The material NA relates to therefractive indices of the core and cladding. NA = n12 - n22where n1 and n2 are refractive indices of core and cladding respectively.
  • 20. In general, fibres with a high bandwidth have a lower NA. They thus allow fewer modes meansless dispersion and hence greater bandwidth. A large NA promotes more modal dispersion, sincemore paths for the rays are provided NA, although it can be defined for a single mode fibre, isessentially meaningless as a practical characteristic. NA in a multimode fibre is important tosystem performance and to calculate anticipated performance.Numerical Aperture of fiber* Light Ray A : Did not Enter Acceptance Cone - Lost* Light Ray B : Entered Acceptance Cone - Transmitted through the Core by TotalInternal Reflection.OFC SplicingSplices are permanent connection between two fibres. The splicing involves cutting of the edgesof the two fibres to be spliced.Splicing MethodsThe following three types are widely used : 1. Adhesive bonding or Glue splicing. 2. Fusion splicingAdhesive Bonding or Glue SplicingThis is the oldest splicing technique used in fibre splicing. After fibre end preparation, it isaxially aligned in a precision V–groove. Cylindrical rods or another kind of reference surfacesare used for alignment. During the alignment of fibre end, a small amount of adhesive or glue ofsame refractive index as the core material is set between and around the fibre ends. A twocomponent epoxy or an UV curable adhesive is used as the bonding agent.Fusion SplicingThe fusion splicing technique is the most popular technique used for achieving very low splicelosses. The fusion can be achieved either through electrical arc or through gas flame.The process involves cutting of the fibers and fixing them in micro–petitioners on the fusionsplicing machine. The fibers are then aligned either manually or automatically core aligning (incase of S.M. fiber ) process. Afterwards the operation that takes place involve withdrawal of thefibers to a specified distance, preheating of the fiber ends through electric arc and bringingtogether of the fiber ends in a position and splicing through high temperature fusion
  • 21. MOBILE COMMUNICATIONA mobile phone uses radio wave signal for its connectivity with the subscriber.Mobile Phone TowersThe mobile phone works on the frequency signal and each mobile phone connection has its ownfrequency. These frequencies are sending from the basic lower station tower. Each tower has arange of 5 km in the city circle and there are a number of towers in the city to provideconnectivity to each mobile phone subscriber. The city is divided into imaginary hexagon as itsarea plans out and each hexagon point has a tower for providing frequency signals to the mobilesubscriber. When the mobile sends signals to the base tower then it is called uplink signal. Whenthe base tower sends signal to the mobile then its downlink signals on the highways the range ofbase tower of sending signal to the mobile phone subscribers is 25 km.Basic terms in mobile communication are:- 1. MSC: TAX for mobile phones 2. HLR: Home Location Register 3. TRC: Traffic Controller 4. VLR: Visitors Location Register 5. MNC: Mobile Network Code 6. BSC: Base Station ControlMSC:It acts as a trunk automatic exchange (TAX). All the switching is done here in this TAX. Eachand every call made by the mobile subscribers is first collected from the base station are send tothe MSC where all the necessary verification of the subscriber is made and then the switching of
  • 22. the call is made by the MSC. The OSS is a component within the MSC which maintains theMSC. The functions of OSS are maintenance of MSC.HLR:The Home Location Register stores each and every data of the mobile subscriber. Before the callis switched for the mobile subscriber the MSC verifies the subscriber and all the verification datais provided by the HLR. When the subscriber is on roaming facility, the MSC of that areacollects all the necessary information of the subscriber from its home MSC through its HLR.TRC:The traffic controller controls the traffic for MSC and also controls the traffic of subscribertrying to make contact with the MSC when call is made or received.VLR:The Visitor Location Register keeps a track record of subscribers who are on roaming facilityand all the records of the visitor coming from a different MSC area.MNC:Each and every country and its states have a unique Mobile Network Code (MNC) which makesa difference between the mobile subscriber of two different countries and also within the states.The MNC for India is 404and for Jharkhand BSNL mobile is INA76 where INA refers to theIndian Network.BSC:The Base Station acts as important media for call transfer and call receiving for the mobilesubscribers. It sends frequency signals for the connectivity of mobile subscriber. The BSC isconnected to its towers through 2 MB link and is directly connected to the MSC where all callswitching takes place for the mobile subscribers. Each base station is provided 124 frequenciesand a time slot of 8 channels for every call.
  • 23. GSM Network ComponentsThe GSM network is divided into two systems. Each of these systems is comprised of a numberof functional units which are individual components of the mobile network. The two systems are:Switching System (SS)Base Station System (BSS)GSM networks are operated, maintained and managed from computerized centers.Subscriber Identity Module (SIM)SIM card is the key feature of the GSM. It contains information about the subscriber and must beplugged into the ME to enable the subscriber to use the network with the exception of emergencycalls MS can only be operated if a valid SIM is present.These store three types of subscriber related information: 1. Fixed data stored before the subscription is sold such as authentication key and security algorithms. 2. Temporary network data such as the location area of the subscriber and forbidden PLMNS. 3. Service data such as language preference advice of charge.There are two types of SIM cards:-ID-SIM: The format and layout of the ID-SIM complies with ISO standards for integrated circuitcards.PLUG-In SIM: The plug-in SIM is smaller than the ID-SIM and is intended for semi permanentinstallation in the MNS.
  • 24. INTODUCTION TO GSM TECHNOLOGYWhat is GSM?If you are in Europe, Asia or Japan and using a mobile phone then most probably you must beusing GSM technology in your mobile phone. GSM stands for Global System for Mobile Communication and is an open, digital cellular technology used for transmitting mobile voice and data services. The GSM emerged from the idea of cell-based mobile radio systems at Bell Laboratories in the early 1970s. The GSM is the name of a standardization group established in 1982 to create a common European mobile telephone standard. The GSM standard is the most widely accepted standard and is implemented globally. The GSM is a circuit-switched system that divides each 200kHz channel into eight 25kHz time-slots. GSM operates in the 900MHz and 1.8GHz bands in Europe and the 1.9GHz and 850MHz bands in the US. The GSM is owning a market share of more than 70 percent of the worlds digital cellular subscribers. The GSM makes use of narrowband technique for transmitting signals. The GSM was developed using digital technology. It has an ability to carry 64 kbps to 120 Mbps of data rates. Presently GSM support more than one billion mobile subscribers in more than 210 countries throughout of the world. The GSM provides basic to advanced voice and data services including Roaming service. Roaming is the ability to use your GSM phone number in another GSM network.A GSM digitizes and compresses data, then sends it down through a channel with two otherstreams of user data, each in its own time slot. It operates at either the 900 MHz or 1,800 MHzfrequency band.Specifications for different Personal Communication Services (PCS) systems vary among thedifferent PCS networks. The GSM specification is listed below with important characteristics.Modulation:Modulation is a form of change process where we change the input information into a suitableformat for the transmission medium. We also changed the information by demodulating thesignal at the receiving end.The GSM uses Gaussian Minimum Shift Keying (GMSK) modulation method.
  • 25. Access Methods:Because radio spectrum is a limited resource shared by all users, a method must be devised todivide up the bandwidth among as many users as possible.GSM chose a combination ofTDMA/FDMA as its method. The FDMA part involves the division by frequency of the total 25MHz bandwidth into 124 carrier frequencies of 200 kHz bandwidth. One or more carrierfrequencies are then assigned to each BS. Each of these carrier frequencies is then divided intime, using a TDMA scheme, into eight time slots. One time slot is used for transmission by themobile and one for reception. They are separated in time so that the mobile unit does not receiveand transmit at the same time.Transmission Rate:The total symbol rate for GSM at 1 bit per symbol in GMSK produces 270.833 Ksymbols/second. The gross transmission rate of the time slot is 22.8 Kbps.GSM is a digital system with an over-the-air bit rate of 270 kbps.Frequency Band:The uplink frequency range specified for GSM is 933 - 960 MHz (basic 900 MHz band only).The downlink frequency band 890 - 915 MHz (basic 900 MHz band only).Speech Coding:GSM uses linear predictive coding (LPC). The purpose of LPC is to reduce the bit rate. The LPCprovides parameters for a filter that mimics the vocal tract. The signal passes through this filter,leaving behind a residual signal. Speech is encoded at 13 kbps.Access Network: Access network, the network between local exchange and subscriber, in the Telecom Networkaccounts for a major portion of resources both in terms of capital and manpower. So far, thesubscriber loop has remained in the domain of the copper cable providing cost effective solutionin past. Quick deployment of subscriber loop, coverage of inaccessible and remote locationscoupled with modern technology have led to the emergence of new Access Technologies. Thevarious technological options available are as follows : 1. Multi Access Radio Relay 2. Wireless In Local Loop 3. Fibre In the Local Loop
  • 26. Wireless in Local Loop (WILL)Fixed Wireless telephony in the subscriber access network also known as Wireless in Local Loop(WLL) is one of the hottest emerging market segments in global telecommunications today.WLL is generally used as ―the last mile solution‖ to deliver basic phone service expeditiouslywhere none has existed before. Flexibility and expediency are becoming the key driving factorsbehind the deployment of WILL.WLL shall facilitate cordless telephony for residential as well as commercial complexes wherepeople are highly mobile. It is also used in remote areas where it is uneconomical to lay cablesand for rapid development of telephone services. The technology employed shall depend uponvarious radio access techniques, like FDMA, TDMA and CDMA.SPREAD SPECTRUM PRINCIPLEOriginally Spread spectrum radio technology was developed for military use to counter theinterference by hostile jamming. The broad spectrum of the transmitted signal gives rise to “Spread Spectrum”. A Spread Spectrum signal is generated by modulating the radio frequency(RF) signal with a code consisting of different pseudo random binary sequences, which isinherently resistant to noisy signal environment.A number of Spread spectrum RF signals thus generated share the same frequency spectrumand thus the entire bandwidth available in the band is used by each of the users using samefrequency at the same time.Frequency of operation: 824-849Mhz and 869-894 MhzDuplexing Mehtod: Frequency Division Duplexing (FDD)Access Channel per carrier: Maximum 61 ChannelsRF Spacing: 1.25 MhzCoverage: 5 Km with hand held telephones and approx. 20 Km with fixed units.
  • 27. Hand Offs in CDMAAs the phone moves through a network the system controller transfers the call from one cell toanother, this process is called ―handoff‖. Handoffs maybe done with the assistance of the mobileor the system controller will control the process by itself. Handoffs are necessary to continue thecall as the phone travels. Handoffs may also occur in idle state due to mobility.Types of Handoffs in CDMA: There are primarily three types of Handoffs in CDMA. They are Soft Hard and Idle.The type of handoff depends on the handoff situation.To understand this we should know the cellular concept used in CDMA.CDMA frequency- reuse planning (cellular concept):Each BTS in a CDMA network can use all available frequencies. Adjacent cells can transmit atthe same frequency because users are separated by code channels, not frequency channels. BTSsare separated by offsets in the short PN code This feature of CDMA, called "frequency reuse ofone," eliminates the need for frequency planningSoft Handoff:A soft handoff establishes a connection with the new BTS prior to breaking theconnection with the old one. This is possible because CDMA cells use the samefrequency and because the mobile uses a rake receiver. The CDMA mobile assiststhe network in the handoff. The mobile detects a new pilot as it travels to the nextcoverage area. The new base station then establishes a connection with the mobile.This new communication link is established while the mobile maintains the linkwith the old BTS.Soft handoffs are also called "make-before-break." Soft handoff can take place only when theserving cell and target cell are working in the same frequency.
  • 28. INTRODUCTION TO INTERNET AND BROADBAND INTERNETThe internet connection requires a computer which has Internet Explorer software signaland analog signal to digital signal, a telephone line connection. The data is sent throughtelephone line connection to the local exchange, from where it is then sent to the mainexchange.The main exchange consists of a Node. The Node consists of a control card and a modemfrom where it is sent to its main. Node is in the form of packets. It has two parts- LAN andControl Card.The main Node is connected to the main server which is located at New Delhi. From here itis sent to gateway, which is connected to the World Wide Web (WWW)
  • 29. INTERNET CONNECTIVITYTelephone Local Exchange (through PCM) LANControl Card (routers, packet switching) ModemWAN Patna (through OFC, B2 Node) DelhiNetwork Connection Gateway OVERVIEW OF BROAD BANDDefinition of Broad BandBroadband is often called high-speed Internet, because it usually has a high rate of datatransmission. In general, any connection to the customer of 256 kbit/s or more is consideredbroadband.
  • 30. HOW IS BROADBAND DIFFERENT FROM DIAL-UP SERVICE? Broadband service provides higher speed of data transmission—Allows more content to be carried through the transmission ―pipeline.‖ Broadband provides access to the highest quality Internet services—streaming media, VoIP (Internet phone), gaming and interactive services. Many of these current and newly developing services require the transfer of large amounts of data which may not be technically feasible with dial-up service. Therefore, broadband service may be increasingly necessary to access the full range of services and opportunities that the Internet can offer. Broadband is always on—does not block phone lines and no need to reconnect to network after logging off.What is Broadband Service?Broadband refers to a connection that has capacity to transmit large amount of data athigh speed. Presently a connection having download speeds of 256 kbps or more isclassified as broadband. When connected to the Internet broadband connection allowssurfing or downloading much faster than a dial-up or any other narrowband connections.BSNL offers 2 Mbps minimum download speed for its Broadband connections.Requirement for providing Broad Band connection Personal Computer ADSL Modem Land Line Connection Splitter for separating telephone from Personal computer.Services available through Broadband  High speed Internet Access: This is the always-on Internet access service with speed ranging from 256 kbps to 8 Mbps.  Bandwidth on Demand: This will facilitate customer to change bandwidth as per his / her requirement. For example a customer with 256 kbps can change to 1 Mbps during the video Conferencing session.  Multicasting: This is to provide video multicast services, video-on-demand etc. for application in distance education, telemedicine etc.
  • 31.  Dial VPN Service: This service allows remote users to access their private network securely over the NIB-II infrastructure. Video and Audio Conferencing: Content based Services: Like Video on Demand, Interactive Gaming, Live and time shifted TV Video on Demand: Customers can view any movie of their choice from a pool of movies stored in a central server. The movies can be viewed either on a TV or a PC. Audio on Demand: It is a similar service where person can listen to any music of his choice. TV channels through broadband connection: The TV channels may be available in the broadband connection. In fact, there may be other new channels, particularly the educational and scientific channels, depending on demand. Additional equipments required in the customers premises are Set Top Box (STB) - The STB converts the digital IP based signal to a form compatible with the TV set. PC and TV The TV services envisaged are: i. S-VoD : Subscription based Video Content, as in Pay Channels. ii. Video-On-Demand iii. N-VoD : Near Video-On-Demand. NVOD provides playouts on fixed time bands which people can watch against payment. iv. T-VOD : Transaction or Pay-Per-View service. The video content will have Hindi, international and regional movies, music, soaps and serials, sports, news, interactive gaming, e-learning and niche channels. "The driver in entertainment will be on-demand movies, interactive gaming, broadband Internet connectivity and e-learning," Billing: To provide a means to bill for the aforesaid services by either time-based or volume-based billing. It shall provide the customer with the option to select the services through web server To provide both pre-paid and post paid broadband services IP Telephony Messaging: plain and feature rich, Multi-site MPLS VPN with Quality of Service (QoS) guarantees. Wi-Fi Web hosting & web co-location. Lease line service.
  • 32. CONCLUSIONThe working in the project was an interesting and an all together learning experience. Newtechnologies, new progress and new competition are the order of the day. The core area to lookfor is highly fragmented and information intense activity sequence that involves a number ofplayer and audiences.The project mainly revolves around: EWSD, TAX, internet node, mobile communication, WLLand intelligence network.The emphasis of the different parts of the project is to throw light on the systems working inPatna Main Exchange. The project also deals with modern technologies attributes and the scopeof implementation of the same in Patna. The area under study was limited to Patna MainExchange.The scope of the study is very vast and the topic under study deals with the volatile technologyworld. After the study, suggestions and strategy has been formulated keeping in view thelimitations of the field.Evolution of this technological world is occurring every minute. Thanks to telecom and webtechnologies, countries are coming closer day by day.