Training on Optical Fiber Networks by Arun Rawat [Compatibility Mode]

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Transcript of Training on Optical Fiber Networks by Arun Rawat [Compatibility Mode]

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    RailTel Corporation of India Ltd.

    Training

    onOptical Fiber Networks

    By: Arun Singh RawatDeputy Manager/Project

    E-mail: arunsrawat@railtelindia.comContact no.:09958018833

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    How fiber cable look like

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    Advantages of Optical Communication

    Explosive demand for higher bandwidthLow bandwidth of copper

    Nearly 25THz possible with fiberLow Loss-Longer distance transmission(Less Repeaters)No EMI in fiber-based telecom

    Less cross-talk, more reliabilityMore secure communications

    Lighter than copper

    Lower cost per unit bandwidth(made of silica which is very cheap)Safer and more advantages

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    What is Optical Communication?Optical communication is any form of telecommunication that uses light as thetransmission medium.

    transmitter , which encodes an electronic pulseinto an optical signal , which carries the signal to

    its destination, and a receiver , which reproducesthe message from the received optical signal.

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    Journey through the Optical TunnelJourney through the Optical Tunnel

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    Transmit-Receive OverviewTransmit-Receive Overview

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    Optical FiberThe most common type of channel for opticalcommunicationsFlexible optically transparentfiber made of glass or plasticthrough which light can betransmitted by the process of totalnterna re ect on

    Consists of a core , cladding andcoatingCore is the inner glass layer of high refractive index

    Cladding is the outer layerwhich covers the core/ has a lowerrefractive indexCoating is the outer most layerwhich provides environmental andphysical protection for the fiber

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    Theory of Optical FiberTransmits light along its axis using the process of total internal reflectionBased upon the principle of Snells Law

    Snells Law Total internal reflection can occur when light attempts to move from amaterial with high index of refraction to one with lower index of refraction

    In an optical Fiber, the core has highre rac ve n ex n w c e g en er ng efiber is guided

    Cladding has a refractive index slightly lessthan that of the core

    By principle of total internal reflection thelight entering the fiber (core) at one end travelsalong the fiber by bouncing repeatedly of theinside of the interface of the glass with thesurrounding medium (cladding)

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    How Does an Optical Fiber Transmit Light?

    The light in a fiber-optic cable travels through the core by constantly

    bouncing from the cladding (mirror-lined walls), a principle called totalinternal reflection. Because the cladding does not absorb any light from thecore, the light wave can travel great distances.

    gna egra es w t n t e eressentially due to

    Impurities in glass

    Wavelength of transmitted light

    850 nm 60-75% per Km

    1300 nm 50-60% per KM

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    Types of Optical FiberOptical Fibers are classified as Single Mode or MultiMode fiberMulti mode fiber has a core diameter around 50um andcladding diameter of 125 umSingle mode fiber core is less than 10um and can support

    only one mode of propagationOptical fiber are also grouped as step index and gradedindex fiberIn a step index fiber, the refractive index of the core isconstant throughoutA graded index fiber has core with varying refractiveindex

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    Types of Optical Fiber

    125um 125um

    Single Mode Fiber Multi Mode Fiber

    9.2um 50um

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    Fiber Optic CommunicationHistoryFiber Optic Communication SystemBenefits of Optic Communication

    Limitation of Optic Communication

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    HistoryEarly People used light Signal to communicate

    Telegraphs, coaxial cables and micro wave systemsDue to their limitation in communicating between long distances, inthe second half of the 20 th century, the idea of optical carrier of information arrived and found that it is better than other existing carrier

    Due to lack of suitable coherent light source and better transmissionmedium no remarkable even took place until 1960In 1960 laser was developed and ten years later optical fiber wasdeveloped

    Between 1970 and 1980, the first commercial fiber optic system wasdeveloped with a bit rate of 45Mbps and a repeater spacing of 10 Km

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    Fiber Optic communication SystemFour major parts in the system

    Optical Transmitter Semi conductors like LED or Lasersconvert electrical signals to Optical signals to send it into theoptical fiber

    and buildings carry the light signal between transmitters,amplifiers and receivers

    Optical Amplifier amplifies the light signals to reduceeffects of distortions and attenuation

    Optical Receiver Recovers the light signal back to theelectrical signal

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    BenefitsPermits transmission over longer distances and at higherbandwidth (data rates) than other forms of communication.Signals travel along them with less loss and are alsoimmune to electromagnetic interference

    No electromagnetic interference hence better S/N ratioHigh electrical resistance makes it safer to use whereelectrical isolation is requiredLight weight and small size makes them ideal formultiple applicationsHigh on security, difficult to tap in and read data beingtransmitted

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    LimitationsDispersion; spreading of optical pulses as theytravel along fiberAttenuation; caused by combination of material

    Material absorption of silica is 0.3 db/km, but impuritiesincrease this amount to 1000 db/km

    Modern fiber has attenuation of 00.3 db/km Microscopic fluctuation in density and imperfect

    splicing increases attenuation

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    ContentsPlesiochronous Digital HeirarchySynchronous Digital HierarchyWave Division Multiplexing

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    Plesiochronous Digital Heirarchy Plesiochronous is a Greek word meaning

    Almost Synchronous , but not fullysynchronous.

    In Plesiochronous system every equipment isgenerating its own clock for synchronization.

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    Plesiochronous TransmissionPulse Code Modulation

    Voice Frequency ranges upto 4 Khz Sampling the Voice Signal @ 8 Khz (Double the Max. Frequency) 8 bits per sample =

    Building up the Base Stream (2MB)

    30 Voice Channels @ 64 Khz

    One channel for Frame (64 K) One channel for Signaling (64 K) Total number of Channels = 32 Bit Rate: 32 X 64 K= 2048 Khz (2Mb)

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    PDH Bit RatesE1-2048 Kbps (2Mb) [30 Voice Channel]

    E2-8448 Kbps (8Mb) [120 Voice Channel]E3-34368 Kbps (34Mb) [480 Voice Channel]

    -

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    Bit-Interleaved Multiplexing It is TDM

    One bit will be taken from all Tributaries.

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    Stuffing and Justification In a PDH multiplexer individual bits must be running at the

    same speed otherwise the bits cannot be interleaved The possible Plesiochronous difference is catered for by

    using a technique known as Justification

    Extra bits are added (stuffed) into the digital tributaries whicheffectively increases the speed of the tributary until they are allidentical

    The speed of the higher order side is generated by an internaloscillator in the multiplexer and is not derived from theprimary reference clock

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    PDH Multiplexing / Demultiplexing is time consuming

    Incompatibility of standard equipment fromdifferent vendors

    US and Euro ean s stems have too little in common - Expensive mediators for transatlantic transmission

    No self checking - expensive manual check and repairsystem

    No standard for high bandwidth links - proprietary

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