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Lecture3 DCN

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    Physical Media

    PHYSICAL MEDIA

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    Physical Media

    Physical Media

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    Physical MediaMagnetic Media/optical discs etc.

    CopperCoaxial Cable Baseband and broadbandUnshielded Twisted Pair - CAT 3,4,5,5e&6

    Optical FiberMultimodeSinglemode

    WirelessRadio waveIR waveMicrowaveSatellite

    Physical Media

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    Copper Media: Coaxial CableCoaxial cable is a copper-cored cable surroundedby a heavy shielding andis used to connectcomputers in a network.

    Outer conductor shieldsthe inner conductor frompicking up stray signalfrom the air.

    High bandwidth but lossychannel.

    Repeater is used toregenerate the weakenedsignals.

    Physical Media

    Category Impedance Use

    RG-59 75 Cable TV

    RG-58 50Thin

    Ethernet

    RG-11 50Thick

    Ethernet

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    Copper Media: Twisted PairTwisted-pair is a type ofcabling that is used fortelephone communicationsand most modern Ethernetnetworks.

    A pair of wires forms acircuit that can transmitdata. The pairs are twistedto provide protection

    against crosstalk, the noisegenerated by adjacent pairs.

    There are two basic types,shielded twisted-pair (STP)and unshielded twisted-pair

    (UTP).

    Physical Media

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    Shielded Twisted Pair (STP)

    Physical Media

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    Unshielded Twisted Pair (UTP)

    Physical Media

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    Unshielded Twisted Pair (UTP)Consists of 4 pairs (8 wires) ofinsulated copper wires typicallyabout 1 mm thick.

    The wires are twisted together in ahelical form.

    Twisting reduces the interferencebetween pairs of wires.

    High bandwidth and High attenuationchannel.

    Flexible and cheap cable.Category rating based on number oftwists per inch and the material used

    CAT 3, CAT 4, CAT 5, Enhanced CAT5 and now CAT 6.

    Physical Media

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    Categories of UTPUTP comes in several categories that are based onthe number of twists in the wires, the diameter of thewires and the material used in the wires.

    Category 3 is the wiring used primarily for telephone

    connections.Category 5e and Category 6 are currently the mostcommon Ethernet cables used.

    Physical Media

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    Categories of UTP: CAT 3

    Bandwidth 16 Mhz

    11.5 dB Attenuation

    100 ohms ImpedanceUsed in voice applications and 10baseT (10Mbps)Ethernet

    Physical Media

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    Categories of UTP: CAT 4

    20 MHz Bandwidth

    7.5 dB Attenuation

    100 ohms ImpedanceUsed in 10baseT (10Mbps) Ethernet

    Physical Media

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    Categories of UTP: CAT 5

    100 MHz Bandwidth

    24.0 dB Attenuation

    100 ohms ImpedanceUsed for high-speed data transmission

    Used in 10BaseT (10 Mbps) Ethernet & Fast Ethernet(100 Mbps)

    Physical Media

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    Categories of UTP: CAT 5e

    150 MHz Bandwidth

    24.0 dB Attenuation

    100 ohms ImpedanceTransmits high-speed data

    Used in Fast Ethernet (100 Mbps), Gigabit Ethernet(1000 Mbps) & 155 Mbps ATM

    Physical Media

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    Categories of UTP: CAT 6

    250 MHz Bandwidth

    19.8 dB Attenuation

    100 ohms ImpedanceTransmits high-speed data

    Used in Gigabit Ethernet (1000 Mbps) & 10 GigEthernet (10000 Mbps)

    Physical Media

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    Fiber Media

    Optical fibers use lightto send informationthrough the optical

    medium.It uses the principal oftotal internal reflection.

    Modulated lighttransmissions are usedto transmit the signal.

    Physical Media

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    Fiber MediaLight travels through the optical media by the way oftotal internal reflection.

    Modulation scheme used is intensity modulation.

    Two types of Fiber media :MultimodeSinglemode

    Multimode Fiber can support less bandwidth thanSinglemode Fiber.

    Singlemode Fiber has a very small core and carryonly one beam of light. It can support Gbps datarates over > 100 Km without using repeaters.

    Physical Media

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    Propagation of Signals inOptical Fiber

    Advantages Low loss ~0.2dB/km at1550nm Enormous bandwidth at least 25THz Light weight Flexible Immunity to interferencesDisadvantages and Impairments Difficult to handle dispersion Absor tion &Ra lei h Scatterin

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    Single and Multimode FiberSingle-mode fiber

    Carries light pulsesalong single pathUses Laser Light

    SourceMultimode fiberMany pulses of lightgenerated by LEDtravel at different

    angles

    Physical Media

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    A fiber optic ring LAN

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    Fiber MediaThe bandwidth of the fiber is limited due to thedispersion effect.

    Distance Bandwidth product of a fiber is almost aconstant.

    Fiber optic cables consist of multiple fibers packedinside protective covering.

    Physical Media

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    Fiber-Optic CableContains one or severalglass fibers at its core

    Surrounding the fibers isa layer called cladding

    Physical Media

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    Fiber Optic CableFO Cable may have 1 toover 1000 fibers

    Physical Media

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    Wireless MediaVery useful in difficultterrain where cablelaying is not possible.

    Provides mobility to

    communication nodes.Right of way and cablelaying costs can bereduced.

    Susceptible to rain,atmospheric variationsand Objects intransmission path.

    CLASS NOTES

    Physical Media

    h i l di

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    Frequency Bands

    Physical Media

    Band RangePropagatio

    nApplication

    VLF 3 30 KHz Ground Long-range radio navigation

    LF 30 300 KHz Ground Radio beacons andnavigational locators

    MF 300 KHz 3 MHz Sky AM radio

    HF 3 30 MHz Sky Citizens band (CB),ship/aircraft communication

    VHF 30 300 MHz Sky andline-of-sight

    VHF TV,FM radio

    UHF 300 MHz 3 GHz Line-of-sight

    UHF TV, cellular phones,paging, satellite

    SHF 3 30 GHz Line-of-sight

    Satellite communication

    EHF 30 300 GHz Line-of-sight Long-range radio navigation

    Ph i l M di

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    Wireless LAN

    Physical Media

    Internet Router Switch

    Access Point

    Access Point

    PC

    PC

    Ph i l M di

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    Terrestrial MicrowaveMicrowaves do notfollow the curvature ofearth

    Line-of-Sight

    transmissionHeight allows thesignal to travel farther

    Two frequencies fortwo waycommunicationRepeater is used toincrease the distanceHop-by-Hop

    Physical Media

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    Ph i l M di

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    Satellite Communication

    Physical Media

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    + CLASS NOTES-------------


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