Domov technika Communication medium

Communication medium



Classificationoftransmissionmedia

1.Wiredmedia

  1. Coaxialcable

  2. Twistedpair

  3. Opticalfiber

2.Wirelessmedium

  1. Infrared

  2. Electromagneticwaves

Introduction

Thefirstthingyouneedtoconnecttothenetworkisthetransmissionline,whichItistheminimumrequirementofallnetworks.Therearefourbasictypesofcommontransmissionlines:coaxialcable,twistedpair,opticalfiberandradiowave.Eachtypemeetscertainnetworkneedsandsolvescertainnetworkproblems.

Coaxialcable

Thecenterofthecoaxialcableisacoppercore,theuraniumcoreiscoveredwithaninsulatinglayer,andthereisashieldinglayeroutsidetheinsulatinglayer.TheshieldinglayerofhydrogenwireisveryWrapitwell,andthentheouterskinwillbetheouterskin.Duetothestructureofthecoaxialcable,ithasastronganti-interferenceabilitytotheoutsideworld.Coaxialcableisthemostcommonlyusedtransmissionmediumforlocalareanetworks.

Twisted-paircable

Inlocalareanetworks,twisted-paircablesarewidelyused,mainlybecauseoftheirlowcost,highspeedandhighreliability.Therearetwobasictypesoftwistedpair:ShieldedTwistedPair(STP)andUnshieldedTwistedPair(UTP),bothofwhicharetwistedtogethertoformatransmissioncircuit.Thetwowiresaretwistedtogethertopreventinterference(thedifferentialsignalonthepairhastheeffectofcommonmodesuppressionofinterference).

Opticalfiber

Somenetworkapplicationsareverydemanding.Itrequiresreliable,high-speedandlong-distancedatatransmission.Inthiscase,opticalfiberisanidealchoice.Theopticalfiberhasacylindricalshapeandconsistsofthreeparts:thecore,thecladdingandthesheath.Thecoreistheinnermostpart,whichconsistsofoneormoreverythinstrandsorfibersmadeofglassorplastic.Eachfiberiscoveredbyitsowncladding.Thecladdingisaglassorplasticcoating,whichhasdifferentopticalpropertiesfromthecore.Theoutermostlayeristhesheath,whichwrapsoneorabundleofcoatedfibers.Thesheathismadeofplasticorothermaterials,anditisusedtopreventmoisture,abrasions,crushingorotherexternalhazards.

Wirelessmedium

Inadditiontothecoaxialcable,twistedpair,andopticalfiber,thetransmissionlinesystemalsousesnowiresatall.Thisisradiocommunication,whichuseselectromagneticwaves.Orlightwavesareusedtotransmitinformation,whichcanbeusedtoconnectnetworkswithoutlayingcables.Radiocommunicationincludestwouniquenetworks:wirelessLANnetworksformobilenetworks.UsingaLANnetwork,machinescanbeconnectedthroughtransmittersandreceivers;usingamobilenetwork,machinescanbeconnectedthroughacellularcommunicationsystemprovidedbytheradiocommunicationsdepartment.

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