Classificationoftransmissionmedia
1.Wiredmedia
Coaxialcable
Twistedpair
Opticalfiber
2.Wirelessmedium
Infrared
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.