计算机网络高级教程ppt课件.ppt

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1、ThePhysicalLayerChapter2TheTheoreticalBasisforDataCommunicationFourierAnalysisBandwidth-LimitedSignalsMaximumDataRateofaChannelBandwidth-LimitedSignalsAbinarysignalanditsroot-mean-squareFourieramplitudes.(b)–(c)Successiveapproximationstotheoriginalsignal.Bandwidth-LimitedSignals(2)(d)–(

2、e)Successiveapproximationstotheoriginalsignal.Bandwidth-LimitedSignals(3)Relationbetweendatarateandharmonics.GuidedTransmissionDataMagneticMediaTwistedPairCoaxialCableFiberOpticsTwistedPair(a)Category3UTP.(b)Category5UTP.CoaxialCableAcoaxialcable.FiberOptics(a)Threeexamplesofalightrayfr

3、ominsideasilicafiberimpingingontheair/silicaboundaryatdifferentangles.(b)Lighttrappedbytotalinternalreflection.TransmissionofLightthroughFiberAttenuationoflightthroughfiberintheinfraredregion.FiberCables(a)Sideviewofasinglefiber.(b)Endviewofasheathwiththreefibers.FiberCables(2)Acomparis

4、onofsemiconductordiodesandLEDsaslightsources.FiberOpticNetworksAfiberopticringwithactiverepeaters.FiberOpticNetworks(2)Apassivestarconnectioninafiberopticsnetwork.WirelessTransmissionTheElectromagneticSpectrumRadioTransmissionMicrowaveTransmissionInfraredandMillimeterWavesLightwaveTrans

5、missionTheElectromagneticSpectrumTheelectromagneticspectrumanditsusesforcommunication.RadioTransmission(a)IntheVLF,LF,andMFbands,radiowavesfollowthecurvatureoftheearth.(b)IntheHFband,theybounceofftheionosphere.PoliticsoftheElectromagneticSpectrumTheISMbandsintheUnitedStates.LightwaveTra

6、nsmissionConvectioncurrentscaninterferewithlasercommunicationsystems.Abidirectionalsystemwithtwolasersispicturedhere.CommunicationSatellitesGeostationarySatellitesMedium-EarthOrbitSatellitesLow-EarthOrbitSatellitesSatellitesversusFiberCommunicationSatellitesCommunicationsatellitesandsom

7、eoftheirproperties,includingaltitudeabovetheearth,round-tripdelaytimeandnumberofsatellitesneededforglobalcoverage.CommunicationSatellites(2)Theprincipalsatellitebands.CommunicationSatellites(3)VSATsusingahub.Low-EarthOrbitSatellitesIridium(a)TheIridiumsatellitesfromsixnecklace