Tanenbaum《计算机网络》原版课件第2章

ThePhysicalLayerChapter2TheTheoreticalBasisforDataCommunication•FourierAnalysis•Bandwidth-LimitedSignals•MaximumDataRateofaChannelBandwidth-LimitedSignalsAbinarysignalanditsroot-mean-squareFourieramplitudes.(b)–(c)Successiveapproximationstotheoriginalsignal.Bandwidth-LimitedSignals(2)(d)–(e)Successiveapproximationstotheoriginalsignal.Bandwidth-LimitedSignals(3)Relationbetweendatarateandharmonics.GuidedTransmissionData•MagneticMedia•TwistedPair•CoaxialCable•FiberOpticsTwistedPair(a)Category3UTP.(b)Category5UTP.CoaxialCableAcoaxialcable.FiberOptics(a)Threeexamplesofalightrayfrominsideasilicafiberimpingingontheair/silicaboundaryatdifferentangles.(b)Lighttrappedbytotalinternalreflection.TransmissionofLightthroughFiberAttenuationoflightthroughfiberintheinfraredregion.FiberCables(a)Sideviewofasinglefiber.(b)Endviewofasheathwiththreefibers.FiberCables(2)AcomparisonofsemiconductordiodesandLEDsaslightsources.FiberOpticNetworksAfiberopticringwithactiverepeaters.FiberOpticNetworks(2)Apassivestarconnectioninafiberopticsnetwork.WirelessTransmission•TheElectromagneticSpectrum•RadioTransmission•MicrowaveTransmission•InfraredandMillimeterWaves•LightwaveTransmissionTheElectromagneticSpectrumTheelectromagneticspectrumanditsusesforcommunication.RadioTransmission(a)IntheVLF,LF,andMFbands,radiowavesfollowthecurvatureoftheearth.(b)IntheHFband,theybounceofftheionosphere.PoliticsoftheElectromagneticSpectrumTheISMbandsintheUnitedStates.LightwaveTransmissionConvectioncurrentscaninterferewithlasercommunicationsystems.Abidirectionalsystemwithtwolasersispicturedhere.CommunicationSatellites•GeostationarySatellites•Medium-EarthOrbitSatellites•Low-EarthOrbitSatellites•SatellitesversusFiberCommunicationSatellitesCommunicationsatellitesandsomeoftheirproperties,includingaltitudeabovetheearth,round-tripdelaytimeandnumberofsatellitesneededforglobalcoverage.CommunicationSatellites(2)Theprincipalsatellitebands.CommunicationSatellites(3)VSATsusingahub.Low-EarthOrbitSatellitesIridium(a)TheIridiumsatellitesfromsixnecklacesaroundtheearth.(b)1628movingcellscovertheearth.Globalstar(a)Relayinginspace.(b)Relayingontheground.PublicSwitchedTelephoneSystem•StructureoftheTelephoneSystem•ThePoliticsofTelephones•TheLocalLoop:Modems,ADSLandWireless•TrunksandMultiplexing•SwitchingStructureoftheTelephoneSystem(a)Fully-interconnectednetwork.(b)Centralizedswitch.(c)Two-levelhierarchy.StructureoftheTelephoneSystem(2)Atypicalcircuitrouteforamedium-distancecall.MajorComponentsoftheTelephoneSystem•LocalloopsAnalogtwistedpairsgoingtohousesandbusinesses•TrunksDigitalfiberopticsconnectingtheswitchingoffices•SwitchingofficesWherecallsaremovedfromonetrunktoanotherThePoliticsofTelephonesTherelationshipofLATAs,LECs,andIXCs.AllthecirclesareLECswitchingoffices.EachhexagonbelongstotheIXCwhosenumberisonit.TheLocalLoop:Modems,ADSL,andWirelessTheuseofbothanaloganddigitaltransmissionsforacomputertocomputercall.Conversionisdonebythemodemsandcodecs.Modems(a)Abinarysignal(b)Amplitudemodulation(c)Frequencymodulation(d)PhasemodulationModems(2)(a)QPSK.(b)QAM-16.(c)QAM-64.Modems(3)(a)V.32for9600bps.(b)V32bisfor14,400bps.(a)(b)DigitalSubscriberLinesBandwidthversusdistancedovercategory3UTPforDSL.DigitalSubscriberLines(2)OperationofADSLusingdiscretemultitonemodulation.DigitalSubscriberLines(3)AtypicalADSLequipmentconfiguration.WirelessLocalLoopsArchitectureofanLMDSsystem.FrequencyDivisionMultiplexing(a)Theoriginalbandwidths.(b)Thebandwidthsraisedinfrequency.(b)Themultiplexedchannel.WavelengthDivisionMultiplexingWavelengthdivisionmultiplexing.TimeDivisionMultiplexingTheT1carrier(1.544Mbps).TimeDivisionMultiplexing(2)Deltamodulation.TimeDivisionMultiplexing(3)MultiplexingT1streamsintohighercarriers.TimeDivisionMultiplexing(4)Twoback-to-backSONETframes.TimeDivisionMultiplexing(5)SONETandSDHmultiplexrates.CircuitSwitching(a)Circuitswitching.(b)Packetswitching.MessageSwitching(a)Circuitswitching(b)Messageswitching(c)PacketswitchingPacketSwitchingAcomparisonofcircuitswitchedandpacket-switchednetworks.TheMobileTelephoneSystem•First-GenerationMobilePhones:AnalogVoice•Second-GenerationMobilePhones:DigitalVoice•Third-GenerationMobilePhones:DigitalVoiceandDataAdvancedMobilePhoneSystem(a)Frequenciesarenotreusedinadjacentcells.(b)Toaddmoreusers,smallercellscanbeused.ChannelCategoriesThe832channelsaredividedintofourcategories:•Control(basetomobile)tomanagethesystem•Paging(basetomobile)toalertuserstocallsforthem•Access(bidirectional)forcallsetupandchannelassignment•Data(bidirectional)forvoice,fax,ordataD-AMPSDigitalAdvancedMobilePhoneSystem(a)AD-AMPSchannelwiththreeusers.(b)AD-AMPSchannelwithsixusers.GSMGlobalSystemforMobileCommunicationsGSMuses124frequencychannels,eachofwhichusesaneight-slotTDMsystemGSM(2)AportionoftheGSMframingstructure.CDMA–CodeDivisionMultipleAccess(a)Binarychipsequencesforfourstations(b)Bipolarchipsequences(c)Sixexamplesoftransmissions(d)RecoveryofstationC’ssignalThird-GenerationMobilePhones:DigitalVoiceandDataBasicservicesanIMT-2000networkshouldprovide•High-qualityvoicetransmissio