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Chapter9UsingTelephone

andCableNetworksforDataTransmissionCopyright?TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.19-1TELEPHONENETWORKTelephonenetworksusecircuitswitching.Thetelephonenetworkhaditsbeginningsinthelate1800s.Theentirenetwork,whichisreferredtoastheplainoldtelephonesystem(POTS),wasoriginallyananalogsystemusinganalogsignalstotransmitvoice.MajorComponentsLATAs

SignalingServicesProvidedbyTelephoneNetworksTopicsdiscussedinthissection:2Figure9.1Atelephonesystem3Intra-LATAservicesareprovidedbylocalexchangecarriers.

Since2019,therearetwotypesofLECs:incumbentlocalexchangecarriersandcompetitive

localexchangecarriers.Note4Figure9.2SwitchingofficesinaLATA5Figure9.3Pointofpresences(POPs)6Thetasksofdatatransferandsignalingareseparatedinmoderntelephonenetworks:datatransferisdonebyonenetwork,signalingbyanother.Note7Figure9.4Datatransferandsignalingnetworks8Figure9.5LayersinSS799-2DIAL-UPMODEMSTraditionaltelephonelinescancarryfrequenciesbetween300and3300Hz,givingthemabandwidthof3000Hz.Allthisrangeisusedfortransmittingvoice,whereagreatdealofinterferenceanddistortioncanbeacceptedwithoutlossofintelligibility.ModemStandardsTopicsdiscussedinthissection:10Figure9.6Telephonelinebandwidth11Modemstandsformodulator/demodulator.Note12Figure9.7Modulation/demodulation13Figure9.8TheV.32andV.32bisconstellationandbandwidth14Figure9.9Uploadinganddownloadingin56Kmodems159-3DIGITALSUBSCRIBERLINEAftertraditionalmodemsreachedtheirpeakdatarate,telephonecompaniesdevelopedanothertechnology,DSL,toprovidehigher-speedaccesstotheInternet.Digitalsubscriberline(DSL)technologyisoneofthemostpromisingforsupportinghigh-speeddigitalcommunicationovertheexistinglocalloops.ADSLADSLLiteHDSLSDSL

VDSLTopicsdiscussedinthissection:16ADSLisanasymmetriccommunicationtechnologydesignedforresidentialusers;itisnotsuitableforbusinesses.Note17Theexistinglocalloopscanhandlebandwidthsupto1.1MHz.Note18ADSLisanadaptivetechnology.

Thesystemusesadataratebasedontheconditionof

thelocalloopline.Note19Figure9.10Discretemultitonetechnique20Figure9.11BandwidthdivisioninADSL21Figure9.12ADSLmodem22Figure9.13DSLAM23Table9.2SummaryofDSLtechnologies249-4CABLETVNETWORKSThecableTVnetworkstartedasavideoserviceprovider,butithasmovedtothebusinessofInternetaccess.Inthissection,wediscusscableTVnetworksperse;inSection9.5wediscusshowthisnetworkcanbeusedtoprovidehigh-speedaccesstotheInternet.TraditionalCableNetworksHybridFiber-Coaxial(HFC)NetworkTopicsdiscussedinthissection:25Figure9.14TraditionalcableTVnetwork26CommunicationinthetraditionalcableTVnetworkisunidirectional.Note27Figure9.15Hybridfiber-coaxial(HFC)network28CommunicationinanHFCcableTVnetworkcanbebidirectional.Note299-5CABLETVFORDATATRANSFERCablecompaniesarenowcompetingwithtelephonecompaniesfortheresidentialcustomerwhowantshigh-speeddatatransfer.Inthissection,webrieflydiscussthistechnology.BandwidthSharing

CMandCMTSDataTransmissionSchemes:DOCSISTopicsdiscussedinthissection:30Figure9.16DivisionofcoaxialcablebandbyCATV31Downstreamdataaremodulatedusingthe64-QAMmodulationtechnique.Note32Thetheoreticaldownstreamdatarate

is30Mbps.Note33UpstreamdataaremodulatedusingtheQPSKmodulationtechnique.Note34Thetheoreticalupstreamdatarate

is12Mbps.Note35Figure9.17Cablemodem(CM)36經(jīng)常不斷地學(xué)習(xí),你就什么都知道。你知道得越多,你就越有力量StudyConstantly,And

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