Networkaccessequipment
Modem
Theso-calledmodulationistheconversionofdigitalsignalsintoanalogsignalstransmittedonthetelephoneline;demodulationistheconversionofanalogsignalsIntoadigitalsignal.Collectivelyreferredtoasamodem.
Theroleofthemodemisthe"interpreter"ofanaloganddigitalsignals.Therearetwotypesofelectronicsignals,oneis"analogsignal"andtheotheris"digitalsignal".Thetelephonelineusedtransmitsanalogsignals,whilethedigitalsignalsaretransmittedbetweencomputers.SowhenyouwanttoconnectyourcomputertotheInternetthroughatelephoneline,youmustuseamodemto"translate"thetwodifferentsignals.AfterconnectingtotheInternet,whenthePCsendsinformationtotheInternet,becausethetelephonelinetransmitsananalogsignal,amodemmustbeusedto"translate"thedigitalsignalintoananalogsignalbeforeitcanbetransmittedtotheInternet.Thisprocessiscalled"modulation"".WhenthePCobtainsinformationfromtheInternet,sincetheinformationtransmittedfromtheInternetthroughthetelephonelineisallanalogsignals,thePCmustalsousethemodem"translation"tounderstandthem.Thisprocessiscalled"demodulation"..Ingeneral,itiscalled"modulationanddemodulation."
Switch
Inacomputernetworksystem,aswitchisanetworkdevicebasedonMACaddressrecognitionandcapableofencapsulatingandforwardingdataframes.TheEthernetswitchissimilartoadedicatedcomputer.Itconsistsofacentralprocessingunit(CPU),randomaccessmemory(RAM)andinterfaces.ItworksonthesecondlayeroftheOSImodelandisusedtoconnectworkstations,servers,routers,hubs,andOtherswitches.Itsmainfunctionistoquicklyexchangeandaccuratelyforwarddataframes.
Switchescanbedividedintotwo-tierswitchesandthree-tierswitches.Inthelocalareanetworkaccess,thetwo-layerswitchismainlyused.Usedtoconstructthemainconnectionpartofthelocalareanetwork.
Router
RouterisadevicethatconnectstovariouslocalareanetworksandwideareanetworksintheInternet.Itwillautomaticallyselectandsetroutingaccordingtothechannelconditions,andusethebestpath.Sendsignalsinsequence.TherouteristhehuboftheInternet,the"trafficpolice".Routershavebeenwidelyusedinallwalksoflife,andvariousproductsofdifferentgradeshavebecomethemainforceinrealizingvariousbackbonenetworkinternalconnections,backbonenetworkinterconnections,andbackbonenetworkandInternetinterconnectionservices.ThemaindifferencebetweenroutingandswitchesisthatswitchesoccuratthesecondlayeroftheOSIreferencemodel(datalinklayer),whileroutingoccursatthethirdlayer,thenetworklayer.Thisdifferencedeterminesthattheroutingandtheswitchneedtousedifferentcontrolinformationintheprocessofmovinginformation,sothetwowaystoachievetheirrespectivefunctionsaredifferent.
Therouterhastwotypicalfunctions,namelythedatachannelfunctionandthecontrolfunction.Datachannelfunctionsincludeforwardingdecision,backplaneforwardingandoutputlinkscheduling,etc.,whicharegenerallycompletedbyspecifichardware;controlfunctionsaregenerallyimplementedbysoftware,includinginformationexchangewithneighboringrouters,systemconfiguration,systemmanagement,etc..
AmongthemanywaysofaccessingtheLANtotheWAN,accessingtheInternetthrougharouteristhemostcommonway.ThebiggestadvantageofusingrouterstointerconnectthenetworkisthateachInternetsubnetremainsindependent,andeachsubnetcanusedifferenttopologies,transmissionmedia,andnetworkprotocols.Thenetworkstructureishierarchical,andsomeroutershaveVLANmanagementfunctions.ConnectingtotheInternetthrougharoutercancompletelyshieldthecompany'sinternalnetworkandactasafirewall.Therefore,usingaroutertoaccesstheInternetcanalsoensurethesecurityoftheinternalnetwork.
Broadbandaccessequipment
Broadbandnetwork
Theso-calledbroadbandnetworkreferstodigitalcommunicationswithahigherdatatransmissionrate.Generally,theupperlimitofdial-upInternetaccessrateis56Kb/s.Networkswithdatatransmissionrateslessthan56Kb/sarecallednarrowbandnetworks,andnetworkswithdatatransmissionratesgreaterthan56Kb/sarecalledbandwidthnetworks.MainlyuseDSLtechnologytoaccessbroadbandnetworkbywire.
DSL
Digitalsubscriberlinesusetelephonelinesasthetransmissionmediumandcantransmitdataandvoicesignalsonthesametwistedpairline.Afrequencybandoutsidethefrequencyrangeofthevoicesignalisusedfortransmission.However,traditionalmodemsusefrequenciesthathumanearscandistinguishtotransmitdata,sothetransmissionrateisrelativelylow.
DSLtechnologyismainlydividedintosymmetricalandasymmetricaltwotypes,whethersymmetricalornotdependsonwhetherthetransmissionrateofupstreamdataanddownstreamdataarethesame.AmongvariousDSLtechnologies,AsymmetricDigitalSubscriberLoop(ADSL)technologyisthemostpopular.ADSLcanprovideuserswithanuplinkdatarateof1Mb/sandadownlinkdatarateof8Mb/s,withatransmissiondistanceof3~5km.
ADSL
(1)ADSLmodem
TheADSLmodemhasanRJ-45interfaceandanRJ-11interface,whichcanmodulateanddecodeuserdataTuneandprovidedatatransmissioninterface.
(2)ADSLsplitter
ThefunctionoftheADSLsplitteristoseparatetheaudiosignalandhigh-frequencydigitalmodulationsignalontheline,andsendtheaudiosignaltothetelephoneexchange.ThedigitalsignalissenttotheADSLmodem.Therefore,theADSLsplitterhasoneRJ-11interfaceatoneend,andtwoRJ-11interfacesattheotherend,andthetwoRJ-11interfacesoutputhigh-frequencysignalsandlow-frequencysignalsrespectively.
XDSLR
xDSLisageneraltermforvarioustypes,includingADSL,RADSL,VDSL,SDSL,IDSL,HDSL.