F新版CCNA培训教材ch15

15WANIntroductionCERTIFICATIONOBJECTIVES15.01WideAreaNetworkingOverview15.02HDLCp15.03PPP✓Two-MinuteDrillQ&ASelfTestCertPrs8/CCNACiscoCertifiedNetworkAssociateStudyGuide/Deal/222934-9/Chapter15BlindFolio15:1D:\omh\CertPrs8\934-9\ch15.vpMonday,August04,200312:15:12PMColorprofile:GenericCMYKprinterprofileCompositeDefaultscreenThelastfewchaptersintroducedyoutoconfiguringIPfeaturesonyourCiscorouter.Thischapterintroducesyoutowideareanetworking(WAN)conceptsandsomebasicpoint-to-pointconfigurations,includingHDLCandPPP.Thetwochaptersfollowingthis,FrameRelayandISDN,focusonpacket-switchedanddialupconnections,respectively.CERTIFICATIONOBJECTIVE15.01WideAreaNetworkingOverviewTypically,LANconnectionsarewithinacompanyandWANconnectionsallowyoutoconnecttoremotesites.Typically,youdon’towntheinfrastructureforWANconnections—anothercompany,suchasatelephonecompany,providestheinfrastructure.WANconnectionsareusuallyslowerthanLANconnections.AderivativeofWANsolutionsisthemetropolitanareanetwork(MAN).MANssometimesusehigh-speedLANconnectionsinasmallgeographicareabetweendifferentcompanies,ordivisionswithinacompany.MANsarebecomingmoreandmorepopularinlargecitiesandevenprovideconnectionsoveraLANmedium,suchasEthernet.OneofthemajorfactorswhenchoosingaWANorMANprovideriscost.Theseconnectionsarebilledinmultipleways:flatmonthlyleasecost,per-packetcost,per-minutecost,andmanyothermethods.Ontopofthis,youhavemanysolutionstochoosefromtosolveyourWANconnectionproblems.Inordertochoosetherightsolution,you’llneedtoweighyourconnectionrequirements,yourtrafficpatterns,andthecostofthesolution.EquipmentandComponentsWANconnectionsaremadeupofmanytypesofequipmentandcomponents.Figure15-1showssomeoftheseWANterms.Table15-1hasalistofthetermsanddefinitions.AsyoumayrecallfromChapter2,aDCEterminatesaconnectionbetweentwositesandprovidesclockingandsynchronizationforthatconnection;itconnectstoaDTE.TheDCEcategoryincludesequipmentsuchasCSU/DSUs,NT1s,andmodems.ADTEisanend-userdevice,2Chapter15:WANIntroductionCertPrs8/CCNACiscoCertifiedNetworkAssociateStudyGuide/Deal/222934-9/Chapter15ThemostimportantfactorinchoosingaWANserviceiscost.ItisimportanttoremembertheWANtermsinTable15-1.D:\omh\CertPrs8\934-9\ch15.vpMonday,August04,200312:15:12PMColorprofile:GenericCMYKprinterprofileCompositeDefaultscreensuchasarouterorPC,thatconnectstotheWANviatheDCEequipment.Insomecircumstances,thefunctionoftheDCEmightbebuiltintotheDTE’sphysicalinterface.Forinstance,certainCiscorouterscanbepurchasedwithbuilt-inNT1sorCSU/DSUsintheirWANinterfaces.WideAreaNetworkingOverview3CertPrs8/CCNACiscoCertifiedNetworkAssociateStudyGuide/Deal/222934-9/Chapter15FIGURE15-1WANtermsTermDefinitionCPE(customerpremisesequipment)Thisisyournetwork’sequipment,whichincludestheDCE(modem,NT1,CSU/DSU)andyourDTE(router,accessserver).DemarcationpointThisiswheretheresponsibilityofthecarrierispassedontoyou;thiscouldbeinsideoroutsideyourlocalfacility.Pleasenotethatthisisalogicalboundary,notnecessarilyaphysicalboundary.LocalloopThisistheconnectionfromthecarrier'sswitchingequipmenttothedemarcationpoint.CO(centraloffice)switchThisisthecarrier'sswitchwithinthetollnetwork.TollnetworkThisisthecarrier'sinternalinfrastructurefortransportingyourdata.TABLE15-1WANTermsandDefinitionsD:\omh\CertPrs8\934-9\ch15.vpMonday,August04,200312:15:14PMColorprofile:GenericCMYKprinterprofileCompositeDefaultscreenConnectionTypesAsmentionedatthebeginningofthissection,youhavetwomajorconcernswhenchoosingaWANsolution:costandthetypeofsolution.TherearemanyWANsolutionstochoosefrom,includingthefollowing:analogmodemsandISDNfordialupconnections,ATM,dedicatedpoint-to-pointleasedlines(dedicatedcircuits),DSL,FrameRelay,SMDS,wireless(includingcellular,lasermicrowave,radio,andsatellite),andX.25.Asyoucanseefromthislist,youhavealotofchoices.Notallofthesesolutionswillbeavailableineveryarea,andnoteverysolutionisidealforyourneeds.Therefore,oneofyourfirsttasksistohaveabasicunderstandingofsomeoftheseservices.Chapter1providedabriefoverviewofsomeoftheseservices.Thischaptercoverssomeoftheseservicesbriefly,andChapters16and17expandonsomeoftheothers.Typically,WANconnectionsfallunderoneoffourcategories:■Leasedlines,suchasdedicatedcircuitsorconnections■Circuit-switchedconnections,suchasanalogmodemanddigitalISDNdialupconnections■Packet-switchedconnections,suchasFrameRelayandX.25■Cell-switchedconnections,suchasATMandSMDSThefollowingthreesectionswillintroduceyoutothesethreeconnectiontypes.Leased-LineConnectionsAleased-lineconnectionisbasicallyadedicatedcircuitconnectionbetweentwosites.Itsimulatesasinglecableconnectionbetweenthelocalandremotesites.Leasedlinesarebestsuitedwhenbothoftheseconditionshold:■Thedistancebetweenthetwositesissmall,makingthemcost-effective.■Youhaveaconstantamountoftrafficbetweentwositesandneedtoguaranteebandwidthforcertainapplications.Eventhoughleasedlinescanprovideguaranteedbandwidthandminimaldelayforconnections,otheravailablesolutions,suchasATM,canprovidethesamefeatures.Themaindisadvantageofleasedlinesistheircost—theyarethemostexpensiveWANsolution.Leasedlinesusesync