通信及基础工程29

Unit4TextBFibertothexFibertothexFibertothex(FTTX[1])isagenerictermforanybroadbandnetworkarchitectureusingopticalfibertoprovideallorpartofthelocalloopusedforlastmiletelecommunications.Asfiberopticcablesareabletocarrymuchmoredatathancoppercables,especiallyoverlongdistances,coppertelephonenetworksbuiltinthe20thcenturyarebeingreplacedbyfiber.TextTextWordsNotesDiscussionHomeFTTXisageneralizationforseveralconfigurationsoffiberdeployment,arrangedintotwogroups:FTTP/FTTH/FTTB(Fiberlaidallthewaytothepremises/home/building)andFTTC/N(fiberlaidtothecabinet/node,withcopperwirescompletingtheconnection).TextTextWordsNotesDiscussionHome1.DefinitionsThetelecommunicationsindustrydifferentiatesbetweenseveraldistinctFTTXconfigurations.Thetermsinmostwidespreadusetodayare:• FTTP(fiber-to-the-premises):ThistermisusedeitherasablankettermforbothFTTHandFTTB,orwherethefibernetworkincludesbothhomesandsmallbusinesses.TextTextWordsNotesDiscussionHome• FTTH(fiber-to-the-home):Fiberreachestheboundaryofthelivingspace,suchasaboxontheoutsidewallofahome.Passiveopticalnetworksandpoint-to-pointEthernetarearchitecturesthatdelivertriple-playservicesoverFTTHnetworksdirectlyfromanoperator'scentraloffice.• FTTB(fiber-to-the-building,-business,or-basement):Fiberreachestheboundaryofthebuilding,suchasthebasementinamulti-dwellingunit,withthefinalconnectiontotheindividuallivingspacebeingmadeviaalternativemeans,similartothecurborpoletechnologies.TextTextWordsNotesDiscussionHome• FTTO(fiber-to-the-office):Fiberconnectionisinstalledfromthemaincomputerroom/coreswitchtoaspecialmini-switch(calledFTTOSwitch)locatedattheuser´sworkstationorservicepoints.Thismini-switchprovidesEthernetservicestoenduserdevicesviastandardtwistedpairpatchcords.Theswitchesarelocateddecentrallyalloverthebuilding,butmanagedfromonecentralpoint.• FTTN/FTTLA(fiber-to-the-node,-neighborhood,or-last-amplifier):Fiberisterminatedinastreetcabinet,possiblymilesawayfromthecustomerpremises,withthefinalconnectionsbeingcopper.FTTNisoftenaninterimsteptowardfullFTTH(fiber-to-the-home)andistypicallyusedtodeliver'advanced'triple-playtelecommunicationsservices.TextTextWordsNotesDiscussionHome• FTTC/FTTK(fiber-to-the-curb/kerb,-closet,or-cabinet):ThisisverysimilartoFTTN,butthestreetcabinetorpoleisclosertotheuser'spremises,typicallywithin1,000feet(300m),withinrangeforhigh-bandwidthcoppertechnologiessuchaswiredEthernetorIEEE[2]

1901powerlinenetworkingandwirelessWi-Fitechnology.FTTCisoccasionallyambiguouslycalledFTTP(fiber-to-the-pole),leadingtoconfusionwiththedistinctfiber-to-the-premisessystem.TextTextWordsNotesDiscussionHomeTopromoteconsistency,especiallywhencomparingFTTHpenetrationratesbetweencountries,thethreeFTTHCouncilsofEurope,NorthAmerica,andAsia-PacificagreedupondefinitionsforFTTHandFTTBin2006,withanupdatein2009,2011andanotherin2015.TheFTTHCouncilsdonothaveformaldefinitionsforFTTCandFTTN.TextTextWordsNotesDiscussionHomeTextTextWordsNotesDiscussionHomeAschematicillustratinghowFTTXarchitecturesvarywithregardtothedistancebetweentheopticalfiberandtheenduser.Thebuildingontheleftisthecentraloffice;thebuildingontherightisoneofthebuildingsservedbythecentraloffice.Dottedrectanglesrepresentseparatelivingorofficespaceswithinthesamebuilding.TextTextWordsNotesDiscussionHome2.BenefitWhilefiberopticcablescancarrydataathighspeedsoverlongdistances,coppercablesusedintraditionaltelephonelinesandADSLcannot.Forexample,thecommonformofgigabitEthernet(1Gbit/s)runsoverrelativelyeconomicalcategory5e,category6oraugmentedcategory6unshieldedtwisted-paircoppercablingbutonlyto100m(330ft).However,1Gbit/sEthernetoverfibercaneasilyreachtensofkilometers.Therefore,FTTPhasbeenselectedbyeverymajorcommunicationsproviderintheworldtocarrydataoverlong1Gbit/ssymmetricalconnectionsdirectlytoconsumerhomes.FTTPconfigurationsthatbringfiberdirectlyintothebuildingcanofferthehighestspeedssincetheremainingsegmentscanusestandardEthernetorcoaxialcable.GoogleFiberprovidesspeedof1Gbit/s.TextTextWordsNotesDiscussionHomeFiberisoftensaidtobe"future-proof"becausethedatarateoftheconnectionisusuallylimitedbytheterminalequipmentratherthanthefiber,permittingsubstantialspeedimprovementsbyequipmentupgradesbeforethefiberitselfmustbeupgraded.Still,thetypeandlengthofemployedfiberschosen,e.g.multimodevs.single-mode,arecriticalforapplicabilityforfutureconnectionsofover1Gbit/s.TextTextWordsNotesDiscussionHomeFTTC(wherefibertransitionstocopperinastreetcabinet)isgenerallytoofarfromtheusersforstandardEthernetconfigurationsoverexistingcoppercabling.Theygenerallyusevery-high-bit-ratedigitalsubscriberline(VDSL)atdownstreamratesof80Mbit/s,butthisfallsextremelyquicklyoveradistanceof100meters.TextTextWordsNotesDiscussionHome3.FibertothepremisesFibertothepremises(FTTP)isaformoffiber-opticcommunicationdelivery,inwhichanopticalfiberisruninanopticaldistributionnetworkfromthecentralofficeallthewaytothepremisesoccupiedbythesubscriber.Theterm"FTTP"hasbecomeambiguousandmayalsorefertoFTTCwherethefiberterminatesatautilitypolewithoutreachingthepremises.TextTextWordsNotesDiscussionHomeFibertothepremisescanbecategorizedaccordingtowheretheopticalfiberends:• FTTH(fiber-to-the-home)isaformoffiber-opticcommunicationdeliverythatreachesonelivingorworkingspace.Thefiberextendsfromthecentralofficetothesubscriber'slivingorworkingspace.Onceatthesubscriber'slivingorworkingspace,thesignalmaybeconveyedthroughoutthespaceusinganymeans,includingtwistedpair,coaxialcable,wireless,powerlinecommunication,oropticalfiber.TextTextWordsNotesDiscussionHome• FTTB(fiber-to-the-buildingor-basement)isaformoffiber-opticcommunicationdeliverythatnecessarilyappliesonlytothosepropertiesthatcontainmultiplelivingorworkingspaces.Theopticalfiberterminatesbeforeactuallyreachingthesubscriberslivingorworkingspaceitself,butdoesextendtothepropertycontainingthatlivingorworkingspace.Thesignalisconveyedthefinaldistanceusinganynon-opticalmeans,includingtwistedpair,coaxialcable,wireless,orpowerlinecommunication.TextTextWordsNotesDiscussionHomeAnapartmentbuildingmayprovideanexampleofthedistinctionbetweenFTTHandFTTB.Ifafiberisruntoapanelinsideeachsubscriber'sapartmentunit,itisFTTH.Ifinsteadthefibergoesonlyasfarastheapartmentbuilding'ssharedelectricalroom(eitheronlytothegroundfloorortoeachfloor),itisFTTB.TextTextWordsNotesDiscussionHome4.Fibertothecurb/cabinet/nodeFibertothecurb/cabinet(FTTC)isatelecommunicationssystembasedonfiber-opticcablesruntoaplatformthatservesseveralcustomers.Eachofthesecustomershasaconnectiontothisplatformviacoaxialcableortwistedpair.The"curb"isanabstractionandcanjustaseasilymeanapole-mounteddeviceorcommunicationsclosetorshed.Typicallyanysystemterminatingfiberwithin1,000ft(300m)ofthecustomerpremisesequipmentwouldbedescribedasFTTC.TextTextWordsNotesDiscussionHomeFibertothenodeorneighborhood(FTTN),sometimesidentifiedwithandsometimesdistinguishedfromfibertothecabinet(FTTC),isatelecommunicationarchitecturebasedonfiber-opticcablesruntoacabinetservinganeighborhood.Customerstypicallyconnecttothiscabinetusingtraditionalcoaxialcableortwistedpairwiring.Theareaservedbythecabinetisusuallylessthanonemileinradiusandcancontainseveralhundredcustomers.(Ifthecabinetservesanareaoflessthan1,000ft(300m)inradius,thearchitectureistypicallycalledFTTC/FTTK.)TextTextWordsNotesDiscussionHomeFTTNallowsdeliveryofbroadbandservicessuchashigh-speedinternet.High-speedcommunicationsprotocolssuchasbroadbandcableaccess(typicallyDOCSIS)orsomeformofdigitalsubscriberline(DSL)areusedbetweenthecabinetandthecustomers.Dataratesvaryaccordingtotheexactprotocolusedandaccordingtohowclosethecustomeristothecabinet.TextTextWordsNotesDiscussionHomeUnlikeFTTP,FTTNoftenusesexistingcoaxialortwisted-pairinfrastructuretoprovidelastmileserviceandisthuslesscostlytodeploy.Inthelongterm,however,itsbandwidthpotentialislimitedrelativetoimplementationsthatbringthefiberstillclosertothesubscriber.TextTextWordsNotesDiscussionHomeAvariantofthistechniqueforcabletelevisionprovidersisusedinahybridfiber-coaxial(HFC)system.ItissometimesgiventheacronymFTTLA(fiber-to-the-last-amplifier)whenitreplacesanalogamplifiersuptothelastonebeforethecustomer(orneighborhoodofcustomers).TextTextWordsNotesDiscussionHomeFTTCallowsdeliveryofbroadbandservicessuchashigh-speedinternet.Usuallyexistingwireisusedwithcommunicationsprotocolssuchasbroadbandcableaccess(typicallyDOCSIS)orsomeformofDSLconnectingthecurb/cabinetandthecustomers.Intheseprotocols,thedataratesvaryaccordingtotheexactprotocolusedandaccordingtohowclosethecustomeristothecabinet.TextTextWordsNotesDiscussionHomeWhereitisfeasibletorunnewcable,bothfiberandcopperEthernetarecapableofconnectingthe"curb"withafull100Mbit/sor1Gbit/sconnection.Evenusingrelativelycheapoutdoorcategory5copperoverthousandsoffeet,allEthernetprotocolsincludingpoweroverEthernet(PoE)aresupported.MostfixedwirelesstechnologiesrelyonPoE,includingMotorolaCanopy,whichhaslow-powerradioscapableofrunningona12VDCpowersupplyfedoverseveralhundredfeetofcable.TextTextWordsNotesDiscussionHomeWhereitisfeasibletorunnewcable,bothfiberandcopperEthernetarecapableofconnectingthe"curb"withafull100Mbit/sor1Gbit/sconnection.Evenusingrelativelycheapoutdoorcategory5copperoverthousandsoffeet,allEthernetprotocolsincludingpoweroverEthernet(PoE)aresupported.MostfixedwirelesstechnologiesrelyonPoE,includingMotorolaCanopy,whichhaslow-powerradioscapableofrunningona12VDCpowersupplyfedoverseveralhundredfeetofcable.TextTextWordsNotesDiscussionHomeByavoidingnewcableanditscostandliabilities,FTTCcostslesstodeploy.However,italsohashistoricallyhadlowerbandwidthpotentialthanFTTP.Inpractice,therelativeadvantageoffiberdependsonthebandwidthavailableforbackhaul,usage-basedbillingrestrictionsthatpreventfulluseoflast-milecapabilities,andcustomerpremisesequipmentandmaintenancerestrictions,andthecostofrunningfiberthatcanvarywidelywithgeographyandbuildingtype.TextTextWordsNotesDiscussionHomeHistorically,bothtelephoneandcablecompaniesavoidedhybridnetworksusingseveraldifferenttransportsfromtheirpointofpresenceintocustomerpremises.Theincreasedcompetitivecostpressure,availabilityofthreedifferentexistingwiresolutions,smartgriddeploymentrequirements(asinChattanooga),andbetterhybridnetworkingtools(withmajorvendorslikeAlcatel-LucentandQualcommAtheros,andWi-Fisolutionsforedgenetworks,IEEE1905andIEEE802.21protocols,andSNMP[3]improvements)allmakeFTTCdeploymentsmorelikelyinareasuneconomictoservewithFTTP/FTTH.TextTextWordsNotesDiscussionHomegenericadj.类的；一般的；非商标的widespreadadj.普遍的，广泛的；分布广的boundaryn.边界；范围；分界线curbn.&vt.抑制；路边；控制；勒住Ethernetn.

[计]以太网ambiguouslyadv.含糊不清地WordsWordsTextWordsNotesDiscussionHometerminatev.结束，终止；结果distinguishv.区别，区分；辨别deployn.&v.部署；配置；展开acronymn.首字母缩略词liabilityn.责任；可能性；不利因素backhauln.回程；载货反航WordsTextWordsNotesDiscussionHomebillvt.宣布；开账单；用海报宣传maintenancen.维护，维修；保持；生活费用uneconomicadj.不经济的；浪费的WordsTextWordsNotesDiscussionHome[1]FTTx是新一代的光纤用户接入网，用于连接电信运营商和终端用户。FTTx的网络可以是有源光纤网络，也可以是无源光网络。用于有源光纤网络的成本相对较高，实际上在用户接入网中应用很少，所以目前通常所指的FFTx网络应用的都是无源光纤网络。TextWordsNotesDiscussionNotesHome[2]IEEE（InstituteofElectricalandElectronicsEngineers）：电气和电子工程师协会是一个国际性的电子技术与信息科学工程师的协会，是目前全球最大的非营利性专业技术学会。IEEE致力于电气、电子、计算机工程和与科学有关的领域的开发和研究，在太空、计算机、电信、生物医学、电力及消费性电子产品等领域已制定了900多个行业标准，现已发展成为具有较大影响力的国际学术组织。TextWordsNotes