《通信工程专业英语（第二版）》课件Unit 4

Unit4TextAFiveReasonsWhyFiberIstheWayoftheFutureFiveReasonsWhyFiberIstheWayoftheFutureWithallofthetalkaboutfiberfloatingaroundtheInternet,especiallyinrelationshiptoGoogle’sgigabitbroadbandservice,manymightbewonderingjustwhyfiberopticsaresoimportant.Thatiscertainlyafairenoughquestiontoponder,andthetruthisthatfiberopticshavemanyadvantagestooffercustomersandnetworkarchitectsalike.Beforecoveringtheseindividualbenefits,itmightbeworthtakingastepbackandlookingatthefundamentaldifferencesbetweentraditionalmetalwiresandfiberoptics.TextTextWordsNotesDiscussionHome1.MetalWiresOverHundredandFiftyYearsofDataTransmissionMetalwireshavebeensendingelectricalsignalsalmostaslongastheUnitedStateshasbeenanindependentnation,andthatissayingsomething.Thewiresoftodayarefarmoresophisticatedthanthoseofyesteryear,buttheystillworkinthesameway:electricityisappliedtooneendofthewiresandittravelstothefarendwhereitisreceivedasasignal.Alongtheway,thesignalstrengthdegradesastheenergyexperiencesatypeofelectricalfrictioncalledimpedance.Impedanceresultsinthesignaldecayingoverdistanceandthewirebecomingwarmer,whichcancausesomeproblemsthatwillbeoutlinedlater.TextTextWordsNotesDiscussionHome2.FiberOpticsThePowerofLightistheFuture.Fiberopticsusespecializedfibers

thatarecapableofcarryingtransmissionsmadeofpurelight.Justlikeelectricalwiring,adatatransmissionstartsatoneendofafiberopticcableandtransfersallthewaytotheendwhereitisreceivedanddecoded.TextTextWordsNotesDiscussionHomeBenefit1:LessSignalDegradation.Whilelightdoesdegradeoverdistance,thefactthatthesun’slightshinesbrightlyuponussaysonething:lighttravelsalotfurtherthantheconstantEMPwavesthesunemitsbecauselightdegradesmuchslowerthanelectricitydoes.Intermsofabroadbandserviceproviderandtheircustomers,thismeansthatmoreresidencesandbusinessescanbeserved.AnyonewhoremembersthedawnofDSLwillprobablyrecallthelimitationsthatwerecausedbythedistancesinvolved;ifonedidnotlivepracticallynextdoortoaDSL[1]networknode,theywereoutofluck.Thingsgotbetterovertime,butfiberopticshasthisproblemsolvedfromdayone.TextTextWordsNotesDiscussionHomeBenefit2:MoreUntappedOverhead.Metalwiresarealreadynearingtheirphysicalpotentialduetotheheatcausedbydatatransmissions.Toomuchloadonanysetofwireswillresultinthosewiresmeltingintoafineslagandbecominguseless,andthatisexactlywhathappenswhentoomuchisdemandedofoldwires.Fiberopticscarrylight,notelectricity,andlighthasanegligibleheatfootprintinmostcases.Thisisespeciallytrueoflightcreatedforfiberopticsystems,whichisfarlesspotentthantheUVlightemittedbythesun.TextTextWordsNotesDiscussionHomeBenefit3:EasierUpgrades.WhileDSLandcableserviceprovidershavebeenabletosystematicallyincreasetheperformanceoftheirnetworksovertime,theentireacthasbeenexpensive.Often,wholesegmentsofwiresneedtobedugupandreplacedbecauseoftheheatproblem.Fiberopticshavethecombinationofsubstantiallygreaterdistancebetweennetworknodesandsubstationsandmoreuntappedoverhead,whichmakesupgradeslessofahasslefornetworkcarriers.Thisinturnmeanslessfeesthathavetobepassedontotheconsumers.AgoodcaseinpointwouldbeVerizon’sFiOS[2]network,whichhasdramaticallyincreasedintermsofrawperformancesinceitspublicdebutinamannerthatDSLandcableserviceshavenot.TextTextWordsNotesDiscussionHomeBenefit4:FiberisGreen.Startingtothinkthatsendingdataviaelectricityovermetalwiresiswasteful?Ifso,thenyouwouldbecorrect;datasentovermetalwirestakesdozensoftimestheenergythatittakestosendalightsignal.Theadditionalsubstationsandnodesneededtokeepthatsignalstrongovergreaterdistancesonlyaddstothewoesofmetalwires,andmakesfiberopticslookthatmuchbetterbycomparison.Furthermore,upgradestonetworksarealotlesswastefulonthefiberopticsideofthefence.Whatdotelecomsandcableprovidersdowithallofthose‘old’networknodeswhentheyupgrade?Whoknows,butfiberopticshavefewersubstationsandnodestoreplaceandupgrade.Addtothisthefactthatthecablesvirtuallynevergobad,anditissimpletoseewhyfiberopticsareconsideredagreenalternativetometalwiresandelectricityinanyform.TextTextWordsNotesDiscussionHomeBenefit5:Psst…aSecret.BigDSLandCableserviceprovidersalreadyknowhowusefulfiberopticsare,andchancesaregoodthattheirnetworksusefiberopticstogetmuchclosertothehomesandbusinessesoftheirconsumersthantheywouldliketoleteveryoneknow.Inmanycases,thefiberopticnetworksofDSLand/orcableprovidersactuallygowithinamileorsoofmanyofthecustomerstheyserve.Why?Becausetheyknowthatfiberopticsarethemostcosteffectivesolution,andtheyknowthatbyputtingfiberclosetothehomesandbusinessesthattheyservethattheystandaverygoodchanceofmakingthetransitiontoanall-fibernetworkthatmucheasier.TextTextWordsNotesDiscussionHome3.Newformoflightdiscovered,maychangethefutureoffiberopticsPhysicistsinIrelandhaveturnedquantummechanicsonitshead.Theyhavediscoveredanewformoflightthatchallengestheverynatureofhowwehaveviewedandstudiedlightupuntilnow.Italsospellsbigthingsforthefutureoffiberopticsanddatacommunication.TextTextWordsNotesDiscussionHomeUntilnow,lighthasbeenseenasafixedconstant.Literally,yourabilitytoseelightisbasedonPlanck’sconstantandangularmomentum,anumberthatisamultiplebasedonPlanck’smathematicalequationwhichmeasuresabeamoflight.Now,thisteamatTrinityhavefoundanangularmomentumwhereabeamoflighttakesonlyhalfthevalueofPlanck’sconstant.Thatqualifiesitasanewformoflight.TextTextWordsNotesDiscussionHomeProfessorJohnDoneganisinterestedtofindouthowwecanusethisnewformoflightineverydaylife.Oneofthemostimmediateandimpactfulwayswillbeinfiberopticscommunication.Fiberopticsisthefoundationforcomputerdata.Bytransmittingflashesoflightthroughglassorplasticthreads,itisnowpossibletosendupto400Gbit/sofdatathroughasinglechannel.Withthisnewdiscovery,thatdatatransmissionratecouldgomuchhigher,andbemoresecure.TextTextWordsNotesDiscussionHomeNow,thisideathatangularmomentumwasn’tfixedhasbeenfloatingaroundforsometime.Thisteamfinallywasabletocreateatestenvironmenttoseeifthiscouldbeachieved.Todoso,theywentbacktothebasicsofthestudyoflightandtookapagefromphysicistHumphreyLloydandmathematicianWilliamRowanHamilton.Inthe1830s,theyobservedconicalrefraction.Utilizingcrystals,theysawhowarayoflightcouldbeformedintoasinglecone,orbeam.Planckdevisedthemathbehindit,asitrelatedphotos,andnowProf.JohnDonegan,AssistantProfessorPaulEastham,andtheirteamhavetakenittothenextlevel.TextTextWordsNotesDiscussionHomeThediscoveryisstillinitsinfancy,butalreadytheDirectorofCRANN,ProfessorStefanoSanvitoknowstheimportanceofthisfind,“thisdiscoveryisabreakthroughfortheworldofphysicsandsciencealike.”It’sjustamatteroftimebeforedatacommunicationcompaniescomeknockingonthedoorsofTrinityCollegeDublin[3],wantingtobringthisnewtechtotheforefrontofmasscommunications.ByMeredithPlackoTextTextWordsNotesDiscussionHomefibern.光纤opticsn.光学sophisticatedadj.复杂的；精致的；富有经验的degradevt.降低，贬低；使降级frictionn.摩擦；冲突，不和；摩擦力impedancen.阻抗，全电阻，电阻抗WordsWordsTextWordsNotesDiscussionHomedecayvi.衰退，衰败，衰落nearv.接近，临近slagn.矿渣；熔渣potentadj.有效的，强有力的；烈性的emitvt.发出；发射；颁布substantialadj.大量的；牢固的；重大的WordsTextWordsNotesDiscussionHomesubstationn.变电站，变电所untappedadj.未开发的，未利用的hasslen.困难的事情；麻烦的事情；争论noden.结点；（计算机网络的）节点spellv.导致；拼写；意味着angularadj.有角的；用角测量的，用弧度测量的WordsTextWordsNotesDiscussionHomemomentumn.[物]动量；势头；动力；要素impactfuladj.有效的，有力的conicaladj.圆锥（形）的refractionn.折射（程度）；折射角conen.圆锥体，锥形物；（松树的）球果WordsTextWordsNotesDiscussionHome[1]DSL的中文名是数字用户线路，是以电话线为传输介质的传输技术组合。DSL技术在传递公用电话网络的用户环路上支持对称和非对称传输模式，解决了经常发生在网络服务供应商和最终用户间的“最后一公里”的传输瓶颈问题。TextWordsNotesDiscussionNotesHome[2]Verizon公司是由美国两家原地区贝尔运营公司——大西洋贝尔和Nynex合并建立BellAtlantic后，独立电话公司GTE合并而成的，公司正式合并后，Verizon一举成为美国最大的本地电话公司、最大的无线通信公司，全世界最大的印刷黄页和在线黄页信息的提供商。FiOS（FiberOpticService）就是Verizon所提供的采用光纤电缆传输数据的数据通信服务。TextWordsNotesDiscussionHome[3]TrinityCollegeDublin都柏林圣三一学院，全称为：CollegeoftheHolyandUndividedTrinityofQueenElizabethnearDublin（伊丽莎白女王在都柏林附近神圣不可分割的三一学院）位于爱尔兰首都都柏林，是1592年英国女王伊丽莎白一世下令为“教化”爱尔兰而参照牛津、剑桥大学模式而兴建。TextWordsNotesDiscussionHomeQuestionsfordiscussion1.Whyaremetalwiresinferiortofiberoptics?2.Whyarefiberoptics,comparedwithmetalwires,mucheasiertoupgrade?3.WhydothoseofferfiberopticnetworksofDSLtendtohavetheirfiberclosetothehomesoftheircustomersaspossibleastheycan?4.WhatdoyouthinkofthediscoverymadebytheteamatTrinity?

TextWordsNotesDiscussionHomeAnswerstoquestionsfordiscussionTextWordsNotesDiscussionHome1.Whyaremetalwiresinferiortofiberoptics?Whileelectricitytravelsfromoneendtothefarend,thesignalstrengthdegradesastheenergyexperiencesatypeofelectricalfrictioncalledimpedance,whichresultsinthesignaldecayingoverdistanceandthewirebecomingwarmer,whichcancausesomeproblems.Ontheotherhand,fiberopticsarecharacterizedbylesssignaldegradation,moreuntappedoverheadandeasierupgrades.TextWordsNotesDiscussionHome2.Whyarefiberoptics,comparedwithmetalwires,mucheasiertoupgrade?Fiberopticshavethecombinationofsubstantiallygreaterdistancebetweennetworknodesandsubstationsandmoreuntappedoverhead,makingupgradeslessofahasslefornetworkcarriers,which,inturn,meanslessfeesthathavetobepassedontotheconsumers.TextWordsNotesDiscussionHome3.WhydothoseofferfiberopticnetworksofDSLtendtohavetheirfiberclosetothehomesoftheircustomersaspossibleastheycan?Becausetheyknowthatfiberopticsarethemostcosteffectivesolution,andtheyknowthatbyputtingfiberclosetothehomesandbusinessesthattheyservethattheystandaverygoodchanceofmakingthetransitiontoanall-fibernetworkthatmucheasier.TextWordsNotesDiscussionHome4.WhatdoyouthinkofthediscoverymadebytheteamatTrinity?Inspiteofthefactthatthisdiscoveryisstillinitsinfancy,it,inasense,isabreakthroughfortheworldofphysicsandsciencealike.It’sjustamatteroftimebeforedatacommunicationcompaniescomeknockingonthedoorsofTrinityCollegeDublin,wantingtobringthisnewtechtotheforefrontofmasscommunications.TextWordsNotesDiscussionHomeThankyou!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-LucentandQ