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1、PointtopointtechniquesThispapergivesabriefreviewoftypicalpointtopointtechniquesthatcanbeappliedinofferingopticalaccesstoresidentialbusinessusers.Someofthepresentedtechniquescanalsobeappliedaslocalareasolutionsi.e.tocarry
2、databeyondtheONUs.1PlesiochronousDigitalHierarchyPlesiochronousDigitalHierarchy(PDH)isanoldertechniquedevelopedfconventionalvoicetranspt.PDHisstillwidelyusede.g.inmobilewkstotransptdatabetweenthebasestationsbasestationco
3、ntrollers.ThePDHconcepthasahierarchicalstructurewithlineratesof64kbits2.048Mbits8.448Mbits34.368Mbits139.264MbitswhichareknownasE0E1E2E3E4respectively.ThestardPulseCodeModulation(PCM)techniqueisusedtodecodetheanaloguevoi
4、cesignaltodigitalfm.OnedigitalPCMcodedvoicechanneliscarriedinoneE0.2SynchronousDigitalHierarchySynchronousDigitalHierarchy(SDH)itsAmericancounterpartSynchronousOpticalwk(SO)arewidelyusedintransptwkswldwide.Althoughtheset
5、echniquesweredevelopedalreadyin1980.sitseemsthattheyarenotgoingtobereplacedfalongtime.Onereasonfthisistherecentenhancementsmadetothestardsanotherreasonisthelargeinvestmentmadeinthesetechniques.Fthesereasonsoperatsarenotw
6、illingtoreplacetheirSDHSOwkswithothersolutionsinashttimescale.SDHisahierarchicaltransptconceptwithlineratesof155.52Mbits622.082488.32Mbits9953.28MbitsnamedasSTM1STM4STM16STM64respectively.Eachlineratehasitsownframefmatth
7、eOAMfunctionalityisanintegralpartoftheframestructure.Irrespectiveofthelineratetransmissionofeachframelastsexactly125s.2.1NextgenerationSDHTheconventionalSDHisoptimisedftransptingvoicechannelswhichsetsquitedifferentrequir
8、ementsfthewkthandatatranspt.Ithasbeenpredictedthatenterpriseswillmovetopacketbasedvoiceservicesinafewyearsthenumberofconventionalvoiceserviceuserswilleventuallydecreaseclosetozero.Thetechniqueenablingthepacketbasedvoices
9、ervicesiscalledVoiceoverInterProtocol(VoIP)whichhasgainedalotofinterest.ThisimpliesthatinthefuturethelegacySDHcannotsupptthegrowingdataservicedem.Itisalsogoodtokeepinmindthatthelegacyserviceusersarenotgoingtovanishoverni
10、ght.ThenextgenerationSDHhasatransptmechanismwhichenablestheconcurrentexistenceofthelegacynewservicesoverthesamewkwithoutinterferingeachother.ThetechniquebehindthenextgenerationSDHiscommonlyknownastheDataoverSDH(DoS)conce
11、pt.DoSisatransptmechanismthatprovidesmeanstoaccommodatevariousdatainterfacesefficientlyintoSDH.Mostimptantlytheallocationofbwidthbetweentheseinterfacescanbedonewithoutdisturbingwk(WAN)services.Basicallytheseservicescanbe
12、classifiedintopointtopointmultipointtomultipointservices.DespitethecategisationsomescalabilityreliabilitychallengesarepresentintheallEthermetrowks[24][25]asgiveninthelistbelow.?Restrictionsonthenumberofcustomers.VirtualL
13、ocalArewkidentifier(VLANID)usedftrafficidentificationis12bitsthusrestrictsthecarrierto4096customers.?Servicemoniting.Etherdoesnothaveembeddedmechanismfservicemoniting.?ScalingtheL2backbone.Spanningtreeprotocoldoesnotscal
14、efbwidthbutblockssomenumberofptstopreventloopsinringtopologies.?Serviceprovisioning.VLANtagneedstobecarriedoverthewholewkwhichisnotaneasytaskresultsinimpossiblewkscaling.?Interwkingwithlegacydeployments.FrameRelayiswidel
15、ydeployedthereisaneedffunctionalityenablingEtherFrameRelayservicestowktogether.Pointtopointservice.ThisisalsoknownasEtherLineService(ELS)itcanbedividedintotwotypesofservice:EtherWireService(EWS)EtherRelayService(ERS).EWS
16、istheEtheranaloguetotheprivatelineprivatewireservice[24]whereasinglephysicalconnectionisestablishedbetweentwosites.Dependingontheusedtransptmethod(frameencapsulationnativeentitytranspt)differentfunctionalitycanbeprovided
17、betweentheendpoints.ERSistheEtheranaloguetoFRservice[24]wheremultiplepointtopointconnectionsareestablishedbetweentwosites.ThisrequiresthecodinationofEtherVLANIDsenablesservicemultiplexingbetweensites.AsaresultitoffersHub
18、SpokeenterpriseconnectivityaswellasInterServiceProvider(ISP)tocustomerconnectivity.Multipointtomultipointservice.ThisisalsoknownasEtherLANService(ELAN)itcanalsobedividedintotwocategies:EtherMultipointService(EMS)EtherRel
19、ayMultipointService(ERMS).EMSistheWANanaloguetothemultipointEtherLANcapability[24].UnicastframesaredeliveredusingstardselflearningfwardingcapabilitiesoftheEtherbridgesbroadcastframesarereplicatedtoallsites.FexampleEMSisa
20、goodwaytoconnectmultiplecampusestogether.ERMSisacombinationofEMSERSitenablessimultaneoususeofmultipointlayer2servicesInteraccessoverthesameUNI.ItisexploitedbyISPsthatareinterestedinofferingservicemultiplexedmultipointtom
21、ultipointservices.4OpticalTransptwkSDHcannotfullyexploitthepossibilitiesoftheWDMtechnique.ToeasethemanagementtasksintheWDMwksITUTstudygroup15hasdefinedasetofrecommendations(G.709.x)fopticaltranspt[26].Theseincludearchite
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