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13/10/2015 3.CreatingthetopologyWDMtheTransmodewayWDMtheTransmodeway(html)TechnologiesTransmode
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TechnologiesTechnologiesOverview
WDMCWDM
DWDM
iWDM
FlexibleOpticalNetworksROADM
NativePacketOptical2.0CarrierEthernet2.0
MPLSTP
SoftwareDefinedNetworking
100G
iAccessiWDMPONAccessNetworks
iSync
LowPowerDesign
HighDensityDesign
WDMtheTransmodewayIntroductionandContent
1.Opticsandcommunications
2.WDMnetworkingtechnologies
3.Creatingthetopology
4.Addingtraffic
5.Operatingthenetwork
Summary
Index
3.Creatingthetopology3.1Executivesummaryofchapter3Usingthetransmissionandmultiplexingtechnologiesdescribedinchapter2,endtoendlightpathspassingmultipleintermediatenodescanbecreated.Thelightpathsactasopticalcircuitsthatareroutedthroughthenetworkpermanentlyorsetupbydemand.Inchapter3thefocusisontheselightpaths:
UsingWDMwavelengthstocreateacompleteopticaltransportnetwork.Routingofwavelengthsbetweennetworknodesusingadddropmultiplexers(OADMandROADM)andwhytherearemultipletypesofROADMs.WDMintheaccessnetwork.HowWDMlightpathscanbeconfiguredtoprotectthetransportnetworkandmakeitmoreresilient.
3.2TransportnetworksintelecomTheequipmentandfibershandlingthephysicaltransportofsignalsinthetelecommunicationsnetworkareoftenreferredtoasthetransportnetwork.Howshouldsuchanetworkbedesignedandoperated?Therearedifferentwaystosolvethistask.
Whetheranationwideormetropolitannetworkisbeingconstructed,thenetworkdesignermustconsidertwodifferentaspectsofnetworklifeitsplannedexpansionovertimeanditsdaytodayoperations.
PLANNEDEXPANSIONTHELONGERTERMPERSPECTIVEPlanningofthenetworkisalongertermactivitytypicalperformedofflineinanofficeenvironment.Whenplanningthetransportnetwork,factorssuchastheseareimportant:
Locationofnodesbasedonsiteavailabilityandcost.Availabilityandcostoffiberssinglefiber,fiberpairs,owncables,leaseddarkfiber.Customer/userlocations,typesoftraffic,capacityneedsnowandinthefuture.Futureexpansionofthenetworktopologyandcapacity.Needofredundantlinksandequipmentforprotectionagainstfaults.
OPERATIONSTHESHORTERTERMPERSPECTIVETheoperationalperspectivecoversthedaytodayoperationsofthenetwork.Thesetasksareperformedindirectcontactwiththeopticalnetwork,typicallyfromanetworkmanagementcenter(NMC).Examplesofoperationaltasksthatinfluencethenetworkdesignandputrequirementsontheflexibilityofthenetworkare:
Proceduresforconnectinguserstothenetwork.Proceduresforexpandingthenetworkandaddingmorelinks.Manualorautomaticproceduresforprotectionswitching,i.e.thereroutingoftrafficonalternativelinksincaseofanodefailureorlinkoutage.
Boththelongerandshortertermactivitiesrequireasetofflexibleandmanageablenetworkelementsthatcanformthetransportnetwork:TheseelementsaretheTMSeries.
3.3WDMasthetransportnetworkTheTMSeriesisafourthgenerationopticalnetworkingsystemthatcombinesthemostadvancedopticaltransmissiontechnologieswiththeswitchingoflightpathsandthepacketizationofinformationintoamultifunctionalpacketopticaltransportnetwork.Itsprincipalelementsarethetranspondersandmuxpondersthatallowtraffictoenterandleavetheopticalnetworkandtheopticalfilters,multiplexers/demultiplexersandreconfigurableopticaladddropmultiplexersthatmultiplexandsendwavelengthsoflightindifferentdirectionsasdirectedbythecontrollingmanagementsystem.(Figure28)
Figure28.AtypicalWDMopticalnetworkcoveringaccesstolonghaul.
Anopticalnetworkprovidescircuitswitchedendtoendopticalchannelsorlightpathsbetweennetworknodesandtheirusers,theclients.Alightpathismadeupofawavelengthbetweentwonetworknodesthatcanberoutedthroughmultipleintermediatenodes.Theintermediatenodesdirectthewavelengths.Theopticalnetworkmaythusbethoughtofasawavelengthroutingnetwork.Lightpathsaresetupandtakendownasrequiredbytheusersofthenetwork.
ItisimportanttorememberthatthelightpathsinaWDMnetworkareendtoendconnections,andshouldbeconsideredastheequivalentsofuninterruptedwires,stretchingfromonepointinthenetworktoanotherwhilepassingoneorseveralnodes.ThisisasignificantdifferencefromtheprinciplesofclassicalTDMopticaltransportnetworks,suchasSDHandSONET,wherethesignalsareregeneratedateachnodetheequivalentuninterruptedwirestretchesonlybetweentwonodes.Hence,aWDMnetworkrequirescarefulwavelengthplanning,todefinewhereeachwavelength(wire)startsandends,whileanSDH/SONETnetworkmakesallsignalsavailableineverynodepassed.Theendtoendaspectalsoaffectshowthepowerbudget(i.e.signalattenuation)iscalculated:InaWDMnetwork,theopticaltransmissioncharacteristicsforawavelengthhastobecalculatedforthecompletedistancethelightpathtraverses;forSDH/SONETanewpowerbudgetiscalculatedforeachhopbetweentwoadjacentnodes.(Figure29)
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Figure29.ComparisonbetweenanSDH/SONETandaWDMnode.IntheSDH/SONETnode(left)alltrafficsignalsareregeneratedandswitched,makingthemavailableforaddanddrop.IntheWDMnode(right)onlyselectedsignals(wavelengths)areavailableforaddanddrop,therestareglassedthrough.
Thelightpathsoftheopticalnetworkhaveseveralimportantcharacteristics:
Theyaretransparent,i.e.theycancarrydataatvariousrates,withdifferentprotocolsetc.Thisenablestheopticallayertosupportavarietyofhigherlayerprotocolsconcurrently.Wavelengthanddatarateusedaresetbytheterminatingnodes.Henceanindividuallightpathmaybeupgradedtohighercapacitybysimplychangingtrafficunitsinthestartandendnodes,withoutaffectinganyequipmentinintermediatenodes.ThisisafundamentaldifferencetoSDH/SONETaswellasnetworksofinterconnectedEthernetswitches.Lightpathscanbesetupandtakendownondemand,equivalenttotheestablishmentofcircuitsinacircuitswitchednetwork.Alternativelightpathscanbeconfiguredandkeptinstandbymodesothatintheeventofafailure,trafficmaybereroutedandtheservicemaintained.Wavelengthscanbereused.Ifalightpathusingaparticularwavelengthendsinonenode,thesamewavelengthcanbereusedinanotherlightpathheadinginanotherdirection.ThewholeconceptofWDMandlightpathsisbasedonanalogopticaltransmissiontechniques,makingparameterssuchasdispersion,signalattenuation,opticalsignaltonoiseratioandinterferenceoverthewholelengthofthepathimportanttocontrol.
3.4NodesandnetworkelementsThelightpathsoftheopticalnetworkpassnodesofdifferenttypes,eachcomprisingoneormoremanagednetworkelements.Theprincipalnodesoftheopticalnetworkfromatopologyperspectivearetheterminalmultiplexer,theopticaladd/dropmultiplexer(OADM)andthereconfigurableopticaladd/dropmultiplexer(ROADM).Thesenodesallow
lightpathstoentertheopticalnetworkandtoberoutedtoanydesiredpointofexit.9
3.4.1TheterminalmultiplexerClientsoftheWDMopticalnetworkareinterfacedtothenetworkviatranspondersandmuxponders.Theprincipaldifferenceisthatatransponderisasignal/wavelengthconverter(onesignalinandonesignalout),whilethemuxponderhascircuitrythatcombinesseveralclientsignalsintoonelinesignalandviceversa.Thetransponder/muxponderandanassociatedmultiplexer/demultiplexerareoftenreferredtoasaterminalmultiplexer
(terminalmux)orterminalnode.10
9Theopticalcrossconnect(OXC)issometimesalsoreferredtoasaprincipalnodeofanopticalnetwork.However,inmostcasesthesamefunctionalitycanbeachievedwithcombinationsofROADMunits;hencetheOXCisnotdescribedhere.10Theterminalmultiplexerissometimescalledanopticallineterminal(OLT),especiallyinresidentialbroadband
accessnetworkapplications.
Thetransponder/muxponderisanopticalelectricalopticalunitthatadaptstheincomingsignaltoaformatforuseinsidetheopticalnetwork.Theincomingwavelengthmayneedtobeconverted.Overheadfornetworkmanagement,forwarderrorcorrectionandotherpurposesmustbeadded.Biterrorscountedandstatisticsforwardedtothemanagementsystem.Andinthecaseofthemuxponder,severalbitstreamsaretimedivisionmultiplexedintoahigherratebitstream.Thenextchapterdescribesthefunctionsofthetranspondersandmuxpondersinmoredetail.(Figure30and31)
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Figure30.Blockdiagramofaterminalmultiplexerwithatransponderandamuxponder.
Figure31.ATMSeriesterminalmultiplexercombining2.5Gbit/sand10Gbit/sdataratesonCWDMandcomprisingtwomuxponders,atransponderandaCWDMmultiplexer/demultiplexer.Allunitsarehousedinonesinglechassis.
3.4.2Theopticaladd/dropmultiplexer(OADM,ROADM)ThelightpaththathasenteredtheopticalWDMnetworkviaaterminalmultiplexermustberoutedtoitsdestinationviaintermediatenodesthatcandirectthewavelengthtowardsthedesiredpointofexit.Thetaskofroutingthelightpathsisperformedbytheopticaladd/dropmultiplexer(OADM)andthereconfigurableopticaladd/dropmultiplexer(ROADM).(Figure32)
Figure32.AnationalopticaltransportnetworkcomprisingmultipleOADMandROADMnodesthatroutelightpathsbetweenvariousclientsofthenetwork.
Consider,forexample,thesituationdepictedinthefollowingdiagram.Afiberringspansametroarea,withtrafficoriginatingandleavingtheringat10locations,wherelocationsHUBAandHUBBareactingascentralhubsforthetraffic.(Figure33)
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Figure33.Anexampleofametropolitanfiberringwithprotection(trafficissentintwodirections)andadd/dropofDWDMwavelengths.Thisisalsoanexampleofhowthesamewavelengthmaybereusedondifferentsegmentsofthering.
Sucharingtopologyrequiresanopticalelementthatcanremoveandaddwavelengthsfromtheringatdemandandforwardthemtowardstheclientfacingequipmentitrequiresanadd/dropmultiplexer.Severalapproachescanbeusedwhenimplementinganadd/dropmultiplexer,andtheTMSeriescomprisesopticalfilters,bandsplitterunits,mux/demuxesandcompleteROADMsforthispurpose.
3.4.2.1TheopticalfilterasOADMAfullypassiveopticalfiltercanbeusedinCWDMandDWDMnetworkstoadd/droponeormorewavelengths.Themainadvantageoftheopticalfilterapproachisitssimplicityanddirectscalabilityonlywhenmorechannelsaretobedropped,morefiltersneedtobeinstalled.Themaindisadvantageistheattenuationthatisintroducedateachfilterpointandtheplanningrequiredinassigningwavelengthstothedesiredlightpaths.(Figure3435)
Figure34.Principleofapassive,filterbased,opticaladd/dropmultiplexer.Onewavelength(1)ispassedthroughtheOADM,andanotherwavelength(2)isdropped.Newsignalsarethenaddedwhenthewavelengthiscontinued.
Figure35.TheopticalfilterusedasanOADM
3.4.2.2Themux/demuxasOADMAnalternativeapproachforaddinganddroppingchannelsatanintermediatesiteistodemultiplexallthelinewavelengthsandextract/addthedesiredchannels,whilelettingtherestofthewavelengthspassthrough.(Figure36)
Figure36.Add/dropofawavelengthsusingapairofmux/demux.
Thisapproachismoreefficientthanfiltersifmanychannelsaretobedroppedatonelocation.Sinceallwavelengthsarecateredforfromthebeginningandthemux/demuxhasafixedattenuation,thisapproachalsobecomesmoreflexibleandrequireslessadvanceplanningthanwithopticalfiltersinseries.However,theamountofequipmentneededandthusthecostishigherthanforafiltersolution.Also,theamountofpatchcordsforinterconnectingthewavelengthstobepassedthroughaddstothecomplexityandcancreatehandlingproblems.
FortheTMSeriesadd/dropwithopticalmux/demuxcanbeusedonbothsinglefiberandfiberconfigurationswithCWDMandonfiberpairconfigurationswithDWDM.
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CWDMandonfiberpairconfigurationswithDWDM.
Whenlargernumbersofchannelsaretobedroppedtheaboveprinciplecanbeextendedbyuseofabandsplitterunit,whichextracts/insertsawholebandofwavelengthsfordemultiplexingbyamux/demuxasshowninthefollowingdiagram.(Figure37)
Figure37.OADMina40channelDWDMsystem.8channelsareadded/droppedasabandbythebandsplitterunitandmadeindividuallyavailableviatwomux/demuxes.Theremaining32channelsarepassedthroughthebandsplitterunittransparently.
3.4.3TheROADMInasmallandstaticopticalnetwork,OADMnodesoftheabovetypesmaybethebestsolution.However,inlargernetworks,thefrequentestablishmentandreassignmentoflightpathsmakeremotereconfigurabilityaverydesirableattributeinanOADM.Reconfigurabilityreferstotheabilitytoselectthedesiredwavelengthstobedroppedandaddedonthefly,asopposedtohavingtoplanaheadanddeployappropriateequipment.Reconfigurabilityallowslightpathstobesetupandtakendowndynamicallyasneededbetweennetworknodesandisthetaskofthereconfigurableopticaladd/dropmultiplexer,theROADM.(Figure38)
Figure38.Theaddingofnewlightpathswithredandbluewavelengthsrequireschangesinnodeconfigurations.
ROADMsareusedinbusandringnetworkstoenableflexibleadd/dropofwavelengthsandhitlessexpansionwherewavelengthscanbeaddedwithoutinterruptionsoftrafficonadjacentchannels.Whenusedinameshedopticalnetwork,ROADMscanprovidetotalflexibilityintheroutingoflightpaths.TheflexibilityofROADMsthusbenefitstheoperatorwantingtoadapttochangingsubscriberrequirements,aswellasincreasingnetworkavailabilitybysimplifyingprotectionswitchingandrestorationoflightpaths.Itcanevenbeusedforsettinguplightpathsdynamicallyondemandinspecialapplications,forexampleifthereisamajormediaeventatasiterequiringbandwidthjustforafewhours.(Figure39)
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Figure39.Exampleofameshedopticalnetwork.WithmultidegreeROADMnodesinthenodesthelightpathscanbedirectedtoanydestination,providingmaximumflexibilityforthenetworkoperatorandsuperiorresiliencetolinkoutages.
AROADMbasednetworkdecreasestheoperatorstimetorevenuesinceservicescanbeprovidedrapidlywhenlightpathsaresetupremotelywithouttheneedofdispatchingtechnicianstonetworknodes.CommissioningandoperationoftheentirenetworkbecomessimplifiedandthecentralizedmanagementofROADMnodesenablesmoreautomation,reducingtheriskformanualerrors.
ROADMnodesalsohavesignificantadvantagesfromanetworkplanningperspective.FreewavelengthallocationwithROADMnodessimplifiesnetworkplanningandreducestheeffectsofinaccuratetrafficforecasting.ROADMnodessimplifytrafficengineeringandoptimizationofnetworkuse.Theyallowforbetterwavelengthutilizationsincewavelengthsaremanagedseparatelyratherthanincompletebands.TheTMSeriesROADMunitsalsoincludeintegratedvariableopticalattenuators(VOAs)foreachwavelength,whichgreatlysimplifiespowerbalancingofthelightpaths.
3.4.3.1ROADMprinciplesROADMunitscanbedesignedaroundmux/demuxesandopticalswitches,butthemostcommonarchitecturetodaymakesuseofa1xNwavelengthselectiveswitch(WSS)thatindividuallycanswitchthewavelengthsonitsinputstoitsoutput.(Ndenotesthenumberofinputstotheswitch.)TheTMSeriesROADMunitshaveaWSSontheaddside,i.ewhereaddedsignalsarecombinedwiththelinesignal.Thisarrangementgivesfullcontrolofallsignallevelsonaddedandpassedchannels,aprerequisiteforsecurenetworkoperationswithoutanytransmissionlevelproblems.
RecenttechnologydevelopmentshavemadeWSSbasedROADMunitsaffordable,notonlyinlonghaulnetworks,butalsointhemetronetworks.HavingthecapabilitytodeployROADMnodesinmetroapplicationsisofsignificantvaluesinceconfigurationchangesarenormallyquitefrequentinmetroandmetroaccess.HencetheTMSeriesROADMnodesareanoptimalchoicewhenimplementingaregional,metroormetroaccessopticalnetwork.(Figure40)
Figure40.ThemainelementsoftheTMSeries1x2ROADMpluginunit.
Asshowninthefigureabove,theincomingwavelengthsfromwestareallsplitviaanopticalcouplerandmadeindividuallyavailablelocallyviaademuxwhenusingtheTMSeries1x2ROADMpluginunit.Localwavelengthstobeaddedaremultiplexedandaddedtotheincomingsignalfromeastinthe2x1WSS.EachoftheincomingWSSportsissettoacceptoneorseveralwavelengths,theonlylimitationbeingthatnotwowavelengthsoverlap,i.e.arethesame.Thus,theWSScanforeachwavelengthdecideifitshouldbetakenfromlineeastorbelocallyadded.
TheROADMunitinthediagramabovehasfiberlinksintwodirections,asforexampleinaringtopology.Thenumberoffiberlinkdirectionsto/fromaROADM(oranyotheropticalnetworknode)isoftenreferredtoasthedegreeoftheROADM.Inmeshnetworksandinterconnectedringtopologiestherearenodesthathaveahigherdegree,forexample3or4,referredtoasmultidegreeROADMnodes.
Ifwewanttocreateacomplete2degreeROADMnodewhereanywavelengthcanbeaddedordroppedinboththewestandeastdirections,twoofthejustdescribed1x2ROADMpluginunitsarecombinedbacktoback.(Figure
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westandeastdirections,twoofthejustdescribed1x2ROADMpluginunitsarecombinedbacktoback.(Figure41)
Figure41.Acomplete2degreeROADMnode.
3.4.3.2ColorlessROADMFurtherflexibilitycanbeaddedtotheROADMbymakingthemux/demuxunitswavelengthindependent,i.e.makingitpossibletoaddordropanyatanyoftheirports,creatingacolorlessROADMnode.(Figure42)
Figure42.Acolorless2degreeROADMnode.
Whencombinedwithtunabletransceiversintheattachedtransponders/muxponders,theoperatorcannowchangethewavelengthforaservicewithoutmovingthetransponder/muxpondertoanewportonthemux/demux.FortheTMSeriesROADMnodes,suchwavelengthreconfigurationscanbemadecompletelyremotelyfromtheTransmodeNetworkManager(TNM)systemwithouttheneedtovisitthesite.(Figure43)
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Figure43.ManagementofwavelengthswiththeTransmodeNetworkManager(TNM).
AfurtheradvantageoftheTMseriesROADMunitsisthattheyareallimplementedaspluginunitswhichmaybelocatedinanyoftheavailablechassis.Thismeansthatanynode,largeorsmall,easilycanbeupgradedwithROADMfunctionalitywhenthenetworkgrows.
3.4.3.3DirectionlessROADMIntheROADMnodeconfigurationsinthepreviouschapters,aparticularaddedisphysicallydeterminedtogoeitherintheeastorwestdirection,dependingonwhichofthetwomuxesthetransponder/muxponderisconnectedto.Thiscanbeadisadvantage,forexampleinprotectiveswitchingandmaymeanawasteofavailablewavelengths.Byaddingonemore1x2ROADM,itispossibletocreateadirectionlessROADMnodewheretrafficfromanyaddedportcanbesentineithereastorwestdirections.(Figure44)
Figure44.Adirectionless2degreeROADMnode.
3.4.3.4HigherdegreeROADMnodesUsing4x1and8x1WSSunitsitispossibletodesignROADMnodesformeshednetworks,withnodesofhigherdegreethantwoandwithmorethantwoincomingandoutgoingfiberdirections.TheTMSeriescomprisesone1x4ROADMunitfor40channelDWDMsystemsandtwo1x8ROADMunitsfor40or80channelDWDMsystems,allsuitablefortheseapplications.
The4or8addportsuseawavelengthselectiveswitch(WSS)todynamicallyselectwhichoftheDWDMchannelsontheITUTCbandgridtobeaddedtothelinesignalforeachaddport.AnOpticalCouplerisusedtodistributetheincominglinesignaltothedropports.ADWDMadddropfilterorMux/Demuxunitisalwaysusedforthelocallyterminatingtraffic.
Similarlytothe1x2ROADMpluginunit,theTMSeries1x4and1x8ROADMsalsoincludevariableopticalattenuator(VOA)functionalityonallwavelengthsaddedtothelinesignalbytheWSS.Thisfacilitateschannelpowerbalancinginamplifiednetworks.
Groupingofportsondifferentunitscanbemadeinthenodemanagementsoftwaretoenablethesettingofidenticalchannelselection.Alsorestrictionsonchannelsselectioncanbemadeonindividualorgroupedportstosimplifycommissioningandminimizeriskforfaultyhandling.
Boththe1x4andthe1x8ROADMunitsconsumeslessthan6W.Lowpowerconsumptionincombinationwithasmallfootprintreducessitecostsandenablesmorecapacitytobehandledatsiteswithrestrictionsonpowerconsumption,coolingandspace.
3.4.3.5ContentionlessROADMUsingacombinationof1x4and1x2ROADMsafullycontentionlessROADMnodefor2degreesmaybedesigned.Asshowninthefollowingdiagram,wavelengthscannotbeassignedarbitrarilyinthedirectionlessROADMdescribedearlier:Ifonewavelength1issentine.g.thewestdirection,thesamewavelength1cannotbereusedintheeastdirection.Byaddinganextrasetof1x2ROADMunitsfullfreedomofwavelengthallocationispossible;theROADMnodebecomesbothdirectionlessandcontentionless.However,especiallyforhigherdegreenodes,theamountofequipmentneededforacontentionlessROADMmaymakeitscostprohibitive,althoughexpectedtodecreaseasnewcomponentsbecomeavailable.(Figure45)
Figure45.Adirectionlessandcontentionless2degreeROADMnode.Themux/demuxunitscanbemadecolorlessandcombinedwithtrafficunitshavingtunabletransceiversforadditionalflexibility.
Thefourindividualadddropportsofthe1x4ROADMenablehitlessredirectionoftrafficinmultidegreenodes.Bygroupingfourunitsandinterconnectingtheadddropports,a4degreenodeiscreated,wheretrafficfromanylinecanbedirectedtoanyotherlineorbelocallydropped.(Figure46)
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Figure46.Afourdegreenodeimplementedbyfour1x4ROADMs.
The8individualadddropportsofthe1x8ROADMenablehitlessredirectionoftrafficinevenhigherdegreenodes.Bygroupingupto8unitsandinterconnectingtheadddropports,upto8degreenodescanbecreated,wheretrafficfromanylinecanbedirectedtoanyotherlineorbelocallydropped.A50GHzcompatibleMux/Demuxisusedtoseparatetheterminatedchannels.(Figure47)
Figure47.An8degreenode.Allconnectionsarejustshownforline1.
Itispossibletocreatedirectionlesshigherdegreenodesbyusinganextra1x8ROADMunittodirectthelocaltraffictothepreferredlinefiber.Eachwavelengthcanbedirectedasrequiredonanindividualbasis.Itispossibletohavebothfixedanddirectionlessadd/dropsinthesamenode.(Figure48)
Figure48.Afourdegreenodewithbothfixedanddirectionlesstraffic.
3.5WavelengthmanagementTrafficunitswithpluginandtunabletransceivers,multidegreeROADMsandcolorlessmux/demuxunitsenableatremendousflexibilityinopticalnetworkdesignandoperations,butalsoputstringentrequirementsonwavelengthmanagement.TheTransmodeEnlighten11softwaresuiteforplanning,design,commissioningandmanagementofanintegratedpacketopticalnetworkincludesthenecessarytoolsforthistask.CentralizedwavelengthmanagementisperformedfromtheTransmodeNetworkManager(TNM),acomprehensive,carrierclassElement,NetworkandServiceManagerforTransmodesintegratedlayer1andlayer2networkingsolutions.
TNMincludesseveralfeaturesofhighvalueforefficientwavelengthmanagement,forexample:
Theextensiveinventorymodule.TheROADMprovisioningapplication.TheOpticalControlPlanewithitsapplications.Integratedhandlingofalienwavelengths.
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NotonlydoestheinventorymoduleofTNMkeeptrackofallactiveequipmentinaTMSeriesopticalnetwork.Theinventorymayalsobeusedtoregistereveryfilter,mux/demuxandotherpassiveunitinthenetworkandthenkeeptrackofhowthevariouswavelengthsareallocated.Havingalsothepassiveelementsavailableintheinventorygreatlysimplifiesplanningandallocationofwavelengthsthroughouttheopticalnetwork.
TheROADMprovisioningapplicationinTNMautomaticallyreadsROADMparametersettingsfromthenodesandenablestheoperatortoremotelyaddchannelstoanadd/dropport.IftheROADMprovisioningapplicationisactivated,theTNMautomaticallyidentifiespotentialchannelsthroughtheunconfiguredROADMsofthenetwork.TNMchecksthatnowavelengthconflictsoccurthroughouttheopticalpathandthenautomaticallyconfigurestheROADMstocreatetheopticalpath,includingstartingnecessarycontrolloops.Thishighlyautomatedprocessgreatlyreducestheriskformisconfigurationswhilereducingtheconfigurationtimebyupto90%.
3.5.1TheOpticalControlPlaneinTNMTheOpticalControlPlane(OCP)inTNMprovidesadvancedfunctionalitytosimplifycentralizedcommissioning,tuningandplanningoftheopticalnetwork.Currently,theTNMOpticalControlPlanecomprisestwomodules:TransmissionControlandChannelControl.
3.5.1.1TransmissionControlTransmissionControlisaTNMapplicationthatsupportscommissioningandtuningofamplifiedopticalnetworks,therebyreducingtheoperationalcostsassociatedwithsettingupandmaintainingsuchnetworks.TransmissionControlworksinconcertwiththeOpticalChannelMonitoring(OCM)units,theVariableOpticalAttenuators(VOAs)andthetransceiversinthenetworktomeasureandpresentpowerlevelsatvariouspointsofanopticallightpath.TransmissionControlallowstheoperatortoselectoneormorelightpathsinthenetwork,showthepowerlevelineachpointthathasmeasurementcapabilityandthenmaketheoptimalpowersettingsinattenuatorsandamplifiers.
3.5.1.2ChannelControlChannelControlisaTNMapplicationthatallowstheoperatortoselectanumberofopticallinksandshowtheroutingofusedandavailablechannels()andsubchannels(sub)throughouttheselectedlightpath.
ChannelControlprovidesroutinginformationforchannelsandsubchannelsandidentifieschannelsas:
ActiveChannelschannelsthatarecarryingtraffic.Activechannelhavetranspondersconnectedandcliententriesdefined.PossibleChannelspreprovisionedchannelsthatareavailabletobetakeninservice.Possiblechannelsmayormaynothavetranspondersconnectedbutnocliententriesaredefined.ReservedChannelspreprovisionedchannelsthathavebeendedicatedforparticularfuturepurpose.Reservedchannelsmayormaynothavetranspondersconnectedbutnocliententriesdefined.
3.5.1.3HandlingofalienwavelengthsAnalienwavelengthisastandardCWDMorDWDMwavelengththattransportstrafficthatdoesnotoriginateandterminateinTransmodeequipment,e.g.IPpacketssentbetweentworoutershavingopticalinterfacesconnecteddirectlytotheportsoftwomux/demuxunits.SuchtrafficdoesnotpassanyTMSeriestrafficunitsandisonlytransportedthroughtheopticalnetworkbetweentwopassiveports.AlthoughnotbeingofTMSeriesorigin,thefollowingTNMmanagementfeaturesarestillavailableforalienwavelengths:
TransmissionControl,i.e.thealienwavelengthispowerbalancedinthesamewayandtogetherwiththeTMSeriesnativewavelengths.Opticalprovisioning.Aseparatepassiveadministrativestate.Servicetopology.Servicealarmsifthewavelengthpassesanopticalchannelmonitoring(OCM)unit.
(Figure49)
Figure49.Analarmcanbetriggeredalsoforanalienwavelengthifitpassesanodewithanopticalchannelmonitoring(OCM)unit.
3.6WDMintheaccessnetworkModernizationoftheaccessnetworkisapressingissueformanyoperators,duetotherapidlyincreasingtrafficvolumesgeneratedbynewapplicationsdemandedbytheirsubscribersandusers.Mobileoperatorsaredeployingfourthgeneration(HSDPA,LTE)mobilenetworkstosupportsmartphones,tabletsandmobilecomputing,thusrequiringlinkswithGbit/sdataratestothecellsites.Enterprisesareincreasinglydependentoncentralizedcloudcomputing,whiletheresourceswithinthecloudneedtobeinterconnectedbyhighcapacitylinks;bothtrendsdrivinguptheneedformoredatatransportcapacityintheaccessnetwork.Inparallel,consumerssubscribetovideoondemandandotherInternetbasedmediaservices,making100Mbit/saccessandmorearequirementforeachhousehold.
WDMasatechnologyanswersmanyoftheoperatorsdemandsandhasanimportantroleinthemodernizationoftheaccessnetwork.
3.6.1WDMaggregationringsAnimportantapplicationofWDMandtheTMSeriesisforefficientcapacityupgradesoftheaggregationnetworks,carryingtrafficfrommultipleremoteaccesssitesto/fromacentralhubsite.Forexamples,theremotesitesmaybeamobilecellsite,aDSLAMservingresidentialInternetusersoranEthernetdemarcationunitinanindustrycampus.WithWDM,eachsuchremotenodecanbeallocatedadedicatedwavelengthoverthering,carryingitstrafficto/fromthecentralhub.(Figure50)
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thecentralhub.(Figure50)
Figure50.ComparisonofanaggregationnetworkbuiltwithEthernetswitchesandaWDMaggregationnetwork.
InaWDMring,alltheremotenodeshavetheirownpredeterminedcapacityonthelinktowardsthehub,resultinginadeterministictrafficpatternandeasybandwidthmanagement.Ethernetrings,ontheotherhand,sharetheavailablelinkcapacitybetweenalltheremotenodes.Anincreaseincapacityononenodestealscapacityfromtherest.
Ethernetringsalsorequirethesameuplinkinterfaceonallswitches/nodeswhichleadstoexpensiveforkliftupgrades,shouldcapacityonanyofthenodesneedtoberaised.InaWDMnetworkeachnodeuplinkisindependentfromalltheothersandeachnodecanbeupgradedindividuallywhenneeded.
InaWDMringeachnodeequipmentisindependentoftheothers(nosharedhardware)andtheprotectioncanbehandleddirectlyonlayer1withlessthan50msdelay.Ethernetringsaresensitivetosingleunitfailureandneedcomplexlayer2orlayer3redundancyschemestoovercomethis.
WithWDMaggregationitiseasytocombineEthernetandTDMtrafficbackhaulingonthesamefiber,whileEthernetringsneedmorecomplexremappingsolutions(pseudowireetc.)orseparatefiberpairstocopewithlegacyTDMtraffic.ThisisofspecificvaluetomobileoperatorswhichoftenrequiretransportofbothlegacyTDMtrafficandnewEthernettrafficfromthecellsites.
TheTMSeriesisideallysuitedforbuildingWDMaggregationrings.LowcostCWDMringsolutionsusingonlypassiveopticalfiltersandcoloredinterfacesonalreadyexistingroutersandswitchesareeasilyimplemented.Byincludingactivetranspondersandmuxponders,thetrafficaggregation,protectionandmonitoringcanbemademoreefficient.Andforlongerdistancesandmorechannels,completeDWDMsystems,ifnecessarywithamplifiers,canbedeployed.Inaddition,thepacketopticalfunctionalityoftheTMSeriestranspondersandmuxpondersenablesintegrationoflayer2functionspreviouslyresidingintheEthernetswitchesdirectlyintotheopticalaggregationring.
3.6.2PointtopointandPassiveOpticalNetworks(PON)inaccessExpandingthetelecommunicationsnetworktoeachandeveryhouseholdandeachandeveryenterpriseistherealchallengeofanynetworkdesigner.Thenumberofendpointsterminatingthenetworkbecomesmassive,andsodoestheassociatedcostofcivilworksandequipmentneeded.Whilemostlargerandmediumsizedenterpriseshavehaddedicatedconnections(leasedlines)fordatatraffictotheirpremisessincethe1980s,residentialInternetusershaveprimarilybeenrestrictedtouseaccessnetworksthattakeafreerideonthealreadyinstalledinfrastructureof
telephonylinesorCATVHFC12networks.
12CableTV(CATV)usinghybridfiberandcoax(HFC)distributionnetworks.
Thecostofdeployingnewfiberisobviouslyaprohibitingfactorforamorerapidexpansionofhighspeedaccess,andvariousschemesareusedtoreducethenumberoffibermilesintheaccessnetworks.Thetwomaincompetingcategoriesarepointtopointfiberaccessnetworksandpassiveopticalnetwork(PON)accessnetworks.Aswewillsee,WDMhasanimportantroleinextendingthecapacity,securityandflexibilityofthesenetworks.
Apointtopointfiberaccessnetworkisafairlystraightforwardstructurethatmimicstheclassicaltelephonyaccessnetworkinthatithasacentralnodewithindividualfibercablesreachingouttoeachsubscriber.Thenetworkisstarshaped;sometimesendinginthebasementofamultidwellingbuilding,whereanopticalelectricalconversionisdoneandatraditionalstarshaped,electricalEthernetLANisinstalledreachingouttoeachandeveryapartment.(Figure51)
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Figure51.Topologyofapointtopointbroadbandaccessnetwork.
Themainadvantagesofapointtopointaccessarchitectureareitstopologicalsimplicityandthestrictseparationoftrafficto/fromeachsubscriber.Significantdisadvantagesarethedeploymentcostofalltheindividualfibers,themassiveamountoffibersthatmustbeterminatedatthecentralnodeandthatpointtopointaccessnormallyrequiresactiveequipment(typicallyanEthernetswitch)ateverysubscriberlocation.AlthoughpopularinsomeNordiccitynetworksforresidentialaccessandoftenusedforenterpriseaccess,pureEthernetbasedpointtopointbroadbandaccessisnotlikelytodominatethefuturebroadbandaccessnetworks.
Apassiveopticalnetwork(PON)isapointtomultipoint,accessarchitectureinwhichpassiveopticalsplittersareusedtoenableasingleopticalfibertoservemultiplepremises,typically16128.APONconsistsofanopticallineterminal(OLT)attheserviceproviderscentralofficeandanumberofopticalnetworkterminals(ONTs)nearendusers.PONreducestheamountoffiberandcentralofficeequipmentrequiredcomparedwithpointtopointarchitectures.(Figure52)
Figure52.Topologyofapassiveopticalbroadbandaccessnetwork(PON).
TwomaintypesofPONsystemshavebeenstandardized:TDMPONandWDMPON.TDMPONs(i.e.BPON,EPON,GPON)useseparatewavelengthsforthedownstreamandupstreamdirectionsonthesinglefiberandtimedivisionmultiplexingbetweentheindividualsubscribersconnectedtothefiber.DownstreamsignalsarebroadcasttoallpremisessharingmultiplefibersandonlyreceivedbytheappropriateONT.Upstreamsignalsarecombinedusingamultipleaccessprotocol,usuallytimedivisionmultipleaccess(TDMA).TheOLTsallowsatimeslotassignmentsforupstreamcommunicationfromeachoftheOLTsinturn.BecauseaTDMPONreliesupontimesharing,ithasaninherentcapacitylimitation,aswellasasecurityproblem,sinceallinformationistheoreticallyavailableateveryendpoint.
AWDMPONcombinesthededicatedbandwidthofapointtopointnetworkwiththefibersharingarchitectureinherentinthePONtopology.AWDMPONusesafiltertoseparatethewavelengthsofaWDMstreamfordeliverytoeachindividualsubscriberONT.Thus,onlyonefiberisrequiredatthecentralsitewhilethewavelength(channel)topologyispointtopoint.
AkeyadvantageofWDMPONistheuseofacompletelyseparatedownstreamwavelengthforeachofthesubscribers.Thisseparatewavelengthprovidesmorebandwidthtoeachsubscriber,bettersecurity,andenhancedoperationalcontrolsincethereisnopotentialinterferencebetweenwavelengths.Similarly,adedicatedupstreamwavelengthprovidesalmostunlimitedcapacitytoeachsubscriber,coveringallpotentialfuturegrowth.(Figure53)
Figure53.PrincipleofaWDMPONaccessnetwork.
3.6.3TheTransmodeiWDMPONsolutionWhileWDMPONsatisfiesallfuturecapacityandsecurityrequirementsinbroadbandaccess,itisstillatechnologyinitsinfancy,withvariousimplementationalternativesunderstandardization.Severalofthesuggestedstandardsrelyuponspecialcomponentshavinghighcostsduetosmallseriesandlimiteddeployment,e.g.whenWDMPONisimplementedwithCandLbandtransmissionandnonITUstandardizedwavelengths.
TransmodehasthereforeselectedanalternativeapproachtoWDMPON:UsingthesamebasicelementsasformetroandlonghaulWDM,TransmodesiWDMPONsolutionoperatesintheCband.Byusingthesamewavelengthsfor
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andlonghaulWDM,TransmodesiWDMPONsolutionoperatesintheCband.Byusingthesamewavelengthsforaccessasthoseusedinthemetroandlonghaulnetworks,itispossibletodevelopacommonWDMaccessstructurethatcombineslegacyenterprisetraffic,mobilebackhaul,residentialInternetaccessandhighcapacityWDMPONusersinthesameopticalnetwork.(Figure54)
Figure54.ATransmodeiWDMPONaccessnetwork.Usingonewavelengthfromaccesstocoreprovidesopticaltransparencyandeliminatesopticalelectricconversions.
TheadvantagesofusingITUstandardWDMintheaccessnetworkarevaried:
EasytocombineFTTB,mobilebackhaul,Enterpriseleasedlinesandmoreinthesameinfrastructure.Providesonesolutionforalltypesofdataratesandapplications.Eachservice(SDH/SONET,GbE,FC,FICON)canbeallocateditsownwavelength.OpenandstandardizedDWDMgridanduseofthestandardITUCbandmakesitpossibletocapitalizeonstandardcomponentdevelopmentcurveandpricereductions.Opticaltransparencyfromaccesstocoreeliminatestheneedforopticalelectricconversions.
TransmodesiWDMPONsolutionleveragesthepassiveandactivecomponentsalreadydescribed,butalsoincludesspecialelementstofacilitatewavelengthallocationtosubscribers,accordingtonormalWDMPONprinciples.Akeyelementistheuseofpluggable,colorlessDWDMSFPswithinjectionlockedFPlasersintheONTatthecustomersite.ThecolorlessSFPisautomaticallytunedtotheincomingseedingwavelength,thuseliminatingmanualtuningateachsubscriber.(Figure55)
Figure55.WavelengthallocationiniWDMPON:TheseedingboardinstalledintheTMSeriescentralofficeOLTbroadcastsabroadbandlightsource.AfilterforwardsasinglewavelengthtotheSFP,whichlocksonthecorrectfrequency.
3.7NetworktopologiesOpticalnetworkscanbeclassifiedaccordingtotheirtopologies:Lineorpointtopoint,star,ringandmeshshaped.Thelineandstartopologieshavesinglepointsoffailure,andshouldbeavoidedwhenresilienceagainstoutagesisimportant.Therearemanyargumentsaboutwhicharethebest:Ringormesh.Veryoften,thedebatemixesupthetopologyofthephysicalfibersinstalledandthelogicalconnectivitythatcanbeachievedbyswitchingandroutingoverthefibersathigherlayers.Thephysicalconnectivitymattersmostwhenresilience,distanceanddelayarebeingconsidered.
Manymetropolitannetworksstartasringsandevolvesgraduallytomeshthecrossoverdependsonfibercosts,equipmentcosts,trafficloading,degreeofmeshrequiredforresilienceetc.Ascanbeseenfromthediagrambelow,thecostofameshednetworkishighatlowertrafficvolumes,butbecomesincreasinglyattractiveastrafficgrows.Thediagramisbasedonsimulations.
WiththeadventoftodayscostefficientROADMnodes,itisnowpossibletoimplementresilientandflexiblemeshednetworksalsointhemetroareaandmetroaccessareas.(Figure56)
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Figure56.Simulationofnetworkcostasafunctionoftrafficfordifferenttopologies.
3.8Resilienceandprotection
3.8.1CalculatingtheavailabilityBeingafundamentalpartofthetelecommunicationsinfrastructure,theopticalnetworkmustalwaysbeoperational.Threevariablesdefinethequalityofanetworkfromaresilienceperspective:
Availabilityisthefractionoftotaltimethatafunction,forexampleanetworkconnection,isavailablei.e.whattheusersexperienceasaworkingsystem.Availabilityismeasuredin%oftimeandtypicallyliesintherangeof99.999%(fivenines)ormore.
Thereliabilityofanetworkelementisthefractionoftotaltimethatanobjectisworking.Reliabilityisoftenmeasuredasmeantimebetweenfailures(MTBF)atimethatshouldbeaslongaspossible.Therepairtimedefineshowquicklyanobjectcanberepairedandputbackinservice.Repairtimeismeasuredasmeantimetorepair(MTTR)andshouldpreferablybeasshortaspossible.
LetuslookataconcreteexampleonhowprotectionswitchingandringtopologiescanhelpimprovetheavailabilityonanopticallightpathfromGlasgowtoLondon.ThecalculationisbasedonSDHtechnologyandpurelyforillustrativepurposes,i.e.thevaluesusedforactivecomponentsarenotdirectlyapplicablefortheTMSeries.
Lookingfirstatanunprotectedlightpath,thephysicalnetworkcanbedrawninamoreeasilyunderstoodform.Thetotalavailabilityoftheunprotectedpathissimplyfoundbymultiplyingtheavailabilitiesofeachoftheelementsinthechain.(Figure57)
Figure57.Availabilityforanexamplenetwork.
Usingprotectionswitchinginthenodes,thelightpathmayfindalternativeroutesbetweenitsendpoints,forexample,shouldafiberbreakoccur.(Figure58)
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Figure58.Availabilityforaprotectedandarestoredexamplenetwork.
Calculationoftheavailabilityinaprotectednetworkisabitmorecomplicatedthaninanunprotectednetwork:
1. Firstmultiplytheavailabilitiesoftheunprotectedpartstogether(inthiscasethetributarycardateitherendofthepath).
2. Calculatetheavailabilitiesofthetwodiversepathsbymultiplyingtheavailabilitiesofeachoftheelementsinbothchains.
3. Combinethetwochainsbymultiplyingtheirunavailabilitystogether(unavailability=1availability).4. Finallymultiplytheavailabilityfromstep1withtheavailabilityfromstep3.
Therestoredexamplebreaksthesingle,long,diverserouteintoseveral,shorter,diversesections.Theresultofthisisthatitcansurvivemultiplesimultaneousfailureswhilsttheprotecteddesigncanonlysurviveasinglefailure.
3.8.2TMSeriesresiliencefeaturesTheTMSeriesincludesnumerousfeaturesthatcanbeusedtominimizetheimpactofbothfiberbreaksandfailuresinindividualcomponentsontheoverallnetworkavailability.
Oneliveandoneredundantclientsystemmay,forexample,beconnectedtotwoseparateandindependenttranspondersormuxponderssharingthesameopticalfiberviaapassiveopticalcouplerunit.Incaseoffailureoftheliveclientsystemorthecorrespondingtransponder/muxpondertraffic,theredundantpathisautomaticallymadeactiveinlessthan50ms.Thetransponders/muxpondersmayevenbelocatedinseparateTMSerieschassistofurtherminimizetheriskofsinglepointoffailure.(Figure59)
Figure59.ClientandequipmentprotectionwiththeTMSeries.
Transponderscanbeequippedwithmultipleoutputsforalternativefiberroutesandsignalsfromincomingfiberscanbesplitintotwoormorepaths.Switchingbetweentheworkingpathandthealternativepathisfullyautomaticandtakeslessthan50ms.Therefore,multipathlineprotectioncaneasilybeachievedinTMSeriesopticalnetworks
withouttheneedforGMPLS/ASON13software.(Figure60)
Figure60.Threeexamplesoflineprotectionwithtransponders.
13GeneralizedMultiProtocolLabelSwitching(GMPLS)isaprotocolsuiteextendingMPLS(seechapter4)tomanage
furtherclassesofinterfacesandswitchingsuchastimedivisionmultiplexers,layer2switchesandwavelength
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furtherclassesofinterfacesandswitchingsuchastimedivisionmultiplexers,layer2switchesandwavelengthswitches.ASON(AutomaticallySwitchedOpticalNetwork)isaconceptfortheevolutionoftransportnetworkswhichallowsfordynamicpolicydrivencontrolofanopticalorSDHnetworkbasedonsignalingbetweenauserandcomponentsofthenetwork.
Ifseveralfibersareavailableonagivenlink,theTMSeriesalsoallowsforfiberprotection,byusingamechanicalfiberprotectionunit.(Figure61)
Figure61.Fiberprotection.