Background
ThebirthofSDHtechnologyhasitsinevitability.Withthedevelopmentofcommunication,theinformationrequiredtobetransmittedisnotonlyvoice,butalsotext,data,imagesandvideos.Coupledwiththedevelopmentofdigitalcommunicationandcomputertechnology,inthe1970sand1980s,T1(DS1)/E1carriersystems(1.544/2.048Mbps),X.25framerelay,ISDN(IntegratedServicesDigitalNetwork)andFDDI(Opticalfiberdistributeddatainterface)andothernetworktechnologies.Withtheadventoftheinformationsociety,peoplehopethatmoderninformationtransmissionnetworkscanprovidevariouscircuitsandservicesquickly,economically,andeffectively.However,duetothemonotonicityoftheirservices,thecomplexityofexpansion,andthelimitationofbandwidth,theabove-mentionednetworktechnologiesareonlyintheoriginalModificationsorimprovementswithintheframeworkarenolongerhelpful.SDHwasdevelopedunderthisbackground.Amongvariousbroadbandopticalfiberaccessnetworktechnologies,theaccessnetworksystemusingSDHtechnologyisthemostwidelyused.ThebirthofSDHsolvestheproblemofbeingunabletokeepupwiththedevelopmentofthebackbonenetworkanduserservicerequirementsduetothebandwidthlimitationoftheinboundmedia,whichhascausedtheaccess"bottleneck"betweentheuserandthecorenetwork,andatthesametime,ithasincreasedalargeamountofbandwidthonthetransmissionnetwork.Utilizationrate.SincetheintroductionofSDHtechnologyinthe1990s,ithasbeenamatureandstandardtechnology.Itiswidelyusedinbackbonenetworksandthepriceisgettinglowerandlower.TheapplicationofSDHtechnologyintheaccessnetworkcanreducethehugebandwidthinthecorenetwork.Advantagesandtechnicaladvantagesarebroughtintothefieldofaccessnetworks,makingfulluseofSDHsynchronousmultiplexing,standardizedopticalinterfaces,powerfulnetworkmanagementcapabilities,flexiblenetworktopologycapabilitiesandhighreliabilitytobringbenefits,andlong-termbenefitsintheconstructionanddevelopmentofaccessnetworks.
Perusperiaatteet
SD:n hyväksymää tietorakennetta kutsutaan synkroniseksi kuljetusmoduuliksiSTM-N(SynchronousTransportMode,N=1,4,16,64),perusmoduuliksiSTM-1, neljäSTM-1synkroninenTM-multipleksointi-4,synkroninenTM-multipleksointi1-tai ingformSTM-16 ja neljä STM-16 synkronista multipleksointimuotoaSTM- 64.Jopa neljä STM-64synkronista multipleksointirakennettaSTM-256;SDHaadoptsblockframestructure, joka kuljettaa tietoja, jokainen kehys koostuu 9 rivistä pystysuorassa ja 270 × N sarakkeessa tavuja aina vaakasuunnassa, jokainen tavu sisältää 8 bittiäviimeksi,ja (SOH)alue,STM-N-payloadareaandManagementUnitPointer(AUPTR)alue.Näitä ylimääräisiä alueita käytetäänpääasiassa verkon käyttöön,hallintaan,huoltoon ja toimeksiantoon sen varmistamiseksi, että tietoja voidaan siirtää normaalisti ja joustavasti, ja se on jaettuRegenerator(RS-adyload)MSaOveraHeult-Ohe; käytetään tallentamiseenbitteihin ja pieni määräbittiä tosiasiallisesti käytettyjä tietopalveluihin. ;hallintayksikön osoitinta käytetään osoittamaan ensimmäisen tiedon tarkan sijainnin maksukuormituksessaSTM-N-kehyksessä, jotta maksukuorma voidaan erottaa oikein vastaanotettaessa.SDH-kehyslähetys järjestetään sarjakoodivirtana vasemmalta oikealle ja ylhäältä alas. 00 kehystä lähetetään sekunnissa.STM-1:lle jokainen kehysbittimäärä on 8 bittiä × (9 × 270 × 1) = 19 440 bittiä, silloinSTM-1:n lähetysnopeus on 19440 × 8000 = 155,520 Mbit/s;ja lähetysnopeus 1 × 5 / 5 STM-5. =622,080 Mbit/s;STM-16:n lähetysnopeus on 16 × 155,520 (tai 4 × 622,080) = 2488,320 Mbit/s.
WhenSDHtransmitsservicesignals,theframesofvariousservicesignalstoenterSDHmustgothroughthethreestepsofmapping,positioningandmultiplexingasfollows:
(1)MappingistocombinevariousThesignaloftherateisfirstloadedintothecorrespondingstandardcontainer(C)afterthecoderateisadjusted,andthenthechanneloverhead(POH)isaddedtoformthevirtualcontainer(VC).Thedeviationoftheframephaseiscalledtheframeoffset.
(2)Asemointi on prosessi, jolla vastaanotetaan kehyspoikkeamatiedot osayksikköön (TU) tai hallintayksikköön (AU). Se ohittaa osayksikön osoittimen (TUPTR) tai hallintayksikön osoittimen (AUPTR) -toiminnon.
(3)Theconceptofmultiplexingisrelativelysimple.Multiplexingisawayofadaptingsignalsfrommultiplelow-levelchannellayerstohigher-levelchannellayers,oradaptingmultiplehigh-levelchannellayersignalsTheprocessofenteringthemultiplexinglayer.MultiplexingistheprocessoforganizingTUintohigh-levelVCororganizingAUintoSTM-Nthroughbyteinterleaving.SincetheVCtributarysignalsprocessedbyTUandAUpointersarephase-synchronized,themultiplexingTheapplicationprocessisthattheprincipleofsynchronousmultiplexingissimilartotheserial-to-parallelconversionofdata.
Content
ThecontentofSDHincludestransmissionrate,interfaceparameters,multiplexingmodeandOAMofhigh-speedSDHtransportnetwork.ThemaincontentisbasedontheSONet(SynchronousOpticalNetwork)proposalsubmittedbyBellcore(nowTelcordiaTechnologies)toANSIin1985.ITU-Thasmadesomemodificationstoit,andmostofthemodificationsareinthelowermultiplexinglayer.Inordertomeetthecomplexityrequirementsoftheinterconnectionofvariouscountriesandregions.RelatedrecommendationsarecontainedinG707,G.708andG.709.SDHequipmentisonlypartiallycompatiblewithSONet,andthetwosystemscancarryeachother'sbusinessflows,butthealarmandperformancemanagementinformationbetweenthetwosystemscannotbeinteroperable.
Jotta tukeakseen useiden palvelujen lähetystä, SDH on määrittänyt, että alhaisen nopeuden multipleksoiminensaa suuria nopeuksia,ja suuren nopeuden multipleksauksensaa suuremman nopeuden, jotta saadaan eri tiedonsiirtonopeuksia. SDHisSTS-1(SpaceTransportationSystem) määrittää synkronisen lähetyssignaalin ensimmäisen tason. 544 Mbps ,T2=6.312Mbps,T3=44.736Mbps.Kolmikanavainen STS-1multipleksoidaan ja lähetetään perussynkroniseen lähetysmoduuliinSTM1-linjaan.
AdvantagesandDisadvantages
Advantages
(1)SDHtransmissionsystemhasaunifiedframestructuredigitaltransmissionstandardrateandstandardopticalinterfaceintheworld,sothatthenetworkmanagementThesystemisinteroperable,soithasgoodhorizontalcompatibility.ItcanbefullycompatiblewiththeexistingPDHandaccommodatevariousnewbusinesssignals,formingaglobalunifieddigitaltransmissionsystemstandard,andimprovingthereliabilityofthenetwork.
(2)DifferentlevelsofcodestreamsoftheSDHaccesssystemarearrangedregularlyinthepayloadareaoftheframestructure,andthepayloadissynchronizedwiththenetwork.Itusessoftwaretotransferhigh-speedsignalsonceDirectlyaddandinsertlow-speedtributarysignals,whichrealizesthecharacteristicsofone-timemultiplexing,andovercomestheprocessofPDHquasi-synchronousmultiplexingtodecomposeallhigh-speedsignalsstepbystepandthenregenerateandmultiplexthem.SinceDXCisgreatlysimplified,theback-to-backisreduced.Interfacemultiplexingequipmentimprovesthetransparencyofnetworkservicetransmission.
(3)Duetotheuseofmoreadvancedadd/dropmultiplexers(ADM),digitalcross-connect(DXC),networkself-healingfunctionandreorganizationfunction,itisverypowerfulandhasastrongsurvivalRate.Because5%oftheoverheadbitsofthesignalarearrangedintheSDHframestructure,itsnetworkmanagementfunctionisparticularlypowerful,anditcanformaunifiednetworkmanagementsystem,whichcanhelpthenetworkautomation,intelligence,channelutilization,andreducenetworkmaintenanceandmanagementfees.Survivabilityplayedapositiverole.
(4)DuetothemultiplenetworktopologiesofSDH,thenetworkitconstitutesisveryflexible.Itcanenhancenetworkmonitoring,operationmanagementandautomaticconfigurationfunctions,optimizenetworkperformance,andalsomakenetworkoperationflexible,Safeandreliable,makingthenetworkfunctionverycompleteanddiversified.
(5)SDHhastheperformanceoftransmissionandswitching.Thecompositionofitsseriesofequipmentcanbefreelycombinedthroughfunctionalblockstorealizenetworksofdifferentlevelsandvarioustopologies,whichisveryflexible.
(6)SDHisnotexclusivetoacertaintransmissionmedium,itcanbeusedfortwistedpair,coaxialcable,butSDHisusedtotransmithighdataratesandrequiresopticalfiber.ThisfeatureshowsthatSDHissuitableforuseasatrunkchannelaswellasabranchchannel.Forexample,mycountry'snationalandprovincialcabletelevisiontrunknetworksuseSDH,anditisalsocompatiblewithfiberopticcablehybridnetworks(HFC).
(7)FromthepointofviewoftheOSImodel,SDHbelongstothephysicallayerofthebottomlayer,anddoesnothavestrictrestrictionsonitsupperlayers.ItisconvenienttoadoptvariousnetworktechnologiesonSDHandsupportATMorIPtransmission.
(8)SD on tiukasti synkronoitu,mikä varmistaa, ettäkoko verkkoonvakaa ja luotettava,vähemmän virheitä,jahelpostikäyttöäjasäätää.
(9)Thestandardopenopticalinterfacecanachievehorizontalcompatibilityonthebasicopticalcablesection,reducingnetworkingcosts.
Disadvantages
(1)Effectivenessandreliabilityareacontradiction.Increasingeffectivenesswilldefinitelyreducereliability,andincreasingreliabilitywillalsoreduceeffectivenessaccordingly.AgreatadvantageofSDHisthatthereliabilityofthesystemisgreatlyenhanced(thedegreeofautomationofoperationandmaintenanceishigh),whichisduetotheadditionofalargenumberofoverheadwordsforOAMfunctionsintheSDHsignal-STM-NframeSection,thiswillinevitablyleadtothetransmissionofthesameamountofeffectiveinformation,onlywhenthePDHsignalis140Mbit/smultiplexedintotheSTM-1signalframe,theSTM-1signalcanaccommodate63×2Mbit/sTheamountofinformation,butatthistimeitssignalrateis155Mbit/s,whichishigherthantheE4signal(140Mbit/s)withthesameinformationcapacityofPDH,whichmeansthatthetransmissionfrequencybandoccupiedbySTM-1isgreaterthanthetransmissionofPDHE4signalfrequencyband.
(2) Osoittimensäätömekanismi on monimutkainen
TheSDHsystemcandirectlydownloadlow-speedsignalsfromhigh-speedsignals,eliminatingtheneedformulti-stagemultiplexing/demultiplexing.Therealizationofthisfunctionisaccomplishedthroughthepointermechanism.Theroleofthepointeristoindicatethepositionofthelow-speedsignalatalltimes,sothattherequiredlow-speedsignalcanbecorrectlysplitduring"unpacking",whichensuresthattheSDHisseparatedfromthehigh-speedsignal.Realizationofthefunctionofdirectlydownloadinglow-speedsignalsinthemiddle.ItcanbesaidthatpointersareamajorfeatureofSDH.Buttherealizationofthepointerfunctionincreasesthecomplexityofthesystem.ThemostimportantthingistomakethesystemproduceauniquejitterofSDH-combinedjittercausedbypointeradjustment.Thiskindofjittermostlyoccursattheboundaryofthenetwork,anditslowfrequencyandlargeamplitudewillcausetheperformanceoflow-speedsignalstodeteriorateafterbeingremoved,anditwillbequitedifficulttofilterthiskindofjitter.
(3)Ohjelmistojen laajan käytön vaikutus järjestelmän turvallisuuteen
OneofthemajorcharacteristicsofSDHisthehighdegreeofautomationofOAM,whichalsomeansthatthesoftwareoccupiesaconsiderableamountoftimeinthesystem.Theproportion,whichmakesthesystemvulnerabletocomputerviruses,especiallyintoday'subiquitouscomputerviruses.Inaddition,humanerroroperationsandsoftwarefailuresatthenetworklayerhaveafatalimpactonthesystem.Inthisway,thesecurityofthesystemhasbecomeaveryimportantaspect.Therefore,themaintenancepersonneloftheequipmentmustbefamiliarwiththesoftwareandchooseareliablenetworktopology.
Application
DuetothemanycharacteristicsofSDHmentionedabove,ithasmadetremendousdevelopmentinthefieldofwideareanetworkandprivatenetwork.TelecomoperatorssuchasChinaMobile,ChinaTelecom,ChinaUnicom,andRadioandTelevisionhaveallbuiltSDH-basedbackboneopticaltransmissionnetworksonalargescale.Utilizelarge-capacitySDHlooptocarryIPbusiness,ATMbusinessorleasethecircuitdirectlytoenterprisesandinstitutions.Andsomelarge-scaleprivatenetworkshavealsoadoptedSDHtechnologytosetupSDHopticalloopswithinthesystemtocarryvariousservices.Forexample,thepowersystemusesSDHloopstocarryinternaldata,remotecontrol,video,voiceandotherservices.
FortheunitsthataremoreurgentfornetworkingandhavenopossibilitytosetupdedicatedSDHloops,manyofthemhaveadoptedthemethodofleasedcircuitsfromtelecomoperators.BecauseSDHisbasedonthecharacteristicsofthephysicallayer,unitscancarryvariousservicesonleasedcircuitswithoutbeingrestrictedbytransmission.Therearemanybearermodes,whichcanbetheuseofintegratedmultiplexingequipmentbasedonTDMtechnologytoachievemultipleservicemultiplexing,ortheuseofIP-basedequipmenttoimplementmulti-servicepacketswitching.SDHtechnologycantrulyguaranteethebandwidthofleasedcircuits,andisbetterthanVPNsintermsofsecurity.SDHleasedlineshavebeenwidelyusedingovernmentagenciesandcompaniesthatattachgreatimportancetosafety.Generallyspeaking,SDHcanprovideE1,E3,STM-1orSTM-N(N=4,16,64)andotherinterfaces,whichcanfullymeetvariousbandwidthrequirements.Atthesametime,intermsofprice,ithasalsobeenacceptedbymostunits.
Developmenttrend
Asanewgenerationofidealtransmissionsystem,SDHhastheabilityofautomaticroutingselection,convenientupperandlowercircuits,strongmaintenance,control,andmanagementfunctions,unifiedstandards,andhighertransmission.Theadvantagesofhigh-speedservices,etc.,canwellmeettheneedsoftherapiddevelopmentofcommunicationnetworks.Sofar,SDHhasobtainedunprecedentedapplicationanddevelopment.Intermsofstandardization,aseriesofrecommendationsthathavebeenestablishedandwillbeestablishedhavebasicallycoveredallaspectsofSDH.Ithasbeguntobewidelyusedintrunknetworks,long-distancenetworks,relaynetworks,andaccessnetworks.Inaddition,researchandapplicationarealsoactivelycarriedoutinopticalfibercommunication,microwavecommunication,andsatellitecommunication.
Inrecentyears,on-demandTV,multimediaservices,andotherbroadbandserviceshavesprungup,providingabroadspaceforSDHapplicationsinaccessnetworks.TheadvantagesofSDHtechnologyappliedtotheaccessnetworkare:1)Forlarge-scaleenterpriseusersthatrequirehighreliabilityandhigh-qualityservices,SDHcanprovideidealnetworkperformanceandservicereliability.2)Thescopeofnetworkmanagementcanbeextendedtotheuserside,simplifyingmaintenancework.3)UtilizingtheinherentflexibilityofSDHenablesnetworkoperatorstoprovideuserswithlong-termandshort-termbusinessneedsfasterandmoreeffectively.
Fromatechnicalpointofview,therelativebandwidthrequirementoftheaccesslayerisrelativelysmall,anditneedstoprovideEthernet,TDM,andpossiblyATMandotherintegratedservicetransmission.BasedontheSDHsystemandcapableofprovidingEthernetandATMtransmissionandprocessingsystems(includingTDM,EthernetandATMinterfaces,andevenEthernetandATMswitchingmodules)willbethemainmethodtosolvetheaccesslayertransmission.ThismethodcanbecheapProvidehigh-qualityprivateline,ATM,Ethernetandotherservicesaccess,transmissionandprotectiononaserviceprovisionpoint(POP).
Asthebackbonetransmissioncapacitycontinuestoincrease,theaccesscapabilitiesofthemetrotransmissionnetworkarealsodiversified.However,IP-basednetworkservicesarestillunpredictable,whichrequiresthetransmissionnetworktohavebetteradaptivecapabilities,andthisadaptivecapabilityisnotonlytheadaptabilityofthenetworkinterfaceornetworkcapacity,butalsorequirestheautonomyofnetworkconnections.adaptability.Ingeneral,low-cost,flexibleandfastcompletionofserviceaccessandserviceconvergencefromtheoperator'sendofficetotheuserendarethemainrequirementsforthefuturemetropolitanareanetworkaccesssystem.
Simplyspeaking,thiswayofusingSDHtotransmitEthernetandotherservicesistomaptheservicesofdifferentnetworklevelstoeachtimeslotoftheSDHcircuitthroughtheVCcascademethod,andtheSDHThenetworkprovidesacompletelytransparenttransmissionchannel,whichisanintegratedwholefromtheperspectiveofphysicallayerequipment.Thissolutioncangreatlyreducethescaleofinvestment,reduceequipmentfootprint,reducepowerconsumption,andtherebyreducetheoperatingcostsofnetworkoperators.Atthesametime,theabilitytoprovidemultipleservicescanalsoenablenetworkoperatorstoquicklydeploynetworkservices,increaseservicerevenue,andenhancemarketcompetitiveness.
Tosumup,SDHhasbecomethemainstreamoftransmissionnetworkdevelopmentwithitsobviousadvantages.ThecombinationofSDHtechnologyandsomeadvancedtechnologies,suchasopticalwavelengthdivisionmultiplexing(WDM),ATMtechnology,Internettechnology(PacketoverSDH),etc.,makeSDHnetworksmoreandmoreimportant.SDHhasbeenincludedintheapplicationprojectsofhigh-speedcommunicationnetworksinthe21stcenturybyvariouscountries.Itisarecognizeddevelopmentdirectionofdigitaltransmissionnetworksinthetelecommunicationsindustryandhasgreatcommercialprospects.