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DevelopmentHistory
Thedevelopmentofthedigitalsynchronizationnetworkhasgonethroughtwostages.
Hybridsynchronizationnetwork:usetheswitchclockasthesynchronizationnetworknodeclock.
Independentsynchronizationnetwork:Useanindependentclockdevice(ieBITS)asthenodeclockofthesynchronizationnetwork.
Asthecommunicationnetworkevolvesfromanalogtodigital,thereisaneedfornetworksynchronization.Inordertomakethenetworkreachasynchronousoperationstate,asynchronousnetworkwasgraduallyestablished.
Thedigitalsynchronizationnetwork,thetelecommunicationsmanagementnetwork,andthesignalingnetworkarejuxtaposedasthethreemajorsupportingnetworks.Thispositioningisveryaccurate.Thisisbecausethesynchronizationnetworkdoesnotdirectlyfacecustomersandcannotproducedirecteconomicbenefits.Itsserviceobjectsarevariousbusinessnetworks,anditprovidestimingforvariousbusinessnetworkstoensuretheservicequalityofthebusinessnetwork.
Theinformationtransmittedbythesynchronizationnetworkthroughthesynchronizationlinkisthesynchronizationinformation.
Workingprinciple
Thestructureofthedigitalsynchronizationnetworkmainlydependsonthesizeofthesynchronizationnetwork,thetimingdistributionmethodandtheclocksynchronizationmethodinthenetwork,butbecausethedigitalsynchronizationnetworkisasupportnetwork,Therefore,fundamentallyspeaking,theabove-mentionedmanyfactorsdependonthescale,structureandsynchronizationrequirementsofthebusinessnetwork.
Synchronizationinformationistheinformationofthesynchronizationnetworktransmittedbythesynchronizationlink,sofirstexplainthetwotiminglinksofthesynchronizationlink.
Synchronizationlink
MethodforPDHtotransmitsynchronizationnetworktiminginformation:ThetraditionalsynchronizationnetworkisestablishedinthePDHenvironment,andthe2Mbit/schannelofPDHisusedtotransmitthesynchronizationnetworktiminginformation.Thelinkincludes2Mbit/sdedicatedlineand2Mbit/sbusinessline.
Thetransmissionsystemadjuststhepositivecoderateofthe2Mbit/ssignal,andthebitsaremultiplexedtothehigherordergroup(8Mbit/s,34Mbit/s,140Mbit/s,etc.),andtransmittedthroughthePDHlinesystem.Thetransmissionequipmentisnotsynchronizedwiththe2Mbit/sclock.Therefore,thejitterandwanderdamageintroducedbythetransmissionsystemaresmall,andthe2Mbit/schannelofthePDHtransmissionequipmentissuitablefortransmittingsynchronizationnetworktiming.Atthesametime,becausethereisnotransmissionsystemclockinterventionbetweenthesynchronizationnetworknodes,whenthetiminglinkfails,thedownstreamclockcanquicklyfindthefailure,entertheholdingstateorswitchtothestandbyreferencetimingsignal,thatis,thetimingrecoverycanbequicklyperformed.
SDHtiminglinkreferstotheuseofSDHtransmissionlinktotransfersynchronizationnetworktiming.
DifferentfromthePDHtiminglink,theSDHtiminglinkusestheSTM-Nsignaltotransmittiming,andtheordinary2Mbit/ssignalinSDHcannotbeusedtotransmitsynchronizationnetworktiming.Afterretimingprocessing,the2Mbit/ssignalcantransmittiminginalocalrange.Beforelarge-scaleuse,thedelayproblemmustbesolved.
ThemethodofSDHnetworktransmittingsynchronizationnetworktiming:DuetoSDHpointeradjustmenttechnology,2Mbit/stributarysignalsarenotsuitablefortransmittingsynchronizationnetworktiming,andSTM-Nlinesignalsaregenerallyusedtotransmittiming.TheSDHnetworkelementatthebeginningofthetiminglinkreceivesthesynchronizationnetworktimingthroughtheexternalclocksignalinputport,andcarriesthetimingsignaltotheSTM-N.IntheSDHsystem,theSTM-Nsignalistransmittedsynchronously,andtheSDHnetworkelementclockreceivesLinesignaltimingandprovidetimingforthelinesignalsent.Inthisway,thesynchronizationnetworktimingsignaliscarriedontheSTM-NandpassedonthroughtheSDHsystem.
WhentheSDHsystemisusedtotransferthesynchronizationnetworktiming,theSDHnetworkelementclockwillbeserializedintothetiminglink,sothattheSDHnetworkelementclockandtransmissionlinkarecalledcomponentsofthesynchronizationnetworkandneedtobeincludedWithinthescopeofmanagementandmaintenanceofthesynchronizationnetwork.
Secondly,ontheSDHtiminglink,itnotonlyincludesthetransmissionoftimingsignals,butalsothetransmissionofsynchronizationstatusinformation(SSM).
Synchronizationnode
Thesynchronizationnetworknodeistheplacewhereclocksatalllevelsaresetuponthesynchronizationnetwork,usuallyineachcommunicationcenterorcommunicationbuilding.Aphysicallocationisasynchronizationnetworknode,andasynchronizationnetworknodecanhavemultiplesetsofsynchronizationnetworkdevices.Onthesynchronizationnetworknode,variouscommunicationdevicescandirectlyobtainsynchronizationnetworktiming,thatis,synchronizationinformation,fromthenodeclock.
First-levelsynchronizationnetworknode-setthefirst-levelclock(iereferenceclock)
ThereferenceclockreferstotheclockthatmeetstheperformancespecifiedintherecommendationG.811,whichcanbeusedfortheentirenetwork.Providetimingreference.
Therearetwotypesofreferenceclocks:PRCcomposedofcesiumatomicclocksandPRScomposedofGPSwithrubidiumclocks.
PRSischaracterizedbylowcost,longlife,andeasymaintenance.GPSiscontrolledbytheUnitedStates,whichbringssomeinstabilityfactors.Forexample,deliberatelyreducetheGPSaccuracy;turnofftheGPSsignalinacertainarea;increasetherandomscramblingcode;thesurroundingenvironmentinterfereswiththeGPSwirelesssignal,etc.
Internationally,somecountriesusePRCasareferenceclock.Thereferenceclockisgenerallysetinthenationalcapitalorregionalcenter.Theregionalreferenceclockisgenerallysetinthecommunicationcenterbureauofeachprovince,autonomousregion,andmunicipalitydirectlyundertheCentralGovernment.
Secondarysynchronizationnetworknode-setthesecondaryclock.
Therearetwotypesofsecondaryclocks:secondaryclockscomposedofrubidiumclocksandsecondaryclockscomposedofcrystaloscillators.However,nomatterwhichtypeofsecondaryclock,itshouldmeettheperformanceindicatorsofthesecondaryclock.
Three-levelsynchronizationnetworknode-setthethree-levelclock.
Thetertiaryclockisgenerallycomposedofacrystaloscillator,whichmeetstheperformanceindicatorsofthetertiaryclock.Thetertiaryclockisgenerallysetinthetandemofficeorendofficeinthelocalnetwork.