Introduction
Theso-calledaccessnetworkreferstoalltheequipmentbetweenthebackbonenetworkandtheuserterminal.Itslengthisgenerallyseveralhundredmeterstoseveralkilometers,soitisvividlycalledthe"lastkilometer".Sincethebackbonenetworkgenerallyusesanopticalfiberstructureandhasafasttransmissionspeed,theaccessnetworkhasbecomethebottleneckoftheentirenetworksystem.Theaccessmethodsoftheaccessnetworkincludecopperwire(ordinarytelephoneline)access,opticalfiberaccess,opticalfibercoaxialcable(cabletelevisioncable)hybridaccess,andwirelessaccess.
Accordingtothelocationofopticalaccessnodes,opticalfiberaccessmethodsaredividedinto:FTTH,FTTB,FTTCandFTTO.Themainaccessmethodsofthetraditionalaccessnetworkare:V5access,passiveopticalnetworkaccess(PON),xDSLaccess,andfiber/coaxialhybridnetworkaccess(HFC).Theclassificationoftheaccessnetworkisshowninthefigurebelow.
Definitionofaccessnetwork
The13thgroupoftheInternationalTelecommunicationUnion(ITU-T)passedthenewrecommendationG.902ontheframeworkoftheaccessnetworkinJuly1995,Thedefinitionoftheaccessnetworkisasfollows:
Theaccessnetworkconsistsofaseriesoftransmissionentities(suchaslineequipmentandtransmissionfacilities)betweentheservicenodeinterface(SNI)andtheuser-networkinterface(UNI).)Iscomposedofanimplementationsystemthatprovidestherequiredtransportandbearercapacityfortheprovisionoftelecommunicationservices,whichcanbeconfiguredandmanagedviathemanagementinterface(Q3).Inprinciple,thereisnorestrictiononthetypeandnumberofUNIandSNIthatcanbeimplementedbytheaccessnetwork.Theaccessnetworkdoesnotinterpretthesignaling.Theaccessnetworkcanberegardedasatransmissionnetworkthathasnothingtodowithservicesandapplications,andmainlycompletescross-connection,multiplexingandtransmissionfunctions.
Thedelimitationoftheaccessnetwork
AccordingtotheITUrecommendationontheaccessnetworkframework(G.902),theaccessnetworkcanbedefinedbythreeinterfaces,thatis,thenetworksidepassesthroughthebusinessThenodeinterface(SNI)isconnectedtotheservicenode(SN),theusersideisconnectedtotheuserterminalequipmentbytheuser-networkinterface(UNI),andthemanagementsideisconnectedtothetelecommunicationmanagementnetwork(TMN)viatheQ3interface.
SN(ServiceNode)isanentitythatprovidesservices.Itisanetworkelementthatcanbeconnectedtovariousswitchedornon-switchedtelecommunicationservices.SNisdifferentfromtraditionalnetworknode(NN).InadditiontotheswitchingfunctionofNN,SNalsoincludesswitchingservicesandtypes.Theservicenodesthatcanprovideprescribedservicesincludelocalexchanges,leasedlineservicenodes,orspeciallyconfiguredVODandbroadcastTVservicenodes.
SNI(ServiceNodeInterface)istheinterfacebetweentheaccessnetworkandtheservicenode.Itisindependentoftheservicenodeandtheswitch.ItconnectstheSNofdifferentservicestotheaccessnetworkthroughdifferentSNIs.Usersprovideavarietyofdifferentbusinessservices.ItcanbedividedintoSNIthatsupportssingleaccessandSNIthatsupportsintegratedaccess.ThestandardizedinterfacesthatsupportsingleaccessmainlyincludetheV1interfacethatprovidesISDNbasicrate(2B+D)andtheV3interfaceofprimaryrate(30B+D).TheinterfacesthatsupportintegratedserviceaccesscurrentlyhaveV5interfaces,includingV5.1,V5.2interface.
UNI(User-NetworkInterface)istheinterfacebetweentheaccessnetworkandtheuserterminal.Itcansupportthevariousaccesstypesandservicesthatthecurrentnetworkcanprovide.ThedevelopmentoftheaccessnetworkshouldnotlimitthecurrentSomeservicesandaccesstypes.Fordifferentservices,correspondingtodifferentinterfacetypes.UNIisdividedintoindependenttypeandsharedtype,independenttypeUNIsupportsoneservicenodeforoneUNI,andsharedtypeUNIsupportstheaccessofmultipleservicenodesforoneUNI.
Q3isastandardinterfaceconnectingTMN(TelecomManagementNetwork)withvariouspartsofthetelecommunicationnetwork.ThemanagementoftheaccessnetworkshouldbeincludedinthecategoryofTMNinordertocoordinatethemanagementofdifferentnetworkelementsinaunifiedmanner.Themanagementoftheaccessnetworkmustnotonlycompletethemanagementofeachfunctionalblockoftheaccessnetwork,butalsocompletethetestandfaultlocationofthesubscriberline.
WANstructuredivision
ThecoreoftheaccessnetworkconceptistodividetheentiretelecomWANintothreeparts:corenetwork,accessnetworkanduserpremisesnetwork,accessnetworkandcoreThenetworkconstitutesthetelecommunicationspublicnetwork,andtheaccessnetworkisasystemcomposedoftransmissionentitiesthatprovidetelecommunicationsservicesbetweentheServiceNodeInterface(SNI)andeachUserNetworkInterface(UNI)associatedwithit.
Theaccessnetworkisresponsibleforuseraccess,andthecorenetworkisresponsibleforbusinessprocessing.Thedivisionofthetwoisbasedondifferentfunctions.Withthisdefinition,theaccessnetworkandthecorenetworkhaveacleardivisionoflabor:theaccessnetworkadaptstothediversityofusers,andtheinconsistencyofusersisshieldedbytheaccessnetwork;whilethecorenetworkfacesthesameusers.Greatsimplificationclarifiesthenetworkarchitecture.
Inaddition,theabovecorenetworkcanbesubdividedintotwoparts:transmissionnetworkandNSPcorenetwork.ThepartofthenetworkthattransmitsdatatotheNSPcorenetworkintheaccessnetworkofthedatasenderuserortheNSPcorenetworktransmitstotheaccessnetworkofthereceiveruserisspecificallyresponsiblefordatarelaytransmission,whichiscalledthe"transmissionnetwork".TheNSPcorenetworkisusedfordataexchangeprocessing,called"switchingnetwork"
Inthisway,theentiretelecommunicationsnetworkisdividedintothreepartsaccordingtonetworkfunctions:transmissionnetwork,switchingnetworkandaccessnet.Theaccessnetworkisresponsiblefortransparentlytransmittingtelecommunicationsservicestousers.Specifically,accessistheconnectionbetweenthelocalexchangeandtheuser,whichusuallyincludessubscriberlinetransmissionsystems,multiplexingequipment,cross-connectequipment,oruser/networkterminalequipment.Infact,theentitythatprovidestheserviceistheservicenode.
Featuresoftheaccessnetwork
Accordingtotheframeworkandsystemrequirementsoftheaccessnetwork,theimportantfeaturesoftheaccessnetworkcanbesummarizedasfollows:
1.Theaccessnetworkprovidesthecarryingcapacityfortheaccessedservicesandrealizesthetransparenttransmissionoftheservices.
2.Theaccessnetworkistransparenttousersignaling.Exceptforsomeusersignalingformatconversion,signalingandserviceprocessingfunctionsarestillintheservicenode.
3.Theintroductionoftheaccessnetworkshouldnotrestricttheexistingvariousaccesstypesandservices,andtheaccessnetworkshouldbeconnectedtoservicenodesthroughlimitedstandardizedinterfaces.
4.Theaccessnetworkhasanetworkmanagementsystemindependentofbusinessnodes.ThesystemconnectstotheTMNthroughastandardizedinterface,andtheTMNimplementstheoperation,maintenanceandmanagementoftheaccessnetwork.
Differencefromcorenetwork
Ithasmultiplexing,cross-connectionandtransmissionfunctions,andgenerallydoesnothaveswitchingfunctions.ItprovidesanopenV5standardinterface,whichcanbeRealizetheconnectionwithanykindofswitchingequipment
Theaccessnetworksupportsmultipleservices,buttheservicedensityislowcomparedwiththecorenetwork.
Therequirementsforoperatingconditionsarenothigh.Comparedwiththecorenetworkequipmentgenerallyplacedinthecomputerroom,theaccessnetworkequipmentisusuallyplacedoutdoors,sotheperformanceandtemperatureadaptabilityoftheequipmentAndreliabilityhashighrequirements.
Strongnetworkingcapability,accessnetworkhasmultiplenetworkingforms.
Avarietyofaccesstechnologiescanbeused,suchascopperwireaccess,opticalfiberaccess,opticalfibercoppershafthybridaccess,wirelessaccess,etc.
Comprehensivenetworkmanagementfunctions,inadditiontoconnectingtoTMNthroughtheQ3interface,itcanalsobeconnectedtothelocalnetworkmanagementsystemthroughrelatedprotocols,whichismanagedbythelocalnetworkmanagementcenter.
Theaccessnetworkcoversawidearea.Theaccessnodecoversthewholecountry,andalltheplaceswherethetelephoneisconnectedcanaccesstheInternet.
Structure
(1)Bus-shapedstructure.Referstoanetworkstructureinwhichopticalfiberisusedasapublicbusandeachuserterminalisdirectlyconnectedtothebusthroughacoupler.Itischaracterizedbysharingthebackbonefiber,savinglineinvestment,easytoaddordeletenodes,highdynamicrangerequirements,andlessinterferencewitheachother.Thedisadvantageistheaccumulationofloss,andtheuseracceptsastrongdependenceonthebackbonefiber.
(2)Ringstructure.Referstoanetworkstructureinwhichallnodesshareanopticalfiberlink,andtheopticalfiberlinksareconnectedendtoendtoformaclosedloop.Thecharacteristicisthatitcanrealizeself-healing,thatis,withoutexternalintervention,thenetworkcanautomaticallyrecoverthetransmittedservicefromthefailurefailureinashorttime,andthereliabilityishigh.Thedisadvantageisthatthenumberofuserslinkedtoasingleringislimited,andtheinteroperabilityofmultipleringsismorecomplicated,whichisnotsuitablefordistributedservicessuchasCATV.
(3)Starstructure.Thisstructureisactuallyapoint-to-pointmode,andeachuserterminalexchangesinformationthroughastarcouplerwithcontrolandswitchingfunctionsatthecentralnode.Itischaracterizedbysimplestructure,convenientuseandmaintenance,easyupgradeandexpansion,relativeindependenceamongusers,goodconfidentiality,andstrongbusinessadaptability.Thedisadvantageisthatthecostoftherequiredopticalfiberishigh,thenetworkflexibilityispoor,andthereliabilityofthecentralnodeisextremelyhigh.
(4)Treestructure.Similartotheshapeofatreebranch,ithasahierarchicalstructure.Multiplesplittersareusedatthetransferboxandthejunctionboxtodistributethesignallevelbylevel.Themostadvancedendofficehasastrongcontrolandcoordinationability.Thecharacteristicisthatitissuitableforbroadcastingbusiness.Thedisadvantageisthatthepowerlossislarge,andthetwo-waycommunicationismoredifficult.
Technologydevelopmentpower
Sofar,thecommunicationnetworkhasundergoneearth-shakingchanges,fromanalogtodigital,fromcabletoopticalcable,fromPDHtoSDH,fromSTMtoATM,fromATMToIP/DWDM...,newtechnologiesandnewsystemsareemergingfromgenerationtogeneration.However,mostofthenewtechnologiesandnewsystemsareappliedtothebackbonenetwork,andtheuseraccessnetworkisstilldominatedbytheanalogtwistedpairtechnology.Duetothedevelopmentofsocialeconomyandcommunicationtechnology,purevoiceserviceshavebeenunabletomeettheneedsofusersandthemarket,especiallytheemergenceofopticalfibertechnology,andtheincreaseinusers’demandfornewservices,especiallybroadbandimageanddataservices.Thestructureofthenetworkhasbroughtanimpact,andithasalsobroughtaturningpointforthetransformationandrenewaloftheuser'saccessnetwork.Inshort,users'demandforbroadbandintegratedservicesandtherapiddevelopmentofcommunicationtechnologyhavebecomethetwomajordrivingforcesforthedevelopmentofaccessnetworktechnology.
Implementationtechnology
Traditionalaccessnetworksmainlyprovideuserswithgeneralvoiceservicesandasmallamountofdataservicesintheformofcoppercables.Withthedevelopmentofsocietyandeconomy,people’sdemandforvariousnewservices,especiallybroadbandintegratedservices,isincreasing.Aseriesofnewaccessnetworktechnologieshaveemerged,includingthemorewidelyusedcoppercablesbasedonexistingtwistedpairs.Newcabletechnology,hybridfiber/coaxial(HFC)technologyandhybridfiber/wirelessaccesstechnology,wirelesslocallooptechnology(WLL/DWLL)andEthernettothehometechnology[ETTH(fibertotheroadside,fibertothebuilding,ThecollectivenameofFibertoAnywhere)+ETTH(EthernetTotheHome)].
(1)Newcoppercabletechnologybasedontwistedpair.Atpresent,theuseraccessnetworktechnologyismainlycomposedofcoppercablescomposedofmultipletwistedpairs.Itcostsalotofmoney.Howtomakeuseofitsbenefitsandmeettheneedsofmultiplenewservicesasmuchaspossibleisthemaintopicforthedevelopmentofuseraccessnetworks,anditisalsothemainmeansfortelecomoperatorstocopewithcompetition,reducecosts,andincreaserevenue.Thedevelopmentofnewtechnologiesandthefulluseoftwisted-paircableshavealwaysbeenafocusofthetelecommunicationsindustry.Theso-calledcopperwireaccesstechnologyreferstotheuseofadvanceddigitalprocessingtechnologytoincreasethetransmissioncapacityoftwisted-pairwiresonnon-inductivesubscriberlines,andtoprovideuserswithvariousservices,mainlydigitalpairgain(DPG)),highbitratedigitalsubscriberline(HDSL),asymmetricdigitalsubscriberline(ADSL),veryhighdataratesubscriberline(VDSL)andothertechnologies.
(2)Hybridfiber/coaxial(HFC)network.Hybridopticalfiber/coaxialnetworkisabroadbandaccesstechnologybasedonfrequencydivisionmultiplexingtechnology.Itsbackbonenetworkusesopticalfiberandusesfrequencydivisionmultiplexingtotransmitavarietyofinformation.Thedistributionnetworkusestreetopologyandcoaxialcables.Thesystemisusedtotransmitanddistributeuserinformation.HFCisaneweconomicevolutionstrategythatgraduallypushesopticalfibertousers,anditcanrealizemultimediacommunicationandinteractivevideoservices.Atpresent,manyinternationalorganizationsandforums,includingITU-T,arestandardizingthenext-generationdigitalHFCsystemcombiningMPEG-2andATM,whichwillsurelyfurtherpromoteitsdevelopment.
(3)FTTx+ETTH.FTTH+ETrHisafibertothebuilding,fibertothesideoftheroad,andEthernettotheuser.Itprovidesuserswithhigh-reliabilitybroadbandguarantees,trulyrealizinggigabittoresidentialarea,100megabittobuildingunitandtenmegabittohome.Withthefurthergrowthofbroadbanddemand,itcanbesmoothlyupgradedtoachieve100megabitstoThefamilydoesnotneedtore-wiring.Fullyrealizeservicessuchasmultimediacommunicationandinteractivevideoservices.Forexample,thebroadbandaccesssystemoftheHaijunLianbaoErlilivingquarteradoptsthistechnology.
(4)Wirelesssubscriberloopaccessnetwork.Thewirelesssubscriberloopcanalsobecalled"wirelessuseraccess".Itusesmicrowave,satellite,wirelesscellularandotherwirelesstransmissiontechnologiestorealizethebusinessaccessofmultiplescatteredusersorusergroupsinremoteareasandislandsintheblindspotsofsubscriberlines.Incomingusersaccessthesystem.Ithasthecharacteristicsoffastconstructionspeed,fastandflexibleequipmentinstallation,andconvenientuse.Inthecaseofwireless,thecostofuseraccessisnotsensitivetotransmissiondistanceanduserdensity.Therefore,itisverysuitableforareaswithlongaccessdistanceandlowuserdensity.
Thenecessityandimportanceofaccessnetworkconstruction
1.Inevitablerequirementsforbusinessdevelopment
Businessneeds
·ThepromotionandapplicationofSDHandATMtechnologyonthetrunknetwork
·Theaccessnetworkisrequiredtoprovideabroadbandtransmissionchannel
·CopperusernetworkThechannelcapacityissmall,thefrequencybandisnarrow,anditisnoteasytoexpandanddigitize.
Ithasbecomeabottleneckintherealizationoftelecommunicationsnetworks
·Thedevelopmentdirectionoftelecommunicationsservicesisthedigitization,integration,andintegrationofcommunicationnetworks.
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Broadband,intelligenceandpersonalization
·Thecontradictionbetweenthebroadbandization,digitalizationandintegrationofbusinessneedsandthecurrentbackwardaccessmethodshasbeenBecomeoneofthemaincontradictionsintheconstructionoftelecommunicationsnetworks.
2.Animportantlinkinreducingbusinesscostsandimprovingeconomicbenefits
·Program-controlledswitchesandopticalfibercablesforrelaytransmission
·Thetelephoneofficetotheuser(accessnetwork)isstillanalogtransmission
·Theaccessnetworkisthewindowoftheentiretelecommunicationsnetwork,anditisalsothe"lastpublic
in"ofthetelecommunicationsnetwork,Theinvestmentproportionaccountsforabout50%ofthetotalinvestmentinthetelecommunicationsnetwork
·Thequalityofanalogtransmissionisnotgood,thebearerserviceislimited,andalargeamountofnon-ferrousgoldisconsumed
Belongto—copper
·Cablepricesaregraduallyincreasing
·Thepricesofopticalfibertransmissionsystemsareonadownwardtrend
·WiththeprovisionandpracticalizationofV5interfaces,thecostofaccesssystemswillbefurtherreduced
·Maintenancecostsaremuchlowerthanusingcoppercables
·Vigorousandcomprehensivedevelopmentofaccessnetworksisalsoaninevitablerequirementforoperatingcostaccounting.
3.Optimizethenetworkstructureanddeepenthereformofthetelecommunicationsnetworkoperationandmaintenancesystem
·BuildanewgenerationofaccessnetworkandlaytheopticalfiberclosesttotheuserPlace
(community,building)
·Dismantlepointsandconnecttothegrid,buildtheoverallsituation,optimizethenetworkstructure
·Centralizemaintenancepersonnel,centralizedmonitoringandmaintenance.
4.Theneedforcompetitioninthetelecommunicationsmarket
·Thenetworkisclosetousers,quicklyprovidesavarietyofservices,andhasmarketinitiative
·Theexclusivemonopolyofpostandtelecommunicationshasbeenbroken
·Twoadvantages:oneistalentadvantage,andtheotherisnetworkadvantage
·ExpandingandmaintainingnetworkadvantagesandvigorouslydevelopingaccessnetworksareTelecommunicationnetworkconstruction
Strategicmeasuresfordevelopment.
Developmenttrend
Withthedisappearanceofthemonopolymarketinthetelecommunicationsindustryandtheopeningofthetelecommunicationsnetworkbusinessmarket,thetelecommunicationsbusinessfunctionsandaccesstechnologycontinuetoimprove,andtheaccessnetworkalsodevelops.Mainlymanifestedinthefollowingpoints:
(1)Thecomplexityoftheaccessnetworkisconstantlyincreasing.Thecompetitionandcomprehensiveuseofdifferentaccesstechnologies,aswellasthesupportforalargenumberoftelecommunicationservices,haveincreasedthecomplexityoftheaccessnetwork.
(2)Theservicerangeoftheaccessnetworkisexpanding.Withthedevelopmentofcommunicationtechnologyandcommunicationnetwork,thecapacityoflocalexchangesisconstantlyexpanding,andthenumberofexchangesisdecreasingdaybyday.Wherethecapacityissmall,hubsandmultiplexersareusedinstead,whichmakestheaccessnetworkThescopeofservicescontinuestoexpand.
(3)Thestandardizationofaccessnetworksisincreasingdaybyday.AfterlocalexchangeofficesgraduallyadoptopeninterfacesbasedontheV5.Xstandard,telecomoperatorsaremorefreetochooseaccessnetworktechnologyandsystemequipment.
(4)Theaccessnetworkshouldsupporthigher-endservices.Thedevelopmentofthemarketeconomyhaspromptedcommercialandcorporatecustomerstorequirelargercapacityaccesslinesfordataapplications,especiallylocalareanetworkinterconnections,requiringreliableandshort-termconnections.Withtheextensionofopticalfibertechnologytousernetworks,thedevelopmentofCATVhasbroughtopportunitiesforthedevelopmentofuserloops.
(5)Thetechnologiessupportingtheaccessnetworkaremorediversified.Althoughthecontentofopticaltransmissionintheaccessnetworkisincreasing,howtomakebetteruseoftheexistingtwisted-paircableisstillpaidattentionto,butforthelarge-capacityaccesslinethatrequiresrapidconstruction,youcanchooseWirelesslink.
(6)Opticalfibertechnologywillbemoreappliedtotheaccessnetwork.Withtheexpansionofopticalfibercoverage,opticalfibertechnologywillincreasinglybeusedinaccessnetworks.Fromadevelopmentperspective,SDH,ATM,andIP/DWDMarecurrentlyonlyapplicabletotrunkopticalcablesectionsanddigitalcentralofficeinterfaces.Withthedevelopmentofbusiness,theopticalfiberinterfacewillbefurtherextendedtotheroadside,andfinallyintothehome,realizingbroadbandopticalfiberaccess,andrealizingaunifiedbroadbandall-opticalnetworkstructure.Therefore,thetelecommunicationsnetworkwilltrulybecomeasolidinformationhighwayinthiscentury.Networkfoundation.
Thedevelopmentoftheaccessnetworkhasgonethroughthefollowingfourstages:
Thefirststageoftheaccessnetwork-purevoiceaccessandopticalfiberaccess.
Thesecondphaseoftheaccessnetwork-preliminaryintegration,includingPOTS,ISDN,DDN,etc.
Thethirdstageoftheaccessnetwork-broadbandandnarrowbandintegration,suchascombinedtypeandconvergedtype.
Thefourthstageoftheaccessnetwork-evolutiontoNGN,toachievethedockingwithNGN,andacomprehensivetransitiontoapacketnetwork.
Supportservices
Servicessupportedbytheaccessnetwork
·Voiceservices:programcontrolNewtelephoneservices,magneticcardtelephoneservices,etc.
·Dataservices:DDNservices,packetswitchingservices,etc.
·Imagecommunicationservices:ConferenceTVservices,videophoneservices,etc.
·Multimediaservices:homeoffice,shopping,VOD,telemedicine,etc.