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Access Network



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

  1. Ithasmultiplexing,cross-connectionandtransmissionfunctions,andgenerallydoesnothaveswitchingfunctions.ItprovidesanopenV5standardinterface,whichcanbeRealizetheconnectionwithanykindofswitchingequipment

  2. Theaccessnetworksupportsmultipleservices,buttheservicedensityislowcomparedwiththecorenetwork.

  3. Therequirementsforoperatingconditionsarenothigh.Comparedwiththecorenetworkequipmentgenerallyplacedinthecomputerroom,theaccessnetworkequipmentisusuallyplacedoutdoors,sotheperformanceandtemperatureadaptabilityoftheequipmentAndreliabilityhashighrequirements.

  4. Strongnetworkingcapability,accessnetworkhasmultiplenetworkingforms.

  5. Avarietyofaccesstechnologiescanbeused,suchascopperwireaccess,opticalfiberaccess,opticalfibercoppershafthybridaccess,wirelessaccess,etc.

  6. Comprehensivenetworkmanagementfunctions,inadditiontoconnectingtoTMNthroughtheQ3interface,itcanalsobeconnectedtothelocalnetworkmanagementsystemthroughrelatedprotocols,whichismanagedbythelocalnetworkmanagementcenter.

  7. 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.

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