Packet switched network

Introduction

PacketSwitchedDataNetwork(PSDN)technologyoriginatedinthelate1960s,withmaturetechnologyandcompleteregulations,andiswidelyusedincountriesallovertheworld.Thebackbonenetworkofmycountry'spublicpacketswitcheddatanetworkwasofficiallyopenedforbusinessinSeptember1993.ItwasthefirstpublicdatacommunicationnetworkestablishedbytheformerMinistryofPostsandTelecommunications.Thebackbonenetworkhasacapacityof5,800portsintheinitialstageofnetworkconstruction,andthenetworkcovers31provincialcapitalsandmunicipalitiesdirectlyundertheCentralGovernment.Subsequently,eachprovincesuccessivelyestablishedapacket-switcheddatacommunicationnetworkwithintheprovince.Thebusinessofthenetworkisdevelopingrapidly,andbySeptember1998,thenumberofusershasexceeded100,000.Sincetheopeningofthenetwork,thenumberofpacketswitchingnetworkportshasgrownfrom5,800tonearly300,000.Thenetworkcoveragehasexpandedfrom31citiesto2,278citiesatthecountylevelandabove,andisconnectedtopacketdatanetworksin23countriesandregions.Thenetworkscaleandtechnicallevelhaveenteredtheworld'sadvancedranks.TheopeningofChinaPAChasgreatlyfacilitatedthecomputernetworkingoffinancial,government,multinationalenterprisesandothercustomers,realizedtheintegrationofdomesticdatacommunicationwithinternationalstandards,improvedthecomprehensivecompetitivenessofdomesticenterprises,andmetthedatacommunicationneedsofreformandopeningup.

Packetswitching

Packetswitchingisanadvancedcommunicationmethoddevelopedtoadapttocomputercommunication.ItisbasedonCCITTX.25recommendationsandcanmeetdifferentspeedsanddifferenttypesofterminalsThecommunicationwiththeterminal,theterminalandthecomputer,thecomputerandthecomputer,andthelocalareanetworkrealizesthesharingofdatabaseresources.Thepacket-switchednetworkisthebasicnetworkofdatacommunication,andvariousvalue-addedservicescanbedevelopedusingitsnetworkplatform,suchas:electronicmail,electronicdataexchange,visualtext,faxstorageandforwarding,anddatabaseretrieval.

Theoutstandingadvantageofpacketswitchingnetworkisthatmultiplevirtualcircuitscanbeopenedononecircuitatthesametime,whichcanbeusedbymultipleusersatthesametime.Thenetworkhasdynamicroutingfunctionandadvancederrorcorrectionfunction,andthenetworkperformanceisthebest.good.ChinaPublicPacketSwitchedDataNetworkisanationwidepacketswitcheddatanetworkoperatedbyChinaTelecom.Thenetworkhasdirectlycoveredallprefecturesandcitiesandmostcounties.Thetelephonenetworkcancoverallcitiesaccessibletothetelephonenetwork.Userscanusededicatedlinesnearby.Ordialintothenetworkbytelephoneandusepacketswitchingservices.

Features

–Hightransmissionquality

–Highreliabilityanddynamicroutingfunction.Whenthenetworkfails,aslongasthereisacommunicationroute,theswitchwillCanchoosetrouble-freeroutingtotransmitpackets.

–Highlineutilization,communicationnetworkresourcesusestatisticaltimedivisionmultiplexing

–Therate,codetype,andprotocolcanbeconverted,allowingdifferenttypes,differentrates,differentencodingformats,andTocommunicatewitheachotherbetweenterminalsofdifferentcommunicationprocedures,flowcontrolmeasurescanbeadopted.

BusinessfunctionsprovidedbyCHINAPAC

CHINAPACprovidestwobasicservices

Circuit(SVC)

Whenausercommunicates,avirtualcircuitisestablishedthroughacall,andthevirtualcircuitisreleasedafterthecommunicationends.Switchedvirtualcircuitsareflexibletouse,andvirtualcircuitscanbeestablishedwithdifferentuserseachtime,andthecommunicationfeeisrelatedtotheamountofcommunication.CHINAPACcanopenmultiplevirtualcircuitsforusers.

Permanentvirtualcircuit(PVC)

Permanentvirtualcircuitissimilartoafixeddedicatedline.Itisproposedbytheuserwhenapplying,andthetelecommunicationsdepartmentfixesit,andtheuserwillestablishthecircuitassoonasitisturnedon.,Itisnotnecessaryforeachcommunicationtobetemporarilyestablishedandreleased.Itisusedforuserswithafixedpoint-to-pointconnection.

OtherservicesprovidedbyCHINAPAC

Prioritygrouping,multiplenetworkaddresses,ignorecheckinglocaladdresses,billingtransfer,mnemonicnameaddressing,virtualprivatenetwork,packetmulticast.

UseraccessprotocolssupportedbyCHINAPAC

CCITTX.25,X.28,X.29,X.32,X.3,X.75protocols,etc.

IBMSNAnetworkprotocol,T3POS,tokenring,framerelay,TCP/IPprotocol,etc.

Networkaccesscommunicationrate

1.Dial-upaccess:Connectamodem(modem)tothephoneanddial-upaccesstothenetwork,andtheuserneedstoapplyforanetworkaccessidentificationcode.ItcanbedividedintoX.28AsynchronousdialingintothenetworkorX.32synchronousdialingintothenetworkorX.32synchronousdialingintothenetwork,therateofdialingintothenetworkis1200-9600bpsandadaptivedownwards.

2.Dedicatedlineaccesstothenetwork:leaseapairoflocaltelephonelinestoconnecttothecentralofficepacketswitchingequipment,thecommunicationrateis600bps～64kbps.ItcanbedividedintoX.28asynchronousdedicatedlineintothenetworkorX.25/SDLCsynchronousdedicatedlineAccesstothenetwork,accesstothenetworkdedicatedlinescanbedividedintoanalogdedicatedlinesandDDNdigitaldedicatedlines.Inthecaseofanalogdedicatedlines,therateis1200-19200bps.InthecaseofDDNdigitaldedicatedlines,therateis1.2-256Kbps

Thepacketswitchingnetworkisasafeandreliabledatacommunicationnetworkplatform.Thepacketswitchingnetworkisbasedontheadvancedmoderntelecommunicationsnetwork,andthenetworkisatwo-levelnetworkcombiningmeshnetworkandstarnetwork.Thenetworkhasacircuitousroutingfunction,whichhasbetterreliabilityanderrorresistanceperformance;thepacketswitchingnetworkhasadvancedThecentralizednetworkmanagementcentercanprovideuserswithmoresatisfactoryservices;thepacketswitchingnetworkmainlyadoptsimportedequipment,withstrongsystemprocessingcapacityandunifiednetworkfunctions.Itcantransitiontothebroadbandswitchingnetworkinabalancedmanner.Itisanidealchoicefordatacommunication.

Inrecentyears,theconstructionofChina'spublicdatacommunicationnetworkhasbeenrapid.ThetelecommunicationssectorhasestablisheddigitalcommunicationnetworkssuchasCHINAPAC,CHINADDN,andCHINAFRN,formingmycountry'spublicdatacommunicationnetwork.

Development

ChinaPublicPacketExchangeDataNetwork(ChinaPAC)wasopenedinSeptember1993.Bytheendof1996,ithascoveredcitiesabovethecountylevelandsometownshipsindevelopedregions,andhasreached23countriesintheworld.Interconnectedwith44datanetworksintheregion.

(1)NetworkstatusThepacketswitchingnetworkistheearliestbasicdatacommunicationnetworkconstructedanddevelopedbythepostandtelecommunicationsdepartment.ThepacketswitchingnetworkisbasedontheCITTX.25recommendation,whichcanmeetthecommunicationbetweenterminalsandcomputersofdifferentspeeds,differentmodels,computersandcomputers,andcomputerlocalareanetworks.Thepacketswitchingnetworkisabasicdatacommunicationnetwork,andvariousvalue-addedservicescanbeconstructedonitsnetworkplatform,suchas:electronicmail,electronicdataexchange,faxstorageandforwarding,etc.

CHINAPACiscomposedofthenationalbackbonenetworkandtheintra-provincialnetworkofeachprovince(cities,districts).Atpresent,thebackbonenetworkcoversallprovincialcapitalcities,andtheintra-provincialnetworkcoversallcitiesanddevelopedtownsthathavebusinessrequirements.Throughtheinterconnectionwiththetelephonenetwork,CHINAPACcancoverallareasreachedbythetelephonenetwork.CHINAPAChasaprimaryswitchingcenterandasecondaryswitchingcenter.Anincompletemeshstructureisusedbetweentheprimaryswitchingcenters,andastarstructureisusedbetweentheprimaryswitchingcenterandthesecondaryswitchingcenter;CHIANIPAChasinternationalofficesinBeijingandShanghai.Forentrancesandexits,GuangzhouhasentrancesandexitstoHongKongandMacautocompletethenetworkwithinternationaldata.

(2)Networkcharacteristicsandbusinessfunctions.Theoutstandingadvantageofthepacketswitchingnetworkisthatmultiplevirtualcircuitscanbeopenedonaphysicalcircuitatthesametime,whichcanbeusedbymultipleusersatthesametime;thenetworkhasdynamicroutingfunctionsandcomplexityCompleteerrorcorrectionfunction.TheX.25protocolwasdevelopedwhenthetransmissionqualityofthephysicallinkisverypoor.Inordertoensurethereliabilityofdatatransmission,itmustperformerrorcheckinganderrorretransmissiononeachlink;thiskindofcomplexerrorAlthoughtheverificationmechanismlimitsitstransmissionefficiency,itdoesprovideagoodguaranteeforthesecuretransmissionofuserdata.

TheservicesprovidedbyCHINAPACareasfollows:

l.Basicbusinessfunctions

Basicbusinessfunctionsrefertothebasicbusinessfunctionsprovidedbyanydigitalterminalequipment(DTE).Itcanmeetthebasicrequirementsofusersforcommunication.Therearetwotypesofbasicservices,switchedvirtualcircuit(SVC);permanentvirtualcircuit(PVC)

2.Optionalbusinessfunctions

UserscanchoosebusinessfunctionstosatisfyusersSpecialneeds,specialservicefunctionsprovidedtousers,suchasincomingcallblocking,outgoingcallblocking,unidirectionalinboundlogicalchannel,unidirectionaloutboundlogicalchannel,etc.

3.Otherbusinessfunctions

CHINANETalsoprovidesotherbusinessfunctionsrecommendedbyITU-T,suchasvirtualprivatenetwork(VPN),TCP/IP,packetmulticast,callChangedirectionandsoon.

(3)Useraccessmethod

Accessmethod

1.Dedicatedlinemethod

Suitableforlargecommunicationtrafficandfrequentuse,Applicationsthatrequirehighreliabilityandnoloss,butneeddedicatedlines,andthecostisrelativelyhigh.Thenetworkaccessrateofthededicatedlineis9.6~64KBPS.

2.Telephonedialingissuitableforapplicationsthathavelowbusinessvolume,longintermittenttime,andcantoleratecallfailures.Becauseitusestheexistingtelephoneline,noadditionalinvestmentisrequired,andthedatacanbesharedwiththevoiceline,soinvestmentisgreatlysaved,anditisanidealaccessmethodforscatteredusers.Itcanbedividedintox.28asynchronousdial-upnetworkaccessorX.32synchronousdial-upnetworkaccess.Thedial-upnetworkaccessrateisl200-9600BPS

TariffPolicy

CHINAPACcurrentlyhastwochargingmethods,oneisHourlymeteringcharges,andthesecondisamonthlyfee.Hourlymeteringcharges.WideapplicationfieldandbusinesspositioningComparedwithDDNandframerelay,packetservicechargesarecheaper,anditisthemosteconomicalchoiceforuserstoconstructtheirinternalWAN.Inthecaseofsimultaneousestablishmentofmulti-pointconnections,thevirtualcircuitfunctionofthepacket-switchednetworkcanreplaceexpensivemulti-pointDDNdedicatedlines.However,duetothecomplexityoftheX.25protocolitself,packetservicesareusedinlow-speedapplicationswheretherateislowerthan64K.Forexample,withthecontinuousadvancementofthegoldcardproject,theuseofPOSmachinesisbecomingmoreandmorepopular.ThePOSbusinessvolumeissmall,butthereal-timerequirementsarehigh.Non-packetnetworkinterconnectionisaverygoodsolutiontorealizethecommunicationbetweenthePOSmachineandthehost..