Introduction
Itissuitableforthecommunicationbetweencomputersandcomputers,computersandterminals,andterminalsandterminalsofdifferenttypesandspeeds,soastorealizethesharingofinformationresourcesstoredinthecomputer.Atthesametime,variousvalue-addedservicescanbedevelopedonthepacket-switcheddatanetwork[1].
Advantages
1.Multi-partycommunicationcanberealized,greatlyimprovinglineutilization;
2.Hightransmissionrate,safeandreliableinformationtransmission;
3.Thechargehasnothingtodowiththedistance,anditischargedaccordingtotheamountofinformationandtimeofuse,whichshowsincomparablesuperiorityforremotecommunication;
4.Strongerrordetectionandcorrectioncapabilities;applyforanaccount,Password(NUI),canrealizenationalroaming.
Providingservices
3.1Basicbusiness
1.Switchedvirtualcircuit(SVC):Itcancommunicatewithdifferentusersatthesametime,whichisconvenientandflexible.TwodataWhentheterminalwantstocommunicate,usethecallingprogramtoestablishthevirtualcircuitfirst,andusethereleaseprogramtoreleasethevirtualcircuitafterthecommunicationends.Avirtualcircuitisalogicalconnectionbetweentwodataterminalsincommunication.Itisonthetrunklinebetweenitssubscriberlineandtheswitch.Accordingtotheneedsofthemessage,itoccupiesmultipletimeslotsintheunitofpacketlengthandthecorrespondingswitchintheswitch.storage.Thevirtualcallserviceprovidesreliabledeliveryofpacketsanddeliversthemtotheuserinthesameorderasthepacketsreceivedbythenetwork.
2.Permanentvirtualcircuit(PVC):Itcanestablishafixedconnectionwithoneormoreusers.Permanentvirtualcircuit(PVC)providesapermanentlogicalconnectionfortwodataterminalsinthepacketnetworkduringtheappliedcontractperiod,withouttheneedforcallestablishmentandreleaseprocedures,andisthesameasVCinthedatatransmissionstage.
3.2Optionalbusinessfunctions
1.Closedusergroup(CUG):Communicationislimitedtospecificuserstoavoidinterferencefromoutsiders.
2.NetworkUserIdentity(NUI):Providesstrictsecurityguaranteesandcanrealizenationwideroaming.
3.Broadcastingservice:unidirectionalpoint-to-multipointinformationtransmission.
4.Reversecharging:thecalledpartypays.
5.Quickselection:Thiskindofbusinessissuitableforbankwithdrawalbusiness,butbothpartiesmustbeuserswhocanacceptthequickselectionbusiness.
6.Blockincoming/outgoingcalls:Theuserdoesnotreceivecalls/outgoingcallswithinaperiodoftime,butcanmakeoutgoingcalls/receiveincomingcalls.
7.Callforwarding:Whentheuserisbusyorfails,theswitchautomaticallytransferstheuser'scalltothenumberreservedbytheuser.
8.Searchgroup(HG):Whenauserhasmultiplelinesconnectedtothenetwork,balancetheloadoneachlineinordertoincreasethecall-throughratewhenthecustomeriscalled.
3.3Newbusinessfunctions
1.FrameRelay(FrameRelay):Provideshigherratecommunicationtorealizevoice,data,andimagedata.
2.Comprehensivetransmission;informationcardverificationservice(POS):simultaneoustransmissionofdataonatelephonelinewithoutmutualinterference,2-3timesfasterthantraditionalPOSservices;
3.Virtualprivatenetwork;
4.SNAnetworkenvironment;
5.Token-ringLANsmartbridgefunction;
6.Asynchronouspollinginterface(APT).
Supplementaryservicesoptionalbyusers
Therearetwotypesofsupplementaryservicesoptionalbyusers.Supplementaryservicesonacallbasis.Theformerhasextendedpacketsequencenumbers(modulo128),non-standarddefaultwindowsize,non-standarddefaultpacketlength,closedusergroupacceptanceofreversebillingandacceptanceofquickselectionitems;thelatterhasclosedusergroupselection,reverseQuickselectionofbillingandabbreviatedcalls.
Scopeofapplication
Banking,insurance,securities;customs;taxation;retailindustry;othercompanies,enterprises,andinstitutionsthatneedtorealizecomputernetworking;
TongdaLocation
1.Mostofthecountry,citiesabovethecitylevel,andsometownshipsandcounty-levelcities.
2.InternationalincludesHongKong,Macao,Taiwan,Europe,America,Japanandothercountriesandregions.
Equipmentcomposition
Thepacket-switcheddatanetworkiscomposedofpacketswitches,networkmanagementcenters,remoteconcentrators,sub-assemblyanddisassemblyequipment,andtransmissionequipment.
Packetswitch:Themainfunctionistorealizetheinterfaceprotocol(X.25)betweenthedataterminalandtheswitch,thesignalingprotocolbetweentheswitches(suchasX.75),andprovidestorageandforwardinginpacketmodeSupportspacketnetworkservices,andcooperateswiththenetworkmanagementcentertocompleteroutingmonitoring,billing,control,etc.Accordingtothestatusofthepacketswitchinthenetwork,itcanbedividedintotwotypes:transitswitchandlocalswitch.Theformerismainlyusedtocompletethestorageandforwardingofpacketsbetweenswitchesinthepacketbackbonenetwork,andthelattermainlycompletestheuserinterfaceandlocalswitchingfunctions.Accordingtothecapacityofpacketprocessingcapacityandthenumberofports,therearelarge,mediumandsmallcapacityswitches.Thelarge-capacitypacketswitchcanprocesstensofthousandsofpacketspersecondandhasthousandsofports;thesmall-capacitypacketswitchcanprocesshundredsofpacketspersecondandhasdozensofports.
NetworkManagementCenter:cooperatewiththepacketswitchtoensurethenormaloperationofthenetwork.Thenetworkmanagementcentercanbedividedbyareaandfunction,withoneormore.Itsmainfunctionsincludenetworkmanagement,usermanagement,measurementmanagement,billingmanagement,operationandmaintenancemanagement,routingmanagement,collectingpartialorentirenetworkstatisticalinformation,andnecessarycontrolfunctions.
Padassemblyanddisassemblyequipment(PAD):Themainfunctionistoconvertthenon-packetformatofordinarycharacterterminalsintoagroupformat,andgroupthecharacterdatastreamsofeachterminalintogroups,whichareinterleavedandmultiplexedontheaggregatechannel.,Theotherpartythenconvertsthereceivedpacketformatintheoppositedirection.TheuserportsofsomePADsalsohaveinterfacessuchasX.20,SDLC,etc.,therebyallowingcorrespondingsynchronousterminalstoaccessthePAD.Itsfunctioncanberealizedintheswitch,andcanalsoberealizedbyaseparatedevice.
RemoteConcentrator:Itsfunctionissimilartothatofapacketswitch.ItusuallycontainsthefunctionofPAD,butitcanonlybeconnectedtoapacketswitch,sonoroutingfunctionisneeded.Someconcentratorscanalsobeconnectedtotwopacketswitches,sotheyhavesimpleroutingfunctionsandlocalswitchingfunctions.Itismainlyusedforsynchronousandasynchronousdataterminalsfarawayfromthepacketswitchtoaccessthepacketdatanetworktoreducethelinecostandoccupymorepacketswitchports.