Overview
Packetswitchingtechnologyisthedevelopmentofcomputertechnologytoacertainextent.Inadditiontocallingpeopledirectlytocommunicate,packetswitchingaddsapacketheaderinfrontofeachpackettoindicateTheaddressofthepacketissentto,andthentheswitchforwardsthemtothedestinationaccordingtotheaddressflagofeachpacket.Thisprocessiscalledpacketswitching.
Thecommunicationnetworkforpacketswitchingiscalledthepacketswitchingnetwork.Fromtheperspectiveofthedevelopmenthistoryofswitchingtechnology,dataswitchinghasexperiencedthedevelopmentprocessofcircuitswitching,messageswitching,packetswitchingandintegratedservicedigitalswitching.Packetswitchingisessentiallydevelopedonthebasisof"store-and-forward".Ithastheadvantagesofcircuitswitchingandmessageswitching.Thepacketswitchinglineusesdynamicmultiplexingtechnologytotransmitdatadividedintomanysmallsegmentsaccordingtoacertainlength-packet.Aftereachgroupisidentified,adynamicmultiplexingtechnologyisadoptedonaphysicallinetotransmitmultipledatapacketsatthesametime.Thedatafromtheuseroriginatingterminalistemporarilystoredinthememoryoftheswitch,andthenforwardedinthenetwork.Atthereceivingend,thepacketheaderisremovedandthedatafieldsaresequentiallyreassembledintoacompletemessage.Packetswitchinghashighercircuitutilizationthancircuitswitching,haslesstransmissiondelaythanmessageswitching,andhasbetterinteractivity.
Thepacketswitchingnetworkisanewtypeofswitchingnetworkafterthecircuitswitchingnetworkandthemessageswitchingnetwork.Itismainlyusedfordatacommunication.Packetswitchingisastore-and-forwardswitchingmethod.Itdividestheuser'smessageintopacketsofacertainlength,andusesthepacketasstore-and-forward.Therefore,ithasahigherutilizationratethancircuitswitchingandasmallerdelaythanmessageexchange.,Andhastheabilityofreal-timecommunication.Packetswitchingusestheprincipleofstatisticaltimedivisionmultiplexingtomultiplexadatalinkintomultiplelogicalchannels,andfinallyconstituteaninformationtransmissionpathbetweenthecallingandcalledusers,whichiscalledavirtualcircuit(VC)torealizedatagroupingTransmit.
Thepacketswitchingnetworkhasthefollowingcharacteristics:(1)Packetswitchinghasthecapabilityofmultiplelogicalchannels,sothecircuitutilizationrateofthetrunkishigh;(2)Differentcodetypes,speedsandprocedurescanberealizedonthepacketswitchingnetworkIntercommunicationbetweenterminals;(3)Sincepacketswitchinghastheabilitytodetectandcorrecterrors,theerrorrateofcircuittransmissionisextremelysmall;(4)Thenetworkmanagementfunctionofpacketswitchingisstrong.
Thebasicbusinessofpacketswitchingincludesswitchedvirtualcircuit(SVC)andpermanentvirtualcircuit(PVC).Switchingvirtualcircuitsisthesameasatelephonecircuit,thatis,whentwodataterminalswanttocommunicate,theyfirstestablishacircuit(ievirtualcircuit)withacallprogram,thensenddata,anduseadisconnectprogramtoremovethevirtualcircuitafterthecommunicationisover.Thepermanentvirtualcircuitislikeadedicatedline.Apermanentlogicalconnectionisprovidedbetweentwoterminalsinthepacketnetworkduringthecontractapplicationperiod,withouttheneedforcallestablishmentanddisconnectionprocedures.Inthedatatransmissionstage,itisthesameastheswitchedvirtualcircuit.
Thepacketswitcheddatanetworkiscomposedofpacketswitches,networkmanagementcenters,remoteconcentrators,subassemblyanddisassemblyequipment,andtransmissionequipment.
DevelopmentHistory
PacketswitchingwasinventedbyDonaldDaviesandPaulBaranintheearly1960s.SomepeoplethinkthatLeonardCranrockwasalsotheinventorofpacketswitching,butDaviesarguedthisbeforehisdeathandpointedoutthatCranrock’sresearchisactuallyaboutqueuingtheory,whichisthekeytheoreticalbasisofpacketswitching.Cranrock’spublishedworkdoesnotmentionclearlydividingusermessagesintosegmentsandsendingthemseparatelyviatheInternet.ThisisthemostimportantinnovationofBaranandDavies.
Circuitswitching
Circuitswitchingreferstothecommunicationbetweencomputerterminalswhenonepartyinitiatesacallandmonopolizesaphysicalline.Whentheswitchcompletestheconnectionandtheotherpartyreceivesthesignalfromtheinitiator,thetwopartiescancommunicate.Thetwopartieshavebeenoccupyingthecircuitduringtheentirecommunicationprocess.Itischaracterizedbystrongreal-timeperformance,lowtimedelay,andlowswitchingequipmentcost.However,italsobringsdisadvantagessuchaslowlineutilization,longcircuitconnectiontime,lowcommunicationefficiency,andinabilitytocommunicatebetweendifferenttypesofterminalusers.Circuitswitchingismoresuitableforcommunicationbetweenfixedusers,whicharefrequentlyusedwithlargeamountofinformationandlongmessages.
MessageExchange
Storeusermessagesinthememoryoftheswitch.Whentherequiredoutputcircuitisidle,themessageissenttothereceivingswitchorterminal,andittransmitsdatainthenetworkina"store-and-forward"manner.Theadvantageofmessageexchangeisthattheutilizationrateoftherelaycircuitishigh,andmultipleuserscantransmitonthesamelineatthesametime,anditcanrealizetheintercommunicationbetweenterminalsofdifferentspeedsanddifferentprocedures.Butitsshortcomingsarealsoobvious.Forstoringandforwardinginunitsofmessages,networktransmissiondelaysarelargeandoccupyalargeamountofswitchmemoryandexternalstorage,whichcannotsatisfyuserswithhighreal-timerequirements.Messageexchangeissuitableforcommunicationbetweennetworkuserswithshorttransmittedmessagesandlowreal-timerequirements,suchaspublictelegraphnetworks.
Packetswitching
Packetswitchingisessentiallydevelopedonthebasisof"store-and-forward".Ithastheadvantagesofcircuitswitchingandmessageswitching.Thepacketswitchinglineusesdynamicmultiplexingtechnologytotransmitdatadividedintomanysmallsegmentsaccordingtoacertainlength-packets,andeachpacketistransmittedindependently.Arriveatthereceivingport,andthenreassembleintoacompletedatamessage.Thetransmissionefficiencyofpacketswitchingishigherthanthatofcircuitswitching,andthedelayissmallerthanthatofmessageswitching.
Asynchronoustransmissionmode
Theintegratedservicedigitalnetworkisanetworkthatintegratesvariousservicessuchasvoice,data,fax,videophone,etc.,suitablefordifferentbandwidthrequirementsandDiversebusinessrequirements.AsynchronoustransfermodeATM(AsynchronousTransferMode)isaswitchingtechnologyusedinbroadbandintegratedservicedigitalnetworks.ATMisdevelopedonthebasisofpacketswitching.Itusesfixed-lengthpackets,andusesidlecellstofillthechannel,sothatthechannelisequalizedforashortperiodoftime.Becauseopticalfibercommunicationprovidesatransmissionchannelwithalowbiterrorrate,flowcontrolanderrorcontrolcanbemovedtotheuserterminal,andthenetworkisonlyresponsiblefortheexchangeandtransmissionofinformation,therebyreducingthetransmissiondelay.SoATMissuitableforhigh-speeddataexchangeservices.
Technicalfeatures
Highlineutilization
Packetswitchingusesvirtualcircuitstomultiplexchannelstorealizeresourcesharing.Multiplelogicalchannelsareprovidedontheline,whichgreatlyimprovestheutilizationrateoftheline.Sothatthetransmissioncostissignificantlyreduced.
Communicationwitheachother
Differenttypesofterminalscancommunicatewitheachother:ThepacketnetworkprovidesuserswithastandardinterfacebasedontheX.25protocol,andthedataisstoredandforwardedinthenetworkinunitsofpacketstomakedifferentRateterminals,devicesofdifferentprotocolscancommunicatewitheachotheraftertheprotocolconversionfunctionprovidedbythenetwork.Highreliabilityofinformationtransmission:Wheneachpacketistransmittedinthenetwork,thefunctionoferrorcheckingandretransmissionisadoptedbetweenthenodeswitches,sothebiterrorratetransmittedinthenetworkisgreatlyreduced.Moreover,whenafailureoccursinthenetwork,theroutingmechanisminthenetworkwillmakethepacketautomaticallyselectanewroutetoavoidthefailurepointwithoutcausingcommunicationinterruption.
Packetmultiplecommunication
Becauseeachpacketcontainscontrolinformation,thepackettypeterminalcancommunicatewithmultipleuserterminalsatthesametime,andthesameinformationcanbesenttodifferentusers.
Billing
Networkbillingisbasedondurationandamountofinformation,andhasnothingtodowithtransmissiondistance.Itisespeciallysuitableforuserswhoarenotreal-timeandhavelittlecommunicationvolume.
Networkstructure
Thepacketswitchingnetworkgenerallyconsistsofbasicequipmentsuchaspacketswitches,networkmanagementcenters,remoteconcentrators,subassemblyanddisassemblyequipment,packetterminals/non-packetterminals,andtransmissionlines..
Packetswitchfunction
Providebasicnetworkservices:switchedvirtualcircuitsandpermanentvirtualcircuits,andothersupplementaryservices,suchasclosedusergroups,networkuseridentification,etc.
Whencommunicatingbetweenend-to-endcomputers,routeselectionandflowcontrolareperformed.Itcanprovideavarietyofcommunicationprocedures,dataforwarding,maintenanceandoperation,faultdiagnosis,billingandsomenetworkstatistics,etc.
NetworkManagementCenter
Networkconfigurationmanagementandusermanagement,dailyoperationdatacollectionandstatistics.
Routingselectionmanagement,networkmonitoring,faultalarmandnetworkstatusdisplay.
Completechargingmanagementaccordingtothecharginginformationprovidedbytheswitch.
RemoteConcentrator
Allowstheaccessofpacketterminalsandnon-packetterminals,andhasaprocedureconversionfunction,whichcancentrallyconnecteachterminaltothemediumandhigh-speedlinesofthepacketswitchInterleavedmultiplexing.
Subassemblyanddisassemblyequipment
Thecharacterinformationfromtheasynchronousterminal(non-packetterminal)isassembledintogroupsafterthestartandstopbitsareremoved,andthensenttothepacketswitchingnetwork.Atthereceivingend,thegroupinginformationisrestoredtocharactersandsenttotheuserterminal.Withthedevelopmentofpackettechnology,thereisnodifferencebetweenthefunctionsofRSUandPAD.
Packetterminal/non-packetterminal(PT/NPT)
PacketterminalisadatacommunicationterminaldevicewithX.25protocolinterfacethatcandirectlyaccessthepacketswitcheddatanetwork.Itcanbeconnectedtothenetworkthroughaphysicalline,andcanestablishmultiplevirtualcircuits,andconductconversationswithmultipleusersonthenetworkatthesametime.Forthoseterminalsthatimplementthenon-X.25protocolandthosewithoutprocedures,theyarecallednon-packetterminals.Non-packetterminalsneedtobeassembledanddisassembledbeforetheycanbeconnectedtoswitchports.Throughthepacketswitchingnetwork,packetterminals,non-packetterminals,andpacketterminalsandnon-packetterminalscancommunicatewitheachother.
Transmissionline
Itisoneofthemaincomponentsofthepacketdataexchangenetwork.TherelaytransmissionlinehasPCMdigitalchannel,digitaldatatransmission,andalsousesATMconnectionanditssatellitechannel.Userlinesgenerallyhavedigitaldatacircuitsorlocalanaloglines.Thenetworkstructureofpacketswitchinggenerallyconsistsofbasicequipmentsuchaspacketswitches,networkmanagementcenters,remoteconcentrators,subassemblyanddisassemblyequipment,packetterminals/non-packetterminals,andtransmissionlines.Thefunctionofthepacketswitchincludesprovidingthebasicservicesofthenetwork,switchingvirtualcircuitsandpermanentvirtualcircuits,andothersupplementaryservices,suchasclosedusergroups,networkuseridentification,etc.
Networkaccessmethod
Telephonedial-upaccesstothenetwork:TheuseradoptsX.28orX.32procedures,andusesamodemtoconnecttothepacket-switchednetworkthroughthepublictelephonenetwork(PSTN).
Dedicatedlineaccesstothenetwork:Dedicatedlineuserscanrentlocalanaloglinesordigitaldatadedicatedlines,usingX.28orX.25regulations.ConvenientlyenterCHINAPAC.CHINAPACprovidesuserswithtwobasicbusinessfunctions:
Switchingvirtualcircuits-referstothetemporarylogicalconnectionestablishedbetweentwousers.
Permanentvirtualcircuit-referstoapermanentlogicalconnectionestablishedbetweentwousers.Assoonastheuserpowerson,apermanentvirtualcircuitisautomaticallyestablished.
NetworkStatus
TheChinaPublicPacketSwitchingNetworkestablishedin1993isanetworkopentothewholesocietyandcanprovideavarietyofservicesacrossthecountry.CHINAPACisdividedintoabackbonenetworkandanintra-provincialnetwork.ThebackbonenetworkusesBeijingastheinternationalgatewayandGuangzhouastheHongKongandMacaogateway.Eightcities,includingBeijing,Shanghai,Shenyang,Wuhan,Chengdu,Xi'an,GuangzhouandNanjing,aretheconvergingcenters.Coversallprovinces,municipalitiesandautonomousregionsnationwide.Thetandemcenteradoptsafullmeshstructure,andtheothercontactsadoptanincompletemeshstructure.Eachcontactinthenetworkhas2ormorecircuitsindifferentdirectionstoensurethereliabilityofthenetwork.Therelaycircuitinthenetworkmainlyadoptsdigitalcircuits.Themaximumrateis34Mbps.
Atthesametime,localpacketswitchingnetworksinvariousplaceshavealsoextendedtoprefectures,cities,andcounties.Withitshugenetworkscale,CHINAPACmeetstheneedsofcustomersfromallwalksoflife,andiscompatiblewiththePublicDigitalSwitchingNetwork(PSTN),ChinaPublicComputerInternet(CHINANET),ChinaUtilityDigitalDataNetwork(CHINADDN),FrameRelayNetwork(CHINAFRN)andothernetworksInterconnectiontoachieveresourcesharing.Complementaryadvantages.Providehigh-qualitynetworkservicesforthemajorityofusers.ItisconnectedtopacketnetworksindozensofcountriesandregionsincludingtheUnitedStates,Japan,Canada,SouthKorea,andHongKongtomeettheneedsofinternationaluserssuchaslargeandmedium-sizedenterprises,foreign-investedenterprises,andforeignofficesinthemainland.
Technicalapplication
Servicesprovided
CHINAPACprovidesuserswithtwobasicbusinessfunctions:switchedvirtualcircuitsandpermanentvirtualcircuits.
CHINAPACalsoprovidesuserswithoptionalbusinessfunctions,mainlyincludingclosedusergroups,reversebilling,networkuseridentification,callforwarding,virtualprivatenetworks,broadcastservices,framerelayandotherservices.
Commercialapplications
Packetswitchingiswidelyusedincommerce.Suchasonlinecreditcard(POSmachine)verificationinthebankingsystem.Sincepacketswitchingprovidesthefunctionoferrorcontrol,thereliabilityofdatatransmissioninthenetworkisguaranteed.Firstofall,majorshoppingmallsformalocalareanetwork,andtheonlineserverprovidesthemanagementfunctionofthecard.Aftertheuserswipesthecard,itisconnectedtothecommercialproliferationnetworkthroughtheX.25packetportontheserverortherouterdevice.connect.Thecommercialenrichmentnetworkmainlycompletesthedatalineconnectionfrommajorshoppingmallsandstatisticsonthesalesoftheshoppingmalls.Thesettlementcenterisconnectedtothehostsystemsofmajorbankstorealizecreditcardverificationandcreditcardconsumption.AmongthemajorsupermarketsinChina,aconsiderablenumberofsupermarketshaveusedpacketnetworkstoimprovetheirmanagementmethods,expandthemarket,andachievegoodeconomicbenefits.Anelectronicconsumptionchannelissetupinthesupermarket,andafterswipingthegolddepositcardheldbytheconsumer,theinformationissenttotheback-endserverofthesupermarket.Theroleoftheserveristocalculatetheamountofgoldsavingscardandthestatisticsofsupermarketsales.ThebusinessoutletsofthesupermarketsareconnectedtothesupermarketmanagementcenterthroughadedicatedlinemethodofmultiplexingDOV(DataOverVoice)onthephonetoconductaseriesofsettlementsandstatistics,etc.,toexpandthesupermarket'sconsumermarket.
Applicationinotherfields
Thepacketswitchingnetworkhasthecharacteristicsofhighutilizationrate,goodtransmissionquality,andsimultaneousmulti-channelcommunication,soitseconomicperformanceisalsogood.Insomenationalgroupcompanies,theheadofficeissuesinstructionstobranchesacrossthecountryorevenforeigninstitutions,anditisveryeconomicaltousepacketswitching.COSCOGroup'sbranchesinvariouspartsofChinaformlocalareanetworks,whichareconnectedtothepacketswitchingnetworkthroughrouters,andexchangeinformationwithcustomsandEDIcenters.Itshostsystemisalsoconnectedthroughthepacketswitchingnetworkthroughouttheentireprocess,transmittingbookinginformation,freightstatus,EDImessages,etc.,anditcanalsologintoHongKongremotelytocommunicateinformationwithoverseas.
VirtualPrivateNetwork
VirtualPrivateNetwork(VPN)isavirtualprivatenetworkorganizedbylargegroupsofusersusingpublicnetworktransmissionconditions,networkportsandothernetworkresources.Andyoucanmanagetheportsthatbelongtotheprivatenetworkpartforstatusmonitoring,dataquery,andnetworkmanagementoperationssuchasalarms,billing,andstatistics.VPNismainlyusedforgroupusers,variousprofessionalindustries,etc.
Currentrole
ThebackbonenetworkofChina’spublicpacketswitchingnetworkandlocalnetworkshavebeenestablished.Stabledatacommunicationmarket.Packetswitchingtechnologyismoresuitableforterminal-to-hostinteractivecommunication,transactionprocessing,occasionswhereprotocolconversionisrequired,cross-bordercommunications,occasionsrequiringhighsecurity,andareaswithlow-qualitytransmissioninfrastructure.Despitetheimpactofbroadbandnetworktechnology,inviewoftherelativelyweakcommunicationsinfrastructureinChina,packetswitchingserviceswillstillplayacertainroleforarelativelylongperiodoftimeinthefuture.Withtheupgradingofswitchingequipment,theemergenceoffasterswitchprocessorsmeansthatthetraditionaladvantagesofpacketswitchingcanberealizedathigherspeeds.Theadvantagesofpacketswitching,suchasprotocolconversionfunctionandcontrolfunction,makethenewgenerationofpacketswitchingtechnologyforhigh-speeddatatransmissionpromisingincommercial,civilaviation,andpetroleumsystems.Bytappingpotential,identifyingmarketentrypoints,andseizingbusinessopportunities,wecanbetterleveragetheadvantagesofpacketnetworks.
Theroleofswitchlinkaggregationinthenetwork
1.Spanningtree,STP,themainfunctionistoavoidloops,thereisredundancyinthenetwork,andoftenmultiplelinksareused.Loops,broadcaststorms,andnetworkparalysiswilloccur.Pleasenotethatwhenthenetworkisinvolved,don'tforgettostartthespanningtree.Forexample,ingenerallargeenterprises,thecoreswitchandotherswitchesareconnectedbytwonetworkcables,sothatoneofthemhasanerrorandtheothercanwork.However,ifPC2andPC1communicate,loopsarepronetooccurandbroadcaststormsaregenerated.Spanningtreecanbesolved.thisproblem.
2.Linkaggregation:Itsmainfunctionistoincreasenetworkbandwidth.Oneisbetweenswitches,forexample,twoswitchdevicesarecascadedwitha100Mnetworkcable.Largerwillcauseshieldingandslowerspeed.Atthistime,linkaggregationcanbeused.Usetheport-groupcommandtoestablishlinkaggregation.Usetwomorenetworkcablestoconnecttheswitch,andaggregatetheportsconnectedtothetwoswitchestogether.Canincreasenetworkbandwidth.Anothersituationisthelinkbetweentheswitchandtheserver.Forexample,ifaserverisconnectedtotheswitch,ifthetrafficislarge,theserverwillnotbeabletobearit.Youcanconsiderpressingtwomorenetworkcardsandusinglinkaggregation.Theportsconnectedbythetwonetworkcardsareaggregatedtoreducetheburdenontheserver.