Scambio di messaggi

Detailedexplanation

Eachnodereceivestheentiremessage,checkstheaddressofthetargetnode,andthenforwardsittothenextnodewhenappropriateaccordingtothetrafficsituationinthenetwork.Aftermanystore-and-forwards,itfinallyreachesthetarget,sosuchanetworkiscalledstore-and-forwardnetwork.Theexchangenodemusthaveenoughstoragespace(usuallyadisk)tobufferthelongmessagesreceived.

Theswitchingnodequeuesthemessagesreceivedinalldirections,comparesitwiththenextforwardingnode,andthenforwardsitout,allofwhichbringdelaysinqueuing.Theadvantageofmessageexchangeisthatnodedicatedlinkisestablished,butthelineutilizationrateishigher,whichisduetothewaitingtimedelayincommunication.

E-mailsystem(E-mail) issuitableformessageexchange.

commodaandIncommoda

Messageexchangeisbasedonmessagesastheunitofdataexchange.Messagescarryinformationsuchasdestinationaddressandsourceaddress.Storeandforwardareusedattheswitchingnode.Thetransmissionmethodhasthefollowingadvantagesanddisadvantages:

commoda

①Themessageexchangedoesnotneedtoestablishadedicatedcommunicationlineforbothpartiesinadvance,andthereisnoconnectionestablishmentdelay,andtheusercanSendmessagesatanytime.

②Becauseoftheuseofstore-and-forwardtransmission,ithasthefollowingadvantages:a.Itiseasytosetupcodeinspectionanddataretransmissionfacilitiesinthemessageexchange,andtheexchangenodealsohaspathselection.Whenacertaintransmissionpathfails,anotherpathisselectedtotransmitdata,whichimprovesthereliabilityoftransmission;b.Itiseasytorealizecodeconversionandratematchinginstoreandforward,andeventhesendingandreceivingpartiescannotbeintheavailablestateatthesametime.Thisfacilitatescommunicationbetweencomputersofdifferenttypes,specificationsandspeeds;c.Providesmulti-targetservices,thatis,amessagecanbesenttomultipledestinationaddressesatthesametime,whichisdifficulttoachieveincircuitswitching;d.AllowedEstablishthepriorityofdatatransmissionsothatpacketswithhigherpriorityareconvertedfirst.

③Thecommunicationpartiesdonotoccupyacommunicationlinefixedly,butpartlyoccupythisphysicalpathatdifferenttimes,thusgreatlyimprovingtheutilizationrateofthecommunicationline.

Incommoda

①Becausethedatahastogothroughtheprocessofstorageandforwardingafterenteringtheswitchingnode,itcausesforwardingdelay(includingreceivingmessages,checkingcorrectness,queuing,sendingTime,etc.),andthegreatertheamountofnetworkcommunication,thegreaterthedelaycaused,sothereal-timeperformanceofmessageexchangeispoor,anditisnotsuitablefortransmittingreal-timeorinteractiveservicedata.

② Themessageexchangeisonlyapplicabletodigitalsignals.

③Sincethemessagelengthisnotlimited,andeachintermediatenodemustreceivetheentiremessagecompletely,whentheoutputlineisnotidle,itmayalsostoreseveralcompletemessagestowaitForwardingrequireseachnodeinthenetworktohavealargerbuffer.Inordertoreducecostsandreducethecapacityofthenode'sbuffermemory,sometimesthemessageswaitingtobeforwardedarestoredonthedisk,whichfurtherincreasesthetransmissiondelay.

CircuitSwitching

Becausecircuitswitchingneedstoestablishaphysicalpathbetweenthetwocommunicationpartiesbeforecommunication(bytheswitchingequipmentandlinkbetweenthetwocommunicationpartiessectionbysection)Connected),soithasthefollowingadvantagesanddisadvantages.

①Becausethecommunicationlineisdedicatedtobothusersofthecommunication,andthedataisdirect,thetimedelayofdatatransmissionisverysmall.

②Oncethephysicalpathbetweenthetwocommunicationpartiesisestablished,thetwopartiescancommunicateatanytimewithstrongreal-timeperformance.

③Whenthetwopartiescommunicate,thedataistransmittedintheorderofsending,andthereisnoproblemofout-of-sequence.

④Circuitswitchingisnotonlysuitablefortransmittinganalogsignals,butalsosuitablefortransmittingdigitalsignals.

⑤ Theswitching equipment ( virgas , etc .

Incommoda:

.

②Afterthecircuit-switchedconnectionisestablished,thephysicalpathisexclusivelyoccupiedbybothpartiesinthecommunication.Evenifthecommunicationlineisidle,itcannotbeusedbyotherusers,sothechannelutilizationislow.

③Whenthecircuitisswitched,thedataisdirect,anditisdifficultforterminalsofdifferenttypes,specifications,andspeedstocommunicatewitheachother,anditisalsodifficulttocarryouterrorcontrolinthecommunicationprocess.

Packetswitching

Packetswitchingstillusesstore-and-forwardtransmission,butalongmessageisfirstdividedintoseveralshorterpackets,andthenthesepackets(carryingsourceanddestination)Addressandnumberinformation)aresentoutonebyone.Therefore,inadditiontotheadvantagesofmessages,packetswitchinghasthefollowingadvantagesanddisadvantagescomparedwithmessageswitching:

①Speedsupthetransmissionofdatainthenetwork.Becausethepacketsaretransmittedonebyone,thestorageoperationofthenextpacketcanbeparalleledwiththeforwardingoperationofthepreviouspacket.Thispipelinetransmissionmodereducesthetransmissiontimeofthemessage.Inaddition,thebufferrequiredtotransmitapacketismuchsmallerthanthebufferrequiredtotransmitamessage,sotheprobabilityofwaitingfortransmissionandthewaitingtimeduetoinsufficientbuffersareinevitablymuchless.

②Simplifiedstoragemanagement.Becausethelengthofthepacketisfixed,andthesizeofthecorrespondingbufferisalsofixed,themanagementofthememoryintheswitchingnodeisusuallysimplifiedtothemanagementofthebuffer,whichisrelativelyeasy.

③Reducetheerrorprobabilityandtheamountofretransmissiondata.Becausethepacketisshorter,theerrorprobabilitywillinevitablydecrease,andtheamountofdataretransmittedeachtimeisalsogreatlyreduced.Thisnotonlyimprovesthereliability,butalsoreducesthetransmissiondelay.

④Becauseoftheshortpacketsize,itismoresuitableforadoptingprioritystrategiestofacilitatethetimelytransmissionofsomeurgentdata.Therefore,packetswitchingisobviouslymoresuitableforburstdatacommunicationbetweencomputers.

Incommoda:

①Althoughpacketswitchinghaslesstransmissiondelaythanmessageswitching,itstillhasstore-and-forwarddelay,anditsnodeswitchmusthavestrongerprocessingcapabilities.

②Packetswitchingisthesameasmessageswitching.Eachpacketmustbeaddedwithsource,destinationaddressandgroupnumberinformation,whichincreasestheamountofinformationtransmittedbyapproximately5%to10%,toacertainextentThecommunicationefficiencyisreduced,theprocessingtimeisincreased,thecontroliscomplicated,andthetimedelayisincreased.

③Whenpacketswitchingusesdatagramservices,out-of-sequence,lossorduplicatepacketsmayoccur.Whenthepacketsarriveatthedestinationnode,itisnecessarytosortthepacketsbynumber,whichincreasesthetrouble.Ifthevirtualcircuitserviceisadopted,althoughthereisnodisorderproblem,therearethreeprocessesofcallestablishment,datatransmissionandvirtualcircuitrelease.

Inshort,iftheamountofdatatobetransmittedislargeandthetransmissiontimeismuchlongerthanthecalltime,circuitswitchingismoreappropriate;whentheend-to-endpathconsistsofmanylinks,packetItismoreappropriatetoexchangeandtransmitdata.Fromtheperspectiveofimprovingthechannelutilizationoftheentirenetwork,messageswitchingandpacketswitchingarebetterthancircuitswitching.Amongthem,packetswitchinghasashorterdelaythanmessageswitching,andisespeciallysuitableforburstdatacommunicationbetweencomputers.

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