Základní informace
TheessenceofPacketSwitchingingistoDividEthedaTatatobeTransMitedInTomanygroupSordingToaCilLength.INORDERTOACHUCUCUCURALYTRANSMITTOTHEOTHERPARTY, každý groupismarkedwithmanydifferentDatagroups.TransmissionSperMedonthephysicAllineinadynamicsharingandMultiplexingManner.Inordertomakefulluseofresources,whendatapacketsaretransmittedtotheswitch,theywillbetemporarilystoredinthememoryoftheswitch,andthenaccordingtothecurrentline'sbusynessandidleness,theswitchwilldynamicallyallocatetheappropriateThephysicallinecontinuesthetransmissionofdatapacketsuntiltheyaredeliveredtothedestination.AfterreachingThedestination, thedatapacketErecombinedToformacompleteData.
ThePacketisComposedOfThepacketheaderandtheuserDataparTafterit.ThePacketheaderContainStherecesiingAddressAndControlinformation, AnditSlengthis3-10b.TheLengngthofTheuserDatapartisfixed, withanaverof128bandamaximumaf256b.V tomhle slottheedStobeexpplained:.PacketSwitching: AfterRoutHinghasDerMined theOutputPortAndtheNextNode, SwitchingTechnologyMustSeusedTotransfertHepacketFromTheInputtotheoutptoreToRealizeTRANSMISISEFBithThroughThEtWorkNode.
PacketSwitchingTechnologyIsThedevelofOfComputerTechnologyToaCiveExtenttent.InaditionTomakingDirectCalls, PeopleCancomMunitedBeecomputersAnd -TerminalStroughCmputerSantAssansAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAndAnds.Avšak kvalitaftransmissionLinesisnotHandTenetTworkTorkNologyMeanSinaSimplersituation, anexchangeTechnologyEMergetThehistoricMomenta.
PacketSwitchingisalsAlsocalledPacketSwitching.ItDiviDestHedaTaTransMittesTeuserInToMultIplesMallerPartSofEquallthend.Každý partiscallEdadatasegment.Předběžný kompozicessomeNessAntrolinformationIsAddedinfrontofeachDatasegmentToformapacket.TheHeaderisusedSoIndicathetheaddressWherethepackeTissent, a anthentheswitchforwardsTheDestinationccordingTotheaddressflagofeachPacket.Toto ProcessiscalledPacketSwitching.THEBOMMUNUNICATIONNETWORKORPORKONSSPICTICTISCISCALLEDAPACKETSWITCHINGNETWORK.PacketSwitchingSesensiallyDevelodedonTethebasisof "obchod-and-forward".IthastheadvantagesOfCircuitswitchingandMessageswitching.
InNthePacketswitchingMode, BecausethedatacanbeTemporalyStoreDexChangeDinPacketMode, AfterprocessingBytheswitch, itiseastorealizeToRizeToreToMunicationBetweentminalsOnfferentsPeedSandifferentProceduress.
Developmenthistory
Kolem roku 1970, PeopleBeganTostudyanawformoflong-distancedIGIGITALDatacommunicationArchitecture: Packet Swinginging.Althoughthepacketswitchingtechnologyusedhasmadegreatprogresscomparedwiththattime,thebasictechnologyofpacketswitchingtodayisbasicallythesameasthenetworktechnologyofthe1970s,andpacketswitchingisstilloneofthefeweffectivewaystorealizelong-distancedatacommunication.OneofTheTechnologies.Athetwolatestwantechnologie: Framerelayandm, arebasicalsvariantingofpacketswitching.
PacketSwitchingIsDeveradedaSatechnologyToSolTiNeractiveProcessingapplication.ItisdesigntosupporttransmisionOfburstyDatastreams.THECONTINOUSCONNECTIONTIMEOFTHISSERVICESTERSEMISLONGANDTHESERCETHETHEAMOMNISLISLOW.ThePacketSwitchingNetWorkUsesStatisticMemultiPlexingTechnology, thesis, multiplesessionConnectionscanshareaCommunicationChannel, který sendoubtedlygreatlyimprovesthetransmisionEfficience.SharingTHecommunicationLindroducestimeZpoždění však.Proto AkeyissuewemustConsideRetheFutureishowthepacket-SwitchedNetworkTransMitsZpoždění-sensitiveServiceStreams, tasisreal-timeservicestreams.Inapacket-SwitchedNetwork, PacketEtretedThroughAseriesOfinterMediatenody, obvykle secrossmultIpleNetworks.Oni jsou zapracovaní meziseriesOfPacketswitches (ierouters) Inastore-and-Forwardmanner, a koně.Během průběhu přechodu se informationIsIdIdedIdIndedIntopackets obsahují údržbu asEcencenumber.
Klasifikace
Podle PacketSwitchingCanBidiDidedIndodatagrampacketSwitchingandCircuitPacketSwitching.
DatagrackacketSwitching
DatagrampacketSwitchingRequireSatleasToneDaTATRANSMISSIONPATHBETWEENTTHOMUMUMINGAINGSPARTIES.ThesenderneedStoreparethedatapacketTobetransMitedBerecomunication.TheDataPacketContainStressInformationofThesenderAndthereceiver.TransmisionOfdatapacketssidentendantendependencethother, neotaffecteachother, canreachThedestinationccordingTodifferentroutingMechanisms, andrecombined.
Inthisway, EverypackeTiSattachedwithSourceanddestinationAdsress, PacketNumber, PacketStantAndflags, chyba checkingandotherInformationAnceformat, a distransMiditInTheForMofPacketSetTork.TheretworktriesitsbesttodeliverthepacketstothedestinationHost, butitdoesnotguaranteethatthetransMitedPacketswillotbelost, NorthatthepacketswillarriveattherecesivingendinTheorderInheorderInheorderInheordeorInTheresentesentesentesentesentesentesentesentesentesentesentesentesentesentesentesentesentesentesentesentesentesentesentesentesentesentesentesentesentesentesenterenTheortinTheortin..Proto TheserviceProvidedByTenetworkIsUnReliable athequilationOfServiceIsNotguaranteedeeedeeedeeedeeedeeedeeedeedeeedeeedeeedeeedeeedeeedeeedeeedeeedeeedeeedeeed.Asshowninfigure9-2 (a), somepacketssentfromhosth1toh5Gothnodeabe, SomeGothRoughaceorabce, andsomepacketssentfromhosth2toH6GothRougHnodebde, andsomegotHroughbebe..TheDatagramEthodisgeneraLerallySeable-forshorter, s jedním skupinou.Jeho AdvantageiSthatThransmissionZpožděníissMall a athesubSentPacketTransmissionWillNotBeaffectedsHenanodefails.TheDisadvantageiSTateachPacketHasalotoFADDitionalControlinformation, která se vyskytuje, která je v souladu s tímto.
VirtualCircuitPacketSwitching
Thedifferencebetweenitandthedatagrammethodismainlythatbeforeinformationexchange,alogicalconnectionneedstobeestablishedbetweenthesenderandthereceiverbeforestartingTransferpackets,allpacketsareexchangedandforwardedalongthesamepath,andthelogicalconnectionisremovedafterthecommunicationends.TheEtworkguaranteestHatthetransMittedPacketsarriveattherecesivingendintheorderInhichtheyweresent.Proto TheServiceProvidedByTheNetworkIsReliableAnthequalityOfServiceIsGuaranteed.Asshowninfigure9-2 (b), AllpacketsSentFromhosth1toh5passThroughThesamenodea-b-e, andallpacketssentfromhosth2toH6AsPassThroughThesamenodeb-e.
ThisMethodisNotSitableForURusersWithHighfrequencyofinformationTransmissionSMalltransmissionVolumeeachTime.Avšak od té doby, od té doby, co se týká packetheaderonlyneedStomartHevirtualCircuitIdcidentientidentAnd Sesquencenumber,.Vhodný forLongMessageTransmission.
VirtualCircuitPacketSwitchingIsLikeCircuitswitching.Obě komunikacePartiesNeedToestablishaCaconnection, butunlikecircuitswitching, theConnectionOfPacketSwitchingIsAvirtualConnection (alsoknownasavirtualCircuit) a toreisnoexclusiveConnection antheConnection propojení.Fyzické objevování.Podle virtualcircuitscanbedIdIDiDiDiDiDeDosVirtualCircuitsAntVirtualCircuits.
SwitchingVirtualCircuitsRequiresBothPartiesIncomMunicationToestablishatemPoraryConnectionThroughRughRequest a thenCommunicate.WHEnthecommunications, theTemporaryConnectionIstorndown.
PermanentvirtualCircuitMeanstTetWopartiesIncommunicationDonoTneedTorequest, OnlyedToestablishaConnectionccordingTotheagreethetweenthetwoparties, aequetitfortheagreeTimeTime.
Itcanbeobtained fromThis, thecharacteristicsOfTheConnection-orientovaně zpracovávající methodandthenon-connectionworkingmethod.
(1) Charakteristiky, které jsou orientovány na zpracování
AťISISISAPHYSICKÁLNÍCONNECTIONOROGICKOLICKÁTORKA, THE AMOMMUNDICTIONICEPROCESSCANBEDIDIDIDIDIDIDOTHREESTAGE.
OnCetheConnectionSiseStabled, allinformationoftHecommunicationsMidatedongthiSlinkPath a theorderoftheInformationsGuaranteed (TheorderOfSendingInformationIsconSonSent stheorderOfreceivingInformation).
TheTimeZpožděníofinformationTransmisionSMallerthanthetimeZpožděníofTheConnectionsWorkingMode.
OncetheestaltedConnectionFails, theinformationTransmission-BITERNURNRURNDEDENTONNECTIONSECTHUSTUSTUSTERS, SOITISSENSIVIVIVETOFAILURES.
(2) THECHARACTERISCOFCONNECTECTONTHWARKWORKINGMODE
V tom jeNoconNectioNestablementProcess, a atheroutteisElicted aInformationSistransMitedagain.
TheinformationBelongingTothesamecommunicationarrivesattheDinationatioNongDifferentPaths.ThePathCannotBepRedicdicInAdvanCeororderoftheInformationCannotBeguaranteed (TheorderOfSendingInformationInconSonsistent stheorderOfreceivingInformation).
TheTimeZpožděníofinformationTransmisionSgreaterthanthetimedelayofTheConnection-orientovaný zpracování.
InsensitiveToNetworkFailures.
FunsesOfPacketwitching
(1) ThesmallestunitofinformationTransmissionSispacket
ThePacketConsistsOfagroupHoroupHeaderUndeRuserinformation a athepackethetheaderContainsRoutingandControlinformation.
(2) TwOworkingmodes, orientované na připojení (LogicalConnection) a bez
ThevirtualCircuicuitaDopTStheConnection-orientovaný pracovnímode a athedatagramistheConnectionslessworkingMode
(3) StatisticalTie-DivisionMultiplexing (DynamicBandWidThalocation)
Thebasicprincipleofstatisticaltime-divisionmultiplexingistodividetimeintotimeslicesofunequallength,andtimesliceswithdifferentlengthsaretotransmitdifferentlengthsThetimerequiredforgroupingisnotallocatedafixedtimesliceforeachcommunication,butisusedondemand.ThisMansThhattheLengthitHatthattheMultiPlexlineisusedTotransMittHepacket, který skórovalThestatisticalTie-divisionMultiPlexingdynamickyallocatesbandWidth.
(4) InformationTransmissionSeror kontrolovaný
PacketSwitchingingisasasSwitchingMetSPeciallyDesigndfordatacommunicationNetworks.THECHARACTERISCOFDATaServicesAreliabilityAs a TimeRequirements.ItisNotashighAstelephonecommunication, soinordertoensureliabilityOfDatainformationInPacketSwitching, chyba controlmechanismsscascrccheckandretransmiseareSettomeetTheneedsOfdataServiceCaracteristics.
(5) InformationTransmissionSnottransparent
PacketSwitchingMustProcessStransMittedDatainFormation, takové asspitting areorganizationInformace.
(6) FlowControlBasedonCallZpožděníSystem
Inpacketswitching, whenthedataflowislarge, ThepacketsAreued forprocessinsteadofimmediatecalllosslikeCircuitswitchingthererered, jeho flowcontrolisbasecalldelay.
Výhody
Ve srovnání s výstavbou, switchedNetwork, paketswitchingNetworkHasmanyAdvantAges
HighUtilizationRate
ve srovnání switchedPairChainChannexclusivity, odlišný adatapacketscanbetransMitenthesamelinkinadynamicsharingulTofTHechannel, a the-theUtilizateOfComUnicationSomnelnelnel, a the-the-the-theUtilizateRomUnicationreceSigh..BecausesEassLinkFromnodetonodecanbedynamicalssharedBymanapackets.PacketsAeueDandtransMitonToNthelinkasquicklysAspossible.
Rychlost přenosu dat
ApacketswitchingNetworkCanperformRychlost přenosu datConversion: twostations withdifferentdaratescanexchangepackets, protože OeachStationSesitSownTatherateIsconEdtothisnode.
Mechanismus front
OnTheSamelink, DataOfDifferentTypeSand SpecifificationsCanbetransMitedTeDesametime.WhentereAreAlarGenumberofPacketSthepacketNetwork, thequeuecanbeSacdingTothedaTATRansmissionMechanismtoenSurethatPithshighpriorityareTransMittedfirst.WHEntheLontheCircuit-SwitchedNetworkIsEavy, somecallsareblocked.Onapacket-switchedNetwork, paketsArestiLaccepted, buttheirdeliverydelaywillincrease.
Přednost
Kdyusingpriority, ifanodehasalargemumberofpacketswaitingTobeTransMited, itcanntransmithigh-priorityPacketsFirststststststststststststststststststststststhstststststststststststststststststhststststststststststststststststhststststststststststststststhststststststststststststststhstststststststststststststststhstststststststststststststststhstststststststststststststststhststststststststststststststhststststststststststststststhststststststststststststhststStStStstStStStStStIS.TheSepacketswillthereExPeriencelessDenaythanlowerPřednostPackets.
Nevýhody
Ve srovnání s přepínacími přístavy, paket-switchedNetworksalsohaveSomeDisadvantAges.
Zpoždění
ApacketPassesthroughApacket-SwitchedNetworkErewillbeatimeZpožděníWHenthenodeisconEd, butthereisnosuchtimedelayenthecircuit-switchedNetWork.
Zpožděníjitter
Becausethepacketsbetweenagivensourcestationanddestinationstationmayhavedifferentlengths,theycantakedifferentpaths,ortheycanbeinswitchesalongtheway.Různé podoby areexperienceNetTork, sothetotaltimedelayofTheGroupingMayvarygreatly.ThisphenomenonisCalledJitter.Jitterisundesirableformose aplikace (Forexample, Inreal-Time Applications tayastePlephoneVoiceAndreal-timeImages).
Highroverhead
TotransmitpacketsovertHenetwork, další naopardinformationIncludingTheDestinationdressAndPackeTorderIngerIngInformationMustBeaddeedToeachPacket.Tato informační redulaceSommunicationCapacitytHanbeusedTransporSuserdata.Incircuitswitching, oncetheCircuitiseStabled, thereoverheadsarenolongereded.Kromě toho, ThePacket-SwitchedNetworkIsAcollectionOfDited Packet Swented uzly.Inanidealsituation, AllPacket-SwitchednodesshoulAlwaysUnderStandthestateofTheenTereNetwork.Bohužel, stal setheNodesaredItributed, thisAlwaysAdelayBetweensachangeinthestatePartoftHenetworkTheoterPartThenetworkingThongtHangethechange.Nepřipravování, thetransferofstatusinformationRequiresaceanceAmlountofCost, soapAcket-switchedNetworkNeverOperate „dokonale“.
ExchangePrinciple
THEARETWOTYPESOFTERCEMINGNOTHINGONTHONTHETACKETWITCHingNetwork: PacketTypeterMinalsAndEneraneralterminals.Theso-calledpacket-typeterminalsendsandreceivesinformationintheformofpackets;generally,theinformationsentandreceivedbytheterminalisamessage,whichneedstobeprocessedbythesubassemblyanddisassemblyequipmentbeforeitcanaccessthepacketswitchingnetwork.Ifthesendingterminalisageneralterminal,thePADwillsplitthemessageitsendsintoseveralpacketsandthensendittothepacket-switchednetworkfortransmission;ifthereceivingterminalisageneralterminal,thePADwillre-createseveralpacketsbelongingtoamessage.AssembleTheMessageandSenDitteTothegeneralterminal.
THEBASICPRINCIPLEOFPACKETSWITCHINGISTOUSETHE TECHNOLOGI.BUSAMESSAGEISSENTFOMTHESOURCESTATION, theSessageIsDidedIndedIntoafixedFormatpacket (Packet) a thedestinationdressAddedTothepacket.Afterreceivingthepacketsfromthesourcestation,theswitchesinthenetworktemporarilystoretheminthememory,andthenaccordingtotheprovideddestinationaddresses,theycontinuouslyselectidlepathsforforwardingthroughotherswitchesinthenetwork,andfinallysendthemtothedestinationaddress.ThissolvesthecommunicationBeendifferentTypesofusers, anddotneedTeedToestablishicalPathforoLongTimeduringtransmissionProcesSiccuitswitching, butcanbemultiPlexedontesamelineiNenitofPacket, soitgreatlyimPovestheuTililizationspretiseisitesidedIseiseiseiseideiseiseiseideiseiseideiseideiseiseideiseimesideoviseitisedsidedIsedsideoviseitisedsitesitesimesimesimesimesimesimesitesimesitesitesimesitesitesitesitesitesitesitesitesitesitesitesitesitesitesitesitesitesitesitesitesitesitesitelililililizateReuTililizate..
PacketSwitchingingisasasswitchingTechnologythatcombinestHeadVantAgesOfcircuitswitchingandMessageswitching.TheCircuitswitchingProcessissisiMilartomakingaphoNecall.KdyauserEedStosenddata, theCallingPartenyedStomakeacall, a acalledPartyCompleteStHitchingNetWorkSeestabilishingAphysicalConnectionDatapathwithititititititititititititititititititititititititititititititititititititititititititititititititititititititititititititititititititititititititititititititititititititititititititititititititititititithItItITITHITITHITHITHITITHITHITITHITITHITHITIT.WHEntheConnectionNeedStobeDisconved, itisdoneByeErthetTocommunicationParties..Jeho charakteristika, které jsou uvedeny v souladu se slargequantitiesofinformationatonetime.DuetothelongtimeToestablishaConnection, the EfficienticislowwHentransmittingshortMessages.Aditissitivně kompatibilní s tím, že komunikacePartiesIntermSofinformationTransmissionte, encodingformat, komunikačníprotokol atd.., které limitthecommunicationbetweensesersOfDefferentrates, diferencencodingformats a differentCommunicationProtocolcols.TheBasicprincipleofMessageExchangeisteShothethe "Store-and-Forward" Technology.WhonsendingAmessageFromTheSourcestation, thedestinationAddressIsAddedTotheMessage, athenthentheswitchinthentWortTemporalyStoretheSessageFromTheSourcestationInTheMoryAlEmoryAferReceivingitit., AthenaccordingtotheProvidedDestinationdress, ContinuetoSelectidlePathsforwardingThroughtroughthotherswitcheSintheNetwork, a nafinallySenditothedestinationdressdressdressdressdressdressdressdress.ThissolvesthecommunicationbetweendifferentTypesofusers, a adotneedTeedToestablishicalPatHroLongTimeintransmissionProcesSlikeCircuitswitching, butcanbemultiplexedontesamelinofmesage, sogreatlylyimproveTeTilizace.Tato methodhassalongtimedelayAndlargetimeZpožděníChanges však.ItisNotSuitableForreal-TimeandConversiationalCommunication, butIssuitableForservicessuchase-Mail, ComputerFiles a PUBLICTELLEGRAMS.
Packetswitchingstillusesthe"store-and-forward"technology,butitisnotexchangedintheunitofmessagelikemessageexchange,butthemessageisdividedintofixedformatpackets(Packet)forexchange,Transmission,generally1kbittothousandsofbits,eachpacketisattachedwithsourceanddestinationaddresses,packetnumber,packetstart,endflag,errorcheckandotherinformationaccordingtoacertainformat,andistransmittedinthenetworkinpacketform.WhenthesourceDTEtransmitsthepackettothelocalpacketswitchPSEintheformofabitstring,thelocalPSEreceivestheforwardinginformationrequiredbyeachpacket,regardlessofwhetheritisconnectedtothedestinationaddressdevice,firststoresit,andthenchecksthedestinationaddressandsavesitinthePSEFindthesendingpathspecifiedbythedestinationaddressintheroutingtable,andthePSEwillforwardthepacketatthemaximumallowablesendingrate.Podobně každý TranssitpSestoresandSaseachPackeTintThisWuntiltHepacketisDeredtotheDestinationPse a anthepSeisDeliveredTothedestinationdressdte (SeeFigure8-7).WhatstransMitditedInTheabove-MentioNedwayeDatagramwayinPacketSwitching.Obecně ApplicableShortersIngledPacketMessages.ITSADVANTAGESHIGHTRANSMISSIONRELIBELITAYAndLowTransmissionZpoždění.BecausetheMoryCapacityOnthepSeisrediced, theeconomyisimprovence.TheDisadvantageISTateachPackeTADDDSMoreControlinformace, která se increasestheLengthAndProcessingTimeofTransmisionSformace.GREADItitionAloverhead.
DalšíModeofPacketswitchingingIscAlledVirtualCircuitMode.The theSainDifferencebetweentaDedagramModeiSthatheForeInformationExchange, thesourcedtesendSaspecificCallRequestpacketTothelocalpse, který kontainThEtheDestination.THEADDRESSANDLOGICANLIDENTIDIdentifierofTHEDeareforwardbythepse.Ifthecallisacceptedbythedestinationdte, ThecoresponspondingResponse "Callacceptance" ISANSWERED, ATHETETWORKSENDSA "CallConnection" tothesourcedte.ATTHISTIME, TheCalliseStabledAndaLogicalPathCalledavirtualCircuitiseStabledBetweenthetwodtes., InformationCanbeTransMiteDenthisvirtualCircuituntiltheendofTedataexchange, theVirtualCircuitisremoved, a responspondingLogicallidentifielisResasedatesedseased.Therefore,thevirtualcircuitmethodhasthreestagesofvirtualcircuitestablishment,datatransmissionandremovalduringeachcommunication,whichissimilartothecircuitswitchingmethod,butthetransmissioninthenetworkisthepacketswitchingmethod.ThisMethodisNotSitableForURusersWithHighfrequencyofinformationTransmissionSMalltransmissionVolumeeachTime.Avšak od té doby, od té doby, co se týče packetheadeeedstobemarkedwithAvirtualCircuiciidentiidentiidentidentiidentiidentidIdItidentand, thepacketheaderhassmalloverheadAndandissuitableforLongMessageTransmismision.
Výměnný protokol
ThePublicPacketSwitchEdDataNetWormiasportantPublicCommunicationPlatformthatrealizesLong-DistancedATATRANSMISSIONBETWEENDIFFERENTTYPESOFCOMPOCTORTERS, ADISAWIDIDE-AREACONNONCECOMNOMNYMONCOMONCOMONCEUSEDINTERNALINALINALYPAY.Thex.25ProtocolFollacedBethetheitu-TSS, ThetelCommunicationsAndardDepartmentoftheternationalTecommunicationUnion, Isaninternational StandandarsSupporteDabidedByManyManyTeLomMunicationSorganizationsAnManufacturerSintheworlldlldlldlldlldlldldldlldlldldldldlldlldlldldldldldldldldlldlldldldldlldlldlldldlldlldlldlldlldlldlldlldlldlldldldldldldldldldlldlldldlldlldlldldldlldlldlldlldlldlldlldlldlldlldlldlldld..X.25NetWorkISaPublicDatanetworkwidelyuseusedInternationally.X.25WasintroducedByTyltMetin1970, AnditWasthefirst-GenerationPacketSwitchingSystem.Thex.25NetworksdeveratedTotransmitdata, soitidNidindectCompetitionWithTephoneServiceProviders.X.25PacketSwitchingTechnologyEMergedTomeetTeedSofInterActiveServices.InteractiveProcessingapEaredinthelate1960s.ItisaburstyDatastreamwithalongConnectionTimeButlowDatavolume.X.25ProvideSatechnologythallowsMultiplesSessionStosharethesamecommunicationChannel.
Kdyx.25NetworkProposesx.25Technologie, TheEtworkwasmainlyASiMimulateDenvironment.AmoresoriousproblemwithanalognetworksisTaToisewillBeamplified -spassingThroughSomeamplifiers, který bude srážet.Proto Avalue-AddedServiceProvidedByx.25ISTOIMPLEMEREMERRORCONTROLFOLFUNCTSWITHINTHENTWORK.Od společnosti PacketSwitchingIsIsAstore-and-ForwardTechnology, aTeachInterMediatenode, PacketErrorsMustBedetedeted.IFeveryThingIsnormalforthePacket, TheInterMediateDedElSensedNackNowledgmentMessageToRiginalSensingNode; iftereisaNerorintorintoretEthepTreceivedBeintMeterMediateNode, pakodewillsensedsageTorequestretransmissions.Proto AtanynodeofthepacketPath, ifIsIfoundthattheaccUmulationOfnoiseCausesanerr, TheerrorWillbecoriced, sothatthedatreamcanbetransMitedMoreAccurateorealeorateatealy.Justrikethepstnnetwork, thex.25Packet-SwitchedNetworkIsAlsohierarchical.
Inthex.25PacketSwitchingNetwork, PacketSwitcheSarediviDidedIndotWocategories: (1) OneTypeofSwitchisclosetotheuserend, infact, TheareloCatecattheaccessPofthTheNetwork.The FunctionsOfTHISTYPEOFSwitchincludering, Forwardingpackets, AnrOrdeTectionand arection.Nepřítomnost, inordertosupporttheaccessofdifferentTypeSofCmputers, tokompletetheconversionBeendifferentProtocol, ortheconversionBeendifferentwerEntwerEntwerEntwerEntWormenTingSedSanderenConingMeTodSaeantheacteacteacteactionsheackesSeactesasSessAsCessAsSessAsCessAsSessAsSessAsSessAsSessAsSessAsSessAsSessAsSessAsSessAsSessAsSessAsSessAsSessAsSossAsSosSeasCesasSosstesSeasTeasCesasSessAstesassSosss..Theswitchisdone.Itherwords, protože jeCanPerformThenSeadsConversionWorkcordingToyourRequirements, AnsuSethisconversionSpartoftHenetworkbusiness, Sothroughthex.25Network, YoucanRealizeTheConnectionbetweendifferentTypeSofDevices.(2).Oni darenotProvideTheaForemenTionedhigh-LevelValue-Added-Functions, buttonlycomplepacketut, předávání, AnderrorControlanddectiondectiondection.Nestandardx.25 TerminalsNeedTobeConned toAnx.25NetworkthroughApacketDisassemblyDevice (pad).PadCompletestheConversionOfThocololandgeneretesthepacketsSecifiedBythex.25standardní, sothatthedatacanbetransmitedThroughThex.25Network.TheSepadscanbedondontesesersideronthenetworkside.X.25seSesessiallyASandardaccessProtocolBetweenseUseRequipmentandAcketSwitchingNetWorkSestabledByitu-t.ItdefinestheinterfacethroughwhichtheterminalingethepacketModeConnectstothePublicDataNetWorchedicadedCircuit.Protokoly ThereArealSosoMoMonlyUsedx-Series jsou: jsou::
(1) x.28ISTHESTAndardProtocolBetweenterminalequipmentandAndPad;
(2) x.29ISTheStandardProtocolbetweenpadandthenetwork;
(3) x.75ISagatewayProtocolFortheinConnectionOftwoormorePacket-SwitchedNetworks, OneofCanbeadedPacketDatanetwork, a TheoteroneCanbeapusPacketDatanetwork, ortheybetwodifferentOperatotortworks asoon asoon asoon.
THEADVANTAGESandNevýhodyOfTHEX.25Network:Tojudgetheadvantagesanddisadvantagesofaparticulartechnology,firstofalldependsontheenvironmentinwhichitislocated.Inabasicenvironmentonaloginformace, noiseisaBigproblem, soerrorcontrollisnents.AtheachInterMediatenode, inadditionToSelectingautEtodeterMethenexthop, chybovýControliSalSoimplementeDedoNeachPacket, který bude se stát endtransmissionZpoždění.Becausethex.25Packet-SwitchedNetWormisonlyusesTotransmitdata, delayorPacketlossisNoTyveryCriticalParameterForit.Další controntributionOfx.25ISITSPACKETSIZE.ITUSESRelativněsMallPackets, obvykle128ByteSor256Bytes.EvaluationOfTHeprosandConsofThissuealsochangeSovertime.DuetonoiseFactors, SmallbacketsAreveryAdvantaintousInx.25Networks.Pokud je to.Je zřejmé, že retransmisionOfRelativněsMallPacketSisMoreeffientThanretransmisionOflongChunkSofinformation.Proto x.25ISSPECIFICICICICICIGICEDEDTOUSSESSMALLERPACKETS.Podobně, protože uisitisAnearlyNetwork, itissuitable forworkingOnRelatiativellow-speedLinks.ThelinkRateGenerallyrangesFrom56Kbit/sto2mbit/s.
THEADVANTAGESOFX.25areasfollows: (1) Odx.25isthefirsttoprovidelayer3networkaddressinformation,sothatpacketscanberoutedandrelayedinaseriesofintermediatenodesandnetworksIthasastrongaddressingfunction;(2)Duetotheuseofstatisticalmultiplexingtechnology,itsbandwidthutilizationrateisrelativelyhigh;(3)Thepacketcanbypassthecongestednodeandreconnectthroughotherconnectionsandnodes.Carryingoutrouting,thusimprovingthecongestioncontrolability;(4)Itcancontinuouslydetectandcorrectalltypesoferrorsoneachintermediatenode,sotheerrorcontrolfunctioncanbeimproved;(5)WhennodesandlinesfailTheroutecanbere-selected,sotheavailabilityishigh.
TheNevýhodyOfx.25areasfollows:(1)Thequeuingdelayislarge;(2)Thelow-speedcommunicationlink;(3)Thepacketsizeissmaller,andthebandwidthutilizationrateisnotasgoodasthatofthelargersizepacketThenewprotocolishigh;(4)ThereisnoQoSguarantee,soitisnotsuitablefordelay-sensitiveapplications;(5)Itisonlyusedtotransmitdata,andtodayweareworkinghardtofindacomprehensiveservicesolution.
Úvod.25Protocol: AnimportantPartofusingPublicDataNetWorksisTheinterfaceWithtHem.Theitux.25StandardisAwidelyuseusedInterface.Mnohopeopleusetheterm "x.25Network",whichleadsmanypeopletomistakenlybelievethatX.25DefinesineNetworkProtocol.ButthisNotthecase.X.25 JustDefinestHeagreementBetweendteanddCeconCedTothePublicDataNetwork (obrázek 9-4).Proto x.25CanbestrictlyuseusesAuser-Networkinterfaceorauser-UserInterfacethroughApublicdatanetwork.Thex.25ProtocolrefersteTroTocolFortheinterfaceBetweendaterMinalequipment (DTE) adataCircuitterminalequipment (DCE) použity podle ThroundworkworkworkworkWorkCwathWorkCworkCworkCworkCworkCworkCworkCworkCworkCworkCworkCworkCworkCworkCwathworkworkworkIncHorthatWorkIncInPacketModeandContectRoughprivatecircuitssandDataNetWorkss.Itdefinesthethree-layerprotocolokofthesysicallayer, thedaTalinklayer, a thepacketlayer (tj., Síť), které odpovídají.
(1) PhysicalAllayer: ThebasicFunctionSoestablish, údržba addismantlethysicallinkbeendteanddce, která jefinesthemechanical, elektrická, funkční regulační charakteristikafthephysicallink a apravidesSynchronizace a a pokopoitered-the-po-po-popointBitsMocinChelTuteredLed-hollingonizace, a condovidessynchronizace a pokopoited-colfacelFeynTiMed-hollacesMelizace, a poperedEnSynchronizace a pokopoitered-colfrecepMedSedEdminizace..21Recommendations.(2) DataLinkLayer: Thephysicallinkbetweenthedteandthelocalpacketswitchpse (PacketSwitcheDequipment) PervidestHepacketLayerwithwaitingForretransmissionSrorCrolPackettransmissionService.TheLapbSPecifiedByThiSlayerthe (LinkAccessProcedurebalanced).ItMainlySPeciFiestHeProceduresFortheStablishment areMovalOfDatalinks, TheProceduresForinformationTransmisionSablol, AnDerrorControl, FlowControl atd..Inaddition,thislayeralsostipulatesthemulti-linkprocedureMLP(MultiLinkProcedure),whichcanimprovethethroughputandreliabilityofinformationbysimultaneouslytransmittinginformationframesonmultipleparalleldatalinks.
(3) PacketLayer (NetworkLayer): Hlavně řečeno, žeScrethestHepacketLayerProceduresSontrolinformationAnduserDataontedte/DCEInterface, aspecifiestHevirtualCircuitServiceProcedures, BasicPackettRucture, Datapacketformat, attttrům, AtdtttrucTusiness..ThisLayeradoptStrincipleoftImedivisionMultiPlexingtorealizeThataSourcesAphysicalCircuitTocallMultipleDestinationdtesforPacketDataExchange.Nehospodárny, italsProvidesPermanentvirtualCircuitpvcservice, která se vyvinula.ThesourcedtecEthevirtualCircuitwithouthovingtoestablishacall.TheinterRelationshipshipThevariousLayeredProtocolsinx.25.
Síťová kompozice
TheEtworkStructureOfPacketSwitchingIsgenerallycomposedOnSofPacketSwitchs, NetworkManagementCenters, RemoteConcentrators, SubSsesembly asEnssemblyequipment, Packetterminals/non-Packettermiminals, andtransmissionLines.Kompozice zařízení.(1) ThePacketSwitchrealizeStheinterfaceProtocol (x · 25) BetweenthedaTaterMinallandtheswitch, TheSignalingProtocolbetweentsSwitches (Susisx · 75orinternalProtocol), andprovidespacketWorkServices.Podpory, aoperateswiththenetworkManagementCenterteleteReteRout, monitorování, fakturace, kontrola atd..PodleTothestatusofthepacketswitchinthenTenetwork, itCanBedIDidedIndotWotypes: Transitswitchandlocalswitch; (2) TheEtworkManagementCenter (NMC) a thepacketswitchwitchtogethertoenmalonormaloperationofThenetwork.
ItsMainFunctionsIncludeNetworkmagement, UserManagement, MeasurementManagement, FakturationManagement, OperationAndMainTenanceMagement, RoutingManagement, NetworkStatisticsCollection, andnentryControlfUnctions atd..,whicharenetwork-widemanagement(3)Themainfunctionofthesubassemblyanddisassemblydevice(PAD)istoconvertthenon-packetformatofordinarycharacterterminalsintogroupformats,andgroupthedatastreamsofeachterminalintogroups,whichareinterleavedandmultiplexedingroupsontheaggregatechannel.TheOtherPartyThonvertShereceiveivedPacketformatintheoppositedIdection.(4) Funkce sOplátorucentratorissimilartoapacketswitch, antuzyallycontainsthefunctionFunctionFadadadas.ITISONLYCONTEDTOAPACKETSWITCHWITHOUTHOUTING FUNCTION.ItisusedInAreaseseuserrerelativně koncroted, adisgenerallyInstalledinthetelCommuMunicationSDestant.(5) ProvideTheBasicServicesofthTheNetwork: SwitchvingVirtualCircuitsAntMentvirtualCircuitsAndotsAtherssupmenpmentaryServices, takové, které jsou uchopeny, síťovář, atd. Atd..Když komummunikují mezi nimi na konci, romateselectionAndflowControlarePerformed.ITCanProvideavarityOfCommunicationProcedures, DataForwarding, MaintennanceanDoperation, Faultdiagnosis, BillingandSomeNetworkStatistics atd..