Domov Technika Přetížení sítě

Přetížení sítě



Definition

Networkcongestion(congestion)referstothesituationwherethenetworktransmissionperformanceisreducedduetothelimitedresourcesofthestoreandforwardnodewhenthenumberofpacketstransmittedinthepacketswitchingnetworkistoolarge.Whenthenetworkiscongested,datalossgenerallyoccurs,thedelayincreases,andthethroughputdecreases.Inseverecases,itmayevenleadto"congestioncollapse"(congestioncollapse).Undernormalcircumstances,networkcongestionoccurswhenthenetworkperformanceisdegradedduetoexcessiveincreaseintheloadonthenetwork.Figure2.1canvisuallydescribetheprocessofnetworkcongestion.

Reasonsfornetworkcongestion

Becauseinaresourcesharingnetworkwithoutanypriornegotiationandpermissionrequestmechanism,severalIPpacketsarriveattherouteratthesametimeandexpecttopassthroughthesameoutputportThepossibilityofforwardingexists.Obviously,notallpacketscanbeprocessedatthesametime.Theremustbeaservicesequence.Thebufferontheintermediatenodeprovidescertainprotectionforthepacketswaitingtobeserved.However,ifthissituationhasacertaindegreeofpersistence,whenthebufferspaceisexhausted,therouterhastodiscardthepacket.Inthiscontinuousoverloadstate,networkperformancewilldropsharply.

Omezení úložného prostoru

Eachoutputporthasacertainstoragespace.Ifanoutputportisusedbyseveralinputdatastreams,theinputstreamThedatapacketswillbequeuedinthestoragespaceforoutput.Whentheportforwardingdatarateislowerthanthearrivalrateofthedatapacket,itwillcausethestoragespacetobefull,andthedatapacketsarrivinglaterwillbediscarded.Thisphenomenonofburstdataflowismore.Althoughtosomeextent,theincreaseinstoragespacecanrelievethepressureontheoutputport.However,theunlimitedincreaseinstoragespacewillcausethedatapacketstocompletetheforwarding,theyhavealreadytimedout.Thesourcebelievesthatthesedatapacketsarediscardedduringtransmissionandrequireretransmission,whichnotonlyreducesnetworkefficiency,butalsomakesnetworkcongestionmoreserious.Inaddition,inpracticalapplications,thestoragecapacitycannotbeincreasedindefinitely,whichdoesnotconformtotheactualmeaning.

Omezená kapacita šířky pásma

Ithasbeenprovedthroughpracticethatitisdifficultforlow-speedlinkstocopewiththeinputofhigh-speeddatastreams,resultinginnetworkcongestion.AccordingtoShannon'stheory,thetransmissionrateofthesourcemustbelessthanorequaltothechannelcapacity.Therefore,whenthesourcebandwidthismuchlargerthanthelinkbandwidth,thebandwidthbottleneckisformed,causingdatapacketstoqueueupatthenetworknode,causingnetworkcongestion.

Omezení výkonu procesoru

TheCPUintheroutermainlyperformsfunctionssuchasqueuinginthebufferarea,updatingtheroutingtable,andperformingroutingselection.Meetingtheneedsofhigh-speedlinkswillcausenetworkcongestion.

Inpracticalapplications,complexnetworkstructuresandunreasonableroutingprinciplescanalsocausenetworkcongestion.

Congestioncontrol

Thewaytosolvenetworkcongestioniscongestioncontrol.Congestioncontrolneedstoensurethatthenetworkcancarrythetrafficsubmittedbyusers.Thisisaglobalissuethatinvolvesmanyfactorssuchashostsandrouters.Theparameterstomeasurewhetherthenetworkiscongestedmainlyinclude:packetlossratecausedbylackofbuffers,averagequeuelength,numberofpacketsretransmittedovertime,averagepacketdelay,andpacketdelaychanges.Accordingtocybernetics,congestioncontrolmethodsaredividedintotwocategories:Thefirstcategoryisopen-loopcontrol,thatis,toavoidcongestionbydesigningagoodalgorithm.Whenperformingcongestioncontrol,thecurrentstateofthenetworkisnotconsidered.Commonlyusedalgorithmsare:

1.Source-endcongestion controlalgorithm

2.Propojovací algoritmus řízení zahlcení

Thesecondtypeisclosed-loopcontrol,thatis,givingfeedbackmechanism,Controlcongestionaccordingtothecurrentstateofthenetwork.Thereareseveralfeedbackmethods:

1. Odešlete datový gram alarmu do zdroje informací.

2.Reserveabitorafieldinthestructureofthedatapackettoindicatethatcongestionoccurs.Oncecongestionoccurs,theroutersetsthecorrespondingbitsinalloutputdatagramstoalertneighbors.

3.Thehostoroilfilteractivelyandperiodicallysendsprobestocheckwhethercongestionoccurs.

Pracovní proces řízení přetížení v uzavřené smyčce je následující:

1.Monitorovací systém zjišťuje, kdy a kde dochází k zácpě;

2. Když dojde k zácpě, pošlete zprávu o přetížení na stránku, která může podniknout akci;

3. Upravte provoz systému, abyste vyřešili problém s přetížením.

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