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1、Ef?cientInternetTraf?cDeliveryoverWirelessNetworksRamiG.Mukhtar,StephenV.HanlyandLachlanL.H.AndrewJune16,2003AbstractThehighdemandforwirelessInternetconnectivityhasdriventhede-velopmentofhighlyef?cientradiolinktechnologies.However,theirper-formancecanbecompromisedbyinadvertentinteraction
2、swiththehigherlayerTCP?owcontrolprotocol.Ifwearetomaximizetheperformanceofwirelesslinks,thenwemustensurethatmechanismsoperatingateverylayeroftheprotocolstackinteractef?ciently.Inthisarticleweprovideabrieftutorialofsomeoftheseradiolinkenhancements.Wethenoutlinehowhigherlayer?owcontrolprot
3、ocolsshouldbehave,andoutlinetech-niquesfortamingthebehaviorofTCP,toensurethattheperformanceoflowerlayerenhancementsarenotcompromised.1IntroductionRandomnessisaninherentcharacteristicofwirelesscommunications.Itisafeaturethatstemsfromacombinationofphysicalphenomena,includingspecularre?ecti
4、ons,andmultipleradiopropagationpathstothereceiver.Duetothemobilityofusersand/orotherobjectsintheirvicinity,thesephe-nomenawillinducetimevariationsinthequalityofthechannelbetweentransceivers,whichisoftenreferredtoasfading.Agreatdealofwirelessresearchisfocussedonmitigatingtheseeffects.Inde
5、ed,enormousprogresshasbeenachievedoverthepast50yearsinthisarea,exploitingtechniquesfromcoding,signalprocessingandinformationtheory.Modernwirelesscellulartelephonyisbuiltupontheseadvances.ThedemandforwirelessInternetaccessisgrowing,andnewperfor-mancerequirementsareemerging.Distinctfromthe
6、?xedbandwidthandlatencyrequirementsoftraditionalvoicetraf?c,themajorityofInternettraf-?ciselastic.Elastictraf?cisabroadclassthatencompassesmanyofthemostpopularapplicationsusedontheInternettoday,includingtheWorld1Figure1:OverviewoftheInternetStackArchitecture.WideWeb(WWW),FileTransferProt
7、ocol(FTP),Peer-to-PeerclientsandElectronicMail.Incontrasttovoicetraf?c,thereisaparamountobjectiveforelastictraf?c:minimizationofthetotal?letransmissiontime.Formanyapplications,includingtheWWW,latencyisstillanimportantissue,butthereisnolongerahardconstraintonlatency,asther