IEEE 80211 Wireless LANs.docx

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IEEE 80211 Wireless LANs.docx

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IEEE 80211 Wireless LANs.docx

IEEE80211WirelessLANs

IEEEP802.11

WirelessLANs

IEEE802.11QualityofService–WhitePaper

Date:

February15,2000

Author(s):

ArunAyyagari,YoramBernet,TimMoore

MicrosoftCorporation

OneMicrosoftWay,Redmond,WA98052-6399

Phone:

(425)936-8080

Fax:

(425)936-7329

e-Mail:

aruna@,yoramb@,timmoore@

Abstract

IEEE802.11provideshighbandwidthconnectivityinalocalareanetwork(LAN)environmentthatissuitableformostdataapplications.However,itdoesnotmeetthequalityofservice(QoS)requirementsforreal-timedatatrafficapplicationssuchasvoiceandvideotransmissions.TherehavebeenrecentproposalsonenhancementstotheIEEE802.11Mediumaccesscontrol(MAC)protocoltoprovideexpeditedaccesstothesharedwirelessnetworkforreal-timedatatransmissions.However,theseproposalswouldrequirechangestotheIEEE802.11standardthatmaypotentiallyimpactbackwardcompatibilityandfutureadoptionoftheIEEE802.11wirelessLAN.Therefore,inthiswhitepaperweproposethecombineduseofresourcebasedadmissionandtrafficflowcontrolandexpeditedtransmissionofhigherprioritydataoverthesharedwirelessnetworkasthemechanismstoprovideQoSguaranteeforreal-timeapplicationdatatrafficinIEEE802.11.OurunderlyingobjectivewastodefineaQoSapproachwithoutanychangestothefundamentalIEEE802.11MACprotocol.

Overview

IEEE802.11isasharedwirelesslocalareanetwork(LAN)standardusingthecarriersensemultipleaccess(CSMA)mediumaccesscontrol(MAC)protocolwithcollisionavoidance(CA)[1].Thestandardallowsforbothdirectsequence(DS)andfrequency-hopping(FH)spreadspectrumtransmissionsatthephysicallayer.Themaximumdatarateofferedinitiallybythestandardwas2Mb/s.However,ahigherspeedversionwithaphysicallayerdefinitionundertheIEEE802.11bspecificationallowsadatarateofupto11Mb/susingDSspreadspectrum.TheIEEEstandardscommitteehasalsodefinedphysicallayerspecificationsundertheIEEE802.11aspecificationbasedonorthogonalfrequency-divisionmultiplexing(OFDM)thatwillpermitdatatransferratesupto54Mb/s.WhileIEEE802.11provideshighbandwidthconnectivityinaLANenvironmentthatissuitableformostdataapplications,itdoesnotmeetQualityofService(QoS)requirementsforreal-timedatatrafficapplicationssuchasvoiceandvideotransmissions.

IEEE802.11wirelessstation(STA)isintendedtooperateineitherofthefollowingtwomodes:

∙Adhocnetworkmode:

STAswithinabasicserviceset(BSS)areabletocommunicatedirectlywithpeerSTAswithintheBSS.

∙Infrastructurenetworkmode:

STAscommunicateonlywithanaccesspoint(AP)intheBSS.AnAPprovidesconnectivitytodistributionsystem(DS)servicesinadditiontoperformingasanSTA.STAswithinaBSScommunicatewithotherstationswithinandoutsidetheBSSviatheAP.Therefore,allcommunicationfrom/toSTAsaredirectedto/fromtheAPintheBSS.

Weenvisionthatinmostwirelessenvironmentssuchascorporationsandpublicplaces,infrastructurenetworkmodewillbepredominantlyused.Usageoftheinfrastructurenetworkmodeisdrivenbytheneedtoprovideaccesscontrol,accounting,andcontentprovisioningmechanismsinwirelessenvironmentthatfollowtheclient/serverinteractionparadigmbetweenthewirelessstationandaremoteserver.Adhocnetworkmodewouldstillbeusedinareassuchashomenetworkingenvironments.Inthiswhitepaper,wewillfocusourdiscussionontheinfrastructurenetworkmode,howeveramanyoftheapproachesandconclusionspertaininginfrastructurenetworkmodewouldbeequallyapplicabletotheadhocnetworkmode.

Theneedforresourcebasedadmissionandtrafficflowcontrolisofgreaterimportanceinwirelessnetworksbecausebandwidthinwirelessnetworksismoreconstrainedcomparedtowirednetworks.SinceanAPandalltheSTAscommunicatingwiththeparticularAParegivenequalaccessprioritytothesharedwirelessnetworkinIEEE802.11infrastructurenetworkmode,theAPbecomesabottleneckfortypicalclient/serverinteractions.WhiletheSTA’swouldbeabletotransmitdatatotheAP,datadestinedtotheSTAswouldbequeuedattheAPsinceithastoservicealltheSTAswithinitsBSSwithaccessprioritysimilartotheSTAs.Thereforeinadditiontothelatencyandbandwidthrequirementsforapplicationleveldatatraffic,characteristicsofwirelesscommunicationandnetworkarchitectureevincestheneedforQoSmechanismsinIEEE802.11.ThiswhitepaperpresentanalternativeapproachtoprovideQoSguaranteestoapplicationleveldatatrafficinIEEE802.11wirelessLAN.

Approach

AQoSguaranteeforreal-timeapplicationdatatrafficiscurrentlynotavailableinIEEE802.11.TherehavebeenrecentproposalsfromSharewave(Whitecapprotocol)[2]andLucent(Black-Burstprotocol)[3]onenhancementstotheIEEE802.11MACprotocoltoprovideexpeditedaccesstothesharedwirelessnetworkforreal-timedatatransmissions.However,boththeseproposalswouldrequirechangestotheIEEE802.11standardthatmaypotentiallyimpactbackwardcompatibilityandfutureadoptionoftheIEEE802.11wirelessLAN.Therefore,webelievethatitwouldbeprudenttoavoidorattheleastlimitthechangestotheIEEEMAC802.11protocolbyadoptingQoSapproachesthatdonotwarrantmajorchanges.

WeproposethecombineduseofresourcebasedadmissionandtrafficflowcontrolandexpeditedtransmissionofhigherprioritydataoverthesharedwirelessnetworkasthemechanismstoprovideQoSguaranteeforreal-timeapplicationdatatrafficinIEEE802.11.TheresourcebasedadmissionandtrafficflowcontrolmechanismmanagesthenumberandtrafficflowcharacteristicsofpeerapplicationsessionstoensurethattheirQoSrequirementsaresatisfied.TheexpeditedtransmissionofhigherpriorityframesbytheSTAsoverthesharedwirelessnetworkensuresthatthelatencyrequirementsofreal-timeapplicationsaresatisfied.Thisalsoresultsinsmallerlatencyvariabilityforreal-timeapplicationsthatleadstoabetterutilizationofthesharedwirelessnetworkbyaccommodatingagreaternumberofreal-timepeerapplicationsessions.

ResourceBasedAdmissionandTrafficFlowControl

InordertomaintainQoSguarantees,theresourcebasedadmissionandtrafficflowcontrolwouldassistinthemanagementofapplicationdatatraffictransmissionsoverthesharedwirelessnetwork.Intheproposedapproachresourcereservationprotocol(RSVP)signaling[4-5]andthesubnetbandwidthmanager(SBM)[6]wouldbeusedtoestablishend-to-end,per-conversation,QoStopeerapplicationsbetweentheIEEE802.11STAandaremotestation.WhileRSVPisalayer-3protocol,SBMisalayer-2protocolthatextendsthefunctionalityofRSVPtothesharedwirelessnetwork(betweentheSTAsandAP)andbeyond.Inadditiontotheadmissionandtrafficflowcontrol,theRSVPsignalingdescribingthetrafficcharacteristicsissenttothenetworkdevicesforaggregatetraffichandlingmechanismssuitableforIEEE802.11sharedwirelessnetwork.

Figure1illustratesatypicalIEEE802.11architecturethatconsistsofanumberofBSSsthatareinterconnectedviatheDSformingtheextendedserviceset(ESS).AlltheSTAsintheESSaremembersofasinglesubnet.Inatypicaldeployment,theAPswithintheESSareinterconnectedvialayer-2switchednetwork,forexample,usingapoint-to-pointfull-duplexfastEthernetconnectionbetweenagivenAPandalayer-2switchingdeviceatthecoreofthenetworkintheDS.ResourcebasedadmissionandtrafficflowcontrolwithintheESSmaybeaggregatedacrosstheentireDSforallBSSsorspecifictoeachBSSresultinginSBMprotocolbeingenabledatvariousdensitieswithintheIEEE802network[7].Also,eachSTAwithintheBSSisexpectedtohavefullSBMclientfunctionalityinordertomaintaincontroloftheIEEE802.11sharedwirelessnetworkresources.

AggregationofresourcebasedadmissionandtrafficflowcontrolacrosstheentireDSresultsinthelowestdensitywhereasingledesignatedSBM(DSBM)inthecoreofthelayer-2networkactsastheadmissioncontrolagentfortheentirelayer-2subnet.InthisscenariotheSBMclientateachSTAwithintheBSSdetectsthepresenceofaDSBMintheDS(corenetwork)androutesRSVPsignalingrequestsviatheDSBM.Inaddition,theDSBMmayalsobeconfiguredtoadvertiseaNonResvSendLimitonthemanagedsubnettolimitthemaximumrateatwhichSTAsmaytransmitintheabsenceofapprovedreservation.

Attheotherextreme,eachAPisanadmissioncontrolagent(DSBM)fortheSTAswithinaBSS.Inthiscase,theDSBMelectionprotocolwillresultinthedivisionoftheESSsuchthateachBSSbecomesamanagedsegmentmanagedbyanAP(DSBM).ThehigherdensityofDSBMsresultsinbettermanagementofthesharedwirelessnetworkresourceswithineachBSS.However,thiswouldrequirethateachAPshouldincludetheSBMserverfunctionalityontheportthatinterfaceswiththeSTAswithinitsBSS.SimilartothesingleDSBMscenario,allSTAswithintheBSSdetectsthepresenceoftheDSBMintheAPandrouteRSVPsignalingrequestsviatheDSBM.SinceallthetrafficfromSTAswouldnormallyberoutedviatheAPthisdoesnotdeviatefromthenormaldatatrafficpath.Also,theDSBMco-locatedwiththeAPmayalsobeconfiguredtoadvertiseaNonResvSendLimitonthemanagedsubnettolimitthemaximumrateatwhichSTAsmaytransmitintheabsenceofapprovedreservation.

RelativetowiredLANs,bandwidthismoreseverelyconstrainedinIEEE802l.11sharedwirelessLAN.Therefore,inordertoguaranteeQoSbetweentheSTAandaremotestation,resourcebasedadmissionandtrafficflowcontro

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