WLAN QoS

QoSInWLANByAbdulbasetHassanMuneerBazamaOutline•Introduction•QoSParameters.•802.11mediumaccesscontrolschemes(MAC).•802.11emediumaccesscontrolschemes(MAC).•Conclusion.•Reference.Introduction•Whatis802.11?•802.11referstoafamilyofspecificationsdevelopedbytheIEEEforwirelessLANtechnology.•802.11Standards.•1997-802.11upto2Mbps(900MHZ).•1999-802.11b2.4GHZandupto11Mbps.•1999–802.11a5GHZandupto54Mbps.•200x–802.11g2.4GHZandupto54Mbps.•200x–802.11eforQoS.QualityofService(QoS)•QoSisthecapabilitytoprovideresourceassuranceinanetwork.•QoSParameters:Bandwidth.Delay.Packetlossrate.Jitter.802.11mediumaccesscontrolschemes(MAC).Therearetwobasicmediumaccesscontrol(MAC)modes:•DistributedCoordinationFunction(DCF).•PointCoordinationFunction(PCF).DistributedCoordinationFunction(DCF)•Contention-Based.•BasedonCarrierSenseMultipleAccesswithCollisionAvoidance(CSMA/CA)algorithm.•UsesaContention(Backoff)algorithm.•Designedforabest-effortservice.•SupportsAsynchronoustransmission.ExampleofDCFB1andB2arebackoffintervalsatnodes1and2datawaitB1=5B2=15B1=25B2=20datawaitB2=10LimitationofDistributedCoordinationFunction(DCF)•DoesnotprovideanyQoSguarantees.•Doesnotsupportreal-timeapplication.•Designedforequalpriorities.•Doesnotsupporttheconceptofdifferentiatingframeswithdifferentuserpriorities.PointCoordinationFunction(PCF)•Contentionfree-based.•Usesacentralizedpollingscheme.•DifferentiationConsideredbasedonpriority.•Supportssynchronoustransmission.•Supportstime-boundedmultimediaapplications.LimitationofPointCoordinationFunction(PCF)•poorQoSperformance.•Usesasimpleround-robinalgorithm,whichcannothandlethevariousQoSrequirements.•Transmissiontimeofthepolledstationsisunknown.HybridCoordinationFunction(HCF)Therearetwomethodsofchannelaccess:•EnhancedDCFchannelaccess(EDCA).•HCFcontrolledchannelaccess(HCCA).EnhancedDCFChannelAccess(EDCA)•Contention-Basedchannelaccess.•Providesservicedifferentiation.•Classifiesthetrafficinto8differentclasses.•Eachstationhas4accesscategoriestoprovideservicedifferentiation.EDCA(Cont.)8Userprioritiesmappingto4AccessCategoriesScheduler(resolvesvirtualcollisionsbygrantingTXOPtohighestpriority8UserprioritiesperQSTAPri0Pri1Pri8Backoff(AIFSN3)Backoff(AIFSN2)Backoff(AIFSN1)Backoff(AIFSN0)AC0AC1AC2AC3TransmissionAttemptTransmissionOpportunity(TXOP):isthetimeintervalpermittedforaparticularSTAtotransmitpackets.EDCA(Cont.)PriorityAccessCategory(AC)Designation(Informative)00BestEffort10BestEffort20BestEffort31VideoProbe42Video52Video63Voice73VoiceHCFControlledChannelAccess(HCCA)•OperatesinCFPandCP.•ProvidesGuaranteedServiceswithamuchhigherprobabilitythanEDCA.•CombinestheadvantagesofPCFandDCF.•Coordinatesthetrafficinanyfashion(notjustround-robin).Conclusion•TheIEEE802.11wirelessLAN(WLAN)hasbecomeoneofthemostwidelyusedwirelesstechnologiesinthesedays.•The802.11standardscannotprovideanyQoSguaranteesduetopoorperformance.•The802.11eoffersQoSsupporttotime-sensitiveapplications,suchas,audioandvideocommunications.References1.PaalE.EngelstadandOlavNosterbo,AnalysisofQoSinWLAN,Telektronikk1.2005.()2.PriyankGarg,RushabhDoshi,RussellGreene,MaryBaker,MajidMalek,XiaoyanCheng,UsingIEEE802.11eMACforQoSoverWireless,2003IEEE.3.JieMaYuan'anLiu,BihuaTang,QoSResearchandDesignforWLAN,ProceedingsofISCIT2005.4.J.K.Choi,J.S.Park,J.H.Lee,K.S.Ryu,ReviewonQoSissuesinIEEE802.11W-LAN,Feb.20-22,2006ICACT2006.5.JoseVillalon,PedroCuencaandLuisOrozco-Barbosa,LimitationsandcapabilitiesofQoSSupportinIEEE802.11WLANS,2005IEEE.6.