IEEE 802.11s wireless mesh networks-Framework and

IEEE802.11swirelessmeshnetworks:FrameworkandchallengesXudongWanga,*,AzmanO.LimbaKiyon,Inc.,SanDiego,CA92121,UnitedStatesbNationalInstituteofInformationandCommunicationTechnology,Kyoto,JapanReceived5June2007;accepted11September2007Availableonline22October2007AbstractWirelessmeshnetworkingbasedon802.11wirelesslocalareanetwork(WLAN)hasbeenactivelyexploredforafewyears.ToimprovetheperformanceofWLANmeshnetworks,afewnewcommunicationprotocolshavebeendevelopedinrecentyears.However,thesesolutionsareusuallyproprietaryandpreventWLANmeshnetworksfrominterworkingwitheachother.Thus,astandardbecomesindispensableforWLANmeshnetworks.Tomeetthisneed,anIEEE802.11taskgroup,i.e.,802.11s,isspecifyingastandardforWLANmeshnetworks.Althoughseveralstandarddraftshavebeenreleasedby802.11s,manyissuesstillremaintoberesolved.Inordertounderstandwhatperformancecanbeexpectedfromtheexistingframeworkof802.11sstandardandwhatfunctionalitiesshallbeaddedto802.11sstandardtoimproveper-formance,adetailedstudyontheexisting802.11sstandardisgiveninthispaper.Theexistingframeworkof802.11sstan-dardisfirstpresented,followedbypointingoutthechallengingresearchissuesthatstillexistinthecurrent802.11standard.Thepurposeofthispaperistomotivateotherresearcherstodevelopnewscalableprotocolsfor802.11wirelessmeshnetworks.2007ElsevierB.V.Allrightsreserved.Keywords:Wirelessmeshnetworks;IEEE802.11sstandard;Protocol;Layer-2routing1.IntroductionInatraditionalsetupof802.11wirelessLANs,basicservicesets(BSSs)areconnectedviaEthernetLANs.Suchafixednetworkarchitecturelimitstheflexibilityofnetworkdeploymentandincreasescost.Thus,themobilityofBSSandmultihopnet-workingareneeded.StartingfromthefirstIEEE802.11standard,adhocnetworkinghasbeenspecifiedintheindepen-dentbasicserviceset(IBSS)mode.Inthismode,stations(STAs)canconnecttoeachotherwithoutanycentralcoordinatorlikeaccesspoint(AP).Moreover,thereisnoaccessorconnectiontothedistributedsystem(DS).Thus,STAsaretotallyself-containedasanadhocnetwork.Suchanoper-ationmodehasbeenresearchedinthefieldofadhocnetworking.However,ithasbeenrealizedforalongtime,especiallyinindustry,thattheIBSSmodeisnotenoughformanyinterestingapplication1570-8705/$-seefrontmatter2007ElsevierB.V.Allrightsreserved.doi:10.1016/j.adhoc.2007.09.003*Correspondingauthor.Tel.:[phone].E-mailaddresses:[e-mail](X.Wang),[e-mail](A.O.Lim).Availableonlineat(2008)970–984[1]isneededfor802.11wirelessnet-works.Foryears,manycompanieshavedevelopedtheirproprietarysolutionstobuild802.11basedwirelessmeshnetworks(WMNs).Suchsolutionssharethefollowingcommonfeatures:Thenetworkusuallyincludesthreetypesofnodes:meshrouters,clients,andgateways.Anadhocroutingprotocolisimplementedinmeshrouterstoworktogetherwith802.11MAC.Certainradioawarefunctionsmaybeincludedintheroutingprotocol.802.11MACdriverisenhancedinmeshrouterstoimprovemultihopperformance.Typicalexam-plesincludefine-tuningCSMA/CAparameters,developingalgorithmsformulti-radioordirec-tionalantennas,etc.Certainnetworkconfigurationsareneededtosupportclientaccess,Internetaccess,roaming,andsoon.Inspiteofthesimilarities,theproprietarysolu-tionsareusuallynotinter-operable.Inordertoresolvesuchanissueandmeettheever-increasingdemandsof802.11meshnetworks,itiscriticaltodevelopastandardfor802.11meshnetworks.BeforetheestablishmentoftheIEEE802.11staskgroup,manycompanieshadformedastudygrouptopushastandardfor802.11WMNs.Atthebeginning,manyproposalsweresubmittedtoresolvedifferentissuesinvolvedinmeshnetworking.Theseproposalswerefinallyconsolidatedandmergedintoonepro-posalinearly2006,whichprovidesthebasicframe-workforthecurrent802.11sstandarddraft.Sincethenthe802.11taskgrouphasbeenworkinghardtoresolveissuesintheframework.Draft1.0of802.11sstandardreleasedinNovember2006[2]wentthroughaletterballot,butitfailedinthisprocessbecausemanyissuesstillremain.Currentlypartici-pantsof802.11staskgroupareworkingactivelytoresolvecommentsraisedby802.11voters.Althoughalotofprogresshasbeenmadeandafewnewdraftshavebeenreleasedrecently,thereexistmanyissuesthatdemandenhancedorevennewsolutionsto802.11smeshnetworking.Otherwise,performanceof802.11sWMNscanbeunsatisfactory.However,tothebestofourknowledge,thereisnosignthatthe802.11staskgroupistakingthechallengeofenhancingadoptedsolutionsordevelopingnewsolu-tionsfor802.11smeshnetworking.Withoutputtingeffortsalongthisdirection,itisquitepossiblethatvoterswillcontinuetoraisecommentsandfailthelet-terballot.Consequently,thereleasingdateofanoffi-cial802.11sstandardbecomesunpredictable.Moreimportantly,evenifanofficialstandardisreleasedsomeday,itsmediocreperformancewillpreventitfromsurvivinginacompetitivemarketwithsomanyalternativemeshnetworkingtechnologies.Inthisarticlewegiveadetailedanalysisof802.11sframework.Firstly,themajorfunctional-itiesof802.11sWMNsarepres