無線網路的概觀與802.11無線區域網路(Overview)

IEEE802.11OverviewRong-HongJanDeptofComputerandInformationScienceNationalChiao

TungUniversity802.11Technologies:

Past,PresentandFuture

Approvedandnear-term802.11LetterStandardsFaster:Standards-basedWi-Finowdeliversdataratesupto54MbpstoWi-Ficlients.(11a,11g)Better-performing:Theneedforabetter-performingMAChasbeendrivenbydemandingapplicationsuchasvoiceandvideo.QualityofServiceenhancementshavemodifiedtheMACtoprovideadmissioncontrolandprioritizedchannelaccess.(11e)3Moresecure:Securityenhancementshavebeendevelopedtoaddressaccesscontrolandauthenticationanddataprivacyandintegrity,drivenbythemarketrequirementforenterprise-levelsecurityinwirelessLANs.(11i)Broaderapplicability:Regulatoryenhancementsthatbroadentheapplicabilityof802.11tootherfrequenciessuchas4.9GHzinJapanandotherregulatorydomains.(11j)4PhysicalLayerenhancements11a,11b,11gQualityofService(QoS)enhancements11eSecurityenhancements11iWPARegulatoryenhancements11d11h5Future802.11Standards802.11jThe802.11jTaskGroupisworkingonJapaneseregulatoryextensionstoallowforoperationinthe4.9GHzand5GHzbandsinJapan.Thisisexpectedtobeapprovedin2005.802.11k802.11kisfocusedonstandardizingtheradiomeasurementsthatwillallowuniformmeasurementofradioinformationacrossdifferentmanufacturerplatforms.6Byhavingstandardized,repeatablemeasurements,systemdesignerscanutilizeradioenvironmentinformationtomakebetterdecisionsastofrequencyuse,transmitpowerlevels,etc.802.11nThe802.11nTaskGroupisfocusingoncreatingastandardtofurtherincreasethenetthroughputofwirelessnetworks.Thegoalistoachievegreaterthan150Mbpsusablethroughputoveran802.11.7BothphysicalandMAClayerchangesarebeingconsidered,butbackwardcompatibilityisrequired.802.11rThe802.11rTaskGroupisworkingonreducingthehandofflatencywhenclientdevicestransitionbetweenaccesspointsorcellsinanESS.ThisstandardwillfacilitatethedeploymentofSIP-basedVoiceoverWi-Fi(VoWi-Fi)portablephones.8802.11sThe802.11sTaskGroupisworkingonaninfrastructuremeshstandardtoallow802.11accesspointsorcellsfrommultiplemanufacturerstoself-configureintomulti-hopwirelesstopologies.Exampleusagescenariosformeshnetworksincludeinterconnectivityfordevicesinthedigitalhome,unwiredcampuses,andcommunityareanetworksorhotzones.9StandardsEvolutionof802.1110StandardsEvolutionof802.1111無線區域網路課程內容安排

-大綱(I)課程大綱無線網路的概觀與802.11無線區域網路(Overview)802.11的媒體擷取控制(MAC)與訊框格式802.11e:QoSof802.11802.11的安全:WEP與802.11i802.11的管理機制競爭與非競爭的媒體控制機制12無線區域網路課程內容安排

-大綱(II)實體層的簡介802.11fIAPP(InterAccessPointsProtocol)802.11網路佈建與管理網路分析與效能調整802.11隨意無線區域網路路由方法13無線網路的概觀與802.11無線區域網路(Overview)WirelessvswiredBluetooth,802.11,GSM,GPRS,UTMLWireless–Mobility-Security802.11serialsInfrastructureAdhoc14TypesofNetworksIndependentnetworks(indep.basicserviceset,IBSS),alsoknownasadhocnetworks.Infrastructurenetworks15TwoadvantagesforinfrastructurenetworksThemobilestationsneednottomaintainneighborrelationships.Accesspointsassistwithstationsattemptingtosavepower.Inaninfrastructurenetwork,stationsmustassociatewithanAPtoobtainnetworkservices.(equivalenttopluginthenetworkcable)Anextendedserviceset(ESS)iscreatedbychainingBSSstogetherwithabackbonenetwork.16802.11的媒體擷取控制(MAC)與訊框格式MACaccessingmodesCSMA/CA&NAVInter-framespacesDCFoperation/BackoffFragmentation&De-fragmentationFrameFormatRTS/CTS&PowerSavingsequence17802.11adaptsEthernet-stylenetworkingtoradiolinks.EthernetCSMA/CD802.11CSMA/CAChallengesfortheMACRFlinkquality:802.11busesunlicensedISMbandsasitsradiolink.Itmustassumethatinterferencewillexistandworkaroundit.18ACKisrequired.19MACAccessModesDistributedcoordinationfunction(DCF):Ethernet-like.CSMA/CA.DCFmayuseCTS/RTStoreducethepossibilityofcollisions.Pointcoordinationfunction(PCF):Contention-freeservices.Specialstationscalledpointcoordinatorsareusedtoensurecontention-free.ThecoordinatorsresideinAP.PCFisonlyforinfrastructuremodeandnotwidelyimplemented.2021Contention-basedaccessusingtheDCF22Contention-basedaccessusingtheDCF23Contention-basedaccessusingtheDCF24Carrier-SensingFunctionsandtheNetworkAllocationVectorTwotypesofcarrier-sensingfunctions:thephysicalcarrier-sensingandvirtualcarrier-sensingfunctions.Thevirtualcarrier-sensingisprovidedbytheNetworkAllocationVector(NAV)TheNAViscarriedintheframeheadersontheMACframes(e.g.,RTS,CTS,Beacon,Probe,Association,andsoon)2526FrameFormatFieldsaretransmittedfromlefttoright,andthemostsignificantbitsappearlast.27802.11e:QoSof802.11TrafficdifferentiationHybridcoordinationfunction(HCF)Contention-basedchannelaccess–EDCFControlledchannelaccessDirectlinkprotocol(DLP)BurstACK28802.11的安全:WEP，802.1X與802.11iWEPoperationRC4encryptionalgorithmEAP(ExtensibleAuthenticationProtocol)802.1x:Networkportauthentication802.1xonwirelessLANs2930SupplicantAuthenticator3:EAPOL-StartRadius4:Request/Identity5:Response/Identity5:Radius-Access-Request6:Radius-Access-Challenge7:Radius-Access-Request8:Radius-Access-Accept9:EAPOL-Key(WEP)8:EAP-Success7:EAP-Response6:EAP-RequestEAPOLRADIUS1:Associationrequest2:Associationresponse802.113132802.11的管理機制InfrastructuremanagementScanning：Passive&ActiveAuthentication：Opensystem&Share-keyAssociationRe-associationIBSSmanagementTimesynchronization33PassiveScanningPassivescanningsavesbatterypower.Inpassivescanning,astationmovestoeachchannelonthechannellistandwaitsforBeaconframes.34ActiveScanningForeachchannelinthechannellist:WaitforeitheranindicationofanincomingframeorProbeDelayTimertoexpire.Ifaframeisdetected,thechannelcanbeprobed.SendProbeRequest.Waitforminormaxchanneltime.(Channelbusyornot)IdleminchanneltimenonetworkBusymaxchanneltimeProberesponsesareunicastframessubjecttoACK.35ChoosingwhichBSStojoinisanimplementation-specificdecisionandmayeveninvolveuserintervention.Powerlevel,signalstrength.MatchingparametersTimersynchronizationisanimportanttaskinthejoiningprocess.36AssociationAssociationisrecordkeepingprocedurethatallowsthedistributionsystemtotrackthelocationofeachmobilestation.Afterassociation,anAPmustregistertheMSonthenetworksoframesfortheMSaredeliveredtotheAP.How?(APmaysendagratuitousARP.)802.11forbidsassociatingwithmorethanoneAP.37AssociatedprocedureAssociationreq&repareunicastframes.(ACKisrequired)38Reassociatedprocedure39競爭與非競爭的媒體控制機制PCFvsDCFPCFoperationPCFframeformatPowersavingmodeinDCFPowersavingmodeinPCF40ThePCFallowsan802.11networktoprovideanenforced“fair”accesstothemedium.(LikesAPholdingthetokeninatoken-basedMACschemes)PCFisanoptionalpartof802.11Periodsofcontention-freeservicearbitratedbythepointcoordinatoralternatewiththeDCF-basedservices.41AcycleContentionfree+contentionperiodAtthebeginningofthecontention-freeperiod,theAPtransmitsaBeaconframeandannouncesCFPMaxDuration.AllstationssetNAVtoCFP-MDtolockoutDCF-basedaccess42實體層的簡介PhysicallayeroverviewFrequencyhoppingGFSKDirectsequencespectrumChippingDPSK&QPSKOFDM43802.11fIAPP(InterAccessPointsProtocol)IAPPsecurityrisksIAPPprotocoloverviewADDMOVECACHE-NotifyRADIUSprotocolusageIAPPframeformat44IAPPIAPP(InterAccess-PointProtocol)isdesignedfortheenforcementofuniqueassociationthroughoutaESS(ExtendedServiceSet)andforsecureexchangeofstation'ssecuritycontextbetweencurrentaccesspoint(AP)andnewAPduringhandoffperiod.Basedonsecuritylevel,communicationsessionkeysbetweenAPsaredistributedbyaRADIUSserver.

45ProactivecachingProactivecachingissuggestedtoavoidlonghandoffdelaycausedbyIAPPcommunicationbetweentwoAPsaswellasAPandRADIUSserver.Withproactivecaching,currentaccesspointdistributesthesecuritycontextofthemobilestationtoneighboringaccesspointsBEFOREthestationactuallyhandoffs.46802.11網路佈建與管理ThetopologyarchetypeRoaming&MobilitySpanningmultiplelocationsSecurityProjectplanningThesitesurveyInstallationandthefinalrollout47網路分析與效能調整NetworkanalysisTuningradiomanagementTuningpowermanagementTimingoperations48TuningradiomanagementBeaconintervalDecreasingpassivescanningmorereliable&fasterIncreasingPower-savingcapability(listen,DTIMintervals)Throughput49802.11隨意無線區域網路路由方法MANETRoutinginMANETTable-DrivenRoutingProtoco