硕士论文-上海交通大学-wifi网络切换技术的研究与实现

上海交通大学硕士学位论文WiFi网络切换技术的研究与实现姓名：周洲申请学位级别：硕士专业：通信与信息系统指导教师：徐昌庆20081201IWiFiWiFiIEEE802.11WiFiInternetVoIPWiFiAccessPointAP50-300APHandoffVoIPWiFiWiFiWiFiIEEE802.11APAPIINDISWindowsVoIPWiFiIIIRESEARCHANDIMPLEMENTATIONONHANDOFFTECHNIQUEFORWIFINETWORKSABSTRACTInrecentyearsWirelessLocalAreaNetworksWLANhavedevelopedrapidlyandgainedcommonacceptance,withnumeroussuccessfuldeploymentsinlocalnetworkenvironments.TheIEEE802.11standard(WiFi)hasenabledfast,effectiveandlow-costWLANservices.WirelessnetworksofferaccesstotheInternetfordeliveryofvariousservicessuchasVoIP,multimedia,anddatatransmission.Continuousnetworkconnectivityishighlydesirableformostservices.However,thecoverageofaWiFiaccesspoint(AP)isnormally50to300metersandthesmallcoveragecanonlysupportuserswithlowmobility.HandoffhappensfrequentlywhenthemobilestationisroamingbetweendifferentAPs.Thehandofflatencysignificantlyinfluencesthequalitiesofreal-timeapplicationssuchasVoIP.Thus,handoffhadalwaysbeenacriticalandchallengingissueinrelatedareas.ThispaperfocusesonhandofftechniquesresearchanditsimplementationinWiFinetworks.Firstofall,thesignificanceandcurrentstatusofWiFihandoffresearcharepresented.ThentheprocedureofIEEE802.11handoffisintroducedindetailincludingitsIVperformanceanalysis.Moreoverweproposeafasthandoffschemebasedonbackgroundscanning,whichhelpsthemobilestationtoacquiretheinformationoftheAPsaroundandreducesthescanninglatencyatthesametime.Otherwise,scanthresholdandhandoffthresholdareintroducedtomakethehandoffdecisionefficientandreliable.WhenselectingthetargetAP,wechoosetheRSSIasadominantfactoraswellassecurity,stabilityandcustomerdemands.AtlastweimplementhandoffschemeonWindowsplatform,accordingtotheNDISstandard.Experimentsresultverylowhandofflatencywhichshouldsatisfytherequirementofreal-timeapplicationssuchasVoIPandvideostreamingtransmission.KEYWORDSWLANWiFiHandoffVACKAcknowledgmentAPAccessPointBPSKBinaryPhaseShiftingKeyingBSSBasicServiceSetBSSIDBasicServiceSetIdentificationCCKComplementaryCodeKeyingCFContentionFreeCRCCyclicRedundancyCodeCSMA/CACarrierSenseMultipleAccesswithCollisionAvoidance/CSMA/CDCarrierSenseMultipleAccesswithCollisionDetection/DSSDistributionSystemServiceDSSSDirectSequenceSpreadSpectrumESSExtendedServiceSetESSIDExtendedServiceSetIdentificationFHSSFrequencyHoppingSpreadSpectrumIAPPInterAccessPointProtocolIBSSIndependentBasicServiceSetLANLocalAreaNetworkLLCLogicalLinkControlMACMediumAccessControlMIBManagementInformationBaseMLMEMACLayerManagementEntityMACPCFPointCoordinationFunctionPLMEPhysical-layerManagementEntityVIPOTSPlainOldTelephoneServicePSTNPublicSwitchedTelephoneNetworkQPSKQuadraturePhaseShiftingKeyingRSSIReceivedSignalStrengthIndicationSMESystemManagementEntitySSIDServiceSetIdentificationTIMTrafficIndicationMapVoIPVoiceoverInternetProtocol575811.1IEEE802.11IEEE802802.3Ethernet802.5TokenRing802.3z100BASET19977IEEE802.1119999802.11b[1]WirelessFidelityWiFi802.11WiFi802.111Mbps2Mbps5.5Mbps11MbpsWiFiEthernet802.11ISO1-1IEEE802.11[2]21-1IEEE802.11Figure1-1IEEE802.11architecture1.1.1IEEE802.11IEEE802.11Station,STAPC(AP)(802.3)802.1d802.11PCMCIAPCIISA(802.11)IEEE802.11[3]1-2Ad-hocIndependentBSSIBSSExtendedServiceSetIdentification,ESSID1-3APSTADistributionSystemService,DSSBasicServiceSet,BSSExtendedServiceSetESS3APHubAPBSSAPBasicServiceSetIdentificationBSSIDIEEE802.11BSSIDAPMAC1-4[3]ESSBSS1.1.2IEEE802.111.IEEE802.112.4GHzISMIEEE802.11IEEE802.111-2Figure1-2IndependentnetworkIEEE802.111Mbps2MbpsFHSS(FrequencyHoppingSpreadSpectrum)DSSS(DirectSequenceSpreadSpectrum)FHSSDSSS41-3Figure1-3Infrastructurenetwork1-4BSSESSFigure1-4BSSandESSarchitecture2.802.11b802.11bIEEE802.115.5Mbps11MbpsDSSS802.11b1Mbps2M5bps802.11DSSS802.11DSSS11chippingBarker1110Symbol)1MSps(1Msymbols)BPSK(BinaryPhaseShiftingKeying)2MbpsQPSK(QuadraturePhaseShiftingKeying)QPSKBPSK802.11b11BarkerComplementaryCodeKeyingCCK[4]6485.5MbpsCCK411MbpsCCK8QPSK1.375MSps802.11b802.11b11Mbps11Mbps5.5Mbps2Mbps1Mbps11Mbps3.802.11802.11MAC802.3MAC802.3/(CarrierSenseMultipleAccesswithCollisionDetectionCSMA/CD)[5]802.116802.11CSMA/CD/(CarrierSenseMultipleAccesswithCollisionAvoidanceCSMA/CA)(DistributedCoordinationFunctionDCF)CSMA/CAAcknowledgmentACKACKCSMA/CAACK802.11802.3802.11EthernetMACHiddenNode802.11MACRTS/CTS(RequesttoSend/CleartoSend)RTSRTSCTSACKhiddennodeRTS/CTS()802.11MACCRC802.11EthernetTCP/IP()MAC802.11MAC802.117802.11DSSS14141.1.3WiFiWiFiIEEE802.11WiFiIEEE802.11IEEE802.11IEEE802.115.5Mb/s11Mb/sIEEE802.11bLANIEEE802.11bIEEE802.11IEEE802.11bIEEE802.11WiFi5015[6]WiFi300100WiFi11Mbps100LANPDA8WiFiIEEE802.1110060~70[1]200~1000[7]5PDAWiFiAPAPAPMACWiFiADSLLANAPAPAPWiFiWiFiWiFiWiFiWiFi1.2VoIPVoIP(VoiceoverInternetProtocol)[8]IP9IPVoIPTCP/IPIPVoIPIPInternetIPVoIPIP/InternetInternetVoIPVoIPPSTNVoIP(ISP)Points-of-Presence(POPs)VoIPPC-to-PhonePhone-to-PCIPPSTNVoIPPSTNHiPerVoIPPOTSPC10VoIPVoIP[9]1.38632007AA01Z224WLANVoIPVoWLAN(VoiceoverWLAN)IPWLANVoIPVoWLANE-mailVoWLANIPVoWLANIEEE802.11IEEE802.11WiFiQoSAPQoSIEEE802.11WiFiAP1.41.IEEE802.11VoIP112.3.IEEE802.114.WindowsNDISIEEE802.11APIEEE802.1112IEEE802.11