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LocalAreaNetworkLAN。WirelessLANWLANIEEE802Ethernet。WLANCSMA／CA[1]WLAN。WLANMACMACWLAN。1IEEE802．11WLANIEEE802．11WLANOSIPHYDLC。LLCMACIEEE802．11MAC。LLCIEEE802IEEE802．3、IEEE802．11IEEE802。MAC。。MAC。WLANCSMA。collisionsWLANCS－MA／CD／CSMA／CA／。2IEEE802．11MAC2．1BSSBasicServiceSet。1aABCB。CABBB。。2．2WLAN。1bADBCBAAB。B。3IEEE802．11MACIEEE802．CBAabDABC12009105MAC。WLANMACTP393A1002－2422200905－0001－04StudyofHiddenSitesandExposedSitesinWLANLiFujuanAbstract:TheworkingmechanismofMAClayerisakeyelementtodeterminetheoverallperformanceoflocalareanetwork．Keyword:DCFPCFCSMA／CAWLAN2009－07－07*210012。*。ForthetwomainissuesofthehiddensitesandexposedsitesinWLANMAC,thepaperfirstputsforwardthetwoeffectivesolutionofdistributedcoordinationandpointcoordinationfunction,thencombinedwithCSMA／CAmediumaccesscontrolprotocol,analyzestheprincipleofDCFandPCF,finallydescribesthecharacteristicsoftheirapplica－WLANCSMA／CADCFPCFtionwithanapplicationinstance．WLANCSMA／CADCFPCFAccessPoint·1·11DistributedCoordinationFunctionDCFPointCoordinationFunctionPCF。IEEE802．11DCFPCFadhocPCFPCFDCF。3．1DCFCSMA／CADCFIEEE802．11CSMA／CA。CSMA／CA。2aCSMA／CA。ABCADB。AB2b[2]1ABRTSRequesttoSendB。RTS。RTS。2BARTSACTSCleartoSend。3ABCTSB。ACKABACK。4BAACK。5ABACKBRTS／CTS。RTS／CTSABCD。CD。2aCAARTSC。CARTSCA。ACA。DARTSDABCTS。D。CDRTSCTS。NAVNetworkAllocationVector。IEEE802．11MACDurationNAV。NAVRTSCTS。NAV0NAV0。NAV。DCF。3．22RTS、CTS、ACK。。CSMA／CA[3]。。RTSCTS。3ABRTSCTS。“－”ACK。CABDaAB2ABCSMA／CANAVNAVCTSRTSACKbCSMA／CADCBARTSCTSACKABNAVNAVCTSRTSACK00DCBA1…ACK1…nACKnab3IEEE802．11·2·RTS／CTS。。APAccessPoint。3．3PCFDCFPCF[4]。PCFAP。PCFAP。PCFIEEE802．11APadhocPCF。IEEEPCFDCFAP。APAPAP。3．4DCFPCFDCFPCF。DCFPCF。deadtime。。IEEE802．11MACMACQoSQualityofService。。。IEEE802．114[5]。1ShortInterFrameSpacingSIFS。RTS／CTSACK。2PCFPCFInterFrameSpacingPIFS。PCF。PIFSPIFS。PIFS。3DCFDCFInterFrameSpacingDIFS。DCF。DIFSAP。DIFS。。4ExtendedInterFrameSpacingEI－FS。EIFS。EIFS4。45。ABBSIFSCTSACKASIFS。CNAVACTSNAVRTSDNAVBCTSNAVCTS。RTS／CTS／ACKDIFS。5IEEE802．11WLAN。WLAN。WLANMACDCFPCFQoSMAC。RTS／CTS、ACK、NAV。[1]MattbewS．Gast．802．11[M]．O＇ReillyTaiwan．:2007－12．[2]AndrewS．Tanenbaum．ComputerNetworksFourthEditi－on[M]．:2008－05．[3]ANSI／IEEE802．11－－1999WirelessLANmediumaccesscontrolMACandphysicallayerPHYspecification[S]．2003．ACKSIFSPIFSDIFS4RTSNAVCTSNAVRTSCTSACKDCBASIFSSIFSSIFSDIFS5·3·[4]．WLAN[J]．2009264:1463－1465．[5]．DCF[J]．2005279:57－61．。、、。。11[1]、。2WinPcap、、。2．12WinPcapWinPcaplibpcapWindows。。。2．2。WinPcap。12009105WinPcapWinPcapTP393．08A1002－2422200905－0004－03StudyonPerformanceOptimizationofNetworkIntrusionDetectionSystemBasedonWinPcapXieChangrongLiJuyingZhengYiAbstract:Basedonin－depthstudyofWinPcapstructureandmainmodulesofnetworkintrusiondetectionsystem,thepaperKeyword:、、WinPcap2009－07－01*621000。*。putsforwardmethodsandtheanalysisofoptimizingperformanceofnetworkintrusiondetectionsystembasedonWinPcap,whicharemadeupofsystemstructureoptimization,enhancementofdatacaptureability,protocolanalys－WinPcapismethodoptimizationandapplicationoptimization,andsoon．IntrusionDetectionSystemStructureWinPcapDataCaptureProtocolAnalysis．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．HTTPFTPSMTP……TCPUDPIP／ICMP123123n2·4·