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WirelessLANsWLAN简介无线网络的优点z移动性z可扩展性z灵活性z节省成本z安装优势z苛刻环境中的可靠性z缩短安装时间无线信令技术红外线（Infrared）射频技术（RadioFrequecy）开放2.4GHz频段内的无线传送的3种类型：FHSS（FrequenceHoppingSpreadingSpectrum）DSSS（DirectSequenceSpreadSpectrum）OFDM（OrthogonalFrequency—DivisionMultiplexing）非授权5GHz频段内的无线传送的1种类型OFDM（OrthogonalFrequency—DivisionMultiplexing）WLAN的演进•仓库存储•零售业•卫生医疗•教育•商业•家庭Wireless通信技术无线网络中的术语802.11b/802.11g/802.11aSTA/BSS/IBSS/DS/ESS/RoamingSSID/WEP©2005CiscoSystems,Inc.Allrightsreserved.802.11b802.11b标准•1999年九月被认可•基于2.4-GHz的工作频带•使用directsequencespreadspectrum(DSSS)•定义了4中通信速率–1,2,5.5,11MbpsRegulatoryDomainChannelIdentifierChannelCenterFrequencyChannelFrequencyRange[MHz]AmericasEurope,MiddleEast,andAsiaJapan12412MHz2401–2423XXX22417MHz2422MHz2427MHz2432MHz2437MHz2442MHz2447MHz2452MHz2457MHz2462MHz2467MHz2472MHz2484MHzXXX32406–24282411–24332416–24382421–24432426–24482431–24532436–24582441–24632446–24682451–24732466–24782471–2483XXX4XXX5XXX6XXX7XXX8XXX9XXX10XXX11XXX12XX13XX2473–249514X2.4-GHzChannels802.11b/g(2.4GHz)ChannelReuse802.11bAccessPointCoverage©2005CiscoSystems,Inc.Allrightsreserved.802.11a802.11aStandard•1999年9月被批准•工作在5-GHz频带•使用orthogonalfrequency-divisionmultiplexing(OFDM)•定义了8个通信速率–6,9,12,18,24,36,48,54Mbps©2005CiscoSystems,Inc.Allrightsreserved.802.11g802.11gStandard•June2003•2.4-GHzband–同样适用3个不重叠的信道:1,6,11•使用DSSS和OFDM•定义了12个速率–1,2,5.5,11Mbps(DSSS/802.11b)–6,9,12,18,24,36,48,54Mbps(OFDM)•向后兼容802.11b802.11StandardsComparison802.11b802.11g802.11aRatified19992.4GHz3DSSS1,2,5.5,11Upto620031999Frequencyband2.4GHzNoofchannels3Upto23OFDM6,9,12,18,24,36,48,54Upto225GHzTransmissionDSSSOFDMDatarates[Mbps]1,2,5.5,116,9,12,18,24,36,48,54Throughput[Mbps]Upto28RangeComparisons