新版CCNA200-120PPT文档37-无线

CCNA(640-802),CCNA200-120,WirelessDataTechnologies,WirelessDataTechnologies(Cont.),WirelessLAN(WLAN),AWLANisasharednetwork.无线是共享网络AnaccesspointisashareddeviceandfunctionslikeasharedEthernethub.AP就是共享点，相当于HUBDataistransmittedoverradiowaves.数据传输是无线电波Two-wayradiocommunications(half-duplex)areused.工作在半双工Thesameradiofrequencyisusedforsendingandreceiving(transceiver).相同的电波发送,WLANEvolution,Warehousing仓库Retail零售Healthcare卫生保健Education教育Businesses商业Home家庭,WhatAreWLANs?,Theyare:Local本地的Inbuildingorcampusformobileusers建筑物和校园内移动用户Radioorinfrared无线电波和红外NotrequiredtohaveRFlicensesinmostcountries多数国家不要无线射频许可Usingequipmentownedbycustomers自己建立设备,Theyarenot:WANorMANnetworksCellularphonesnetworksPacketdatatransmissionviacelluarphonenetworksCellulardigitalpacketdata(CDPD)蜂窝移动Generalpacketradioservice(GPRS)普通包分组交换2.5Gto3Gservices,SimilaritiesBetweenWLANandLAN,AWLANisan802LAN.Transmitsdataovertheairvs.dataoverthewire传输数据在无线网络Lookslikeawirednetworktotheuser像有线网络Definesphysicalanddatalinklayer定义了物理和数据链路层UsesMACaddresses用MAC地址Thesameprotocols/applicationsrunoverbothWLANsandLANs.IP(networklayer)IPSecVPNs(IP-based)Web,FTP,SNMP(applications),DifferencesBetweenWLANandLAN,WLANsuseradiowavesasthephysicallayer.WLANsuseCSMA/CAinsteadofCSMA/CDtoaccessthenetwork.用CSMA/CARadiowaveshaveproblemsthatarenotfoundonwires.Connectivityissues.Coverageproblems覆盖问题Multipathissues信号问题Interference,noise干扰问题Privacyissues.WLANsusemobileclients.Nophysicalconnection.无物理连接Battery-powered.要动力WLANsmustmeetcountry-specificRFregulations.,WLANTopologies,Wirelessclientaccess客户模式MobileuserconnectivityWirelessbridging无线桥LAN-to-LANconnectivityWirelessmeshnetworking无线网Combinationofbridginganduserconnectivity,WLANandLAN,ServiceSetIdentifier(SSID),SSIDisusedtologicallyseparateWLANs.SSID是逻辑的网络TheSSIDmustmatchonclientandaccesspoint.在服务器和客户端一样AccesspointbroadcastsoneSSIDinbeacon.广播在同一SSIDClientcanbeconfiguredwithoutSSID.客户不配置SSIDClientassociationsteps:Clientsendsproberequest.客户发送请求Apointsendsproberesponse.服务端发送回答Clientinitiatesassociation.客户发送连接Apointacceptsassociation.服务端接受连接ApointaddsclientMACaddresstoassociationtable.服务端加入MAC,WLANAccessTopology,WirelessRepeaterTopology,AlternativePeer-to-PeerTopology,ServiceSetsandModes,AdhocmodeIndependentBasicServiceSet(IBSS)中立基本服务Mobileclientsconnectdirectlywithoutanintermediateaccesspoint.Infrastructuremode下部结构模式BasicServiceSetMobileclientsuseasingleaccesspointforconnectingtoeachotherortowirednetworkresources.ExtendedServicesSetTwoormoreBasicServiceSetsareconnectedbyacommondistributionsystem.,ClientRoaming,RoamingwithoutinterruptionrequiresthesameSSIDonallaccesspoints.漫游要相同的SSID,Layer2vs.Layer3Roaming,UnlicensedFrequencyBands,ISM:Industry,scientific,andmedicalfrequencyband工业科学利用Nolicenserequired没有许可证,Noexclusiveuse不是专用Besteffort尽力传输Interferencepossible冲突产生,RadioFrequencyTransmission,Radiofrequenciesareradiatedintotheairviaanantenna,creatingradiowaves.Radiowavesareabsorbedwhentheyarepropagatedthroughobjects(e.g.,walls).Radiowavesarereflectedbyobjects(e.g.,metalsurfaces).Thisabsorptionandreflectioncancauseareasoflowsignalstrengthorlowsignalquality.,无线频率周期的发送通过天线当它们通过障碍物时，被繁殖无线电波被吸收无线电波由对象反射这吸收和反射可能导致低信号强度或低信号质量区域。,RadioFrequencyTransmission,Higherdatarateshaveashortertransmissionrange.ThereceiverneedsmoresignalstrengthandbetterSNRtoretrieveinformation.Highertransmitpowerresultsingreaterdistance.Higherfrequenciesallowhigherdatarates.Higherfrequencieshaveashortertransmissionrange.,更高的数据速率有一个更短的传输范围接收器需要更多信号强度和更好的SNR检索信息。更高传送在长距离的电力结果更高的频率允许更高的数据速率。更高的频率有一个更短的传输范围,WLANRegulationandStandardization,RegulatoryagenciesFCC(UnitedStates)ETSI(Europe)StandardizationIEEE802.11/getieee802/CertficationofequipmentWi-FiAlliancecertifiesinteroperabilitybetweenproducts.Certificationsinclude802.11a,802.11b,802.11g,dual-bandproducts,andsecuritytesting.Certifiedproductscanbefoundat.,802.11bStandard,StandardwasratifiedinSeptember1999Operatesinthe2.4-GHzbandSpecifiesdirectsequencespreadspectrum(DSSS)Specifiesfourdataratesupto11Mbps1,2,5.5,11MbpsProvidesspecificationsforvendorinteroperability(overtheair)Definesbasicsecurity,encryption,andauthenticationforthewirelesslinkIsthemostcommonlydeployedWLANstandard,2.4-GHzChannels,802.11b/g(2.4GHz)ChannelReuse,802.11bAccessPointCoverage,802.11aStandard,StandardwasratifiedSeptember1999Operatesinthe5-GHzbandUsesorthogonalfrequency-divisionmultiplexing(OFDM正交频分复用技术)Useseightdataratesofupto54Mbps6,9,12,18,24,36,48,54MbpsHasfrom12to23nonoverlappingchannels(FCC)Hasupto19nonoverlappingchannels(ETSI)RegulationsdifferentacrosscountriesTransmit(Tx)powercontrolanddynamicfrequencyselectionrequired(802.11h),802.11aChannelReuse,802.11hDFSnotavailableManualchannelassignmentrequired802.11hDFSimplementedChannelassignmentdonebyDynamicFrequencySelection(DFS)Onlyfrequencybandscanbeselected,802.11gStandard,StandardwasratifiedJune2003Operatesinthe2.4-GHzbandas802.11bSamethreenonoverlappingchannels:1,6,11DSSS(CCK)andOFDMtransmission12dataratesofupto54Mbps1,2,5.5,11Mbps(DSSS/802.11b)6,9,12,18,24,36,48,54Mbps(OFDM)Fullbackwardcompatiblityto802.11bstandard,802.11gProtectionMechanism,Problem:802.11bstationscannotdecode802.11gradiosignals.802.11b/gaccesspointcommunicateswith802.11bclientswithmax.11Mbps.802.11b/gaccesspointcommunicateswith802.11gclientswithmax.54Mbps.802.11b/gaccesspointactivatesRTS/CTStoavoidcollisionswhen802.11bclientsarepresent.802.11bclientlearnsfromCTSframethedurationofthe802.11gtransmission.Reducedthroughputiscausedbyadditionaloverhead.,802.11StandardsComparison,RangeComparisons,RatifiedIEEE802.11Standards,802.11:WLAN1and2Mbpsat2.4GHz802.11a:WLAN54-Mbpsat5GHz802.11b:WLAN11-Mbpsat2.4GHz802.11d:Multipleregulatorydomains802.11e:Qualityofservice802.11f:Inter-AccessPointProtocol(IAPP)802.11g:WLAN54-Mbpsat2.4GHz802.11h:DynamicFrequencySelection(DFS)TransmitPowerControl(TPC)at5GHz802.11i:Security802.11j:5-GHzchannelsforJapan,/getieee802/,WLANSecurityThreats,MitigatingtheThreats,EvolutionofWLANSecurity,WirelessClientAssociation,AccesspointssendoutbeaconsannouncingSSID,datarates,andotherinformation.AP发送明确的SSIDClientscansallchannels.客户控制隧道Clientlistensforbeaconsandresponsesfromaccesspoints.客户监听响应Clientassociatestoaccesspointwithstrongestsignal.客户发送连接信号给APClientwillrepeatscanifsignalbecomeslowtoreassociatetoanotheraccesspoint(roaming).漫游时在发连接DuringassociationSSID,MACaddressandsecuritysettingsaresentfromtheclienttotheaccesspointandcheckedbytheaccesspoint.MAC地址安全,WPAandWPA2Authentication,WPAandWPA2Encryption,WLANSecuritySummary,WPAPassphraseWEPEncryption,802.1xEAPMutualAuthenticationTKIPEncryptionWPA/WPA2802.11iSecurity,Securi