校园无线网路技术与应用发展(PPT 82页)-英文版

来自校園無線網路技術與應用發展Sheng-TzongCheng鄭憲宗[e-mail]成大資訊鄭憲宗2Outline無線區域網路─IEEE802.11無線應用通訊協定─WAP来自成大資訊鄭憲宗3無線區域網路通訊協定WirelessLocalAreaNetwork(IEEE802.11)来自成大資訊鄭憲宗4無線區域網路標準-IEEE802.11SpecifiesasingleMediumAccessControl(MAC)sublayerand3PhysicalLayerSpecifications.Stationscanoperateintwoconfigurations:Ad-hocmodeInfrastructuremodeThreePHYspecificationsFrequencyHoppingSpreadSpectrum(FHSS).DirectSequenceSpreadSpectrum(DSSS).InfraredPHY.来自成大資訊鄭憲宗5IEEE802.11規範IEEEProject802Charter:Local&MetropolitanAreaNetwork1Mbpsto100Mbpsandhigher2lowerlayersof7LayerOSIReferenceModelIEEE802.11WorkingGroupscope:Wirelessconnectivityforfixed,portableandmovingstationswithinalimitedareaAppeartohigherlayer(LLC)thesameasexisting802standardsApplicationLayerNetworkLayerMACPhysicalLayer...LLCIEEE802.11DataLinkLayer来自成大資訊鄭憲宗61997/6/26通過成為IEEE802系列標準IEEE802.11架構MediaAccessControlLogicalLinkControlInfraredPhysicalLayerFHSSPhysicalLayerDSSSPhysicalLayer来自成大資訊鄭憲宗7AdHoc網路•OneBasicServiceSet•DirectedConnection•LimitedCoverageArea来自成大資訊鄭憲宗8APBSSInfrastructure網路APBasicServiceSetExistingWiredLANDistributionSystemOtherLANsExtendServiceSet来自成大資訊鄭憲宗9Infrastructure網路(cont.)AccessPointandMobileStationDistributedSystemInterconnectMultipleCellsviaAccessPointstoformasinglenetworkExtendsWirelessCoverageAreaMultipleBasicServiceSetsconnectedtogetherformanExtendedServiceSetAllowMobileStationtoaccessfixedresourceSupportRoamingforMobileStationsviaAccessPointPointCoordinationFunction,PowerManagement,TimeSynchronizationsupportthroughAccessPoint来自成大資訊鄭憲宗10IEEE802.11ServicesProvidesserviceswiththefollowingfunctionality:roamingwithinaESS,multipledataratesinBSSsandPowerManagement.TheMACprotocolisCarrierSenseMultipleAccesswithCollisionAvoidance(CSMA/CA)MACservicesAssociationserviceAuthenticationserviceDistributionserviceIntegrationserviceDeauthentication/Deassociationservice来自成大資訊鄭憲宗11SpreadSpectrumTechnologyDSSS（DirectSequenceSpreadSpectrum）11channelsPN-code長度為11-bit展頻寬度為11MHzFHSS（FrequencyHoppingSpreadSpectrum）78hopsequences頻帶範圍為1MHz，跳頻的頻率為每秒2.5次InfraredRay發展趨勢：DHSS往高速無線區域網路系統發展，適合辦公室環境使用；FHSS會往低價網路應用發展，提供SOHO及家庭應用、或周邊設備之無線網路連結。来自成大資訊鄭憲宗12直接序列展頻（DSSS）来自成大資訊鄭憲宗13跳頻展頻（FHSS）来自成大資訊鄭憲宗14IEEE802.11TGaTheTGaisworkingonthehighdata-rateextensioninthe5GHzband,project802.11a,wasabletoproduceanewdraftstandardthathasthesupportofatleast80%ofthemembers.TGaislookingatacandidateforworldwidestandardization!来自成大資訊鄭憲宗15IEEE802.11TGa(cont.)ThespecificationsofthePhysicalLayerencompassdataratesfrom6Mbit/supto54Mbit/s,with20MHzspacingbetweenadjacentchannels.Allimplementationsarerequiredtosupport6,12and24Mbit/s.Optionalextensionsarefor9,18,36,48and54Mbit/s.Themulti-ratemechanismoftheMACprotocolensuresthatalldevicescommunicatewitheachotheratthebestdatarateinthepresentchannel.来自成大資訊鄭憲宗16IEEE802.11TGbTheTGbisworkingontheextensionofthe1and2Mbit/sdataratesinthe2.45GHzbandwith5.5and11Mbit/shasreachedatechnicalcompromisesolutiontoimprovetheco-existenceandinteroperabilitycharacteristicsbetweenoptions.Themulti-ratemechanismwarrantsthatthe11Mbit/soperationcanswitchbackto5.5Mbit/s.Stationsthatareevenfurthercouldswitchbacktothe2and1Mbit/scapabilitiesoftheDSSSmodulation.来自成大資訊鄭憲宗17CSMA/CD(LAN)1.Senddataifthemediumissensed“idle”2.Ifcollideswithotherhost(s),thenbackoffforarandomnumberoftimes3.Re-senddatalater来自成大資訊鄭憲宗18HiddenTerminalProblemBACdatadata来自成大資訊鄭憲宗19SolutiontoHTPBACRequestGrant来自成大資訊鄭憲宗20DetectionofCollisionBACRequestRequest来自成大資訊鄭憲宗21BACRequestAisGrantAisGrantDCollisionAvoidance来自成大資訊鄭憲宗22RTS/CTS/data/ACKandNAVsetting来自成大資訊鄭憲宗23SomeIFSrelationshipsandbasicaccessmethod来自成大資訊鄭憲宗24RandombackofftimeBackofftime=INT(CW*Random())*aSlotTimeINT(x):小於或等於x的最大整數CW(contentionwindowparameter):介於CWmin和Cwmax間的整數,CW依序遞增的順序為(7,15,31,63,127,255,255,255……)Random():介於0到1間的實數aSlotTime:傳送器開啟延遲+媒介傳遞延遲+媒介忙碌偵測反應時間来自成大資訊鄭憲宗25AnexampleofexponentialincreaseofCW来自成大資訊鄭憲宗26Backoffprocedure来自成大資訊鄭憲宗27Transmissionofamulti-fragmentMPDUusingSIFS来自成大資訊鄭憲宗28RTS/CTSwithfragmentedMSDU来自成大資訊鄭憲宗29RTS/CTSwithtransmitterpriorityandmissedacknowledgment来自中