Linux无线网络系统分析

Linux无线网络系统分析孟宁电话讯微博：@mengning997新浪微博：@孟宁V5E-mail：mengning@主页：/~mengning地址：苏州工业园区独墅湖高等教育区仁爱路188号思贤楼504室2013年6月内容组织的逻辑一是硬件上，有哪些东西，他们是如何放置的。硬件：网络+有线网络⇒无线网络⇒80211无线网络二是软件上，通信协议上，是如何实现通信的。软件：Linux网络架构⇒Linux下的80211无线网络架构802.11和OSI模型80211WirelessLANBSSstandsforBasicServiceSet.ThecoverageofanaccesspointiscalledaBSS.STAindicatesawirelessdeviceactinginBSSasaregularSTAtion.IBSSstandsforIndependentBasicServiceSet.ItsbasicallyAd-Hocmode.SSIDstandsforServiceSetIDentifier.TheSSIDisacodeattachedtoallpacketsonawirelessnetworktoidentifyeachpacketaspartofthatnetwork.Thecodeconsistsofastringof1-32octets(usuallyrepresentedascasesensitivealphanumericcharacters).无线信号传输方式窄带无线电通信(Narrow-BandRadio)这种技术类似于无线电台的广播，必须把发送器和接收器都调拨到同一频带。无线电信号可以穿越墙物，在一个很广的域内传播，所以不必把它调聚成束。然而，窄带射频发送有无线电波反射的问题，并受联邦通信委员会管制，它们必须准确地进行调谐，以防其它频率的干扰。扩展频谱通信（SpreadSpectrumCommunication）简称扩频通信，是一种信息传输方式，其信号所占有的频带宽度远大于所传信息必需的最小带宽。频带的扩展是通过一个独立的码序列（一般是伪随机码）来完成，用编码及调制的方法来实现的，与所传信息数据无关在接收端则用同样的码进行相关同步接收、解扩及恢复所传信息数据。这种技术是在一个很宽的频率范围内广播信号，避免在窄带无线电通信中遇到的问题。用一种编码来传播信号，接收站用同一编码来恢复信号。用这种方法，扩频无线电信号能工作在其它信号所占据的频率范围内。扩频无线电信号不会干涉常规的无线电广播，这是因为它的能量十分微弱。80211FrameTypeManagementFramesAuthenticationframe,DeauthenticationframeAssociationrequestframe,Associationresponseframe,DisassociationframeReassociationrequestframe,ReassociationresponseframeBeaconFrame:Authenticationframe,DeauthenticationframeProberequestframe,ProberesponseframeControlFramesRequesttoSend(RTS)frameCleartoSend(CTS)frame(UseRTS/CTStoavoidhiddenstationproblem)Acknowledgement(ACK)frameDataFramesCSMA/CACSMA/CA(CarrierSenseMultipleAccesswithCollisionAvoidance)Astationwishingtotransmitsensestheair,and,ifnoactivityisdetected,thestationwaitsanadditional,randomlyselectedperiodoftimeandthentransmitsifthemediumisstillfree.Ifthepacketisreceivedintact,thereceivingstationissuesanACKframethat,oncesuccessfullyreceivedbythesender,completestheprocess.IftheACKframeisnotdetectedbythesendingstation,eitherbecausetheoriginaldatapacketwasnotreceivedintactortheACKwasnotreceivedintact,acollisionisassumedtohaveoccurredandthedatapacketistransmittedagainafterwaitinganotherrandomamountoftime.MLMEMLMEStandsforMediaAccessControl(MAC)SublayerManagementEntity.MLMEisthemanagemententitywherethePhysicallayer(PHY)MACstatemachinesreside.Linux无线网络架构wext/WE是WirelessExtensions的缩写Linux网络设备工作原理FullMACandSoftMACFullMACisatermusedtodescribeatypeofwirelesscardwheretheMLMEismanagedinhardware.Youwouldnotusemac80211towriteaFullMACwirelessdriver.SoftMACisatermusedtodescribeatypeofwirelesscardwheretheMLMEisexpectedtobemanagedinsoftware.mac80211isadriverAPIforSoftMACwirelesscards,forexample.Radiotap

Radiotap是一个标准，用于802.11的帧接收(framereception)和帧注入(frameinjection)所谓的帧接收，就是硬件（网卡）用中断通知CPU，一个数据帧到了，要CPU去接收。一般是在将无线网卡设置为混杂模式的时候，底层接受到数据帧之后，不处理，而是直接传送给上层处理，一般用于分析无线网络数据传输的时候，分析网络问题到底出现在哪。CodestructureMostimportantfordriverauthors:include/net/mac80211.hThisfiledefinestheAPItomac80211frombelow.CodestructureAllfilesexcepttheheaderfileareinnet/mac80211/.Kconfig,Makefilebuildsystemieee80211i.hmostinternaldatastructuresmain.cmainmoduleentrypointsmainentrypointsfordrivercalls(reg/dereg)iface.cvirtualinterfacehandlingkey.c,key.hkeymanagementstainfo.c,stainfo.hStation(peer)managementpm.cpowermanagement(suspend/hibernate)rate.c,rate.hinternalratecontrolfunctionsrc80211*ratecontrolalgorithmsrx.cframereceivepathtx.cframetransmitpathscan.csoftwarescanningcodeCodestructureht.c,agg-rx.c,agg-tx.cHT/aggregationcodemesh{,hwmp,plink,pathtbl}.{c,h}802.11smeshmlme.cStation/managedmodeMLMEibss.cIBSSMLMEcfg.c,cfg.h,wext.cconfigurationentrypointsevent.ceventstouserspacespectmgmt.cspectrummanagementcodeaes*,tkip.*,wep.*,michael.*,wpa.*WPA/RSN/WEPcodewme.c,wme.hsomeQoScodeutil.cutilityfunctionsled.c,led.hLEDhandlingdebugfs*debugfscodeDatastructuresieee80211_local/ieee80211_hwsta_info/ieee80211_staieee80211_confieee80211_bss_confieee80211_key/ieee80211_key_confieee80211_tx_infoieee80211_rx_statusieee80211_sub_if_data/ieee80211_vifieee80211_local/ieee80211_hweachinstanceofthese(hwisembeddedintolocal)represents

awirelessdeviceieee80211_hwisthepartofiieee80211_localthatisvisibleto

driverscontainsalloperatinginformationaboutawirelessdevicesta_info/ieee80211_starepresentsanystation(peer)couldbemeshpeer,IBSSpeer,AP,WDSpeerwouldalsobeusedforDLSpeerieee80211_staisdriver-visiblepartieee80211_find_stafordriverslifetimemanagedmostlywithRCUieee80211_confhardwareconfigurationmostimportantly-currentchannelintention:hardwarespecificparametersieee80211_bss_confBSSconfigurationforallkindsofBSSes(IBSS/AP/managed)containse.g.basicratebitmapintention:perBSSparametersincasehardwaresupports

creating/associatingwithmultipleBSSesieee80211_key/ieee80211_key_confrepresentsanencryption/decryptionkeyieee80211_key_confgiventodriverforhardwareaccelerationieee80211_keycontainsinternalbook-keepingandsoftware

encryptionstateieee80211_tx_infomostcomplicateddatastructurelivesinsideskb’scontrolbuffer(cb)goesthroughthreestages(substructureforeach)initialisationbymac80211(control)usebydriver(driver_data/rate_driver_data)useforTXstatusreporting(status)ieee80211_rx_statuscontainsstatusaboutareceivedframepassedbydrivertomac80211withareceivedframeieee80211_sub_if_data/ieee80211_vifcontainsinformationabouteachvirtualinterfaceieee80211_vifispassedtodriverforthosevirtualinterfaces

thedriverknowsabout(notmonitor,VLAN)containssub-structuresdependingonmodeieee80211_if_apieee80211_if_wdsieee80211_if_vlanieee80211_if_managedieee80211_if_ibssieee80211_if_meshMainflowsconfigurationreceivepathtransmitpathmanagement/MLMEMainflows–configurationallinitiatedfromuserspace(wextornl80211)formanagedandIBSSmodes:triggersstatemachine(on

workqueue)someoperationspassedthroughtodrivermoreorlessdirectly

(e.g.channelsetting)Mainflows–receivepathpacketreceivedbydriverpassedtomac80211’srxfunction(ieee80211_rx)with

rx_statusinfoforeachinterfacethatthepacketmightbelongtoRXhandlersareinvokeddata:convertedto802.3,deliveredtonetworkingstackmanagement:deliveredtoMLMEMainflows–transmitpathpackethandedtovirtualinterface’sieee80211_subif_start_xmitconvertedto802.11formatsenttomasterinterfacepackethandedtoieee80211_master_start_xmittransmithandlersrun,controlinformationcreatedpacketgiventodrivertransmithandlersieee80211_tx_h_check_associeee80211_tx_h_ps_bufieee80211_tx_h_select_keyieee80211_tx_h_michael_mic_addieee80211_tx_h_rate_ctrlieee80211_tx_h_miscieee80211_tx_h_seq