Linux無(wú)線網(wǎng)絡(luò)系統(tǒng)分析

Linux無(wú)線網(wǎng)絡(luò)系統(tǒng)分析孟寧電話訊微博：@mengning997新浪微博：@孟寧V5E-mail：mengning@主頁(yè)：/~mengning地址：蘇州工業(yè)園區(qū)獨(dú)墅湖高等教育區(qū)仁愛路188號(hào)思賢樓504室2013年6月內(nèi)容組織的邏輯一是硬件上，有哪些東西，他們是如何放置的。硬件：網(wǎng)絡(luò)+有線網(wǎng)絡(luò)?無(wú)線網(wǎng)絡(luò)?80211無(wú)線網(wǎng)絡(luò)二是軟件上，通信協(xié)議上，是如何實(shí)現(xiàn)通信的。軟件：Linux網(wǎng)絡(luò)架構(gòu)?Linux下的80211無(wú)線網(wǎng)絡(luò)架構(gòu)802.11和OSI模型80211WirelessLANBSSstandsforBasicServiceSet.ThecoverageofanaccesspointiscalledaBSS.STAindicatesawirelessdeviceactinginBSSasaregularSTAtion.IBSSstandsforIndependentBasicServiceSet.ItsbasicallyAd-Hocmode.SSIDstandsforServiceSetIDentifier.TheSSIDisacodeattachedtoallpacketsonawirelessnetworktoidentifyeachpacketaspartofthatnetwork.Thecodeconsistsofastringof1-32octets(usuallyrepresentedascasesensitivealphanumericcharacters).無(wú)線信號(hào)傳輸方式窄帶無(wú)線電通信(Narrow-BandRadio)這種技術(shù)類似于無(wú)線電臺(tái)的廣播，必須把發(fā)送器和接收器都調(diào)撥到同一頻帶。無(wú)線電信號(hào)可以穿越墻物，在一個(gè)很廣的域內(nèi)傳播，所以不必把它調(diào)聚成束。然而，窄帶射頻發(fā)送有無(wú)線電波反射的問題，并受聯(lián)邦通信委員會(huì)管制，它們必須準(zhǔn)確地進(jìn)行調(diào)諧，以防其它頻率的干擾。擴(kuò)展頻譜通信（SpreadSpectrumCommunication）簡(jiǎn)稱擴(kuò)頻通信，是一種信息傳輸方式，其信號(hào)所占有的頻帶寬度遠(yuǎn)大于所傳信息必需的最小帶寬。頻帶的擴(kuò)展是通過一個(gè)獨(dú)立的碼序列（一般是偽隨機(jī)碼）來(lái)完成，用編碼及調(diào)制的方法來(lái)實(shí)現(xiàn)的，與所傳信息數(shù)據(jù)無(wú)關(guān)在接收端則用同樣的碼進(jìn)行相關(guān)同步接收、解擴(kuò)及恢復(fù)所傳信息數(shù)據(jù)。這種技術(shù)是在一個(gè)很寬的頻率范圍內(nèi)廣播信號(hào)，避免在窄帶無(wú)線電通信中遇到的問題。用一種編碼來(lái)傳播信號(hào)，接收站用同一編碼來(lái)恢復(fù)信號(hào)。用這種方法，擴(kuò)頻無(wú)線電信號(hào)能工作在其它信號(hào)所占據(jù)的頻率范圍內(nèi)。擴(kuò)頻無(wú)線電信號(hào)不會(huì)干涉常規(guī)的無(wú)線電廣播，這是因?yàn)樗哪芰渴治⑷酢?0211FrameTypeManagementFramesAuthenticationframe,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無(wú)線網(wǎng)絡(luò)架構(gòu)wext/WE是WirelessExtensions的縮寫Linux網(wǎng)絡(luò)設(shè)備工作原理FullMACandSoftMACFullMACisatermusedtodescribeatypeofwirelesscardwheretheMLMEismanagedinhardware.Youwouldnotusemac80211towriteaFullMACwirelessdriver.SoftMACisatermusedtodescribeatypeofwirelesscardwheretheMLMEisexpectedtobemanagedinsoftware.mac80211isadriverAPIforSoftMACwirelesscards,forexample.Radiotap

Radiotap是一個(gè)標(biāo)準(zhǔn)，用于802.11的幀接收(framereception)和幀注入(frameinjection)所謂的幀接收，就是硬件（網(wǎng)卡）用中斷通知CPU，一個(gè)數(shù)據(jù)幀到了，要CPU去接收。一般是在將無(wú)線網(wǎng)卡設(shè)置為混雜模式的時(shí)候，底層接受到數(shù)據(jù)幀之后，不處理，而是直接傳送給上層處理，一般用于分析無(wú)線網(wǎng)絡(luò)數(shù)據(jù)傳輸?shù)臅r(shí)候，分析網(wǎng)絡(luò)問題到底出現(xiàn)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