Linux無(wú)線網(wǎng)絡(luò)系統(tǒng)分析

1、Linux無(wú)線網(wǎng)絡(luò)系統(tǒng)分析孟寧電話騰訊微博：mengning997 新浪微博：孟寧V5E-mail：主頁(yè)：http:/ 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80211 Wireless LAN BSS stands for Basic Service Set. The coverage of an access point is called a BSS. STA ind

2、icates a wireless device acting in BSS as a regular STAtion. IBSS stands for Independent Basic Service Set. Its basically Ad-Hoc mode. SSID stands for Service Set IDentifier. The SSID is a code attached to all packets on a wireless network to identify each packet as part of that network. The code co

3、nsists of a string of 1-32 octets (usually represented as case sensitive alphanumeric characters).無(wú)線信號(hào)傳輸方式窄帶無(wú)線電通信(Narrow-Band Radio) 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(wèn)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（Spread Spectrum Communication） 簡(jiǎn)稱擴(kuò)頻通

4、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(guò)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(wèn)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?0211 Frame Type Management Frames Authenticat

5、ion frame, Deauthentication frame Association request frame, Association response frame, Disassociation frame Reassociation request frame, Reassociation response frame Beacon Frame:Authentication frame, Deauthentication frame Probe request frame, Probe response frame Control Frames Request to Send (

6、RTS) frame Clear to Send (CTS) frame(Use RTS/CTS to avoid hidden station problem) Acknowledgement (ACK) frame Data FramesCSMA/CA CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) A station wishing to transmit senses the air, and, if no activity is detected, the station waits an additi

7、onal, randomly selected period of time and then transmits if the medium is still free. If the packet is received intact, the receiving station issues an ACK frame that, once successfully received by the sender, completes the process. If the ACK frame is not detected by the sending station, either be

8、cause the original data packet was not received intact or the ACK was not received intact, a collision is assumed to have occurred and the data packet is transmitted again after waiting another random amount of time.MLME MLME Stands for Media Access Control (MAC) Sublayer Management Entity. MLME is

9、the management entity where the Physical layer (PHY) MAC state machines reside.Linux無(wú)線網(wǎng)絡(luò)架構(gòu)wext/WE是Wireless Extensions的縮寫Linux網(wǎng)絡(luò)設(shè)備工作原理FullMAC and SoftMAC FullMAC is a term used to describe a type of wireless card where the MLME is managed in hardware. You would not use mac80211 to write a FullMAC wir

10、eless driver. SoftMAC is a term used to describe a type of wireless card where the MLME is expected to be managed in software. mac80211 is a driver API for SoftMAC wireless cards, for example.Radiotap Radiotap 是一個(gè)標(biāo)準(zhǔn)，用于802.11的 幀接收(frame reception)和幀注入(frame injection) 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，

11、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(wèn)題到底出現(xiàn)在哪。Code structure Most important for driver authors: include/net/mac80211.h This file defines the API to mac80211 from below.Code structure All files except the header file are in net/mac80211/. Kconfig, Makefile buil

12、d system ieee80211 i.h most internal data structures main.c main module entry points main entry points for driver calls (reg/dereg) iface.c virtual interface handling key.c, key.h key management sta info.c, sta info.h Station (peer) management pm.c power management (suspend/hibernate) rate.c, rate.h

13、 internal rate control functions rc80211* rate control algorithms rx.c frame receive path tx.c frame transmit path scan.c software scanning codeCode structure ht.c, agg-rx.c, agg-tx.c HT/aggregation code mesh, hwmp, plink, pathtbl.c,h 802.11s mesh mlme.c Station/managed mode MLME ibss.c IBSS MLME cf

14、g.c, cfg.h, wext.c configuration entry points event.c events to userspace spectmgmt.c spectrum management code aes*, tkip.*, wep.*, michael.*, wpa.* WPA/RSN/WEP code wme.c, wme.h some QoS code util.c utility functions led.c, led.h LED handling debugfs* debugfs codeData structures ieee80211_local/iee

15、e80211_hw sta_info/ieee80211_sta ieee80211_conf ieee80211_bss_conf ieee80211_key/ieee80211_key_conf ieee80211_tx_info ieee80211_rx_status ieee80211_sub_if_data/ieee80211_vifieee80211_local/ieee80211_hw each instance of these (hw is embedded into local) represents a wireless device ieee80211_hw is th

16、e part of iieee80211_local that is visible to drivers contains all operating information about a wireless devicesta_info/ieee80211_sta represents any station (peer) could be mesh peer, IBSS peer, AP, WDS peer would also be used for DLS peer ieee80211_sta is driver-visible part ieee80211_find_sta for

17、 drivers lifetime managed mostly with RCUieee80211_conf hardware configuration most importantly - current channel intention: hardware specific parametersieee80211_bss_conf BSS configuration for all kinds of BSSes (IBSS/AP/managed) contains e.g. basic rate bitmap intention: per BSS parameters in case

18、 hardware supports creating/associating with multiple BSSesieee80211_key/ieee80211_key_conf represents an encryption/decryption key ieee80211_key_conf given to driver for hardware acceleration ieee80211_key contains internal book-keeping and software encryption stateieee80211_tx_info most complicate

19、d data structure lives inside skbs control buffer (cb) goes through three stages (substructure for each) initialisation by mac80211 (control) use by driver (driver_data/rate_driver_data) use for TX status reporting (status)ieee80211_rx_status contains status about a received frame passed by driver t

20、o mac80211 with a received frameieee80211_sub_if_data/ieee80211_vif contains information about each virtual interface ieee80211_vif is passed to driver for those virtual interfaces the driver knows about (not monitor, VLAN) contains sub-structures depending on mode ieee80211_if_ap ieee80211_if_wds i

21、eee80211_if_vlan ieee80211_if_managed ieee80211_if_ibss ieee80211_if_meshMain flows configuration receive path transmit path management/MLMEMain flows configuration all initiated from userspace (wext or nl80211) for managed and IBSS modes: triggers statemachine (on workqueue) some operations passed

22、through to driver more or less directly (e.g. channel setting)Main flows receive path packet received by driver passed to mac80211s rx function (ieee80211_rx) with rx_status info for each interface that the packet might belong to RX handlers are invoked data: converted to 802.3, delivered to network

23、ing stack management: delivered to MLMEMain flows transmit path packet handed to virtual interfaces ieee80211_subif_start_xmit converted to 802.11 format sent to master interface packet handed to ieee80211_master_start_xmit transmit handlers run, control information created packet given to drivertransmit handlers ieee80211_tx_h_check_assoc ieee80211_tx_h_ps_buf ieee80211_tx_h_select_key ieee80211_tx_h_michael_mic_add ieee8021