IEEE802.11 protocol Stack

1. Overview

mac80211: is a Linux kernel subsystem that drives developers to write driver-driven frameworks for Softmac wireless devices. MAC80211 implements STA mode in kernel space and implements AP mode (HOSTAPD) in user space.

cfg80211: Used for configuration management of wireless devices, working with fullmac,mac80211 and nl80211.

NL80211: For configuration management of wireless devices, it is a basic NetLink user-State protocol.

Mlme: Mac (Media Access Control) layer Management Entity, which manages the physical layer Mac state machine.

Softmac: Its mlme is implemented by software, and MAC80211 provides an API for SOFTMAC implementations. That is: The SOFTMAC device allows for better control of hardware execution, allowing software to achieve 802.11 frame management, including parsing and generating 802.11 wireless frames. Currently, most 802.11 devices are softmac, while FULLMAC devices are less.

Fullmac: Its mlme is hardware-managed and does not require the use of mac80211 when writing Fullmac wireless drivers.

Wpa_supplicant: is a user-space application that primarily initiates the Mlme command and then processes the related results.

Hostpad: is a user space application, the main implementation station access authentication management.

CFG80211 is the Linux802.11 configuration API. cfg80211 is used for code wext (wireless-extensions), nl80211 is used to configure a cfg80211 device and is used for communication between kernel and userspace. Wext is now processing the maintenance state, no new functions have been added, just modify the bug. If you need to operate through wext, you need to define Onfig_cfg80211_wext.

Cfg80211and nl80211: Based on message mechanism, using NetLink interface

Wext: Based on the IOCTL mechanism (Madwifi wext, etc. have been removed from the Linxu kernel Linux 2.6.26)

STRUCTIEEE80211_HW: Indicates hardware information and status

IEEE80211_ALLOC_HW: Each driver call IEEE80211_ALLOC_HW assigns IEEE80211_HW, and Ieee80211_ops is the parameter

IEEE80211_REGISTER_HW: Each driver call IEEE80211_REGISTER_HW create Wlan0 and Wmaster0, and perform various initializations.

Structieee80211_ops: Each driver implements its member function, and its member function takes STRUCTIEEE80211_HW as the first argument. There are 24 methods defined in Structieee80211_ops, and the following 7 methods must be implemented: Tx,start,stop,add_interface,remove_interface,config and Configure_filter. 2. Architecture

Figure 2-1 System Framework

3. Code Structure

IEEE80211_I.H (main data structure)

MAIN.C (main function entry)

IFACE.C (Virtual interface Processing)

Key.c,key.h (Key Management)

Sta_info.c,sta_info.h (User management)

PM.C (Power Management)

Rate.c,rate.h (Rate control function)

RC80211* (Rate control algorithm)

RX.C (frame receive path code)

TX.C (frame send path code)

SCAN.C (software Scan code)

MLME.C (station/managed mode Mlme)

IBSS.C (Ibssmlme)

CFG.C,CFG.H,WEXT.C (Configure entry code)

aes*,tkip*,wep*,michael*,wpa* (WPA/RSN/WEP code)

Wme.c,wme.h (QoS code)

UTIL.C (Public Function) 4, data structure

IEEE80211_LOCAL/IEEE80211_HW

Each data structure represents a wireless device (IEEE80211_HW embedded in ieee80211_local)

IEEE80211_HW is the visible part of ieee80211_local in the drive

Contains all operational information for wireless devices

Sta_info/ieee80211_sta

On behalf of each station

It could be mesh,ibss,ap,wds.

Ieee80211_sta is the visible part of the drive

ieee80211_conf

Hardware configuration

The current channel is the most important field

Hardware Special parameters

ieee80211_bss_conf

BSS configuration

Multi-bsses type (ibss/ap/managed)

Include, for example, the base rate bitmap

PERBSS parameters in case hardware supports creating/associating withmultiple bsses

ieee80211_key/ieee80211_key_conf

Represents the encryption/decryption key

IEEE80211_KEY_CONF supply driver for hardware acceleration

Ieee80211_key contains book-keeping and software decryption status

Ieee80211_tx_info

Most complex data structures

SKB Internal Control buffer (CB)

Experience three stages: 1, initialized by mac80211, 2, used by drive, 3, used by Send status advertisement

Ieee80211_rx_status

Contains the receive frame state

The drive is transmitted to mac80211 via the receive frame

ieee80211_sub_if_data/ieee80211_vif

Contains information for each virtual interface

Ieee80211_vifis passed to driver for those virtual interfaces The driver Knowsabout (no Monitor,vlan)

The included sub-structures depends on the pattern 5, the main process

Configuration

All originating from user space (Wext or nl80211)

Managed and IBSS modes: Trigger state machine (based on Workqueue)

Some operations are more or less directly transmitted via the driver (e.g. channel settings)

Receive Path

Through functions