802.11 Protocol Architecture
FIGURE 2.4
802.11 Distribution System Services
802.11 MAC Layer Overview
As with any IEEE 802 network, the 802.11 standard defines a common
MAC Layer that controls the operation of stations (STAs) and access
points (APs). Much of the MAC Layer functionality resides in
firmware, and developers and end users have access to many of the
attributes that change the configuration and operation of the wireless
LAN.
The 802.11 MAC Layer provides the following functions and elements:
Scanning
Before authenticating to a BSS, a station may scan for all available
BSSs (as advertised by an access point or station). The scanning
station will find valid BSSs as those having the same service set
identifier (SSID) as the station that is scanning. After association, the
station may continue to scan when conditions occur that indicate the
need to find another BSS. This functionality is implemented differently
among chipset vendors, so it is common to see that one vendor’s card
may scan after association while another vendor’s may not.
