The wireless host (station) needs to associate with an Access Point (AP) before it can send/receive network-layer data. This is a basic 802.11 system management function.
Association is the creation of a 'virtual' ethernet wire between the station and the switch.
The basic three-step procedure followed by the station:
- Locate an AP to associate with; this process can involve passive or active scanning as discussed below.
- Authenticate itself to the AP (and possibly the infrastructure).
- Associate with the AP (create the 'virtual' blue cable).
Now, the station can retrieve an IP address from the subnet and begin TCP/UDP socket communications.
Locate
The first step is to locate the AP you wish to join. The algorithm for locating/selecting an AP is not defined by the 802.11 standards, but by your application. There are two methods provided in 802.11 to discover APs near the station: passive and active scanning, which are illustrated below.
In a typical application, one of the several possible commissioning methods is deployed to get a specific AP's network parameters into your application (channel, SSID, security).
After copying these parameters to your Wi-Fi® sub-system's connection profile, your application will call a WiFi_Connect() API which uses an active scanning method to connect to this specific AP.
Authenticate
Next, the station attempts to authenticate itself to the AP (at a minimum) and possibly the network.
Authentication Protocols:
Associate
The final step in the creation of the 'virtual blue wire'.
After the association is complete, the DHCP process can begin to assign an IP address to the station and enable the application to connect with other hosts on the network.