802.11 Association process explained

Access points are bridges that bridge traffic between mobile stations and other devices on the network. Before a mobile station can send traffic through an AP, it must be in the appropriate connection state.

The three 802.11 connection states are:

• 802.11 probing 
• 802.11 authentication 
• 802.11 association 

802.11 probing

• A mobile station sends probe requests to discover 802.11 networks within its proximity. Probe requests advertise the mobile stations supported data rates and 802.11 capabilities such as 802.11n. Because the probe request is sent from the mobile station to ff:ff:ff:ff:ff:ff all AP's that receive it will respond.
• APs receiving the probe request check to see if the mobile station has at least one common supported data rate. If they have compatible data rates, a probe response is sent advertising the SSID (wireless network name), supported data rates, encryption types if required, and other 802.11 capabilities of the AP. 
• A mobile station chooses compatible networks from the probe responses it receives.

802.11 authentication

• 802.11 was originally developed with two authentication mechanisms. The first one, called “open authentication”, is fundamentally a NULL authentication where the client says “authenticate me” and the AP responds with “yes”. 
• The second type of authentication, namely the WEP/WPA/WPA2, is a shared key mechanism that is widely used in home networks or small Wi-Fi deployments.

802.11 association

• This stage finalizes the security and bit rate options and establishes the data link between the WLAN client and the AP.