authentication algorithm identification (802.11) (AAI)

Authentication Algorithm Identification (AAI) is a specification of WLANs according to 802.11. The AAI protocol element defines the procedure for authentication.

In 802.11 there is the open- system and the shared- key authentication. In general, the WLAN end device must authenticate itself to the access point( AP). It is not possible for the access point to authenticate the WLAN station.

With open-system authentication, the access point accepts all authentication requests. If the access point is working without encryption, any WLAN station that knows the Service Set Identification( SSID) can access the WLAN. If the access point is working with Wired Equivalent Privacy(WEP) enabled, the WEP key is used for access control. If the WLAN station does not have the correct WEP key, the WLAN station cannot transfer any data even if authentication is successful.

With Open System Authentication, the access point first receives an authentication request from the WLAN station with a sequence number. First, the Authentication Algorithm Identification (AAI) is set to 0, indicating that this is an open-system authentication. The sequence number is set to 1, indicating the first frame of the sequence. In the response frame, the access point sends the Authentication Algorithm Identification (AAI) with 0, the following sequence number (2) and the status code indicating that it is the response.