RADIUS (Remote Authentication Dial In User Service ) is the service which based on UDP between client and server. So we can't subject RADIUS for any OSI layer. If you want to, you can say layer at UDP operates.
The IEEE 802.11 standard encompasses the physical layer (PHY) and the lower portion of the data link layer. The lower portion of the data link layer is often referred to as the Medium Access Control (MAC) sublayer.
For 802.11x wireless standards visit following url for more
http://www.sans.org/rr/wireless/WLAN_sec.php
