A thin AP (Access Point) architecture uses two components: an access point that is essentially a stripped-down radio and a centralized management controller that handles the other WLAN (Wireless Local Area Network) system functions. Wired network switches are also required.
A fit AP, a variation of the thin AP, handles the RF (Radio Frequency) and encryption, while the central management controller, aware of the wireless users' identities and locations, handles secure roaming, quality of service, and user authentication. The central management controller also handles AP configuration and management.
A fat (or thick) AP architecture concentrates all the WLAN intelligence in the access point. The AP handles the RF communication, as well as authenticating users, encrypting communications, secure roaming, WLAN management, and in some cases, network routing.