Which technique is used by Cisco WLCs to minimize... roaming?

Which technique is used by Cisco WLCs to minimize the time required on key exchanges during roaming by maintaining a database of clients and keys on behalf of bound APs, and providing those clients and keys to other controllers and bound APs as needed during roaming?

Explanation & Hint:

Cisco controllers offer three techniques to minimize the time and effort spent on key exchanges during roams:

Cisco Centralized Key Management ( CCKM ): One controller maintains a database of clients and keys on behalf of bound APs and provides the clients and keys to other controllers and bound APs as needed during client roams.
Key caching : Each client maintains a list of keys used with prior AP associations and presents the keys as it roams.
802.11r : This 802.11 amendment addresses fast roaming or fast BSS transition. A client can cache a portion of the key of the authentication server and present that to future APs as it roams.