The Cisco Secure Access Control Server (ACS) provides authentication, authorization, and accounting (AAA) services for users of the wireless network.
It is also possible to employ a WLC controller strategy that uses an N+1 approach. When using N+1 architecture, each WLC is configured with a WLC that is designated as a backup WLC in the event of a failure. This controller is not used until there is a failure event upon which all APs using the failed controller switch to the backup WLC. This cost-effective approach provides a high level of availability in the event of a single WLC failure scenario.