While not a call admission control mechanism itself, Automated Alternate Routing cannot function without one, be it location-based or RSVP. Automated Alternate Routing only takes effect when a call is denied for bandwidth reasons, and will not reroute calls if they were rejected by the gateway for any other reason.
To implement Automated Alternate Routing, perform the following:
First, activate the necessary services for AAR (System | Service Parameters).
Select a server from the Server drop-down menu. This should be a server running the CallManager service.
Select the Cisco CallManager service from the Service drop-down menu as shown:
After selecting the CallManager service from the drop-down, the page reloads and the associated parameters are seen.
Near the bottom , the section titled Clusterwide Parameters (System | CCM Automated...