Tuesday, 7 April 2015

CAC Order of Operation

When multiple CAC mechanisms are configured, the selection process follows these steps:
Step 1.
The gateway checks for the max-conn configuration on the outbound dial peer.

If the limit has been reached, the call is rejected. If no max-conn is configured, or the limit has not been reached, the router goes to Step 2.
Step 2.
The router checks for CAC mechanisms based on local system resources, such as CPU use.

If these resources are not configured, or if the test succeeds, the router goes to Step 3.
Step 3.
If a gatekeeper is used, and it is configured to do CAC based on bandwidth, the gatekeeper is checked.

If this test succeeds, or no gatekeeper CAC is used, the router proceeds to Step 4.
Step 4.
If RSVP is configured, an RSVP reservation is attempted. When RSVP is used, this is the last test.

If the call is allowed, call setup continues. If not, the router rejects the call. Only if RSVP is not configured does the router go to Step 5.
Step 5.
Any CAC mechanism that use probes to measure network availability is now checked.

This is the last test. If the call is allowed, setup proceeds. If not, it is rejected.

If any of these tests rejects the call, the process ends at that point, and no further checking is done.


  1. what about locations/ RSVP enable locations

  2. This post is covering IOS CAC not CUCM CAC. None of the points listed above is related to CUCM