The originating server attempts to establish an AC only if one of the following conditions exist:

If the originating endpoint is not in service or is idle, no activity takes place for the AC until the endpoint transitions to the necessary state. The originating server uses the destination address to route the call to the required endpoint. When the server establishes two or more ACs at the same time, the server arranges the connections in order of priority.

AC attempts can fail because:

In the event of a failure, an error is entered into the error log. This error generates an alarm, if your alarming strategy warrants an alarm. You can display AC failures with the display status-administered connection command. The originating server continues to try to establish an AC as long as an AC is scheduled to be active, unless the attempt fails because of an administrative error (for example, a wrong number) or a service-blocking condition, such as outgoing calls are barred).