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

• AC is active.

• AC is due to be active. That is, the AC is a permanent AC, or it is the administered time-of-day for a scheduled AC.

• The originating endpoint is in the in-service or idle state.

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:

• Resources are unavailable to route to the destination.

• A required conversion resource is unavailable.

• Access is denied by Class of Restriction (COR), facilities restriction level (FRL), Bearer Capability Class (BCC), or an attempt is made to route voice-band data over SDDN trunks in the public switched network.

• The destination address is incorrect.

• The destination endpoint is busy.

• Other network or signaling failures occur.

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).

• The administered retry interval of 1 to 60 minutes for each AC determines the frequency with which failed attempts are retried.

• Retries are made after the retry interval elapses, regardless of the restorable attribute of the AC.

• ACs are retried in priority order.

• When you change the time of day on the server, an attempt is made to establish all ACs in the waiting-for-retry state.