From the help files (DID Service)
Incoming DID call processing algorithm
Trunk service digit modification is performed, based on the incoming trunk configuration.
System Speed Calls lookup is conducted.
CRS database is searched for the modified DID number and the associated destination number.
Possible CRS query responses:
NO MATCH - no associated destination number found
EXACT MATCH - the exact one associated destination number found
CONFLICTING MULTIPLE MATCHES - more than one associated destination number found
PARTIAL MATCH - one or more matches associated with the subset of queried digit string found
If an exact match is found in the CRS database, the call is routed to the destination number. Otherwise, the following routing is applied:
If the search returns conflicting multiple matches, no matches are used and the call is routed on the originally dialed digits.
If a partial match is found, the call is routed on the originally dialed digits.
In a rare conflict scenario where: FOPBX (Force-to-PBX) is configured as the CRS option in the Trunk Attributes form, both CRS and DID service are enabled, and the EHDU external number matches the DID number, the call will be handled by CRS and not DID Service.
In the following circumstances a call cannot be routed to its destination and an appropriate intercept handling is applied:
CRS query returns NO MATCH (no destination number is assigned to the DID number) because a suite or a Hotel Room Extension Not In Suite (HRENIS) to which the DID was assigned is now checked out. (This occurs only if the hotel option Cancel All Features on Check-Out is enabled.)
DID destination number cannot be routed for any other reason.
In the above scenarios, Intercept Handling for "Unassigned Directory Number" is applied and the Reorder Tone is returned.
DID destination is out of service.
In this case, Intercept Handling for "Directory Number Out of Service" is applied and the Reorder Tone is returned.
