Called number ID is also a feature provided within a PBX system and is usually combined with the calling number ID. Called number ID is the phone number of the extension being called. When a call is from outside the PBX, it is the number of the trunk receiving the call. The called/calling number ID remains the same when a call is routed through the PBX system.
For example, when a call has been routed through the PBX because the first intended extension was not answered or busy, the final destination answering the call can determine the extension that called plus the extension that was originally called.
Called number ID can also be used by an application to automatically direct a call to an appropriate extension or group of extensions based on the number called (generally the last four digits).
For example, an application may provide specific information about four different programs through an interactive voice response (IVR) system. Depending on the phone number being called, the application can route the caller directly to the desired program:
Program A: 555-1202 (trunk 01)
Program B: 555-1203 (trunk 02)
Program C: 555-1205 (trunk 03)
Program D: 555-1200 (trunk 04)
Using a D/42-xx board and the Unified API, an application can read the called number ID (the trunk line) and route the call depending on which extension receive the call. If the call is received on trunk line 01 it will be routed to the extension for Program A. Without access to the called number ID information, callers would need to listen to a long list of prompts to obtain the four digit extension code to access Program A.
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