Had a request from a customer to see about removing a prefix from the calling party number when a known Mobile (Remote Destination) calls an office extension phone. The prefix was interfering with call-back and visual display in Missed Calls. So the scenario was mobile 0420999xxx would call into the Office, this mobile is configured as a Remote Destination, therefore the system matches it with the internal extension (ext. 4000). The call proceeds to ring an internal extension, however the calling party display number is 04000. Zero is the access code for PSTN Calls.
I found the MGCP Gateway (this also relates to SIP and H323 gateways in CUCM) was directing the call to a translation pattern. This translation pattern was prefixing a ‘0’ to the calling party number. So even though the system matched the remote destination number to an extension the translation pattern still proceeded to prefix a ‘0’. This is because the transformation of the remote destination number to the associated extension is actioned at the gateway level when the call first arrives. But the Translation pattern prefixes a ‘0’ to all calls to extensions from the Gateway including calls from the transformed remote destination.
How to Resolve
There a few options to work around this issue. I was working with an MGCP Gateway, so I will opt to change add a prefix ‘0’ at the Gateway configuration page. There are four rows containing call types. International, National, Subscriber and Unknown. These types cover all possible calling party types. Under the Prefix Digit column, I will enter a ‘0’ into all the rows. I will also ensure the Use Device Pool checkbox is unchecked for each call type.
Then open the translation pattern and remove the Calling Party Prefix digit of ‘0’.
Make a test call and the calling number should only display the extension. Plus all other calls from the PSTN should maintain the ‘0’ prefix.