Calling Number Substitution Policy

The Calling Number Substitution Policy defines the terms and design parameters necessary to conform to the University's interpretation of the 911 service when configuring a shared line or an external calling mask. 

This policy impacts all VoIP instrumentation at University Park provided by TNS.

Every VoIP phone must have a unique direct inward dial (DID) phone number (line) assigned to it. This unique number must appear as one of the line(s) on the phone. All lines on a VoIP phone must also have external masks defined. By default, all external masks will be set the same as the 10-digit line number. Optionally, the masks chosen must all appear as billable phone numbers defined in the TNS billing database.

While shared lines may appear on phones in other locations, all external mask(s) defined to a location can only be used on VoIP phones in that location. Location is defined as the building in which the VoIP phone resides. This leads to three design constraints on mask selection. They are:

1. Any external mask assigned to a VoIP phone must be listed in the TNS billing database and must have the same location listed in the number's location field as that of the phone itself.
2. A shared line that spans buildings cannot have the same external mask on each phone. Each phone must have an external mask unique to the location in which it resides.
3. All lines that are used with a line group, hunt group, automatic call distribution (ACD), or any other function similar to these, must be listed in the TNS billing database. The external calling mask is the number displayed for CallerID for all off system calls and, especially important to note, is included as the identifier with calls placed by dialing 911.

TNS will only provide VoIP service that conforms to this policy.

• Shared Line - A shared line appears on more than one phone and is always a 10-digit DID number.
• External Calling Mask - The external calling mask is a 10-digit DID number that must be assigned to every line on an IP phone. The external calling mask cannot be shared between buildings.