Site to Site Extension Dialing Between SIP PBX and PRI PBX

Is it possible to set up site to site extension dialing between a SIP capable PBX and a PRI PBX?  At Site A we have  a Netvanta 7100 PBX which supports SIP.  At Site B we have a Toshiba CIX670 phone system that is setup with PRI.  Furthermore, Site A uses 4 digit extensions while Site B uses 3 digit extensions.

Yes, it is possible to have site to site extension dialing between a SIP capable PBX and PRI PBX.

First, there must be connectivity between both Site A and Site B; Site A should be able to ping devices on Site B and vice versa.  On a  private MPLS network this should not be a problem.

Second, there must be a SIP capable device at Site B that will process SIP calls to and from Site A on behalf of the Toshiba CIX670.  In this scenario, there is a Netvanta 908e Total Access router acting as SIP gateway that then delivers PRI to the Toshiba.

A SIP Trunk Account needs to be created on the Netvanta 7100 at Site A that points to the IP configured on the 908e at Site B.  A SIP Trunk Account needs to be created on the 908e TA that points to the IP address configured on the 7100 at Site A.  The port used is 5060.

A SIP Trunk Group needs to be created at Site A that includes the new SIP Trunk Account and that permits the digits you plan to use for dialing extensions at Site B. Since Site A is using 4 digit extensions, the permit template could look like 1XXX assuming 1XXX is not being used anywhere else on the system or by any other site that may be part of the VoIP network.

At Site B, a SIP Trunk Group that includes the new SIP Trunk Account needs to be created on the 908e that accepts calls to/from extensions at Site A.  For example, if Site A is using 7XXX extensions, then the SIP Trunk Group on the 908e at Site B needs to permit 7XXX.

At this point, dialing Ext. 1XXX  from Site A should be reaching the 908e on site B.  The next step is to route those calls to the PRI Trunk between the 908e and the Toshiba.  To do so, modify the PRI Trunk Group to permit 1XXX.  Doing this will route 1XXX calls coming in on the newly created SIP Trunk over to the PRI.  You can verify that calls are making it to the PRI by doing a VOICE> SUMMARY debug on the 908e.  While Debug is on, dial a 1XXX extension.  The Debug output should show dialed number 1XXX going from the new SIP Trunk over to the PRI Trunk.  If the Toshiba has not been configured to accept those calls, the call will fail with Unallocated Number message.

On the the Toshiba system, creating a DID table entry that routes incoming digits 1XXX to each of the 3 digit stations is the final step in allowing Site A to dial Site B extensions.

Allowing Site B to dial Site A extensions will require additional setup; hopefully a part II for this post will follow soon.

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