1.5 Administrator's Guide

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  7. Trunk to Trunk Gateway

Trunk to Trunk Gateway


A company has a head office in a major city, and a remote office in another city. The company has an agreement with an internet connectivity provider for a high quality IP link between the two offices. The company requires a PBX system at the head office, with internal extensions at both office locations, the two offices SIP trunks and PSTN trunks provided for call routing at the head office location.


Both the head office and the branch office are provided with Com.X units.


  • Head office extensions configured as 101 – 105

  • Branch office extensions configured as 201 – 205

Sip trunk configuration:

  • Head office SIP trunk configured as provider

  • Branch office SIP trunk configured to register with head office

  • Ensure that Proxy, NAT, connection qualification and codec selection options are configured appropriately.

Outbound route configuration:

  • Head office outbound route routes calls to branch extensions across the SIP trunk

  • Head office outbound route routes all calls to PSTN

  • Branch office outbound route routes all calls (including calls to head office extensions) to head office across the SIP trunk


  • Head office configured with a FlexPath that places calls originating from the SIP trunk either internally or routes them trunk-to-trunk to the PSTN outbound route.