Upgrade a Legacy PBX

Telecom Matters assisted an aircraft manufacturer in the expansion of their existing (TDM) PBX. The PBX was at maximum capacity, and the company was forecasting a significant increase in head count. The existing PBX had two PRI circuits to the PSTN:



We installed an Asterisk IP-PBX and attached the PSTN PRI circuits to the Asterisk server. We then linked the Asterisk server with the legacy PBX with two new PRI circuits (actually cross-over cables). We made no changes to the configuration of the legacy PBX:



Incoming calls from the PSTN passed through the Asterisk system to the legacy PBX. Outside calls from the legacy PBX passed through the Asterisk system to the PSTN. We observed this configuration for several days and had no incidents.

We then installed Polycom SIP telephone sets in the new cubicles and configured these phones to register on the Asterisk server. The new phones were given a unique block of extension numbers in the Asterisk dialing plan. We configured Asterisk dialing plan so that the new SIP sets could make outside calls to the PSTN as well as calls to extensions on the legacy PBX. We configured the legacy PBX to direct a call for a new extension to the outgoing trunk (the Asterisk server).



The company has since opened a new manufacturing facility several hundred miles from the main facility. They have installed SIP telephone sets at the new facility, and these sets register on the Asterisk server.



The company now enjoys a unified dialing plan between its legacy PBX and the new SIP sets at multiple locations. With the Asterisk/VoIP solution, the company was able to retain their investment in the legacy system--their cost savings are enormous when compared with a commercial TDM solution.