Use FXS interface box as Trunk to old PBX

I’m looking for a way of connecting FreePBX to a very old PBX (Siemens MCX). I’m thinking of use a multiport FXS box setup as a Trunk on FreePBX and connecting the ports of this box to the old system. I’m hoping that I can setup the old PBX to see these lines as a normal incoming POTS trunk, and setting the old system ports as DISA or similar. Has anyone tried this or have comments suggestions on this idea? This is to allow some parallel running of our new FrreePBX system along side the old system. We have a large site, and over 700 extensions so rolling it out is a bit of a challenge.

That can be done, but be aware that is up to you to make sure that your FXS ports are set to use the same impedance,ring sinaling, battery voltage, CallerID provisioning and disconnect supervision that your “very old PBX” can be expected to handle on its FXO ports or you might get echo and other hard to diagnose call disruption.

Thanks, a least it sounds possible in theory. I have managed to get hold of the an engineer who looks after the old system and have him coming in next week to see what he can setup on the system and so I can check the various signalling requirements etc with him.

In case anyone interested I have got full 2 way transparent dialling between our very old pbx and our new FreePBX system. Usinf FXO boxes for dialling from FreePBX to the old system, and FXS boxes for dialling from the old system to FreePBX.

A bit complicated but will make the rollout of 700 odd extensions very much easier with this side by side running.