Hello,

the same question was asked here unde a different username (rami azar), and I had answerd it. Here is my answer again.

Hi Rami,

if you user either FXO or FXS on the PBX, the integration will be extremely poor, and certain things will not work at all.

Example: PBX has FSX, Router has FXO. When PBX calls router, users willalways receive a second dial-tone, and enter digits for the destination. This is because PBXs never outpulse DTMF to extensions.

Not to mention, caller-id, clall-transfer, there is 0 possibility for these.

In short, using FXO/FXS to connect PBX and router does not make integration but more likely a recipe for failure.

You must check if the PBX can support ISDN BRI, or a least, E&M. If this is not possible either, the only partial solution is using BOTH of the PBX FXO and FSX lines to connect FXS and FXO on the router, that is you must use BOTH types.

This way, the call direction will be always uni-directional and things will work more or less IF you can program the PBX appropriately.

Hope this helps, if so please rate post!