DTMF forwarding issue

Hi collegues.
I’ve just encountered a problem of forwarding DTMF tones from Siemens HGate gateway to Microsoft Lync 2013 through FreePBX (they can’t work directly with each other).

The problem is that I can’t use DTMF tones when I’m calling to lync’s conferencing room (I should choose proper conference by DTMF). DTMF tones are not forwarded by FreePBX. But if I make a call from Lync to anywhere DTMF codes are forwarded without any exception.

I’ve found FreePBX logs, are empty about DTMF when I’m making a call from HGate’s side, and there are plenty when I’m using Lync > FreePBX > HGate route.

I’ve already tried to change dtmfmode to all available values, nothing happened.

I would be glad for any advice.

Sorry for my eng. I’ve just started to learn. THX