[Serusers] SER + PSTN problem

Hi to all! I'm a new seruser, and I have a problem with SER and a PSTN gw what I can't solve. I have got 2 UAs, 1 SER server, 1 Cisco PSTN gw (by the side of the voip provider). All of them have public IP. Phone1 -------+ | SER --- PSTN gw | Phone2 -------+ When I call from Phone1 to Phone2 directly, it is working properly. But: If I call from Phone1 to Phone2 via the PSTN gw, then it's ringing out, and when I pick up Phone2 I hear the voice of Phone1, but in Phone1 I can't hear the voice of Phone2. If I call from Phone1 to other telephone numbers, I have the same problem. I would like to proxy the media on the server. I'm useing SER 0.8.14. ser.cfg attached Thank you very much for your effort, and sorry for my poor English... Regards, KutiJoe