I have a customer that has the a SIP-based IP PBX (Non-Cisco). I have setup an ATA on the LAN and tested normal telephone calls on it and it works fine, including the call quality.
The problem that I have is that if a fax machine is connected on any of the ATA ports, the fax machine rings when a fax is sent to it. After ringing, the fax displays "receiving" but it pauses for 30 seconds and then it displays "receive failed".
As per the ATA SIP documentation, I have setup the Audio Mode on the ATA to 0x00120012 which puts both ATA ports to FAX MODE.
The settings on the SIP PABX have been set to G.711alaw and as per the debug, the ATA also negotiates to G.711alaw. Also I have set the speed on the fax machine to 14400bps but I have also tried 9600bps with no luck.
The attached file is a debug obtained from the PRSERV program.
Your assistance will be highly appreciated.