I have this kind of connections:
Analog_FAX1 <-PSTN-> VoIP provider <-INTERNET-> Asterisk <-LAN-> ATA Adaptor —> Analog_FAX2
The my voip provider give me a DID number and I’ve configured correctly my asterisk network. The “analog fax2” can recive&transmit telephon calls.
But, when I try to TX/RX fax I always have errors. I set up the extension associated to the fax with G.711 codec and the ATA adaptor in pass-through mode.