Faxes not received successfully by RxFax application - what does the debug info in the log mean?

An otherwise operational PBX is not successfully receiving faxes. With rxfax debug enabled, the log shows a lot of information from app_rxfax.c. Can someone with the experise to understand it please tell me what it means and how faxes can be received successfully.

Changing the rxgain/txgain settings in zapata.conf appears to move the problem forward a little and alters the app_rxfax.c error messages to:
“FLOW Non-ECM carrier training failed"
or even
"FLOW Trainability test failed - longest run of zeros was XXXX”

you might ant to post this question with asterisk as that is where the code comes from. What I can tell you is that faxing using SIP or using ANY compression codec will NOT work. you need to be doing faxing over a non-compressed connection.

Trust me it just will NOT work. compression alters the tone and frequency of the signals slightly making things fail.