I have an extension that should get fax calls only. I do not want to use `tone_detect` or `spandsp_start_fax_detect` apps as they not provide fax tone to caller while detecting, which doesn't let caller that it is a fax line. So directly `rx_fax` runs for these fax lines providing fax signal into call. 

Without pre-detection, when call fails, I want distinguish whether the remote caller was a user or a fax machine. Is it possible to check if call was really from a fax machine by reading some spandsp session variables, or other variables? So I'll be sure that that was a fax call and failed. (I've already compaired spandsp variables with a failed fax call and a user call but not helped)

Thanks in advance.