This took me forever to figure out. I could not get asterisk to detect
inbound fax calls from my SIP provider. Voice calls would go through my
dialplan fine. With a fax call, I'd see the call in the log, asterisk would
answer it, and then it would mysteriously drop. I went through everything
I could possibly think of.
Turns out my SIP provider (race.com) has an E-Fax feature that detects and
intercepts fax calls and stores them on their server (or e-mails them out to
wherever you want). So after asterisk answers, race.com detects a fax,
redirects the call to their fax receiver, and drops the call to my asterisk
box.
Trying to figure out now if there's any way to disable that feature with
them. Their control panel portal doesn't seem to offer any way to disable
it.
Just thought I'd post my discovery here in case anyone else is tearing their
hair out over this :)
-j