[asterisk-users] FAX detection in chan_dahdi 1.8.15

[Jeff LaCoursiere]

Hi,

I recently replaced a site that was using 1.4.[mumble] with 
hylafax/iaxmodem.  They have an RBS T1 and were using about half of 
their 50 DID numbers for "fax to email".  This all broke with the new 
system :(

The original chan_dahdi.conf had no mention of "faxdetect", so I assume 
it was operating with whatever is the default.  Off?

The new box originally had "faxdetect=no", and I found that all my test 
faxes failed with negotiation errors.  When I finally tried 
"faxdetect=incoming" test faxes from another machine running hylafax 
went through fine, and I thought I was done.

The following week the customer reported that inbound faxes weren't 
working.  When I looked at the log, I saw lots of these:

chan_dahdi.c:     -- Redirecting DAHDI/24-1 to fax extension

Which in my FreePBX setup eventually goes to a "no service" message and 
hangs up.  I've never defined a "fax" extension and don't really know 
what that is about.  Turns out that any fax machine that calls ends up 
following this path.  If my other hylafax server calls, it follows the 
normal path and gets answered by my pool of iaxmodems. I don't really 
understand the difference between the two types of calls, first of all.

So it seems from this experience and a recent thread on -users that 
enabling faxdetection in chan_dahdi sets up some additional buffering 
that at least in my case, in 1.8, seems to be required (without it all 
inbound faxes fail from my hylafax server with negotiation problems). 
Unfortunately for me, this also seems to bypass normal DID handling and 
sends calls to an undefined "fax extension".

Can anyone shed some light?

Thanks,

j