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When using a DAHDI device for inbound calls requiring fax detection, the DAHDI faxdetect method is pretty darn reliable in Asterisk. Unfortunately, we had problems when trying to use it via FreePBX inbound routes, fax detect section, method "DAHDI". In analyzing the logs, it appears that selecting the DAHDI method adds an Answer() to the dialplan. As a result, DAHDI faxdetect doesn't work.

Using the same equipment, and processing the call through custom dialplan only, the following dialplan works properly.

[from-the-faxline-in-question] exten => _.,1,Answer exten => _.,n,Ringing exten => _.,n,wait(4) exten => _.,n,NoOp?(call to faxline) exten => _.,n,goto(from-internal,3271,1) exten => fax,1,goto(from-internal,3270,1)

where x3271 is the non-fax destination, and x3270 is the fax machine.

I think the 'bug' is simply an omission of 'Answer' in the dialplan provided by FreePBX when DAHDI faxdetect method is selected.

Freepbx version 2.8.1.4

5 Responses to “Fax not detected by Asterisk”

1. Edwin Lam said:

   Nov 17, 11 at 10:01 pm

   in your dialplan, did you “Answer” the call and “Wait”
   a few seconds for Asterisk to detect the fax tone before
   you do some other things?

2. "Danny Nicholas" said:

   Nov 17, 11 at 10:31 am

   Fax is detected at ring/start level. Check chan_dahdi.conf.

   Sent: Thursday, November 17, 2011 5:30 AM

   Hello List,

   I have an Elastix 2 machine with digium fax modules (with license).
   When I try to create an extension that also works with FAX, Asterisk does not detect any incoming fax. Even when I use ‘fax set debug’, it does not display anything.
   It’s Asterisk 6.2.x . Any ideas what can I do to figure out why it does not detect the arriving faxes ?

   Thanks,

   Ido

3. ik said:

   Nov 17, 11 at 1:35 pm

   The chan_dahdi.conf contain faxdetect=both

4. ik said:

   Nov 18, 11 at 3:43 pm

   Yes, I placed a wait up to 10 seconds just to make sure

5. "Danny Nicholas" said:

   Nov 18, 11 at 3:46 pm

   Maybe a progress() command would help?

   Sent: Friday, November 18, 2011 1:44 PM

   I have an Elastix 2 machine with digium fax modules (with license).
   When I try to create an extension that also works with FAX, Asterisk does not
   detect any incoming fax. Even when I use ‘fax set debug’, it does not display
   anything.
   It’s Asterisk 6.2.x . Any ideas what can I do to figure out why it does not detect
   the arriving faxes ?

   in your dialplan, did you “Answer” the call and “Wait”
   a few seconds for Asterisk to detect the fax tone before
   you do some other things?

   Yes, I placed a wait up to 10 seconds just to make sure

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