Fax for Asterisk / FPBX

I have recently upgraded my Asterisk from 1.4x.x to This successfully broke Digium’s Fax for Asterisk until I downloaded the appropriate updated files for 1.8. These have now been installed and fax show capabilities results as follows:

Description : Digium FAX Driver
Capabilities : SEND RECEIVE T.38 G.711 MULTI-DOC

However, the behaviour of the fax extensions and inbound fax routes seems to have changed - (or maybe I never fully understood it).

My machine and OS is as follows: (Centos 5)

# uname -a
Linux pbx.check-flight.com. 2.6.18-238.19.1.el5 #1 SMP Fri Jul 15 07:32:29 EDT 2011 i686 i686 i386 GNU/Linux

# getconf LONG_BIT

I have carefully followed all of the installation guidance given in the Digium Fax for Asterisk Admin Manual, including running the benchfax utility and selecting the correct version of the files for my particular OS and machine and modifying the /etc/asterisk/modules.conf files to include:

noload => app_fax.so
noload => res_fax_spandsp.so

(this being to avoid conflicts with the previously installed SpanDSP library)

I now have two apparent problems, which may well be inter-related…

1) SIP Extensions:

Given a SIP extension, (in my case 300), I have enabled Fax and given an email address. Now as I recall previously, (under Asterisk 1.4), the extension would continue to operate as a regular extension inasmuch I could call it from any other extension, the phone would ring and a conversation could take place. However if I sent a fax to that extension, then it would detect the fax tones and receive it instead of putting the call through to the phone. This no longer happens. All calls go straight to fax and the phone never rings. As I can’t find a decent description of the intended behaviour (the only hint being “Enable this user to receive faxes”), I’m not sure if this behaviour is intended under Asterisk 1.8 or not. I just seem to recall there was some kind of tone detection before.

Even then, all faxes sent to the extension fail: (The fax test source is Zoiper communicator registered as another SIP extension and sending a TIFF file. Zoiper is supposed to be T38 aware - but I can’t get this working from a “regular” fax machine either).

pbx*CLI> fax show stats

FAX Statistics:

Current Sessions : 0
Reserved Sessions : 0
Transmit Attempts : 0
Receive Attempts : 5
Completed FAXes : 0
Failed FAXes : 5

Digium G.711
Licensed Channels : 1
Max Concurrent : 0
Success : 0
Switched to T.38 : 0
Canceled : 0
No FAX : 0
Partial : 0
Negotiation Failed : 0
Train Failure : 0
Protocol Error : 0
IO Partial : 0
IO Fail : 0

Digium T.38
Licensed Channels : 1
Max Concurrent : 1
Success : 0
Canceled : 0
No FAX : 3
Partial : 0
Negotiation Failed : 0
Train Failure : 2
Protocol Error : 0
IO Partial : 0
IO Fail : 0

2) Inbound Routes

Under the inbound routes, I have a “Fax Detect” option. “Yes” means that Asterisk will try to determine if the inbound call is either a fax or a voice call. I then have three further options under “Fax Detection Type”.

a) DAHDI (which I presume does not apply to me as I have no POTS hardware attached)

b) SIP (T38) - which I have selected

c) NV Fax Detect (which requires NV Fax Detect to be installed and recognised by Asterisk) This is greyed out and various articles I have read imply that NV Fax Detect is not compatible with Asterisk 1.8 and I think this is part of the app-fax.so module that is set to ‘noload’ (see above) to avoid conflicts with the Digium modules.

Basically, either with ‘SIP’ or ‘DAHDI’ detection selected, this just doesn’t work for inbound SIP faxes. Incoming fax calls are never recognised and the calls always drop through the to standard destination selected for that route.

It may well be that my SIP provider does not support T38 for the inbound trunk, but even so, under Asterisk 1.4 and NV Fax Detect, inbound faxes were correctly recognised and processed under G.711 capabilities. This now appears to be broken with the lack of NV Fax Detect.

Does anyone have any ideas how I can solve this?

Absolutely same situation for me.

I’m running Freepbx 2.8 and Asterisk from a fresh installation of PIAF

Bounced… because I’d really like some help with this if possible. Great feature - be nice if I could get it working in 1.8



Unfortunately I’ve not been able to get the Free Fax for Asterisk feature working beyond what I’ve outlined above. Does anyone know if this is due to a fundamental compatibility issue with Asterisk 1.8 / FPBX 2.9 or if it’s more likely to be a configuration issue?

I’d be very happy to provide more information if anyone could help me diagnose the problem so I can get the fax working predictably.

It seems to me that the fax features are not documented in FPBX so I’m really unclear how it should work.



FreePBX does nothing special with faxing. We just hand it off to Asterisk. The Fax detect is all handled by Asterisk Core.

I know we have it working flawless on the Distro with 1.8 so my guess is you missed something somewhere. Did you install res_fax and res_fax_digium

I have been fighting with this as well, I have found a workaround that does not need Fax for Asterisk see: http://www.freepbx.org/forum/freepbx/general-help/help-with-fax-freepbx-distro-with-latest-updates but it is not entirely satisfactory as it requires discrete fax numbers.

Since then I have been able to get Fax for Asterisk installed and it is showing that it is licensed but I still cannot get it to recognize a fax using either Dahdi or SIP.

It seems to me that somewhere along the line I have missed something, any help or suggestions would be very much appreciated.

Still unresolved. Yes I do have res_fax_digium installed. What seems to be missing is some equivalent of NV Fax Detect as fax tones are not recognised.

I have managed to get Fax for Asterisk working with the FreePBX distros with both FPBX 2.9 and 2.10Beta. I loaded res_fax_digium.so, it was a bit of trial but eventually got there by following the Digium instructions.

Firstly, I was using an IAX2 trunk for testing and nothing worked - it seems only to work when the fax arrives on a SIP trunk, the fax tones are not detected when the fax arrives on an IAX2 trunk.

I had both res_fax_spandsp.so and reg_fax_digium.so drivers loaded and it seemed to to default to using res_fax_spandsp.so for receiving fax.

You can check what drivers are there by running the CLI query “fax show capabilities”. I edited the /etc/asterisk/modules.conf file and inserted: noload => res_fax_spandsp.so and restarted asterisk. “Fax show capabilities” then only showed the Digium driver loaded.

I setup an extension to receive fax and gave it an email address to send the fax to and I then set the inbound route to Detect fax: Yes, Fax detection type: SIP, Fax detection time: 2, Fax destination: Fax Recipient and appropriate extension.

Incidentally there seems to be a small bug in the FPBX GUI, the Fax Recipient box seems to disappear when you reload, to get it back you need to go to Fax Detect No and back to Fax Detect Yes. I think it is just a display problem as everything works OK otherwise.

I will be interested to hear if you have any success.

Thanks for your detailed reply. Glad you had some success.

Unfortunately I had followed all your steps before posting this thread (see the first message in the list above).

I also suspect that you are using T38 for the SIP detect, which my inbound telco doesn’t seem to support. Even so, I can’t even get this to work on the extensions. Again, I refer back to my original post.