Hi All,

I have searched online quite a bit and can’t seem to find a definitive answer on using the ‘Fax Machine’ feature built into FreePBX.

I have managed to get a copy of SPANDSP downloaded and installed(0.0.6). I get stuck trying to patch my asterisk makefile with the tx/rx fax stuff. Fails on most of the makefile.

Is there a definitive set of instructions out there on how to make FAX work with FreePBX. I know about all the caveats, just want to get basic functionality working then leave it up to the end user.


It’s more of a asterisk issue then a FreePBX issue. If asterisk is configured properly for a fax setup then FreePBX will just deal with it.

You need to provide a whole lot more details to try and get any pointers. Like what version of things… You’ll find that specific versions of spandsp will work with specific versions of asterisk.

At the same time there are docs out on how to configure another fax bundle which I can’t think of the name off the top of my head. but again without details it’s not possible to provide you with link info as we don’t know versions…

Directions and versions of spandsp for asterisk 1.2.x are not the same as those for 1.4.x for example.

Hi fskrotzki,

I’m running debian etch, asterisk 1.4.21 and FreePBX


There is good information on this site regarding fax and settings as well as just googling it.

The easiest way to get fax working is to install asterisk and FreePBX as you would normally. Install spandsp0.0.6pre3. Install AGX’s Extra Addons from sourceforge. Make sure you use the svn version, not the tarball. The svn version will support spandsp-0.0.6. Follow the instructions in the README and you will have faxing in FreePBX using the latest spandsp libraries.

There is a tip elsewhere on this site (can’t remember where) on a few configuration changes that help. In the asterisk.conf file add two options, use_internal_timing=yes and transcode_via_sln=no in the [Options] section. These two parameters will greatly increase your fax reliability for SIP. A kernel with high_resolution_timers is nice…but we don’t go quite that far.

You can also create a custom destination in extensions_custom.conf for receiving faxes that will listen using NVFaxDetect for a longer period of time and disable V17 (put Set(FAX_DISABLE_V17=1) in your dialplan or put it in globals_custom.conf). Disabling V17 forces the maximum speed to 9600…you can try it with and without. An example would be

exten => custom_fax,1,Set(FAX_DISABLE_V17=1)
exten => custom_fax,n,Answer
exten => custom_fax,n,Playtones(ring)
exten => custom_fax,n,NVFaxDetect(60|dt)
exten => custom_fax,n,SetCallerPres(allowed_not_screened)
exten => custom_fax,n,Goto(app-blackhole,hangup,1)

It is very useful for an Inbound Route dedicated to faxes.

These settings have allowed us to fax reliably with SIP.


I’m running Centos, Asterisk Ver. & FreePBX

I have installed spandsp from

Now I want to install AGX’s Extra Addons so I downloaded
svn co https://agx-ast-addons.svn.sourceforge.net/svnroot/agx-ast-addons agx-ast-addons

I’m new to linux and don’t know how or were to install AGX’s Extra Addons. I have my FreePBX system running perfectly and I need to support incoming faxing.

I have also tried these instructions but some of the links are not valid

Can someone point me to the right direction.

Yeah you are absolutely right: using fax machine on FreePBX is quite a complicated thing. I am searching how to use it right now and thanks God I have found this topic. Those answers under your question have really helped me a lot. Thanks to those helpful users.


Steven Bullord