VoIP and faxes, well any reasonable persons says to forget about faxes and start using e-mail. It's been around for quite some time. Unfortunatly, faxes are still wanted. This tutorial will guide you how to set it up in a thrustworthy and budgetfriendly way on Asterisk with a TDM400P card. Many of these concepts can be recycled for other cards.

Incoming faxes

Our setup is one asterisk box, one TDM400P card with a FXO and FXS module, one classic Fax machine and a moderate intelligent Administrator.

First you need your TDM400P card to behave as it should. Let's say you have your fxs device (the one where you would be plugging in your PSTN line) on channel 4 and your fxo (the one where you would be plugging in your fax line) on channel 3.

In /etc/zaptel.conf you make sure you have the following lines:


The first line defines you'll be using the third device as a FXO, the second line states you'll use the forth device as a FXS. KS stands for koolstart, this one should do the trick.

Next file in line is zapata.conf. You should find it under /etc/asterisk/zapata.conf. Don't get scared by the huge example file.

We won't cover the zapata specifics, but one thing to point out is the rather specific configuration for every channel. For every channel you need to define above "channel => x" the variables. To allow fax detection you need to add the variable: faxdetect=both, or faxdetect=incoming or faxdetect=outgoing, all depending on your need. It allows you zaptel channel to check if it signal would be a fax signal.

In our example we have the following configuration for our channels:


Do note the context 'fax', we'll recycle that in extensions.conf, which is next.

So far, we made sure our card is recognised and can put 'fax'-calls in a 'fax' context.

So we add a three liner to extensions.conf to finalise everything:



Which means, we added a context fax in the extensions.conf, insuring calls being detected as fax calls to be caught and handled, by the description above. Which is, send it on to the 4th channel.

On that channel you're supposed to connect a fax device. This can be your ordinary fax, or a faxmodem with e.g. hylafax.