Fax over ATA adapter


I thought I would pass this little tip along. I routinely install and configure Asterisk installs for customers in the southwest United States. This past week I had to buy a new Fax machine for my home office and decided to eliminate my analog line from my provider.

I pulled a Linksys PAP2T device from stock, changed the RTP packet size to 0.020 (which is standard operating procedure for fax devices), connected it to my PBX here at home. I then drove down to Staples and picked up a cheap Brother MFC-295CN.

I brought the Brother back to my home office, connected it up and went to configure it when I came across this configuration option:

Press Menu, 0, 6.
Press a or b to choose Normal (or
Basic(for VoIP)).
Basic(for VoIP) reduces the
modem speed to 9,600 bps. Unless
interference is a recurring problem
on your telephone line, you may
prefer to use it only when needed.
Normal sets the modem speed at
14,400 bps. (Default)
Press OK.
Press Stop/Exit.

Now… I know most fax machines allow you to adjust the connection speed but this is the first time I have ever seen “VoIP” specifically spelled out on a fax machine configuration screen.

I’m going out on a limb here and wondering if Brother/HP and others may have a marketing opportunity by building in Asterisk/SIP support directly into the device. It would be nice to connect just an ethernet cable, configure it as an extension on a proxy and emulate an analog line over RTP. I’m guessing it would not be terribly difficult to build that PAP device into the scanner/fax directly.

I have had very good results using an ATA and routing calls out of asterisk over SIP trunks but I have never succeeded in getting fax to work routing out over analogue trunks through a digium FXO interface card.

Has anyone any experience of this?

Our first attempt getting faxes through our system was using an FXO interface card (connecting to a Qwest analog line) with the fax machine plugged into an ATA adapter. This setup failed miserably with many blank pages and failed faxes. Just for giggles I ordered an FXS module from Ebay, connected the fax to that card and tried to send and receive faxes which also failed more than 10% of the time.

That is why I posted this message is because I am sure there are plenty of people who assume if it does not work with an FXO port then it must not work with a SIP trunk because SIP trunks are much less stable. I am surprised that I assumed this was correct for so long. I have installed several of these ATA adapters at customer’s sites now and they work exceptionally well as long as you can set the fax machine’s speed to 9600 (or use a VoIP setting on the Brother’s fax machines) and you have a decent internet connection.

Is there a reason why you need to use the FXO interface card?