Support for Fax Machines

(I know this may not work reliably, etc.)

Currently using Asterisk 1.4.x and FPBX 2.3.1…

I’m looking for the best way to set up the following scenario. I have some fax machines that we need to setup to fax out. In our testing so far, we currently setup a prefix to get the call to go out a trunk that forces the codec to be ulaw. We have tested dozens of faxes between 3-15 pages and it’s worked flawlessly. However, I’d like to simplify this, since the users won’t necessarily remember to dal 6 rather than 9 to dial out. Here’swhat I’m thinking as possible solutions:

1 - Use IAXy device, which would allow me to speficy the codec in the definition of the extension, and eliminate the need for dialing 6.
2 - Use external media converter (Quintum/Mediatrix/AudioCodes) to handle the FXS to SIP, and force the codec in the device. Not sure if this can be done, but I don’t see why not.
3 - Setup some sort of custom app/extension that would detect that the extension dialing out is a fax and magically do things…

I’m leaning towards 1 since the cost to some customers would not be a deal breaker. Option 2 would work once the numbe of devices is 4 or more.

My concern is that asterisk will transcode between the ulaw (extension) and g729 (trunk) and ultimately interfere with the delivery of the fax.

Any idead/suggestions?

Thanks in advance,


For faxing you can NOT use any codec that does compression as that creates a loss in quality and that means it will not work. The way we have it working is our fax can only connect on a analog line and then get’s routed out to one of our POTS or PRI lines, and not a SIP trunk.

A fax nothing more then a modem which is designed to listen on a specific frequency for changes to another frequency, if there are changes outside of the spec it will assume a circuit problem and most likely drop the circuit and kill the call.

The only way to do fax over sip is using t.38 which most places do not support yet and if it get’s converted you are screwed…