I'm trying to set up Asterisk and IAXModem to send faxes via T38 (Yes, I know I'm swatting a fly with a Buick...) However, since I'm trying to do something so small with a product so large, I'm having trouble finding samples or how-tos that show me how to set this up.

I've got all three installed, and I THINK I have my IAXModem config correct. I'm pretty sure that I have Hylafax correct (I've used it with T38Modem) so, I need to know which of the Asterisk samples I need to use, and how to use them.

I think I want to use some combination of iax.conf, iaxprov.conf, sip.conf and sip_notify.conf. But I'm not sure where to put them, or what to change...

I'm sure that the answer is RTFM, but I'm not sure WHICH M, or where in it to R...


EDIT On a mailing list, someone told me that this actually WON'T WORK because IAX doesn't do T38. So, is there some other way to get Asterisk to work with Hylafax and send T38? I know that Asterisk does T38, the question is how to get the data from Hylafax and back...


The main reason for using T.38, that I see, is to enable transport across dodgy links. Furthermore, as you said, IAX doesn't do T.38.

What it DOES do is provide HylaFAX an emulated fax modem- this communicates over IAX with asterisk. In extensions.conf, you will issue a Dial(IAX2/iaxmodemname[/extension]) (the optional remote extension is how you would differentiate between different inbound lines).

In the end, it will be iaxmodem and spandsp that are actually doing the fax protocol stuff, with an slin-encoded link between those and asterisk, and hylafax attached at the other end to a virtual modem (ttyIAX0 in my case).

This all works decently across reliable LANs and marvelously over loopback. Don't expect it to work over a WAN or congested LAN link, though.

There is also asterisk's txfax/rxfax. These, from what I've heard, lack ECC and are prone to corrupting faxes. OTOH, it's a much simpler solution that only involved asterisk (instead of asterisk + hylafax + iaxmodem + spandsp).

Googling "iaxmodem hylafax" should get you where you're going. If you're stuck, repost and I'll try to help.


  • Actually, T38 is good for sending faxes in general, because voice encodings are very lossy in the ranges that faxes use... so you don't want to use G711, for example, for the fax... Apr 27 '10 at 17:04

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