I have a Micronet SIP ATA with a fax machine attached and a Micronet SIP FXO gateway connected to the PSTN. They are both registered on Asterisk and work perfectly for voice calls. When I try to send faxes in either direction, I get nothing but stony silence. I have changed the gateways to “peer to peer” mode to test them and they happily talk with each other and do the T.38 thing and faxes flow.
In peer to peer mode, they initially negotiate a G.729 codec, which is the default and then when the receiving end detects the fax tone, it sends SIP invites to re-negotiate the codec and use t38fax. Micronet treats t39 as a codec for the purposes of a SIP transaction which makes perfect sense. Micronet calls the t.39 “codec” t39fax.
When I put the units into proxy mode and connect them back into my Asterisk realm, they connect, but they never get to negotiate T.39. They stay connected with no traffic until the fax machine at the end gives up and goes back on hook.
Now I have learned from my dealings with Asterisk and the newsgroups that Asterisk does not do T.38. However, I take this to mean that Asterisk can’t talk T.38 internally, but I am sure it should let devices do T.38 end to end. My debug traces on the devices certainly bear out the fact that when the unit that detects fax tone tries to change codecs, it doesn’t happen. Asterisk logging shows no errors.
I have chanded sip.conf to allow=all and even added allow=t39fax and there are no explicit rules in the registrations for the gateways.
Does anyone have an idea here?
For this venture to be truly usable, I have to be able to get FAX working at this basic level.
Ultimately I, like many others I suspect, would LOVE to see Asterisk directly talking T.39 for a full Direct Indial fax to email gateway, but for now, I just want to get a fax call from the PSTN to turn up on my cheap little fax machine.