Using T.38 termination with Eutelia provider could present a scenario where you can receive faxes using g729, but not being able to receive it, even if you are able to receive it while using alaw. This makes you to start suspecting of your VoIP Software.
It might be the case that the remote endpoint, Eutelia, will need to detect the Fax Tones and send the T.38 ReINVITE to you, they may not have T.38 enabled. If that’s the case, your Asterisk installation will need to detect the Fax Tones so as to make the decision the incoming call is a fax and then switch to the fax extension. For Asterisk to detect the Fax Tones you will need to set faxdetect to either yes or cng, you will also require using alaw or ulaw codec.
It might be suggested that you configure your incoming calls from Eutelia to go directly to the fax receive function whilst having the g729 codec enabled, I expect you will then see T.38 re-invite come from Asterisk. (more…)