T38 passthrough problem

Hi all,

I try to pass through fax with t38 from asterisk build on Debian. In sip.conf i have t38pt_udptl = yes and nat=yes.

The scenario is :

Sip-Provider --> (SIP)Asterisk1 --> (SIP)Asterisk2

When an INVITE(g729,g711,t38) is send from the Voip Provider to asterisk 1, then asterisk1 is forwarding the INVITE(t38) to asterisk2.
The question is WHY asterisk1 is sending an INVITE only with t38. Asterisk1 is not answering the call so he does not know if is a fax or a voice call.

Anyone any idea ?

thanks in advance



Even when I try with the i get the same behavior from asterisk.


Does anyone had the same experience with this issue?

Best Regards