[asterisk-users] Fax throughput - Asterisk 1.6.1.9

[Cyprus VoIP]

Hello,

We are trying to send faxes by T.38 protocol to a remote SIP proxy from 
a local extension. The local extension sends the INVITE, Asterisk sends 
the call to the Proxy the call is connected with a regular audio codec. 
After a few seconds the remote proxy sends an INVITE with UDPTL and the 
Asterisk sends it to the local extension and it's accepted, but (here 
the problem starts) just after sending the OK with the proper SDP to the 
remote Proxy, the Asterisk initiates a new INVITE to the local extension 
and remote Proxy, with the normal audio codecs again.

We set "t38pt_udptl=yes" in sip.conf and allowed all the codecs to the 
local extension and remote Proxy, but it still forces the call to go 
back to a voice call.

Any idea why it happens and how to debug it? We set verbose and debug to 
20, but no "internal" info is provided to get a clear understanding on 
Asterisk's "thoughts" during that process.

Thank you in advance for your assistance,

Andreas