[Linphone-developers] Wrong behaviour when linphone receives an INVITE request with T.38 SDP

[gegetel]

Hello,

As you already know, I am this strange man who's aim is to send faxes using 
softphones and classical group 3 fax-modems, as I explained here:

http://cherchetout.pagesperso-orange.fr/FaxOverVoIP.html

(The main advantage of softphones over most of adsl boxes is they all offer 
PCMA and PCMU audio codecs.)

When I try to send a fax to a pstn subscriber, her fax machine takes the 
call, listen for my fax specific dial tone (CNG) and then begins to send 
it's specific dial tone (CED + DIS). At this time, for some reason I only 
guess, the gateway of my VoIP provider recognizes this as a fax 
conversation, does something I don't know with for effect my softphone 
receives from proxy an INVITE request with T.38 SDP.
Indead of sending a 501 (Not permitted here) answer, Linphone says OK and 
here starts a dialogue of the deaf, Linphone sending packets that wireshark 
describes as "malformed t.38 packets" and receiving only, from time to time, 
genuine T.38 CED packets, as far as the call aborts some time later.

If somebody is interested in resolving this problem, I can send him in 
private a wireshark capture... and test his solution(s). Many thanks in advance.