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.