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[Linphone-developers] Wrong behaviour when linphone receives an INVITE r

From: gegetel
Subject: [Linphone-developers] Wrong behaviour when linphone receives an INVITE request with T.38 SDP
Date: Mon, 09 Dec 2013 18:43:53 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:25.0) Gecko/20100101 Firefox/25.0 SeaMonkey/2.22


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:

(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.

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