[asterisk-dev] Fax with Asterisk and T38Modem

Thorolf Godawa nospam at godawa.de
Wed Jun 29 16:57:05 CDT 2011


I'm fighting with HylaFAX, Asterisk and T38Modem since some time, to get
fax2mail and mail2fax working, my SIP-provider only supports T38 and
thus using G711 with IAXModem is not an option.

I have got running mail2fax with HylaFAX+ 5.5.0, Asterisk 1.4.20 and
T38Modem 2.0.0 successfull, but I'm not able to upgrade to anything
newer than Asterisk 1.4.24.

I was able to track down this problem to some changes in the chan_sip.c,
where a "improved support for T38 on initial INVITE" has been
implemented, see:

I'm not sure what the problem is, but it seems that the T38 handshake
does not work correct any more bacause the CFR (confirm to receive) is

Goal is, to get running this with the latest Asterisk, right now Is there s.b. who can give me a hint how to solve the problem?

For fax2mail I use Asterisk, but it is not working too, after a
fax call, the connection with T38Modem is established, HylaFAX reports
"ANSWER: FAX CONNECTION DEVICE '/dev/ttyT380'", but a fax is never received.

In the tcpdump I see the correct handshaking between Asterisk and
T38Modem, but finaly T38Modem makes a second REINVITE with "recvonly"
and Asterisk answers with "SIP/2.0 488 Not acceptable here" and the call
ends shortly after that.

As far as I can see, T38Modem does not accept the portchange from rtp to
udtpl and thus tries a REINVITE. Probably there is a problem in
T38Modem, so I filed a bug at sourceforge for that:


But may be, somebody has a solution for this too.

Thanks a lot,

Chau y hasta luego,


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