[asterisk-users] Outbound T.38 via RTP with pjsip does not work as expected

Michael Maier m1278468 at mailbox.org
Thu Apr 6 13:15:40 CDT 2017


I'm trying to send a fax via T.38 to a destination, which should be T.38
capable. My provider supports T.38, too. Unfortunately, it doesn't work.
This means:

Call is started and SDP is negotiated w/ alaw. Callee sends reinvite -
for alaw again (and not for T.38)!! After about 30s, callee hangs up
because of missing data (this is true, because I don't send alaw coded
fax data.

Tracing the signaling shows, that the callee doesn't have any
possibility to recognize, if I'm supporting T.38, because it is never
sent during Invite process.

I'm missing the media feature tag sip.fax in the contact header. Did I
miss some configuration?

That's my setup:
Hylafax sends fax to t38modem and t38modem is connected via SIP to
asterisk as extension. The extension is bound to an outbound route,
which uses the t.38 capable ISP.


t38_udptl_nat=no # there is no nat necessary


Any idea?


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