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

Joshua Colp jcolp at digium.com
Thu Apr 6 13:33:24 CDT 2017

On Thu, Apr 6, 2017, at 03:15 PM, Michael Maier wrote:
> Hello!
> 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?

This is not currently supported in either chan_sip or chan_pjsip.
There's no configuration which will enable it. It would need to be
written. Have you confirmed this is what is needed by them?

Joshua Colp
Digium, Inc. | Senior Software Developer
445 Jan Davis Drive NW - Huntsville, AL 35806 - US
Check us out at: www.digium.com & www.asterisk.org

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