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

Michael Maier m1278468 at mailbox.org
Wed May 3 12:44:32 CDT 2017

On 04/06/2017 at 08:33 PM Joshua Colp wrote:
> 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?

It turned out, that there is a  third provider in between, which doesn't
support T.38 ... .


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