asterisk users - Apr 2017 - Outbound T.38 via RTP with pjsip does not work as expected

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?

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.

pjsip.endpoint.conf:

[ISP]
t38_udptl=yes
t38_udptl_nat=no # there is no nat necessary
t38_udptl_ec=fec

[t38endpoint]
t38_udptl=yes
t38_udptl_ec=fec


Any idea?


Thanks,
Michael

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

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?
No - I have to confirm it. But this may take some time :-).


Thanks,
Michaal

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 ... .


Thanks,
Michael