[asterisk-users] t.38 interop with metaswitch

[Kevin P. Fleming]

On 10/11/2011 01:50 AM, Jeremy Kister wrote:
> I'm trying to receive a t.38 fax from a Metaswitch 7.3. I have full
> control over the metaswitch, but it is in production.
>
> I have the Metaswitch hooked to Asterisk 1.8.7.0 (middleman named s3).
> Then I have the target Asterisk 1.8.7.0 with res_fax_digum 1.8.4_1.3.0
> (named pbx1) registered to s3.
>
> attempts to receive fax over t.38 always error in res_fax with "fax
> session timed-out"
>
> i have debug output at:
> http://jeremy.kister.net/tmp/t38/pbx1.txt
> http://jeremy.kister.net/tmp/t38/s3.txt

It appears that the FAX transaction attempted training a few times and 
failed, then fell back to audio mode (or the calling endpoint hung up).

>
> is the UDPTL debug on pbx1.txt (near line 474) interesting in that
> LOG_TAG(s) is evaluated to 'SIP/' ?

This bug with UDPTL debug messages was just fixed last week.

> I don't think my (sip|udptl|extensions).conf are interesting, but i'd be
> happy to post them. the only interesting tidbit is that when i changed
> 't38pt_udptl=yes' to 'yes,none' or 'yes,redundancy' the fax would fail
> with 't38 negotiation failed".

Well, as a starting point, I'd suggest disabling directmedia 
(canreinvite) on s3. It should be possible for directmedia to be enabled 
for RTP and not interfere with UDPTL, but there could still be lingering 
problems there.

-- 
Kevin P. Fleming
Digium, Inc. | Director of Software Technologies
Jabber: kfleming at digium.com | SIP: kpfleming at digium.com | Skype: kpfleming
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
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