[asterisk-users] T.38 with Audiocodes gateway

Matt Fredrickson creslin at digium.com
Tue May 3 09:43:17 CDT 2016

On Fri, Apr 29, 2016 at 1:34 AM, Olivier <oza.4h07 at gmail.com> wrote:
> Hello,
> I'm helping a colleague (*) which has the following setup:
> ITSP --- <T.38 capable PJSIP trunk> --- Asterisk 13 ---  <PJSIP>--
> Audiocodes MP-112 ---  <FXO/FXS> --- Fax machine
> My issue is the following :
> Audiocodes gateway reject INVITEs with 488 Not Acceptable Here
> It seems this gateway requires t38 settings to be present in SDP body in the
> very first INVITE.
> My questions are the following:
> 1. I expected T.38 to exclusively work with reINVITE where calls are
> established as normal voice calls (PCMA/PCMU in SDP, for instance) and then
> upgraded to T.38 (when CNG is detected, for instance).
> Have you ever heard of T.38 sessions being established right from the start
> (ie with T.38 settings in the first INVITE) ?

No.  It would seem to be extremely broken if it denies a call based on
a lack of T.38 sdp parameters on the initial INVITE.

> 2. Is it possible to configure Asterisk to pass T.38 settings in SDP in the
> first INVITE it sends ?
> 3. Any suggestion with Audiocodes gateway ?

Look for T.38 settings maybe?  See if there is something keeping you
from sending an initial invite with non-T.38 SDP....?

Matthew Fredrickson
Digium, Inc. | Engineering Manager
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA

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