[Freeswitch-users] PCMU fallback for T.38

[Anthony Minessale]

correct, we *do not* proxy re-invites except when bypass_media or
proxy_media is set.


On Tue, Mar 31, 2009 at 11:59 AM, Gabriel Kuri <gkuri at ieee.org> wrote:

> > This part is interesting, and the subject of a discussion we had
> > recently. A number of systems try that second re-invite after a 488, but
> > the SIP specs say the call is pretty much dead after the 488 message is
> > exchanged. Are they just hoping that maybe the other end will be
> > non-compliant enough to keep the call alive, and recover its media mode,
> > or haven't they read the specs?
>
> I think they're hoping the other end is willing to recover it's media
> mode rather than fail the call. I had no idea the call is technically
> dead after the 488. Honestly, it would be nice if the call would still
> be recoverable after that 488 on the T.38 ReINVITE, in order to try and
> negotiate PCMU to try and keep the FAX going, but if that's not how it's
> supposed to work, I'd rather follow the spec.
>
> So for now I've disabled T.38 completely on both the SPA side and I had
> the carrier disable it on my trunk, so they won't try a T.38 reinvite.
> Instead they're trying a PCMU ReINVITE and the problem I'm seeing is
> that if the carrier reINVITEs PCMU after the call initially started out
> as G729, FS fails the call, because it seems to be trying to transcode
> between G729 and PCMU, rather than pass the PCMU reINVITE through to the
> other leg.
>
> 2009-03-31 00:30:50 [DEBUG] sofia_glue.c:1550
> sofia_glue_tech_set_codec() Changing Codec from G729 to PCMU
> 2009-03-31 00:30:50 [DEBUG] sofia_glue.c:1601
> sofia_glue_tech_set_codec() Set Codec
> sofia/cedarwireless.net/1909XXXXXXX at 65.98.2
> 36.38 PCMU/8000 20 ms 160 samples
> 2009-03-31 00:30:50 [DEBUG] sofia_glue.c:1811 sofia_glue_activate_rtp()
> Audio params are unchanged for sofia/cedarwireless.net/
> 1909XXXXXXX at 65.98.236.38.
> 2009-03-31 00:30:50 [DEBUG] sofia.c:2896 sofia_handle_sip_i_state()
> Processing Reinvite
> 2009-03-31 00:30:50 [DEBUG] sofia.c:2542 sofia_handle_sip_i_state()
> Channel sofia/cedarwireless.net/1909XXXXXXX at 65.98.236.38 en
> tering state [completed]
> 2009-03-31 00:30:50 [DEBUG] switch_core_io.c:655
> switch_core_session_write_frame()
> sofia/cedarwireless.net/1909XXXXXXX at 65.98.23
> 6.38 receive message [SWITCH_MESSAGE_INDICATE_TRANSCODING_NECESSARY]
> 2009-03-31 00:30:50 [ERR] mod_g729.c:145 switch_g729_decode() This codec
> is only usable in passthrough mode!
> 2009-03-31 00:30:50 [ERR] switch_core_io.c:723
> switch_core_session_write_frame() Codec G.729 decoder error!
>
> I have inherit_codec=true, set in the dialplan and
> disable-transcoding=true set in the sofia profile, which is what I
> thought would do the trick, but it doesn't seem to be doing anything, FS
> is still trying to transcode between G729 and PCMU. Is there something
> I'm missing to get the PCMU ReINVITE from one of the legs to passthrough
> to the other leg? Does this work only in proxy_media or bypass_media modes?
>
> I am testing this with the latest rev of trunk as well.
>
> Thanks,
>
> Gabe
>
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-- 
Anthony Minessale II

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