[Freeswitch-users] g729 annexa/annexb interoperability

[Javier Gallart]

Thanks David

this is how Cisco sees the g729 issue:
http://www.cisco.com/en/US/tech/tk1077/technologies_tech_note09186a00800b6710.shtml#g729
IIRC the cng packets have 2 bytes payload, if an endpoint does not support
annexb, what should it do about those packets?

Regards

Javi


---------- Forwarded message ----------
> From: David Ponzone <david.ponzone at ipeva.fr>
> To: FreeSWITCH Users Help <freeswitch-users at lists.freeswitch.org>
> Date: Mon, 25 Apr 2011 16:19:39 +0200
> Subject: Re: [Freeswitch-users] g729 annexa/annexb interoperability
> Javier,
>
> I dont think there is anything to transcode.
> G729 and G729B are the same, except the latter uses VAD and CNG.
>
> David Ponzone  Direction Technique
> email: david.ponzone at ipeva.fr
> tel:      01 74 03 18 97
> gsm:   06 66 98 76 34
>
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> Le 25/04/2011 à 13:44, Javier Gallart a écrit :
>
> Hello all
>
> we're using a Sangoma D100 card for transcoding. Our configuration, as far
> as the codec policy is concerned, basically does this:
>
> -In the first offer to the b-leg we use the same codec list we receive
> (<action application="export"
> data="absolute_codec_string=${ep_codec_string}"/>)
> -If the call fails with status 488, we repeat the call using all the codecs
> available. This includes changing from annexb to annexa and viceversa.
>
> Let's suppose a-leg only supports g729 annexA, and B-leg only supports G729
> annexB. My understanding is that those different codec flavours don't
> interoperate; in fact I've experienced many times audio problems when trying
> to set up a call between endpoints supporting different g729 variants.
>
> In the described case, FS sends initially annexb=no, and B-leg rejects it
> with cause 488. We rebuild the offer with annexb=yes, and then the offer is
> accepted by the B-leg. Our concern is that no transcoding resources are used
> in this case, and we might run into audio problems because of that. The
> other concern is that in the answer to the A-leg (in 183 and 200),
> annexb=yes is included. I'm not sure if all devices would support different
> fmtp parameters in the offer and the answer (the RFC, as usual, won't be
> explicit about this).
>
> Is there any way to force the transcoding in a situation like the one I
> described?
>
> Thanks in advance
>
> Javi
>
>
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