[Freeswitch-dev] Can't negotiate L16 at 16000h with Asterisk

[Brian West]

Bug reports are filed at http://freeswitch.org/jira

On Mon, Feb 9, 2015 at 3:45 PM, Antonio Eugenio Burriel <aeburriel at gmail.com
> wrote:

> Yesterday I posted the subject "LIN16 at 16000h Freeswitch <->
> Asterisk" in the user mailing list, but after having taken a peek at
> the source, I thought it was better to share my analysis here:
>
> Problem: Freeswitch can't negotiate L16 at 16000h codec with some peers
> (like Aterisk) which assigns a dynamic PT (over 95) to L16.
>
> Internally Freeswitch assigns a PT of 70 to L16; in
> switch_core_media_negotiate_sdp() we have the following match check:
> match = (!strcasecmp(rm_encoding, imp->iananame) &&
>     ((map->rm_pt < 96 && imp->ianacode < 96) || (map->rm_pt > 95 &&
> imp->ianacode > 95)) &&
>     (remote_codec_rate == codec_rate || fmtp_remote_codec_rate ==
> imp->actual_samples_per_second)) ? 1 : 0;
> Which means that when our peer's codec is dynamic, our match must be
> also dynamic and, if not, out match mustn't.
>
> Except for L16 at 44100h, which has a PT of 10, its PT should be dynamic
> (>95) according to RFC3551. But Freeswitch is internally assigning 70,
> so it will never match.
> Incidentally, Asterisk erroneously assigns to L16 at 8000h a PT of 10,
> which passes the check.
>
> I'm not quite sure which is the proper way to fix this.
> If we change PT from 70 to something over 95, we'll break
> interoperability with older Freeswitches and other peers, such
> LN16 at 800h with Asterisk.
>
> So maybe its cleaner to add a exception to the match check like:
> match = (!strcasecmp(rm_encoding, imp->iananame) &&
>     ((map->rm_pt < 96 && imp->ianacode < 96) || (map->rm_pt > 95 &&
> (imp->ianacode > 95 || imp->ianacode == 70))) &&
>     (remote_codec_rate == codec_rate || fmtp_remote_codec_rate ==
> imp->actual_samples_per_second)) ? 1 : 0;
>
> Any thoughts?
>
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-- 

*Brian West*
brian at freeswitch.org


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