[asterisk-users] Understanding Codecs

[Paul Hales]

I got very excited when I read the title of this email - I was hoping
someone had learnt to speak g729.

Ah well.

PaulH


Adrian Marsh wrote:
>
> Hi,
>
> I’m having problems with an asterisk server that’s not offering Codecs
> for ulaw and alaw as it should.
>
> I’ve three servers in total: a1, a2 and “b”
>
> A1 and A2 have pretty much the same config files, except IP address
> info changes
>
> Server B is configured to accept all inbound invites.
>
> Calls from A1 to B, all work fine, and in a sip debug session I can
> see A1 is offering codecs:
>
> [May 6 16:43:19] WARNING[25404]: channel.c:720 ast_best_codec: Don't
> know any of 0x4000 formats
>
> Audio is at <IP HIDDEN> port 14958
>
> Adding codec 0x2000 (amr) to SDP
>
> *Adding codec 0x4 (ulaw) to SDP*
>
> *Adding codec 0x8 (alaw) to SDP*
>
> Adding non-codec 0x1 (telephone-event) to SDP
>
> But when A2 makes the same call to B, it only offers amr:
>
> [May 6 16:38:44] WARNING[20408]: channel.c:720 ast_best_codec: Don't
> know any of 0x4000 formats
>
> Audio is at <IP HIDDEN> port 15554
>
> Adding codec 0x2000 (amr) to SDP
>
> Adding non-codec 0x1 (telephone-event) to SDP
>
> Its not building ulaw or alaw into its list. Server B doesn’t support
> AMR, so rejects the call.
>
> (I’ve no idea about the 0x4000 error – but I see it on both the good
> and bad servers, so I don’t think its related).
>
> The odd thing is that the sip.conf files for A1 and A2 are exactly the
> same (save IP info).
>
> The build of the Asterisk server is from a 1.4.15 private build to add
> AMR, but, it’s the same source built on both A1 and A2.
>
> I’m trying to figure out why A2 isnt offering ulaw and alaw.
>
> The codec seems ok, and is listed in the show codecs:
>
> 4 (1 << 2) (0x4) audio ulaw (G.711 u-law)
>
> 8 (1 << 3) (0x8) audio alaw (G.711 A-law)
>
> 8192 (1 << 13) (0x2000) audio amr (AMR)
>
> But I cant see why its not transcoding across to ulaw/alaw.
>
> Thanks,
>
> Adrian
>
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