[Asterisk-Users] ULaw not negotiating

[Paul Rodan]

According to the provider's techs, Asterisk isn't properly following the SIP
guidelines about codec negotiation. 

>From my understanding of the convo, Asterisk is expecting multiple codec
capabilities to be in the Capabilities string, in the first header sent
over, if it doesn't find a match, it reports no compatible codecs and drops
the call. But the SIP standard calls more for something like 1 codec per
header, the remote server first sends what its preferred codec is (in this
case g729a), and then a "true SIP device" is supposed to respond and say
that the codec isn't acceptable (mine only accepts G711U), then the remote
system sends over another header with the next preferred codec (in this case
would have been G711ULaw), and so on until there is a match (mine would
accept G711ULaw and proceed with the call). Asterisk is accepting the
information in the first header as the ONLY codecs the remote system
accepts, and doesn't understanding sending a SIP response to the remote
system so that it will then send the next available codec, if any.

Our system has to send a response and say g729 isn't acceptable and to
please send the next available. Their techs are writing a patch for
chan_sip.c now to correct the issue and make sip more compatible with
standards. 

This is what I was told, I also may have misinterpreted the whole thing, I'm
still learning, but it sounds quite feasible. This patch should add that
functionality and make the system work great. 




-----Original Message-----
From: asterisk-users-bounces at lists.digium.com
[mailto:asterisk-users-bounces at lists.digium.com] On Behalf Of Eric Wieling
aka ManxPower
Sent: Friday, January 14, 2005 6:03 PM
To: Asterisk Users Mailing List - Non-Commercial Discussion
Subject: Re: [Asterisk-Users] ULaw not negotiating

Paul Rodan wrote:
> Capabilities: us - 0x4(ULAW), peer - audio=0x100(G729A)/video=0x0(EMPTY),
> combined - 0x0(EMPTY)
> 
> Non-codec capabilities: us - 0x1(G723), peer - 0x1(G723), combined -
> 0x1(G723)
> 
> Jan 14 17:29:55 WARNING[81922]: chan_sip.c:2820 process_sdp: No compatible
> codecs!
> 
>  
> 
> What throws me off is the description format of G729. They said they used
to
> be sending in ULaw and G729, but then I had him turn off G729 all
together.
> But this sip debug doesn't confirm that, I see g729 mentioned several
times.
> But I do see ULaw mentioned in there as well as well as 0x4, under
> Capabilities. So why isn't Asterisk accepting it?

They lie.  They are sending G729 only.
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