[asterisk-users] No compatible codecs!

[Alex Balashov]

Naveen Palani wrote:
> Hi,
>  
> I have the asterisk-1.4.11 set up installation on my Ubuntu machine. 
> When i try making a simple incoming call using xlite softphone. I get 
> the following message when i try calling to the number.
>  
> *CLI> [Feb 19 13:35:40] NOTICE[4137]: chan_sip.c:5331 process_sdp: No 
> compatible codecs, not accepting this offer!
>  
> Which codec is it talking abt here. How can i resolve this.
>  
> My dialplan is as given below:
>  
> extensions.conf:
>  
> exten => 800,1,Answer()
> exten => 800,2,Playback(vm-saved)
> exten => 800,3,Hangup
> 
> Regards,
> **Naveen.Palani**

When two SIP endpoints set up a call to each other and decide to pass 
media, they negotiate a preferred codec (the encoding algorithm used for 
the audio itself) that is mutually acceptable.  Not all endpoints 
support the same codec.  Most endpoints support multiple codecs 
(Asterisk and the soft phone you mentioned certainly do), but that 
doesn't mean that they advertise everything that they support as part of 
their default settings or come to an agreeable resolution.

This is done in the SDP (Session Description Protocol) of the SIP 
INVITE, which you can analyse with a packet sniffer or by doing "sip 
debug" in the Asterisk CLI.

The basic idea is that either Asterisk or your soft phone is announcing 
codecs in the SDP that the other either does not support or 
administratively disallows, so they fail to meet in the middle.

Most likely, you can fix this easily by specifying the codecs you want 
to accept in the SIP peer, in sip.conf, for the soft phone you are 
using.  Just add something like:

   disallow=all
   allow=ulaw

This will enable support for G.711u, and G.711u only.  The X-Lite 
supports this out of the box.

Cheers,

-- 
Alex Balashov
Evariste Systems
Web    : http://www.evaristesys.com/
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