asterisk users - Jul 2007 - Determining the used codec for the IP Trunk (SIP Trunk)

Hi List;

Where I determine the codec to be used for the SIP
Trunk (between Asterik and another SIP softswitch)?

Regards
Bilal


       
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you might use
   sip show peer peername
to see what a peer will allow or
   show channel channelname
(channel name as retrieved from show channels)
to determine what a current conversation is using

Moj

bilal ghayyad wrote:
> Hi List;
> 
> Where I determine the codec to be used for the SIP
> Trunk (between Asterik and another SIP softswitch)?
> 
> Regards
> Bilal
> 
> 
>        
>
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On Tue, 3 Jul 2007, bilal ghayyad wrote:
> Where I determine the codec to be used for the SIP Trunk (between 
> Asterik and another SIP softswitch)?
   Are you asking positively how to determine which codec is being 
negotiated between those two elements, or, normatively, which one is
best to use?

   If the former question, you can look at the SDP (Session Description
Protocol) payload in the INVITEs (and other messages part of the INVITE
transaction).  Find the 'rtpmap' lines.  They look like this:

         a=rtpmap:18 G729/8000

   There may be multiple such lines indicating that endpoint's support
for all of them.  If so, the only way to determine which one is actually
going to be used is to look at the RTP stream with a protocol analyser.
It should be able to tell you.  Wireshark/Ethereal certainly can.

   If you're asking which codec should be used, it depends on the desired 
application, whether the trunk is running over a LAN, WAN, or over the 
public Internet, whether QoS is involved, etc.

-- Alex

--
Alex Balashov
Evariste Systems
Web    : http://www.evaristesys.com/
Tel    : +1-678-954-0670
Direct : +1-678-954-0671

Dear Alex;

I am asking about:

What is the configuration that I can do it to let the
traffic between the two Asterisk PBX and another IP BX
to be g729 or G711 or g723?

In other words, how can I let the ued codec for the IP
Trunk between my Asterisk and the other IP PBX to be
g729 and not g711? Ofcourse, I am assuming that the
other side also supporting g729.

Regards
Bilal 
> Where I determine the codec to be used for the SIP
Trunk (between 
> Asterik and another SIP softswitch)?
   Are you asking positively how to determine which
codec is being 
negotiated between those two elements, or,
normatively, which one is
best to use?

   If the former question, you can look at the SDP
(Session Description
Protocol) payload in the INVITEs (and other messages
part of the INVITE
transaction).  Find the 'rtpmap' lines.  They look
like this:

         a=rtpmap:18 G729/8000

   There may be multiple such lines indicating that
endpoint's support
for all of them.  If so, the only way to determine
which one is
 actually
going to be used is to look at the RTP stream with a
protocol analyser.
It should be able to tell you.  Wireshark/Ethereal
certainly can.

   If you're asking which codec should be used, it
depends on the
 desired 
application, whether the trunk is running over a LAN,
WAN, or over the 
public Internet, whether QoS is involved, etc.



 
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Bilal,

   There are allow= options you can use on the peers in sip.conf to define
what codec capability Asterisk advertises toward them, and therefore, what
the negotiation on both call legs will ultimately settle upon.  When those
legs are bridged -- as Asterisk does unto them -- they will be of a codec
that is within that bounded set.

   You can have multiple allow lines, i.e.

       allow=g729
       allow=ulaw

   ... or just one.

   Does that help?

-- Alex

--
Alex Balashov
Evariste Systems
Web    : http://www.evaristesys.com/
Tel    : +1-678-954-0670
Direct : +1-678-954-0671

Hi Bilal -
>> In other words, how can I let the ued codec for the IP
>> Trunk between my Asterisk and the other IP PBX to be
>> g729 and not g711? Ofcourse, I am assuming that the
>> other side also supporting g729.
>>
>    You can have multiple allow lines, i.e.
>
>        allow=g729
>        allow=ulaw
Be sure to also put in a disallow statement first:

disallow=all
allow=g729


- Noah