7 aug 2006 kl. 14.37 skrev Rich Adamson:
Chan Kwang Mien wrote:
Thanks. By setting allow=g729, sip1 was able to connect to sip2.
Does that mean that Asterisk chooses the codec to be used between the
Caller and Callee ? In this case, since sip1 informs Asterisk that it
supports g.711 and g.729, Asterisk chooses g.729 since the Callee
also
supports g.729. From the SIP Messages exchange, it doesn't seem that
Asterisk chooses the codec.
My previous setting was "allow=all". I was expecting "allow=all"
to work
since that would also imply "allow=g729", isn't it ?
This really belongs on the -users list since it doesn't deal with
developing code. Moving it there now.
Each sip phone essentially negotiates a codec independently with
asterisk, and not as an end-to-end conversation.
Not "a" codec - many codecs.
When sip1 initiates a call, it exchanges sip packets with asterisk
to select a compatible codec. When asterisk places the call to
sip2, it exchanges sip packets with sip2 to select a compatible
codec and it has nothing to do with what sip1 negotiated.
Well, this is changing. With new RFCs they have something to do with
what SIP1 offered. Note that
* More than one codec can be "approved" for a call. Each UA can then
freely switch between the
codecs during a call without a re-invite.
* Different codecs can be used in each direction
You have two choices to correct the behavior. One, change the
asterisk definitions so as to show a preference (disallow=all,
allow=g729,ulaw), or, two, change the sip phone's definition to
prefer g729 as its first choice.
Or use the SIP_CODEC variable in the dialplan to set a prefered codec
for the call.
Even though many sip phones support multiple codecs, the
negotiation is very simple in that it offers up its first choice
codec (only), and if asterisk supports that first choice, that's
what is used. Highly dependent on the sip phone manufacturers coding.
Yes. Asterisk has some interesting behaviour too, that we will have
to change to comply with recent standards.
/O
---
* Olle E. Johansson - [EMAIL PROTECTED]
* Asterisk Training http://edvina.net/training/
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