----- Original Message -----
From: "Klaus Darilion" <[email protected]>
To: "sip-implementors" <[email protected]>
Sent: Wednesday, February 25, 2009 9:29 AM
Subject: [Sip-implementors] asymmetric audio codecs
> Hi!
>
> For a certain application where uplink is low bandwidth and downlink is
> high bandwidth I want to use the best available codec - ie. up G729,
> down G.711.
>
> How can I setup such an asymmetric session?
>
> eg.
> high down
> Alice ------------ Bob
> up low
>
> I think if Alice announces G711 and G729, and Bob answers with G.729,
> Alice must send with G729 and Bob can send with G711 too. Is this correct?
>
> Nevertheless, as this requires that Alice's SIP client support this. Is
> there also a method to explicitly define the asymmetric behavior?
>
> Thanks
> Klaus
You 'should' be able to indicate this with the recvonly and sendonly media
attributes in the SDP.
However, not all SIP clients seem currently to support this feature
correctly. See also:
rfc 3264, par. 5.1 Unicast streams, or rfc 4566, par. 6 SDP attributes:
quote:
'a=recvonly
This specifies that the tools should be started in receive-only mode
where applicable. It can be either a session- or medialevel attribute, and
it is not dependent on charset. Note that recvonly applies to the media
only, not to any associated control protocol (e.g., an RTP-based system in
recvonly mode SHOULD still send RTCP packets). '
Regards,
Stephane van Hardeveld
VirtuosoMedia
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