[AG-TECH] RTP CNAMEs from AG nodes

Robert Olson olson at mcs.anl.gov
Wed May 29 07:09:47 CDT 2002

At 11:23 AM 5/29/2002 +0100, S.Booth wrote:

>I was wondering if it would make sense to modify vic,rat,etc so that all
>RTP streams from an AG node use the same CNAME attribute

It might indeed make sense to do that - it's something I've thought about 
doing but haven't gotten around to.

>At the moment CNAMEs are constructed as <username>@<ip-address>
>so audio and video streams have different CNAMEs on a standard AG node
>but my uderstanding of
>RFC-1889 is that CNAMEs are intended to associate streams from the same
>participant for purposes like lip-sync and audio switching.

There are a lot of SHOULD's in the section defining CNAME as user at host, 
which means with good reason the recommendations there can be changed. I 
think this situation definitely qualifies.

(Latest RTP draft at 

>I know that AG does not need audio switching but this would make it easier
>to interface with other systems.

For instance, I suspect that VRVS in H323-bridging mode may get confused 
with the audio/video separation (it does video-follows-voice switching).

>Even in an AG context it would be nice to be able to get audio switching
>to work because we could re-use the mechanism to highlight the windows
>from the speakers node as this would make it easier to locate people
>in sessions with a large number of sites taking part.


I suspect I'll roll this into the new venue server/ node software work.

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