Re: [rtcweb] Signalling, SDP, and the way we think about interconnecting RTCWEB applications

Wolfgang <wolfgang.beck01@googlemail.com> Sun, 16 October 2011 08:39 UTC

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Date: Sun, 16 Oct 2011 10:39:27 +0200
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From: Wolfgang <wolfgang.beck01@googlemail.com>
To: "<rtcweb@ietf.org>" <rtcweb@ietf.org>
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Subject: Re: [rtcweb] Signalling, SDP, and the way we think about interconnecting RTCWEB applications
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On Sat, Oct 15, 2011 at 5:17 PM, Roy, Radhika R USA CIV (US)
<radhika.r.roy.civ@mail.mil>; wrote:
> Folks:
>
> A given codec type in known, its parameters should also be known per its specifications. So, it the negotiations between codec-types only.
>
> You can see how SDP is used for negotiations between different codec types using SIP. Similar mechanisms can also be used here.
>
> Radhika
So why do we transport some codec parameters outside the media stream
at all? The called device might need information about the media
stream before establishing it.

The server might need access to codec parameters to forward the call
to the best destination: imagine a user with two RTCWEB clients, one
only supports only low resolution video, the other one full HD. A high
resolution video call comes in. How should the server select the
called client if it doesn't have access to the media stream which
carries the resolution parameters?

In my model the server would know what type of call was set up as it
always controls both ends of the call. If some other application
controls the calling party, you need some standardized protocol like
SDP.


Wolfgang