Subject: RE: [MMUSIC] video media control draft

From: "Even, Roni" <[email-masked]>
Date: Tue, 23 Jul 2002 10:49:39 +0300

Hi,
My comment on this item are below

>From an architectural point of view, any RTCP mechanism is not the
> right
> answer for application layer commands. While applications use call
> signaling
> and application media control for media stream establishment and
> manipulation, RTP/RTCP (with the addition of the "RTCP feedback") are
> dealing with congestion, etc. over IP in PARALLEL to the applications
> running above. This allows for a loosely coupled architecture between
> the
> application and the RTP/RTCP modules.

Well, it seems that it has already been done, since apparently an 
existing RFC uses RTCP for picture update. Its just codec specific at 
this point. While I don't think RTCP is ideal here, I don't find it 
architecturally incorrect.

Roni Even: 
This text is from H.261 that was mentioned in the MMUSIC discussion, as can
be seen it says to use the signaling protocol and not the RTP/RTCP for that

4.3 Multipoint considerations
The following facilities are provided to support switched multipoint
operation.
4.3.1	Freeze picture request
Causes the decoder to freeze its displayed picture until a freeze picture
release signal is received or a timeout period of at least six seconds has
expired. The transmission of this signal is via external means (for example
by Recommendation H.221).
4.3.2	Fast update request
Causes the encoder to encode its next picture in INTRA mode with coding
parameters such as to avoid buffer overflow. The transmission method for
this signal is via external means (for example by Recommendation H.221).

As for the RTCP feedback, the AVT group did not agree on requests but on an
indication that will still allow the encoder to ignore the message. As can
be seen from 4.3.2 above the request for full picture will not cause
congestion even in H.320 sine the encoder may reduce quality of the full
picture.

Thanks
Roni Even

_______________________________________________
mmusic mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/mmusic

---

From: Colin Perkins <[email-masked]>
Date: Wed, 24 Jul 2002 16:34:15 -0400

>be seen it says to use the signaling protocol and not the RTP/RTCP for that

This doesn't seem to be a productive argument, since you could argue that
"external means (for example by Recommendation H.221)" requires that a
signalling protocol is used, and I could argue that RTCP is a suitable
"external means" since it's external to H.261. 

>congestion even in H.320 sine the encoder may reduce quality of the full

This is the core point of disagreement, I believe. I would argue that, no
matter how the fast update request message is transmitted, the encoder MUST
be able to ignore the request (because, for example, there may be IP level
congestion). The fact that the encoder can reduce quality so that the bit-
rate does not increase due to the full intra picture is irrelevent, since
it is possible that the network will have insufficient capacity for that
rate too.

Colin