Re: [RAI] Using media stream signaling in media plane or in signaling plane (re-send)

[Magnus Westerlund <[e-mail]>]

On 2012-07-23 16:32, Paul Kyzivat wrote:
> Bo,
> 
> Did you consider the implications if there is more than one stream to be
> paused? (E.g. it's an audio+video call.)
> 
> Presumably that would double the message traffic when done in the media
> streams, but not when done in sip. (But the absolute delays may be no
> different.)

Paul,

When it comes to multiple streams it will highly depend on if the
different streams belong to the same RTP session or not. If they are
within the same RTP session the RTCP based method will add one more FCI
block per SSRC, i.e. for a PAUSE or resume request 8 more bytes. And for
example you can pause one SSRC and resume another with the same RTCP
packet.

If they are from different RTP sessions then different RTCP packets will
be required. Thus you get different scheduling of the request packet and
clearly two RTCP packets bringing up the overhead a bit, to at worst
case a minimal compound RTCP packet, i.e. around 120-140 bytes depending
on CNAME length. It will take at least 5-10 RTP sessions being
simultaneously manipulated using RTCP to have approximately the same
aggregated size as using SIP. I think the main question around this
direction of discussion if any application has very strict requirements
on having atomic operations between RTP sessions. I personally haven't
seen any such case.

And Paul's example of audio and video being paused may not be the best
although in no way prohibited. But one common usage we see for this is
to pause the video stream that is responsible for the larger amount of
data while keeping the audio running to a RTP mixer. Then have that
mixer base its decision on what video streams it provides the other
session participants based on the audio activity. There might be cases
where pausing both audio and video simultaneously is a reasonable usage,
and if you have a more concrete example I would appreciate it.

Cheers

Magnus Westerlund

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