Re: [Dart] draft-dart-dscp-rtp - way forward

"Black, David" <david.black@emc.com> Fri, 29 August 2014 18:27 UTC

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From: "Black, David" <david.black@emc.com>
To: "'csp@csperkins.org'" <csp@csperkins.org>, "'harald@alvestrand.no'" <harald@alvestrand.no>
Date: Fri, 29 Aug 2014 14:23:17 -0400
Thread-Topic: [Dart] draft-dart-dscp-rtp - way forward
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Cc: "'ben@nostrum.com'" <ben@nostrum.com>, "Black, David" <david.black@emc.com>, "'dart@ietf.org'" <dart@ietf.org>
Subject: Re: [Dart] draft-dart-dscp-rtp - way forward
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If DSCP choice for the reduced number of reports is orthogonal to use of the RTCP multi-stream optimisation, then I think the DART draft paragraph on that optimisation can be removed.

Consideration of the DSCP that will be used to send the reports may be a consideration in selecting the SSRC that reports on behalf of the reporting group (as we've tied the DSCP for RTCP to the originating SSRC), but that's probably better addressed (if relevant) in the multi-stream optimisation draft.

Further comments?

Thanks, --David +++Sent from Blackberry

----- Original Message -----
From: Colin Perkins [mailto:csp@csperkins.org]
Sent: Friday, August 29, 2014 12:04 PM
To: Harald Alvestrand <harald@alvestrand.no>;
Cc: Black, David; Ben Campbell <ben@nostrum.com>;; dart@ietf.org <dart@ietf.org>;
Subject: Re: [Dart] draft-dart-dscp-rtp - way forward

On 29 Aug 2014, at 16:52, Harald Alvestrand <harald@alvestrand.no>; wrote:
> On 08/29/2014 05:14 PM, Black, David wrote:
>> Harald,
>> 
>> I’m about to submit a -05 with the indication that the single DSCP recommendation for SCTP and DCCP may be revised.  The RTCP multi-stream optimisation text will still be in there with Colin's clarification about "received" streams.  I’m about to vanish for about 3 weeks, but could put in a revised -06 over the weekend if you can quickly convince Colin.
> 
> Explicitly pinging Colin - Colin, are you arguing that the sentence
> 
>   RTCP multi-stream reporting optimizations for an RTP session
>   [I-D.ietf-avtcore-rtp-multi-stream-optimisation] assume that the RTP
>   streams involved experience the same packet loss behavior.  This
>   mechanism is highly inappropriate when the RTP streams involved use
>   different PHBs, even if those PHBs differ solely in drop precedence.
> 
> should stay in the draft?

I was, but thinking again, I’m not so sure. 

> I think this recommendation is wrong.
> 
> I can't find anything in your latest messages that speak to this particular point.
> You're one of the authors of -multi-stream, so you should be able to speak clearly to the point.
> 
> Can you clarify?

If I have several SSRCs, and receive several media streams, then provided each of my SSRCs sees the exact same quality for each received stream, then  I can use the multi-stream-optimisation to reduce the number of RTCP cross reports I send. The multi-stream-optimisation draft says that already, and it’s not clear that the DART drafts needs to say anything further on the topic.

Whether I use the same DSCP for all RTCP reports I send is, I think, orthogonal to whether I use the multi-stream-optimisation. The dart draft should possibly say that, but I’m not sure that’s the sentence we have above. 


-- 
Colin Perkins
http://csperkins.org/