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

Colin Perkins <> Fri, 29 August 2014 16:05 UTC

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From: Colin Perkins <>
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Date: Fri, 29 Aug 2014 17:04:54 +0100
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Cc: Ben Campbell <>, "Black, David" <>, "" <>
Subject: Re: [Dart] draft-dart-dscp-rtp - way forward
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On 29 Aug 2014, at 16:52, Harald Alvestrand <> 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