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

"Black, David" <david.black@emc.com> Fri, 29 August 2014 20:10 UTC

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From: "Black, David" <david.black@emc.com>
To: Harald Alvestrand <harald@alvestrand.no>, Colin Perkins <csp@csperkins.org>
Date: Fri, 29 Aug 2014 16:09:43 -0400
Thread-Topic: [Dart] draft-dart-dscp-rtp - way forward
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Cc: Ben Campbell <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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Ok, I see a range of views from skepticism to outright opposition ...

I'll delete the paragraph and reference to the multi-stream optimization
draft and submit the resulting -06 version w/a change note that any interaction
of DiffServ and RTCP multi-stream optimization will be dealt with in the draft
about the latter.

That submission won't happen tonight, as the network in the SAS Lounge in
EWR isn't even close to what we're used to at IETF meetings :-).

Thanks,
--David

> -----Original Message-----
> From: Harald Alvestrand [mailto:harald@alvestrand.no]
> Sent: Friday, August 29, 2014 3:29 PM
> To: Colin Perkins
> Cc: Ben Campbell; Black, David; dart@ietf.org
> Subject: Re: [Dart] draft-dart-dscp-rtp - way forward
> 
> On 08/29/2014 06:04 PM, Colin Perkins wrote:
> > 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.
> >
> >
> I read the sentence above as saying flatly and unconditionally "don't
> use multi-stream-optimization when the RTP streams have different PHBs"
> - which means that if I want to use one PHB for audio and another PHB
> for video, I can't use multi-stream-optimization.
> 
> I'd be sad if that was the case, *especially* if we can't figure out any
> reason to make that recommendation.