Re: [Dart] Treatment of RTCP - proposed text

Ben Campbell <> Thu, 28 August 2014 02:28 UTC

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From: Ben Campbell <>
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Date: Wed, 27 Aug 2014 21:28:07 -0500
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To: "Black, David" <>
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Cc: Michael Welzl <>, "" <>, "" <>, " WG" <>, "Paul E. Jones" <>, Colin Perkins <>
Subject: Re: [Dart] Treatment of RTCP - proposed text
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I do not object to the text per se. 

But I do have a bit of a nagging concern that we may be offering too strong of guidance, given the thought process so far.  Do we believe we understand this well enough to say the sender should to this or that, as opposed to say that these are things the implementer should think about, and that these are probably reasonable choices? 

Is this an area where we need more deployment experience to offer real guidance? (I think it's okay for the doc to say that, if needed.)

But in any case, I will defer to Colin, Paul, and David.

On Aug 27, 2014, at 8:58 PM, Black, David <> wrote:

> Trying to propose some text here:
>   o  Should use a single DSCP for an RTCP session, primarily to avoid
>      RTCP reordering (and because there is no compelling reason for use
>      of different drop precedences).  One of the PHBs and associated
>      DSCP used for the associated RTP traffic would be an appropriate
>      choice.  [Editor's note: This bullet is an open technical issue.]
>   o  Should use the same DSCP for RTCP reports as used for the RTP stream
>      that is being reported on when that DSCP is known by the RTCP sender.
>      When an RTP stream uses multiple DSCPs that differ only in drop
>      precedence, RTCP reports on that RTP stream should use the DSCP with
>      the least likelihood of drop to favor delivery of the RTCP reports.
>      When a single RTCP message reports on multiple RTP streams that
>      are sent with different DSCPs, the RTCP sender should choose one
>      of those DSCPs.  When the RTCP sender does not know what
> 	DSCP or DSCPs were used to send an RTP stream, it should choose
> 	a DSCP that it would use to send a similar RTP stream.
> The latter sentence is courtesy of the fact that there will be cases
> where the RTCP sender will not know what DSCP or DSCPs were used to send
> the RTP stream, due to en-route remarking.
> If that text looks close, I'll edit further and try to get the -05 submitted
> by the end of this week.
> Thanks,
> --David
>> -----Original Message-----
>> From: Paul E. Jones []
>> Sent: Wednesday, August 27, 2014 6:53 PM
>> To: Ben Campbell; Michael Welzl; Colin Perkins; Black, David
>> Cc:;;
>> WG
>> Subject: Re: [Dart] [AVTCORE] Treatment of RTCP (was Re: Colin Perkins
>> comments - WGLC: draft-ietf-dart-dscp-rtp-02)
>> RTCP might not be used for RTT calculations (it might; I just doubt it's
>> terribly useful),  but RTCP might be used to convey QoE measurements or
>> one-way delay information useful for RMCAT.
>> I think there is agreement that the DSCP value applied to the RTCP
>> packet for a given SSRC sender should align with the DSCP value used for
>> the corresponding RTP packets of that sender. In the case where an AFxx
>> class is used, I'm not sure there is agreement (though no disagreement).
>>  I stated my view that we should use the lowest drop precedence in that
>> case, but others should weigh in.
>> Paul
>> ------ Original Message ------
>> From: "Ben Campbell" <>
>> To: "Michael Welzl" <>no>; "Colin Perkins"
>> <>rg>; "Paul E. Jones" <>om>; "Black,
>> David" <>
>> Cc: ""
>> <>rg>; ""
>> <>rg>; " WG" <>
>> Sent: 8/27/2014 4:48:37 PM
>> Subject: Re: [Dart] [AVTCORE] Treatment of RTCP (was Re: Colin Perkins
>> comments - WGLC: draft-ietf-dart-dscp-rtp-02)
>>> On Aug 27, 2014, at 3:45 PM, Michael Welzl <> wrote:
>>>> I don't know the beginning of this but I can help go up the stack:
>>>> for the short dialogue between Colin and me, the conclusion is: Colin
>>>> is right. RTCP probably won't be used by congestion control to
>>>> estimate the RTT.
>>> Thanks, Michael, I think that fits with some earlier conversations as
>>> well.
>>> Colin and Paul (and David):
>>> Are we converging on what guidance to put into the DART draft?
>>> Thanks!
>>> Ben.
>>> _______________________________________________
>>> Dart mailing list