Re: [Dart] Treatment of RTCP - proposed text

"Paul E. Jones" <> Thu, 28 August 2014 03:20 UTC

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From: "Paul E. Jones" <>
To: "Ben Campbell" <>, "Black, David" <>
Date: Thu, 28 Aug 2014 03:21:13 +0000
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Cc: "" <>, "" <>, Colin Perkins <>, Michael Welzl <>, " WG" <>
Subject: Re: [Dart] Treatment of RTCP - proposed text
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I think the answer is really whether we can quickly reach consensus.  I 
have an idea how I'd implement it if I didn't have guidance otherwise, 
which I explained in my last email.

I think this can be resolved pretty quickly.  If not, we can certainly 
leave it open.


------ Original Message ------
From: "Ben Campbell" <>
To: "Black, David" <>
Cc: "Paul E. Jones" <>om>; "Michael Welzl" 
<>no>; "Colin Perkins" <>rg>; 
<>rg>; "" 
<>rg>; " WG" <>
Sent: 8/27/2014 10:28:07 PM
Subject: Re: Treatment of RTCP - proposed text

>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:
>>  OLD
>>    o Should use a single DSCP for an RTCP session, primarily to avoid
>>       RTCP reordering (and because there is no compelling reason for 
>>       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.]
>>  NEW
>>    o Should use the same DSCP for RTCP reports as used for the RTP 
>>       that is being reported on when that DSCP is known by the RTCP 
>>       When an RTP stream uses multiple DSCPs that differ only in drop
>>       precedence, RTCP reports on that RTP stream should use the DSCP 
>>       the least likelihood of drop to favor delivery of the RTCP 
>>       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 
>>  the RTP stream, due to en-route remarking.
>>  If that text looks close, I'll edit further and try to get the -05 
>>  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 
>>>  comments - WGLC: draft-ietf-dart-dscp-rtp-02)
>>>  RTCP might not be used for RTT calculations (it might; I just doubt 
>>>  terribly useful), but RTCP might be used to convey QoE measurements 
>>>  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 
>>>  the corresponding RTP packets of that sender. In the case where an 
>>>  class is used, I'm not sure there is agreement (though no 
>>>   I stated my view that we should use the lowest drop precedence in 
>>>  case, but others should weigh in.
>>>  Paul
>>>  ------ Original Message ------
>>>  From: "Ben Campbell" <>
>>>  To: "Michael Welzl" <>no>; "Colin Perkins"
>>>  <>rg>; "Paul E. Jones" <>om>; 
>>>  David" <>
>>>  Cc: ""
>>>  <>rg>; ""
>>>  <>rg>; " WG" <>
>>>  Sent: 8/27/2014 4:48:37 PM
>>>  Subject: Re: [Dart] [AVTCORE] Treatment of RTCP (was Re: Colin 
>>>  comments - WGLC: draft-ietf-dart-dscp-rtp-02)
>>>>  On Aug 27, 2014, at 3:45 PM, Michael Welzl <> 
>>>>>  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: 
>>>>>  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 
>>>>  well.
>>>>  Colin and Paul (and David):
>>>>  Are we converging on what guidance to put into the DART draft?
>>>>  Thanks!
>>>>  Ben.
>>>>  _______________________________________________
>>>>  Dart mailing list