[Dart] Treatment of RTCP - proposed text

["Black, David" <[e-mail]>]

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 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.]
NEW
   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 [mailto:[e-mail]]
> Sent: Wednesday, August 27, 2014 6:53 PM
> To: Ben Campbell; Michael Welzl; Colin Perkins; Black, David
> Cc: [e-mail]; [e-mail]; [e-mail]
> 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" <[e-mail]>
> To: "Michael Welzl" <[e-mail]>; "Colin Perkins"
> <[e-mail]>; "Paul E. Jones" <[e-mail]>; "Black,
> David" <[e-mail]>
> Cc: "[e-mail]"
> <[e-mail]>; "[e-mail]"
> <[e-mail]>; "[e-mail] WG" <[e-mail]>
> 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 <[e-mail]> 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.
> >
> >
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