Re: [Dart] Open Issue: Guidance for RTCP

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

(as editor)

I believe the core of this issue is the role of RTCP in providing RTT
estimates.  This is the core of open issue [B] and resolving it is
likely to resolve much of open issue [F].

I believe the key question is:

	Is the role of RTCP in providing RTCP estimates important enough
	to serve as the primary basis for providing guidance on DSCP usage
	w/RTCP?

Here's a summary of the "yes it is" viewpoint (from Colin Perkins):

	Using a single
	PHB and DSCP for all RTCP packets within an RTP session might make
	sense, but it's important to note that one role of RTCP is to provide
	an estimate of the round-trip time seen by the media, so the PHB/DSCP
	will have to be chosen with care to avoid biasing that estimate too
	much.

And a summary of the "no it isn't" viewpoint (from Paul Jones):

	it was proposed that RTCP
	should be marked the same as for RTP.  The argument was that this
	is used for RTT calculations.  If that is what was said, I'd like
	to state my disagreement. :-)

	The forward and reverse paths are not necessarily the same and there is
	nothing one should assume about the reverse path to provide guidance about
	the forward path (or vice versa).  As perhaps a gross example, I have the
	ability to download far faster on my home Internet connection than I can
	upload.  Other important traffic characteristics differ in each direction.

Thanks,
--David (as editor)

> -----Original Message-----
> From: Dart [mailto:[e-mail]] On Behalf Of Ben Campbell
> Sent: Monday, August 25, 2014 1:00 AM
> To: [e-mail]
> Subject: [Dart] Open Issue: Guidance for RTCP
> 
> (as chair)
> 
> We have an open issue (Designated issue [B] by David) about what guidance to
> give about RTCP in draft-ietf-dart-dscp-rtp. We need to close this in order to
> progress the draft--meaning we need to do so ASAP.
> 
> Please look at the the following quoted text for background, and offer an
> opinion:
> 
> 
> > (2) PHBs and DSCPs for RTCP.
> >
> > I'm not sure what to say about this, as it looks like I need to set
> > off a discussion (debate?) between you and my co-author, Paul Jones.
> >
> > Colin (from WGLC comments):
> >
> > > Rather, within a single RTP session there are RTCP packets sent
> > > that give information about the RTP streams that are being sent, and that
> > > report on the reception quality of RTP streams being received. Using a
> single
> > > PHB and DSCP for all RTCP packets within an RTP session might make sense,
> but
> > > it's important to note that one role of RTCP is to provide an estimate of
> the
> > > round-trip time seen by the media, so the PHB/DSCP will have to be chosen
> with
> > > care to avoid biasing that estimate too much.
> >
> > Paul (from shortly after the Toronto meeting:
> >
> > > During the meeting, there was discussion of marking RTCP packets.  Some
> > > notes I received on this topic suggested that it was proposed that RTCP
> > > should be marked the same as for RTP.  The argument was that this is used
> > > for RTT calculations.  If that is what was said, I'd like to state my
> > > disagreement. :-)
> > >
> > > The forward and reverse paths are not necessarily the same and there is
> > > nothing one should assume about the reverse path to provide guidance about
> > > the forward path (or vice versa).  As perhaps a gross example, I have the
> > > ability to download far faster on my home Internet connection than I can
> > > upload.  Other important traffic characteristics differ in each direction.
> > >
> > > Further, an RTCP packet might provide information related to several
> different
> > > RTP packets.  I certainly would not want to see one RTCP packet per RTP
> packet.
> >
> >
> 
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