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

Colin Perkins <csp@csperkins.org> Thu, 28 August 2014 18:23 UTC

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From: Colin Perkins <csp@csperkins.org>
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Subject: Re: [Dart] draft-dart-dscp-rtp - way forward
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On 28 Aug 2014, at 19:12, Black, David <david.black@emc.com>; wrote:
> Looking at the list discussion, I think I see enough info to produce a
> -05 version of this draft that should address all the last call items.
> 
> Reminder - we had 6 WG LC open issues and work items:
> 
> [A] Work item: Gorry Fairhurst's item (1), a new Section 5.4 on "single
> PHB/DSCP for a single TCP connection, SCTP association or DCCP connection" -
> I need to write this text, and will try to do that over the weekend.
> 
> --> Done, as noted previously, this text wound up in section 5.1 of the
> --> -04 draft, along with slimming down of the corresponding guideline in
> --> section 6.  I haven't seen a note from Gorry indicating that he's
> --> checked it, though.
> 
> [B] Open issue: PHBs and DSCPs for RTCP.  The RTCP guideline bullet cannot
> be revised until this open issue is resolved on the list.  See:
> 	http://www.ietf.org/mail-archive/web/dart/current/msg00156.html
> 
> --> I think I see rough agreement that for RTCP SRs, the same DSCP should
> --> be used as the RTP stream being reported on, and for RTCP RRs, the 
> --> DSCP to use should be the one that would be used to send a similar
> --> RTP stream.

The distinction between RTCP SR and RR isn’t useful here. What you want to say is that an SSRC needs to use the same marking for the RTCP packets it sends as it uses for the RTP packets it sends. If it doesn’t send any RTP packets, it marks its RTCP packets with the marking it would use if it did send RTP.

> --> Beyond that, when an AF class is used, the DSCP with least likelihood
> --> of drop should be used, and for a single RTCP report on multiple RTP
> --> streams for which different DSCPs apply, it's up to the RTCP
> —> implementation to choose one.

No. An SSRC that uses different DSCPs in the RTP packets it sends needs to use the DCSP with the least likelihood of drop from that set when sending its RTCP packets. 

In both cases, the marking of the RTP packets you receive does not affect how you mark the RTCP packets you send. You chose the marking for your RTCP packets based on the marking of the RTP packet you send, not those you receive.

Colin





> --> There's enough text to write here, including mentioning that RTCP
> --> feedback is not currently used for congestion control, that I think
> --> this should be in a new section 5.4, along with a rewritten guideline
> --> item in Section 6.  I hope to send draft text later today.
> 
> [C] Work item:  Request to Ben Campbell for "additional text on context
> (WebRTC, clue and bundle) for the Introduction and Abstract, plus for a
> better example in Section 4."
> 
> --> Done, text is in -04, with some minor edits coming in -05.
> 
> [D] Open issue: Question to Harald Alvestrand - Does CNAME need to be used
> in section 2.2 text?  I hope not.
> 
> --> Closed via a small text deletion in section 2.1 of -04 draft.
> 
> [E] Open issue: Harald Alvestrand's concerns about "differential treatment"
> wrt Section 5.1 .  I don't completely understand these concerns, and suspect
> that they may require an email discussion across the DART and RMCAT WGs
> to sort through.
> 
> --> Deferred - Harald wanted to think about this, and I've seen nothing
> --> further.  I'd suggest that IETF Last Call as an appropriate opportunity
> --> to share any further thoughts, so I don't think there's anything to be done
> --> about this now.
> 
> [F] Open issue: Harald Alvestrand's concerns about the RTCP multi-stream
> optimization text in section 5.2 .  I don't think there's a problem here,
> but I'm not an expert on the RTCP technology involved, and Harald may not
> agree.  This is a different RTCP issue than [B].
> 
> --> Not an issue - At least Colin Perkins and I believe the existing
> --> DART draft text is fine, so I don't think there's anything that needs
> --> to be done for this.
> 
> I'm about to vanish for 2.5 weeks of vacation w/little to no email access,
> so my goal is to get the -05 version submitted either tomorrow or Saturday.
> 
> Thanks,
> --David
> ----------------------------------------------------
> David L. Black, Distinguished Engineer
> EMC Corporation, 176 South St., Hopkinton, MA  01748
> +1 (508) 293-7953             FAX: +1 (508) 293-7786
> david.black@emc.com        Mobile: +1 (978) 394-7754
> ----------------------------------------------------
> 



-- 
Colin Perkins
http://csperkins.org/