Re: [Dart] Treatment of RTCP (was Re: Colin Perkins comments - WGLC: draft-ietf-dart-dscp-rtp-02)

Colin Perkins <csp@csperkins.org> Tue, 26 August 2014 15:53 UTC

Return-Path: <csp@csperkins.org>
X-Original-To: dart@ietfa.amsl.com
Delivered-To: dart@ietfa.amsl.com
Received: from localhost (ietfa.amsl.com [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id A8ACA1A875A; Tue, 26 Aug 2014 08:53:55 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.9
X-Spam-Level:
X-Spam-Status: No, score=-1.9 tagged_above=-999 required=5 tests=[BAYES_00=-1.9] autolearn=ham
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 9XCUdtDaPUUM; Tue, 26 Aug 2014 08:53:54 -0700 (PDT)
Received: from balrog.mythic-beasts.com (balrog.mythic-beasts.com [IPv6:2a00:1098:0:82:1000:0:2:1]) (using TLSv1.2 with cipher DHE-RSA-AES128-SHA (128/128 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id E71DC1A873A; Tue, 26 Aug 2014 08:53:53 -0700 (PDT)
Received: from [130.209.247.112] (port=57972 helo=mangole.dcs.gla.ac.uk) by balrog.mythic-beasts.com with esmtpsa (TLS1.0:RSA_AES_128_CBC_SHA1:128) (Exim 4.80) (envelope-from <csp@csperkins.org>) id 1XMJ4A-0003Ov-HU; Tue, 26 Aug 2014 16:53:50 +0100
Content-Type: text/plain; charset=us-ascii
Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\))
From: Colin Perkins <csp@csperkins.org>
In-Reply-To: <8D3D17ACE214DC429325B2B98F3AE712077BB42DF4@MX15A.corp.emc.com>
Date: Tue, 26 Aug 2014 16:53:34 +0100
Content-Transfer-Encoding: quoted-printable
Message-Id: <641FDB1F-F602-4F91-9012-514F84C90462@csperkins.org>
References: <em0263d12c-c65b-4a0c-b34d-369b21415bc4@sydney> <5B9EC18C-A2E6-4A62-AF5F-C24A09AEC7F0@csperkins.org> <F6194F9F-701F-459B-8B4D-8FA10F0522FF@nostrum.com> <8D3D17ACE214DC429325B2B98F3AE712077BB42DF4@MX15A.corp.emc.com>
To: "Black, David" <david.black@emc.com>
X-Mailer: Apple Mail (2.1878.6)
X-BlackCat-Spam-Score: -28
X-Mythic-Debug: Threshold = On =
Archived-At: http://mailarchive.ietf.org/arch/msg/dart/snptCGr21FW9mNNxspXgpWXYq9Q
Cc: Ben Campbell <ben@nostrum.com>, "draft-ietf-dart-dscp-rtp.all@tools.ietf.org" <draft-ietf-dart-dscp-rtp.all@tools.ietf.org>, "dart@ietf.org" <dart@ietf.org>, "avt@ietf.org WG" <avt@ietf.org>, "Paul E. Jones" <paulej@packetizer.com>
Subject: Re: [Dart] Treatment of RTCP (was Re: Colin Perkins comments - WGLC: draft-ietf-dart-dscp-rtp-02)
X-BeenThere: dart@ietf.org
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: "\"DiffServ Applied to RTP Transports discussion list\"" <dart.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/dart>, <mailto:dart-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/dart/>
List-Post: <mailto:dart@ietf.org>
List-Help: <mailto:dart-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/dart>, <mailto:dart-request@ietf.org?subject=subscribe>
X-List-Received-Date: Tue, 26 Aug 2014 15:53:55 -0000

On 26 Aug 2014, at 16:39, Black, David <david.black@emc.com> wrote:

>>> Since not all the media sent by a single SSRC has the same marking, my
>> suggestion would be that each SSRC mark the RTCP packets it sends with one of
>> the same code points as it uses to mark the media. Since RTCP is somewhat
>> important, it would make sense for each SSRC to mark the RTCP packets it sends
>> using the highest priority code point it uses to mark the RTP media packets it
>> sends.
>> 
>> That makes sense to me. Paul, and others, do you agree with that last
>> paragraph?
> 
> <editor hat off>
> 
> Sure, when there's a notion of priority or importance.  There won't always
> be one (e.g., is CS2 higher priority than AF2x?  That depends ...).  OTOH,
> we don't need to say much here, e.g., the class selector codepoints (CSx)
> are ordered, and adding a pointer to draft-ietf-tsvwg-rtcweb-qos will be
> helpful.
> 
> </editor hat off>
> 
> Turning to the other RTCP issue, [F] on multi-stream optimization, I wonder
> whether we inadvertently framed that issue backwards.  Given the above, a
> single RTCP report on multiple RTP streams that use rather different DSCPs
> may not result in representative RTT values for all of the streams, because
> the report has to be sent with one DSCP.  If that outcome is a problem,
> one should send separate RTCP reports (duh!). 

Each reporting SSRC sends a separate RTCP report block for each SSRC it receives, so this is not a problem. The question is what marking an SSRC uses for the RTCP packets it sends, given that it uses several different markings for the RTP media packets it sends. 

> That statement seems valuable to make and can be made with a citation of
> RFC 3530, as opposed to the multi-stream optimization draft.
> 
> Harald and Colin - what do you think?

The discussion of the multi-stream-optimisation draft is a separate issue, and is correct as it is.

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