[Dart] WGLC: draft-ietf-dart-dscp-rtp-02

Gorry Fairhurst <gorry@erg.abdn.ac.uk> Wed, 13 August 2014 20:33 UTC

Return-Path: <gorry@erg.abdn.ac.uk>
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 B80AC1A0462 for <dart@ietfa.amsl.com>; Wed, 13 Aug 2014 13:33:14 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -4.869
X-Spam-Level:
X-Spam-Status: No, score=-4.869 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, RP_MATCHES_RCVD=-0.668, SPF_PASS=-0.001] 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 I793hAcZdKrk for <dart@ietfa.amsl.com>; Wed, 13 Aug 2014 13:33:10 -0700 (PDT)
Received: from spey.erg.abdn.ac.uk (spey.erg.abdn.ac.uk [139.133.204.173]) by ietfa.amsl.com (Postfix) with ESMTP id 1A7891A007F for <dart@ietf.org>; Wed, 13 Aug 2014 13:33:10 -0700 (PDT)
Received: by spey.erg.abdn.ac.uk (Postfix, from userid 5001) id 105232B4481; Wed, 13 Aug 2014 21:33:08 +0100 (BST)
Received: from ERG-research.local (gorry-mac.erg.abdn.ac.uk [139.133.207.5]) by spey.erg.abdn.ac.uk (Postfix) with ESMTPSA id 110782B41E7 for <dart@ietf.org>; Wed, 13 Aug 2014 21:33:07 +0100 (BST)
Message-ID: <53EBCB82.9010901@erg.abdn.ac.uk>
Date: Wed, 13 Aug 2014 21:33:06 +0100
From: Gorry Fairhurst <gorry@erg.abdn.ac.uk>
Organization: The University of Aberdeen is a charity registered in Scotland, No SC013683.
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:24.0) Gecko/20100101 Thunderbird/24.6.0
MIME-Version: 1.0
To: dart@ietf.org
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Archived-At: http://mailarchive.ietf.org/arch/msg/dart/HtvUnJtwyeJuT8gOqPBIRz5rd2k
Subject: [Dart] WGLC: draft-ietf-dart-dscp-rtp-02
X-BeenThere: dart@ietf.org
X-Mailman-Version: 2.1.15
Precedence: list
Reply-To: gorry@erg.abdn.ac.uk
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: Wed, 13 Aug 2014 20:33:14 -0000

I can see good points raised on the details, instead I have some 
questions about the overall document strcuture:

(1) This statement appears at the end of section 2:

    "Multiplexing may reduce the complexity and resulting load on an
    endpoint.  A single instance of STUN/ICE/TURN is simpler to execute
    and manage than multiple instances STUN/ICE/TURN operations happening
    in parallel, as the latter require synchronization and create more
    complex failure situations that have to be cleaned up by additional
    code."


I suspect this is all true, but I'd like to ask that section 4 also 
makes a similar summary claim at the end - saying that using a single 5 
tuple and multiplexing multiple streams with *different* QoS expectation 
and therefore different DSCP markings can complicate the transport 
protocol design, by requiring a transport to disambiguate the congestion 
state for each network QoS category that is used. It will also result in 
increased complexity at the transport layer to validate path integrity, 
where a 5-tuple could result in a different routing/forwarding path in 
order to validate that the individual 5-tuples are reachable.  Of 
course, using DSCPs with an AF class can reduce some of the latter 
costs. etc according to what the draft says.

I don't suggest that the extra complexity and additional algorithms are 
as big a problem as being unable to get through a NAPT/Firewall, but it 
seems that this nonetheless extra stuff that I don't recall having been 
worked upon before in the IETF - and a challenge I guess for the RMCAT WG.

(2) I don't know if the document's goal is also to make transport 
recommendations for using multiple code points - i.e.things such as 
must be robust to the network changing a DSCP; needs to independently 
verify that a particular DCSP is not being black-holed, needs to not 
imply relative precedence when interpreting loss or marking of packets 
for a flow using multiple DCSPs etc. ???

If these are out of scope, then maybe the document should say that this 
particular document does not provide this sort of guidance.

Gorry