Re: [Roll] Use of flow-label in RPL (LLN) networks

Philip Levis <pal@cs.stanford.edu> Fri, 26 September 2014 17:19 UTC

Return-Path: <pal@cs.stanford.edu>
X-Original-To: roll@ietfa.amsl.com
Delivered-To: roll@ietfa.amsl.com
Received: from localhost (ietfa.amsl.com [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 1FBF71A8034 for <roll@ietfa.amsl.com>; Fri, 26 Sep 2014 10:19:14 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -4.986
X-Spam-Level:
X-Spam-Status: No, score=-4.986 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, RP_MATCHES_RCVD=-0.786] 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 vp4E_Z_8hHFv for <roll@ietfa.amsl.com>; Fri, 26 Sep 2014 10:19:12 -0700 (PDT)
Received: from smtp1.cs.Stanford.EDU (smtp1.cs.Stanford.EDU [171.64.64.25]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 1B18F1A82E2 for <roll@ietf.org>; Fri, 26 Sep 2014 10:19:12 -0700 (PDT)
Received: from [76.14.58.121] (port=50040 helo=[192.168.1.3]) by smtp1.cs.Stanford.EDU with esmtpsa (TLSv1:AES128-SHA:128) (Exim 4.80.1) (envelope-from <pal@cs.stanford.edu>) id 1XXZAk-0005SL-Gf; Fri, 26 Sep 2014 10:19:11 -0700
Content-Type: text/plain; charset=us-ascii
Mime-Version: 1.0 (Mac OS X Mail 6.6 \(1510\))
From: Philip Levis <pal@cs.stanford.edu>
In-Reply-To: <26959.1410529343@sandelman.ca>
Date: Fri, 26 Sep 2014 10:19:08 -0700
Content-Transfer-Encoding: quoted-printable
Message-Id: <484D9E4C-3202-4E04-984B-43914D6D7897@cs.stanford.edu>
References: <26959.1410529343@sandelman.ca>
To: Michael Richardson <mcr+ietf@sandelman.ca>
X-Mailer: Apple Mail (2.1510)
X-Scan-Signature: 67f4a389e065da33eb5969ecb4726704
Archived-At: http://mailarchive.ietf.org/arch/msg/roll/QwhNXcK-6Sxd7uyTagZq01--4ic
Cc: roll@ietf.org
Subject: Re: [Roll] Use of flow-label in RPL (LLN) networks
X-BeenThere: roll@ietf.org
X-Mailman-Version: 2.1.15
Precedence: list
Reply-To: Routing Over Low power and Lossy networks <roll@ietf.org>
List-Id: Routing Over Low power and Lossy networks <roll.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/roll>, <mailto:roll-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/roll/>
List-Post: <mailto:roll@ietf.org>
List-Help: <mailto:roll-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/roll>, <mailto:roll-request@ietf.org?subject=subscribe>
X-List-Received-Date: Fri, 26 Sep 2014 17:19:14 -0000

On Sep 12, 2014, at 6:42 AM, Michael Richardson <mcr+ietf@sandelman.ca> wrote:

> There are two paths for forward (perhaps more): 
>  A. adopt draft-thubert-6man-flow-label-for-rpl, incorporate 6man feedback,
>     publish (perhaps add to ROLL milestones) 
>  B. create a 6man-flow-label considerations in LLNs document, taking just
>     the issues about resetting flowlabel to zero, and negotiate who (6lo vs
>     ROLL) will adopt draft-bormann-6lo-rpl-mesh 

B is a better approach. draft-bormann-6lo-rpl-mesh does not require any updates, changes, notes, or deviations to RFC6437. I originally said that I thought the reasoning behind draft-thubert-6man-flow-label-for-rpl (improved energy efficiency due to reduced header overheads) was sufficient to warrant a second case in which the flow label was not preserved end-to-end. But that was under the assumption that we had to twiddle with the flow label in this way. If we can achieve the same goals without doing so, that is a technically superior solution.

In short, draft-bormann-6lo-rpl-mesh is more efficient (uses fewer bits) than draft-thubert-6man-flow-label-for-rpl. Furthermore, unlike draft-thubert-6man-flow-label-for-rpl it complies with RFC6437 and requires no exceptions.

I understand that there is a sense of time pressure here, but I think that, in the context of standards, expediency is not a good motivation for decision making. I.e., it's better to have a better standard that will stick and become the solid technical basis for decades to come, rather than get something out quick that we'll have to redo. 

Phil