Re: [core] Robert Wilton's No Objection on draft-ietf-core-senml-data-ct-05: (with COMMENT)

Carsten Bormann <cabo@tzi.org> Wed, 29 September 2021 06:53 UTC

Return-Path: <cabo@tzi.org>
X-Original-To: core@ietfa.amsl.com
Delivered-To: core@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id A32D73A1B62; Tue, 28 Sep 2021 23:53:56 -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, SPF_HELO_NONE=0.001, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
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 k5G0uNsugrim; Tue, 28 Sep 2021 23:53:53 -0700 (PDT)
Received: from gabriel-smtp.zfn.uni-bremen.de (gabriel-smtp.zfn.uni-bremen.de [IPv6:2001:638:708:32::15]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id E6C643A1B6A; Tue, 28 Sep 2021 23:53:51 -0700 (PDT)
Received: from smtpclient.apple (p548dcf6e.dip0.t-ipconnect.de [84.141.207.110]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by gabriel-smtp.zfn.uni-bremen.de (Postfix) with ESMTPSA id 4HK6Xq5zpJz2xLY; Wed, 29 Sep 2021 08:53:47 +0200 (CEST)
Content-Type: text/plain; charset="utf-8"
Mime-Version: 1.0 (Mac OS X Mail 14.0 \(3654.120.0.1.13\))
From: Carsten Bormann <cabo@tzi.org>
In-Reply-To: <163221352718.31036.11922703653380735485@ietfa.amsl.com>
Date: Wed, 29 Sep 2021 08:53:46 +0200
Cc: The IESG <iesg@ietf.org>, draft-ietf-core-senml-data-ct@ietf.org, core-chairs@ietf.org, core@ietf.org, Jaime Jimenez <jaime@iki.fi>
Content-Transfer-Encoding: quoted-printable
Message-Id: <3AF5E977-6DF0-450B-969B-34D518AC26E3@tzi.org>
References: <163221352718.31036.11922703653380735485@ietfa.amsl.com>
To: Robert Wilton <rwilton@cisco.com>
X-Mailer: Apple Mail (2.3654.120.0.1.13)
Archived-At: <https://mailarchive.ietf.org/arch/msg/core/MDAf12jQNuKqqtcZ0vV4B4YPsf8>
Subject: Re: [core] Robert Wilton's No Objection on draft-ietf-core-senml-data-ct-05: (with COMMENT)
X-BeenThere: core@ietf.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: "Constrained RESTful Environments \(CoRE\) Working Group list" <core.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/core>, <mailto:core-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/core/>
List-Post: <mailto:core@ietf.org>
List-Help: <mailto:core-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/core>, <mailto:core-request@ietf.org?subject=subscribe>
X-List-Received-Date: Wed, 29 Sep 2021 06:53:57 -0000

Hi Rob,

thank you for pointing out this concern.

> ----------------------------------------------------------------------
> COMMENT:
> ----------------------------------------------------------------------
> 
> Thanks for this document.
> 
> I have to confess that I am less convinced of the need to have two ways to
> represent this information, i.e., to also support Content-Format-Strings as
> opposed to always requiring a entry in the CoAP Content-Formats registry.  The
> CoAP Content-Formats registry seems to be of reasonable size and have a lot of
> space available for FCFS allocations which would mean that it should be quite
> easy to extend if required.  However, I'm willing to defer to the authors &
> CORE WG expertise here supporting both ways are needed/useful.

Indeed, we actually have an outstanding project to automatically register a Content-Format number for every one of the couple-thousand media-type registration out there (this is mostly stalled on practical issues around how to ensure this is then done for new registrations as well).

However, a Content-Type is not just a media-type name, but also potentially parameters, and content-codings.
Some media-types have a few parameters that can only take a few values, so it would be possible to register content-format numbers for each combination.

text/plain; charset=utf-8 (Content-Format number 0) is the first example where this is breaking down a bit:
We clearly do not want to register the cross-product of media-type names that happen to have charset parameters with the registered charset names, in particular as UTF-8 is the only reasonable value for an interchange format like SenML that targets long-lived applications.

It then gets ugly quickly with actually variable parameters such as sampling rate, source coding parameters etc.

The cross-product consideration also applies to content-coding — more so as new content-codings (beyond the widely used, but ageing, deflate) are becoming more widely used.
It is also quite likely that a SenML processor wants to add a content-coding that has not been on the original sensor data.

So we think there is no way to ensure that content-format numbers are available for all records in a SenML pack, and we need the flexibility to fall back to a content-format-spec.

Grüße, Carsten