Re: Predictable Internet Time

Joe Touch <touch@isi.edu> Tue, 03 January 2017 21:26 UTC

Return-Path: <touch@isi.edu>
X-Original-To: ietf@ietfa.amsl.com
Delivered-To: ietf@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id E2C051296C0 for <ietf@ietfa.amsl.com>; Tue, 3 Jan 2017 13:26:03 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -10
X-Spam-Level:
X-Spam-Status: No, score=-10 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, RCVD_IN_DNSWL_HI=-5, RP_MATCHES_RCVD=-3.1] 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 f1aUhSu5TtX4 for <ietf@ietfa.amsl.com>; Tue, 3 Jan 2017 13:26:02 -0800 (PST)
Received: from boreas.isi.edu (boreas.isi.edu [128.9.160.161]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 8204A12966E for <ietf@ietf.org>; Tue, 3 Jan 2017 13:26:02 -0800 (PST)
Received: from [128.9.160.81] (nib.isi.edu [128.9.160.81]) (authenticated bits=0) by boreas.isi.edu (8.13.8/8.13.8) with ESMTP id v03LPc9T022128 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES128-SHA bits=128 verify=NOT); Tue, 3 Jan 2017 13:25:39 -0800 (PST)
Subject: Re: Predictable Internet Time
To: Tony Finch <dot@dotat.at>
References: <CAMm+LwgfQJ8aG5wB=d3fRbbeje3J9o7Z4_DCuP8DL88ouDeKzw@mail.gmail.com> <504e2cea0d1668c31486b05fec0a967a4446aefe@webmail.weijax.net> <CAMm+Lwi_jU6gjdtdM6a2n_9_89tUvWBNXxnMtSjTEA++h1D4Ew@mail.gmail.com> <e0a43370-751f-808c-3719-9716f9cd57d1@isi.edu> <alpine.DEB.2.11.1701031348430.7102@grey.csi.cam.ac.uk> <f94415b6-d9f7-0a03-cf5b-ce39c109aa71@isi.edu> <1483475689.1348946.836323865.09305276@webmail.messagingengine.com>
From: Joe Touch <touch@isi.edu>
Message-ID: <94226b19-4690-ee8e-526e-04cc54e97b8e@isi.edu>
Date: Tue, 3 Jan 2017 13:25:40 -0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1
MIME-Version: 1.0
In-Reply-To: <1483475689.1348946.836323865.09305276@webmail.messagingengine.com>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
X-ISI-4-43-8-MailScanner: Found to be clean
X-MailScanner-From: touch@isi.edu
Archived-At: <https://mailarchive.ietf.org/arch/msg/ietf/0T9QP7qlYbBSe2QxQ-gZ7d2o4ok>
Cc: Phillip Hallam-Baker <phill@hallambaker.com>, IETF Discussion Mailing List <ietf@ietf.org>
X-BeenThere: ietf@ietf.org
X-Mailman-Version: 2.1.17
Precedence: list
List-Id: IETF-Discussion <ietf.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/ietf>, <mailto:ietf-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/ietf/>
List-Post: <mailto:ietf@ietf.org>
List-Help: <mailto:ietf-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/ietf>, <mailto:ietf-request@ietf.org?subject=subscribe>
X-List-Received-Date: Tue, 03 Jan 2017 21:26:04 -0000


On 1/3/2017 12:34 PM, Tony Finch wrote:
>
> Joe Touch <touch@isi.edu>; wrote:
> > We really need to separate the frames of reference of time - there's no
> > need for smear for internal "seconds since epoch" time.
>
> Well, the problem is that "seconds since the epoch" is not a count of
> UTC seconds,

Correct; it's UTC-(leap seconds since epoch start).

> it is a mapping from broken-down time to a linear time,

Seconds since epoch is as linear as it gets.

> and the mapping is defined in a way that requires 86400 seconds per
> day and does not accommodate leap seconds.

The conversion of epoch seconds to larger units is where the leap
seconds is counted.

A "day" as a unit of time is not exactly 86400 seconds (if it were, we
wouldn't need leap seconds).

> http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_16
>
> Leap smear exists mainly because "seconds since the epoch" does not
> allow for leap seconds.

Seconds since epoch is unambiguous and linear.

It is in the conversion to other representations or aggregations where
leap seconds needs to be considered.

Joe