Re: Predictable Internet Time

Phillip Hallam-Baker <phill@hallambaker.com> Tue, 03 January 2017 17:42 UTC

Return-Path: <hallam@gmail.com>
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 E54E1129404 for <ietf@ietfa.amsl.com>; Tue, 3 Jan 2017 09:42:46 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.897
X-Spam-Level:
X-Spam-Status: No, score=-1.897 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, FREEMAIL_FORGED_FROMDOMAIN=0.001, FREEMAIL_FROM=0.001, HEADER_FROM_DIFFERENT_DOMAINS=0.001, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (2048-bit key) header.d=gmail.com
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 gD1ykvrh65H1 for <ietf@ietfa.amsl.com>; Tue, 3 Jan 2017 09:42:45 -0800 (PST)
Received: from mail-wj0-x230.google.com (mail-wj0-x230.google.com [IPv6:2a00:1450:400c:c01::230]) (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 B9A2E129993 for <ietf@ietf.org>; Tue, 3 Jan 2017 09:42:44 -0800 (PST)
Received: by mail-wj0-x230.google.com with SMTP id tq7so213572661wjb.0 for <ietf@ietf.org>; Tue, 03 Jan 2017 09:42:44 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:sender:in-reply-to:references:from:date:message-id :subject:to:cc; bh=xAX6d0LnrGFWfnEJdJHICxuj8xFlC+Iel3JRWf+DyPw=; b=Qvx+WGoDhSoJf9E0qTf95x3Io0PQgsqGWudDqdUbw0RysJpHOsCQNv/1rq2WFA9dUN HZwj2OjpygKxFFe2zLCbZGmJUiFL2rZEvqx+oTPKPjLzcAB43SZuoszjPR9v2b57TFyk KU9sGV4q0LhnhTm61ahMVbgBM9OaYU352Hd7HNhDySlOvPamSLqW563bTcWm/qaPZ6vE hBs/9PVP0rSGXoYND/rREUXhCf61mqUb5hahAGW30QImBCyFTWp1dqJClU1lU6jSOgkL St+vlgfRV9VAJq+JHzOIdLJLTM8ItcDdATrDdnhuLdec2XEEYH1TuMEbUyxxYftWQS+m FDLA==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:sender:in-reply-to:references:from :date:message-id:subject:to:cc; bh=xAX6d0LnrGFWfnEJdJHICxuj8xFlC+Iel3JRWf+DyPw=; b=bbJ5sYl/HfkaZnHziM2ratZPK1HelFmQkOSImTdubJHaQbGcDfBb0kDuTmI9CCIk20 ca05TpduHwSXHADgerCm/mEllDa0tTDGy3s/35SJSZZHKNis5CkOF2loB7gBfuuFCpVm Y2ePT9dMLuQiwxCh4vfspJZ1h50N6OykiJL+Gxp7aK4/vZMNXra8uf9AwjMkExT9/vSc dWAJxWRX5sDSeBxKkD1vpolrV7tAjSQ42xBA+eP3PWRa9Jyndv7J3UlhfzYGL8OTvSnM G0p9fUrdbP8Gy7lhyudoJyR46rK5WrQu/fL9F8ksurOijEuxKY04tDejpPnGnzBqmlsH Wpfg==
X-Gm-Message-State: AIkVDXKm3CYtsdZ+IWtgElc/fWiFSPVRDFc4a8C2a/ssMKF64NZ6MEfnwy6zaLgL54d3sxc2ZXJWcIni7hTFGQ==
X-Received: by 10.194.14.196 with SMTP id r4mr66319065wjc.54.1483465363159; Tue, 03 Jan 2017 09:42:43 -0800 (PST)
MIME-Version: 1.0
Sender: hallam@gmail.com
Received: by 10.194.83.101 with HTTP; Tue, 3 Jan 2017 09:42:42 -0800 (PST)
In-Reply-To: <0bbfcd7c-11a7-0e7f-56f7-eee959b7a947@gmail.com>
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> <0bbfcd7c-11a7-0e7f-56f7-eee959b7a947@gmail.com>
From: Phillip Hallam-Baker <phill@hallambaker.com>
Date: Tue, 3 Jan 2017 12:42:42 -0500
X-Google-Sender-Auth: Y2RB8cZgIjnAZyAHGc9--HPZSjI
Message-ID: <CAMm+Lwi0sQyRE_2dMCkwTk7xTiK2JbHhHSPYMkdG2FeBw_6CNA@mail.gmail.com>
Subject: Re: Predictable Internet Time
To: Stewart Bryant <stewart.bryant@gmail.com>
Content-Type: multipart/alternative; boundary=047d7b66fd9d01fffb05453432af
Archived-At: <https://mailarchive.ietf.org/arch/msg/ietf/x3XnQIwHcFY_z8mshNZHHt4X-30>
Cc: 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 17:42:47 -0000

Agree 100%

Hence my proposal for supporting multiple time scales for different
purposes:


1) TAI: Use this and only this for any and all purposes that involve
recording the time an event took place. Including forensic and scientific
purposes.

2) PIT: Use this for inter-machine communications. It may also be used to
present TAI in a human readable form because the mapping from TAI to PIT is
fixed.

3) Local Time Zones: For human display purposes


>From the conversation it seems that the best definition for PIT would be

PIT = TAI  + Smear ( Lag (UTC, 50 years ))



On Tue, Jan 3, 2017 at 12:27 PM, Stewart Bryant <stewart.bryant@gmail.com>;
wrote:

>
> Smearing worries me.
>
> If you have an application where tiny fractions of a second make no
> difference, then
> a slow smear is a good approximation to no leap second.
>
> However, there are some highly accurate implementations of NTP, and some
> highly
> sensitive applications that use it, and having a long term interval error,
> which is what
> happens during a smear, is harmful to those applications.
>
> It seems to me that it might be better to freeze NTP on the current leap
> second
> offset. Provide the current leap second offset to the application as a
> parameter
> and let the application deal with it as it chooses.
>
> - Stewart
>
>
> On 03/01/2017 14:08, Tony Finch wrote:
>
>> Joe Touch <touch@isi.edu>; wrote:
>>
>>> Smearing leads to differing interpretations of elapsed time for two
>>> reasons:
>>>
>>> 1) smearing isn't unambiguously specified
>>> 2) smearing doesn't match the clock standards set by the ITU (who
>>> defines UTC)
>>>
>> Since leap smear is becoming more popular, it would be sensible to try to
>> get a consensus on the best way to do it if you do it. Clearly
>> organizations that do leap smear think (2) leap seconds are too much
>> trouble so it's better to diverge from official time in a controlled
>> manner.
>>
>> To clear up (1) there are a few technical choices on which people seem to
>> be working towards some kind of agreement...
>>
>> * If you centre the smear period over the leap second, your maximum error
>>    from UTC is 0.5s, which seems to be preferable to starting or ending
>> the
>>    smear period on the leap second
>>
>> * Linear smear works better than sigmoid smear, since it minimizes the
>>    rate divergence for a given smear period, and NTP's algorithms react
>>    better
>>
>> * Longer smear periods are better, because they give NTP more time to
>>    react to the rate change, and they minimize the rate difference
>>
>> It looks to me like a 24h leap smear from 12:00 UTC before the leap to
>> 12:00 UTC after the leap has a good chance of becoming more popular than
>> other leap smear models.
>>
>> Tony.
>>
>
>