Re: [dtn] DTN time and RFC8877

Brian Sipos <BSipos@rkf-eng.com> Fri, 04 December 2020 17:10 UTC

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From: Brian Sipos <BSipos@rkf-eng.com>
To: Carsten Bormann <cabo@tzi.org>, "R. Atkinson" <rja.lists@gmail.com>
CC: "dtn@ietf.org" <dtn@ietf.org>
Thread-Topic: [dtn] DTN time and RFC8877
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Date: Fri, 04 Dec 2020 17:10:01 +0000
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Subject: Re: [dtn] DTN time and RFC8877
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Scott,
I think the current statement is fine, it's just unusual to mix UTC-the-datum with TAI-the-lack-of-leap-seconds.
Because TAI and UTC only differ by a time-varying offset [1] but use the same rate, these two are identical statements:

  1.  "time elapsed since the start of the year 2000 on the Coordinated Universal Time (UTC) scale" which is what BPbis currently states.
  2.  "time elapsed since 32 seconds after the start of the year 2000 on the TAI scale" which accounts for the TAI-UTC leap second difference of 32 on 1 Jan 2000.

In either case, a statement such as the RFC8877 phrasing of "DTN Time is not affected by leap seconds." would add clarity to the situation without affecting the current agreed requirement text.

[1] https://cdf.gsfc.nasa.gov/html/CDFLeapSeconds.txt
________________________________
From: Carsten Bormann <cabo@tzi.org>
Sent: Friday, December 4, 2020 10:40
To: R. Atkinson <rja.lists@gmail.com>
Cc: Brian Sipos <BSipos@rkf-eng.com>; dtn@ietf.org <dtn@ietf.org>
Subject: Re: [dtn] DTN time and RFC8877

On 2020-12-04, at 15:52, R. Atkinson <rja.lists@gmail.com> wrote:
>
> (or specify that they are ignored).

You can’t say just that, because there are two ways to handle “ignoring” leap seconds, and when you say they are “ignored”, you don’t say which one.

(One way of “ignoring" leap seconds is to stay in TAI, which has no concept of leap seconds.
The other way is actually being cognizant of them and doing work to “ignore” them, i.e., reset the clock after each of them.  This is what UTC does to be able to “ignore” leap seconds.)

Grüße, Carsten