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Re: [Ntp] Antw: [EXT] Re: New Version Notification for draft-gruessing-ntp-ntpv5-requirements-03.txt

Tony Finch <dot@dotat.at> Tue, 19 October 2021 16:00 UTC

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Date: Tue, 19 Oct 2021 17:00:22 +0100
From: Tony Finch <dot@dotat.at>
To: Warner Losh <imp@bsdimp.com>
cc: Danny Mayer <mayer@pdmconsulting.net>, Ulrich Windl <Ulrich.Windl@rz.uni-regensburg.de>, "ntp@ietf.org" <ntp@ietf.org>, Miroslav Lichvar <mlichvar@redhat.com>, james.ietf@gmail.com, Doug Arnold <doug.arnold@meinberg-usa.com>
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Subject: Re: [Ntp] Antw: [EXT] Re: New Version Notification for draft-gruessing-ntp-ntpv5-requirements-03.txt
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Warner Losh <imp@bsdimp.com> wrote:
>
> But even an 8 bit unsigned field with 0 meaning unknown is a huge
> improvement.

8 bits for DTAI will only last about 100 years.

https://www.ucolick.org/~sla/leapsecs/dutc.html

> Be sure to have this field be well defined near leap seconds though. IIRC,
> the number should increment at the start of the leap second in UTC time,

The leap second tables published by the IERS and NIST, and Bulletin C,
state that the new value of DTAI is valid from 0h UTC after the leap
second.

If you are on a POSIX system it's better to bump DTAI just before the leap
second, because that keeps the date correct. (However if you simply
evaluate the time_t formula in POSIX, that puts a positive leap second
just after midnight instead of just before.)

There is no way to represent the time during a positive leap second with
just a timestamp and DTAI: you also need a leap-in-progress flag.

Tony.
-- 
f.anthony.n.finch  <dot@dotat.at>  https://dotat.at/
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