Re: [Ntp] Leap second draft

On Mon, Apr 1, 2019 at 7:14 PM Watson Ladd <watsonbladd@gmail.com> wrote:

> On Sat, Mar 30, 2019 at 8:02 PM Warner Losh <imp@bsdimp.com> wrote:
> >
> >
> >
> > On Sat, Mar 30, 2019, 6:36 PM Daniel Franke <dfoxfranke@gmail.com>
> wrote:
> >>
> >> On Sat, Mar 30, 2019 at 7:53 PM Kurt Roeckx <kurt@roeckx.be> wrote:
> >> > Anyway, I think we should avoid defining what things like NTP
> >> > time, UTC and TAI is. They should all have external definitions
> >> > we can just point to.
> >>
> >> Where the definitions are normative, sure. But as Steve's infodumps in
> >> this thread rather vividly illustrate, readers need a comprehensible
> >> summary; we can't just incorporate the whole body of relevant
> >> standards by reference and leave it at that. The statements in the
> >> background section aren't normative, and should be accurate but don't
> >> have to be comprehensive. And I won't be worried if, for example, the
> >> quoted definition of an SI second gets superseded a month after the
> >> RFC is published, because the quote isn't there to be authoritative;
> >> it's there to illustrate what such a definition can look like.
> >
> >
> > The current definition doesn't help. A reference to the BIPM with the
> latest definition doc at the time of publication would suffice. The hard
> part is getting the right pointers.
> >
> > It doesn't matter what a SI second is. NTP counts them and exchanges
> that count. They could be anything. People have done GPS times (also SI
> seconds) and UT1 times (solar variable length seconds). They've even done
> Julian Time NTP.. Now obviously these different time scales won't
> interoperate, but they are fine so long as everybody exchanging time agrees
> on the rules for the time scale. That brings us to UTC. It's the odd man
> out. It ticks at a fixed rate, and occasionally has seconds inserted into
> it. UTC is related to TAI by a stepwise function that always increases or
> decreases by 1. This increase or decrease historically has always been
> December or June, but technically could be at the end of any month. UTC is
> synchronized to UT1 every so often based on a set of rules. The current
> rule is that | DUT1 | must remain < .9s so you move it when you think it
> might exceed .9 before the next chance to move it. Other rules are
> possible, but just like leaps at the end of any other month than December
> or June not likely.
>
> I've tried citing the BIPM definitions, but they are specified in
> years, months, days, hours, minutes, seconds, and fraction of second,
> while NTP uses seconds and fraction of seconds. Then there is the
> whole document access issue.
>

The definition of an SI seconds has nothing to do with years, etc.

Warner

> >
> > So, it makes sense to just hit these points, and give pointers to the
> underlying details, which don't matter.
> >
> > Warner
> >
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>
>
> --
> "Man is born free, but everywhere he is in chains".
> --Rousseau.
>