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Re: [Ntp] Antw: [EXT] Re: NTPv5 draft

Miroslav Lichvar <mlichvar@redhat.com> Tue, 01 December 2020 08:45 UTC

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Date: Tue, 01 Dec 2020 09:44:48 +0100
From: Miroslav Lichvar <mlichvar@redhat.com>
To: Ulrich Windl <Ulrich.Windl@rz.uni-regensburg.de>
Cc: Steven Sommars <stevesommarsntp@gmail.com>, kurt@roeckx.be, "ntp@ietf.org" <ntp@ietf.org>, Dieter Sibold <dsibold.ietf@gmail.com>
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Subject: Re: [Ntp] Antw: [EXT] Re: NTPv5 draft
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On Tue, Dec 01, 2020 at 09:30:35AM +0100, Ulrich Windl wrote:
> >>> Steven Sommars <stevesommarsntp@gmail.com> schrieb am 30.11.2020 um 21:32 in
> Nachricht
> <CAD4huA79u3NkR8LS96Gqgs58mJguoN7=p=CJnitzgh_RzNWCVg@mail.gmail.com>:
> > Agree, these fields could use better descriptions or (better) replacement.
> > 
> > One manufacturer (LeoNTP) lowers precision to indicate reduced accuracy and
> > claims to obey the NTP specification.
> 
> Actually if you consider precision to be a "runtime value" (as opposed to a "design value") it's obvious that it is actually variable. However the  overhead to update the value was considered too heavy in NTP design, I guess.

I think it depends on the clock. Normally, the precision of the clock
should be constant. If it's a CPU with variable frequency, for
timekeeping performance it is better to set the frequency to a
constant value.

> > Using NTP short format the smallest non-zero root dispersion is 15
> > microseconds.  One can argue for finer granularity
> 
> Not just there: stability (clk_wander) could also need more digits. clk_jitter is another candidate (it looks like a constant here for GPS). Maybe more. Some are heritage of microsecond resolution of NTPv3.

Those values are provided only in the monitoring protocol.

-- 
Miroslav Lichvar

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