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Re: [Ntp] NTPv5 draft

Kurt Roeckx <kurt@roeckx.be> Tue, 01 December 2020 10:25 UTC

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Date: Tue, 01 Dec 2020 11:25:40 +0100
From: Kurt Roeckx <kurt@roeckx.be>
To: Miroslav Lichvar <mlichvar@redhat.com>
Cc: Dieter Sibold <dsibold.ietf@gmail.com>, ntp@ietf.org
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Subject: Re: [Ntp] NTPv5 draft
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On Tue, Dec 01, 2020 at 11:03:05AM +0100, Miroslav Lichvar wrote:
> On Tue, Dec 01, 2020 at 10:51:22AM +0100, Dieter Sibold wrote:
> > Uncertainty and maximum error are different. The uncertainty interval will
> > always be smaller or equal to the max. error.
> 
> Can you describe an example how would the server determine the
> uncertainty?

When talking about uncertainty, we talk about confidence interval.
We can never be sure what the maximum error is. We typically talk
about an expanded uncertainty of 95%, saying that in 95% of the
cases the error will be smaller than the uncertainty.

The 95% comes from 2 * sigma, which covers 95.45%. And we'll write
that as k=2 in case of a normal distribution. For NTP, in most
cases, it will not be a normal distribution, and you'll need a
different k factor for the 95%.


Kurt

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