[ntp:questions] Query about NTP accuracy

Mike K Smith mks-usenet at dsl.pipex.com
Tue Jun 2 13:40:43 UTC 2009


On 2 June, 14:31, Brian Utterback <brian.utterb... at sun.com> wrote:
> David Woolley wrote:
> > smithmi... at googlemail.com wrote:
>
> >> In the case below, will server 3 be treated as a falseticker because
> >> its offset lies outside the dispersion interval of the other two
> >> servers even though there is some intersection between its dispersion
> >> and that of server 2.
>
> > That's basically why I won't be convinced by the four server argument
> > until I've checked the actual code.  I seem to remember that there is an
> > additional constraint, namely that the actual measurement must fall
> > within the intersection.
>
> >> 1
> >>           |--------+--------|
> >> 2
> >>               |----------+----------|
> >> 3                              |------------+------------|
>
> It's the other way around. The interval is expanded to include the
> mid-points. So, even though the overlap between server 2 and 3 is that
> small section, the interval actually used must include their
> mid-points (i.e. their offsets) so the interval used in the downstream
> calculations is the offset of server 2 through the offset of server 3

So the downstream servers reject server 1 as a falseticker as its
offset falls outside that interval?
They are then unable to select either of server 2 or server 3 as the
synchronisation peer since the offset of each is at the extreme end of
the intersection interval?





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