[ntp:questions] Re: Fingerprinting hosts by clock skew

mayer at gis.net mayer at gis.net
Sun Mar 6 20:16:38 UTC 2005


John Ackermann N8UR wrote:
> Mxsmanic wrote:
>
> >David L. Mills writes:
> >
> >
> >
> >>I should add to that proposal using NTP frequency to
> >>reveal outdoor temperature if the IT staff would put the computer
> >>outside the building in a doghouse on the roof.
> >>
> >>
> >
> >That's like saying that you can measure accelerations in a fighter
jet
> >by leaving the flight computers unattached and measuring the error
rates
> >they experience as they bang around the fuselage.  It's much easier
to
> >put in accelerometers that the computers can read.  And in this case
it
> >might be a lot more practical to just put a thermometer outside and
keep
> >the computer indoors, even though it would take NTP out of the
> >weather-prediction loop.
> >
> >
>
> I'm guessing Dave was joking in his comments, but the frequency vs.
temp
> curve actually can provide a very accurate thermometer.  HP
manufactured
> one along those lines, with a crystal and oscillator contained in the

> sensor and a frequency meter for the display, that had something like

> 0.001 degree C resolution.  And, those of us who play with frequency
> standards often see temperature related fluctuations even in units
that
> have ovens or double ovens.
>
> Another example is an antenna that I use to receive Loran-C
> transmissions for frequency monitoring.  The antenna is up on my roof

> and contains an FET preamplifier.  I've seen an 80 nanosecond diurnal

> phase shift as the antenna warms up and cools down each day.
>
> John


No, this isn't as fanciful as it sounds. Physics experiments measure
things using all kinds of indirect methods like this to get results as
accurate as possible. How do you think they measure things like a few
degrees Kelvin? It's not your everyday thermometer. The
experimentalists
have to come up with all sorts of methods utilizing known effects in
order to do this.

Danny




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