[ntp:questions] Questions about joining pool.ntp.org

unruh unruh at wormhole.physics.ubc.ca
Mon Aug 29 21:41:23 UTC 2011

On 2011-08-29, Harlan Stenn <stenn at ntp.org> wrote:
> GPS can be done very affordably and can offer great time.  There are
> several *potential* pitfalls:
> - It is *possible* for the US Gov't to detune the GPS system (locally or
>   in-general).  Since GPS is now increasingly used for "human safety"
>   things, the costs/risks for doing this have gone up significantly so
>   this risk may now be more of a threat than a reality

At worst this would degrade the time of a gps to a few 100ns, rather
than 10s of ns. 

> - bugs happen, and relying on one of anything can cause a problem.  If
>   you have enough souces of time, ntpd will throw away information from
>   a source (including GPS) that it does not believe.

Or GPS jamming either deliberate (in times of war by an enemy, or a
friend, in times of peace by stupid commercial people accidentally
deplying a system whose consequence is to jam the GPS) .

> There are other potential failure modes as well, but most everything has
> these issues.
> H

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