[ntp:questions] Geographical diversity of Stratum 1 servers

Richard B. Gilbert rgilbert88 at comcast.net
Wed Feb 13 14:36:01 UTC 2008

Peter Laws wrote:
> Looking for a reference on geographical diversity of Stratum 1 servers 
> (GPS appliances, in this case).  We have two clocks now (an old Datum 
> TymServ with a Symetricom sticker) and another unknown brand.  We'd like 
> to add a third at a completely different facility a mile or more away.
> What, other than the business continuity angle can I use?  I'm assuming 
> it would be better to have the clocks separated from a GPS perspective, 
> too.
> Cites?

AFAIK geographical diversity does nothing to improve the time.  It does 
add some robustness.  If you are powered from different substations, 
good.  Are the sites far enough apart to avoid being caught in the same 
flood, fire, earthquake, explosion, chemical/biological/radiologcal 
contamination, etc?

There is something called "differential GPS" which can help refine 
position data; e.g. if you have GPS at both a known and an unknown 
location, the difference between readings can be used to refine the 
unknown position.

The GPS computation of location, elevation, and time involves a system 
of four simultaneous equations which can be solved for time, lattitude, 
longitude, and elevation.  Doing an extended "site survey" can refine 
your location and elevation.  The better location data, the better the 
solution for time.

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