The problem with THREE GPS receivers, or just about any other clock, is
that it it can too easily degenerate to the two server case. It is well
known that "a man with two clocks can never be certain what time it is."
Four, five, and seven are the magic numbers for a robust configuration.
Most sites will settle for four. The very paranoid or the very rich
might go for seven.
I'm not rich, so I'm using Garmin GPS 18 and Sure Electronics receivers.
Each stratum-1 server has one GPS receiver, plus a number of other servers
including at least three Internet servers, and two local PC servers,
making a reasonably robust configuration.
In the event that I lost both the Internet connection and one GPS
receiver, then I am still confident that the two remaining GPS receivers
will be near enough that a client PC selecting one or the other server to
sync to will still be well enough within time for my purposes. In the
event of GPS going down altogether, we'll have more problems to deal with!
David
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