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From: ast@cs.vu.nl (Andy Tanenbaum)
Newsgroups: comp.os.research
Subject: Re: Keeping Time Synchronous in a Network
Message-ID: <3187@sdcsvax.UCSD.EDU>
Date: Sun, 17-May-87 09:48:42 EDT
Article-I.D.: sdcsvax.3187
Posted: Sun May 17 09:48:42 1987
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To get the time truly synchronized on a network of machines hundreds of
miles apart, you might consider WWV.  This is a radio station run by the
U.S. Federal Government that broadcasts the time accurately to the microsecond
range.  Special receivers are available for it.  If you really want to be
picky, you should correct for the propagation time from the transmitter
to the receiver, since radio waves only travel 1 foot per nanosecond.

Another thing you might do is check with your local radio astronomers.
They have been doing long-baseline interferometry for years, where long
baseline in this case means roughly the diameter of the earth.  This work
requires very accurate time synchronization, and it is possible they have
published papers on how they do it.  

Andy Tanenbaum (ast@cs.vu.nl)

[ Hmm.  How often would you sample the time?  Isn't the time broadcast only ]
[ every few seconds?  What about clock drift between samples?  --DL         ]