[ntp:questions] Meinberg software running under Vista/Windows 2008

Chris Albertson albertson.chris at gmail.com
Wed Jul 6 21:03:14 UTC 2011

I think a lot of this happens because people don't understand how NTP
works.  Most people just getting into this assume NTP periodically
looks at the time on some network server then zaps the system clock so
it matches.    That method would have horrible results.

At the most basic level NTP adjusts the local clock's RATE by
comparing the local clock to some reference clock and then doing it
again some longish time later and noting if one clock has gained or
lost relative to the other.     In order to detect small differences
in rates you need to wait perhaps for hours.       The details get
complex but this is exactly the same thing you'd do with an old
mechanical clock, you's set it to match a reference and then to the
next day you look to see it it is running fast or slow then adjust the
rate.  and wait and see the next day.  Eventually you get the rate
nailed" and the drift ends.

NTP tries to optimize this process and to decide on it's own which
reference clocks to use and how often it should check (longer periods,
like 30 minutes give more accurate result but slow response, so it
varies the rate based on condition's.)

Bottom line is that manually jumping the system clock by 120 seconds
is outside of what can happen in the real world baring either a
hardware failure or malicious attack on your system.  A good test is
to unplug the Internet fo r a day and see what happens.  a properly
configured NTP system should continue to run in "Orphan Mode" on an
island network and the switch back over when the Internet is restored.

If you are really worried about loosing track of true UTC time then
buy a GPS receiver or if you are very concerned by three of them from
three different manufacturers  Having multiple GPSes that do not share
common parts is nearly fool proof.  These would serve a reference
clocks for three NTP servers.   Doing this is not quite as "nuts" as
it sounds.   I bet you could set up all three for under $1K if you
used existing computers

Chris Albertson
Redondo Beach, California

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