Alexandre Carrausse wrote:
"Richard B. Gilbert" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
David J Taylor wrote:
Hal Murray wrote:
In article <[EMAIL PROTECTED]>,
"Alexandre Carrausse" <[EMAIL PROTECTED]> writes:
Thanks, the GPS would be an option, but in the very secure site I am
working in, I am afraid I will not even be allowed to install an
antenna.
[]
What is the approx cost of such systems?
Do-it-yourself: Under $100 for a Garmin GPS 18 LVC. You also need
a PC. Old ones are probably OK.
For example ..
http://www.david-taylor.myby.co.uk/ntp/FreeBSD-GPS-PPS.htm
.. including an antenna just poking out of the window. Of course, you
probably can't open the windows either!
David
If his site is really secure, he may have Windows but probably doesn't
have windows!!! His electronic equipment may have to meet the "Tempest"
criteria; e.g. any electromagnetic energy emissions do not contain
recoverable information. Add inner and outer chain link fences topped
with barbed wire, armed guards, and dogs. Your imagination can't be to
vivid!!!! ;-)
It is not fort knox but almost ;-)
No windows and no telecommunication devices are allowed in the computer
room, no gsm, no antenna, no copper.
Thank your for your help. Today I have tested some monitoring tools, and
overall the situation is good.
Our system is 9 minutes below the real time (my wristwatch:-)
Here is how looks our client tcp.conf file file :
server serverA
As suggested, I am thinking about improving it to have
server serverA
server serverB
server serverC
server serverD
server serverE
On serverA, I am thinking about having the following conf
peer serverB
peer serverC
peer serverD
peer serverE
and so on for BCDE.
Does this make sense?
Alex
If you are not allowed ANY external reference, I suppose it's the best
you can do. Your cell phone has time that is correct to within a few
microseconds. Of course it probably only displays hours and minutes but
the rollover of the minute should be within microseconds. From that
you can probably set your watch within a second or so if you have good
reflexes.
Set the correct time on your server(s) and let them run for, say, seven
days. You will need to know the exact time you set and the exact error
seven days later. Knowing how far the servers drifted in seven days,
you should be able to compute a frequency correction in parts per
million. The number you come up with should have an absolute value of
less than 500 and probably will be less than 50. Put this number in
your drift file (or use it in adjtimex()or equivalent) to correct your
freqency. For a check, 500 PPM works out to something like 43.2 seconds
per day. It's hardly state-of-the-art timekeeping but I don't know what
else you can do.
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