[ntp:questions] Problem with system clock refresh
David J Taylor
david-taylor at blueyonder.not-this-bit.nor-this-part.co.uk.invalid
Tue Nov 24 09:27:11 UTC 2009
"JuanFran" <juanfranciscojara at gmail.com> wrote in message
news:6a4e421a-318b-4fa1-9105-6ef77a861ec8 at p19g2000vbq.googlegroups.com...
> Hi! My system should be accurate to within approximately 10
> milliseconds .I think forcing upgrade all computers in my LAN at the
> beginning should be enough. Thank you very much for the anwser!
Be aware that the timing resolution on Windows is in the order of 10
milliseconds, so you are asking a lot. Having a local stratum-1 server
(GPS-driven), and using a LAN polling interval of 64 seconds (or even 16
seconds - maxpoll 4), this should /just/ be possible with Windows XP in a
reasonably temperature controlled environment, and with no highly variable
CPU loads or other factors which induce timing changes. A better way
which two of us have suggested might be to distribute an RS-232-level NMEA
and PPS signal to /all/ the PCs (hope they have serial ports!) and run
them /all/ as stratum-1 NTP devices.
Be aware that PC clocks can easily have an error of 100 parts per million
(ppm) - that's about 8 seconds per day, so a 10 millisecond error could
build up in about a minute and a half. Syncing once at the beginning is
not enough. NTP allows for PC clock errors five times that - up to 500
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