[ntp:questions] Re: time
bg at lysator.liu.se
Tue Nov 29 07:55:31 UTC 2005
"Richard B. Gilbert" <rgilbert88 at comcast.net> writes:
> K wrote:
> >I know about NTP v3 and v4 and use it on some systems. I need a time
> >accuracy of < 1 ms.
> >I know that the linux os is compiled for something like 1 ms precision
> So it can be done. I think that the Motorola GPS has a great deal to
> do with it.
The motorola should carry you down towards 1us, but K was only asking
for a thousand times less accuracy... :-)
> clock would be much less stable. 10 ms is about the best accuracy I
> would expect from a client synchronized to a server that synchronized
> over the internet.
Even with a DSL-line - if its not overloaded - sub 1ms is easily
attained with good internet servers. Looking at a machine with four
external servers, I get see,
/usr/sbin/ntpq -c pe
remote refid st t when poll reach delay offset jitter
LOCAL(0) 188.8.131.52 5 l 25 64 377 0.000 0.000 0.001
xxx .PPS. 1 u 219 256 377 11.476 -0.235 0.779
xxx .PPS. 1 u 102 256 377 17.818 -0.140 75.660
xxx .PPS. 1 u 217 256 377 21.575 0.203 0.235
xxx .PPS. 1 u 192 256 377 20.889 0.385 0.142
This machine usually have two GPS-refclocks and they show no
systematic offsets wrt the Internet servers.
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