[time-nuts] Need Time Help
attila at kinali.ch
Tue Oct 4 17:34:29 EDT 2016
On Tue, 4 Oct 2016 15:41:58 +1100
Larry Hower <hower at hower.net> wrote:
> Ultimately we want sub-millisecond accuracy.
If you want to go that way, you will have to leave windows as
this operating system does not offer the facilities to get down
to such a low level....Unless you calibrate the whole path by injecting
a time pulse into the signal path like Jim Lux and TvB suggested
With linux you can get systems synchronized to better than 1ms by
using a PTP server in the local network or by directly using PPS.
This should get you in the order of better than 100µs probaly 20-30µs.
BTW: A word of advice against using NTP servers over the internet
for accurate time distribution. I recently set-up two NTP servers
to be used as stratum 2 servers (server A and B). Both synchronize
to the same stratum 1 server (server S), but are at different ISPs
and thus use different paths. NTP on both A and B reports the following
values (current snapshot, values are representative):
Link delay offset jitter
A-S 4.205 0.020 0.081
B-S 2.112 0.039 0.079
A-B 0.606 -0.877 3.192 (as reported by A)
I.e. even though A and B use the same server S as reference, the
time difference between both servers is 800-900µs. I am not sure
where this path asymmetry comes from, but my guess would be on
the connectivity of A (there are two groups of stratum 2 it syncs
to and one of them shows the same ~900µs offset). I also do not
know why the jitter between A and B is so large even though the
delay is pretty low (seems to be a weirdness at a router inbetween).
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
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