[ntp:questions] NTP.ORG MEINBERG KEEP TIME ACCURATE to 10MS
unruh at invalid.ca
Thu Nov 15 07:22:02 UTC 2012
On 2012-11-15, David Taylor <david-taylor at blueyonder.co.uk.invalid> wrote:
> On 14/11/2012 21:40, gbusenberg at yahoo.com wrote:
>> Below ntpq -p from my 10.1.126.202 server which gets time from 10.1.126.204. I see there is a lot of Jitter. Is the offset of 259ms.
>> remote refid st t when poll reach delay offset jitter
>> *10.1.126.204 188.8.131.52 3 u 1006 1024 77 0.043 -259.69 165.850
>> driftfile "C:\Program Files (x86)\NTP\etc\ntp.drift"
>> server 10.1.126.204 iburst minpoll 4
> In which case, there must be something grossly wrong. The jitter I see
> with LAN servers to LAN clients is usually well under a millisecond, and
> on Windows Vista 0.977 milliseconds. Even WAN servers only show 2 - 10
> milliseconds (typically the low end of that range). Offsets are in the
> order of 0.5 milliseconds for LAN servers, and less than 10 milliseconds
> for WAN servers.
> So for a LAN connection to show 259 milliseconds offset and 165
> milliseconds of jitter suggests a problem. Perhaps 10.1.126.204 is
> really not very stable at all? Perhaps, as was suggested, you are tying
> too closely to the off-site server? Perhaps the LAN is saturated? I do
> suggest that you consider a GPS/PPS for one of your local servers (or
> even the PC if one is on 24 x 7 and has a serial port). You could even
> use a box as simple as the Raspberry Pi computer coupled with a GPS with
> the total solution coming to around US $100 and providing within 50
> microseconds accuracy.
Actually more like 2 microseconds accuracy should be possible, unless
the Raspberry Pi's servicing of the GPIO interrupt is really very bad.
> Stick it somewhere on your LAN where there is a view through a window!
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