[ntp:questions] Bizzare half second disagreement between ntp hosts

Unruh unruh-spam at physics.ubc.ca
Tue Jan 1 00:26:13 UTC 2008

I have a very weird situation. I am running a GPS PPS (Garmin GPS18LVM)
with a few machines as a backup/initialization. 

Sudeenly for about half and hour, my GPS failed for some reason ( still do
not know what was wrong since it had come back on air by the time I noticed
something wrong). Every hour I run a ntpq -p just to check that my gps is
on air. I got this report.

     remote           refid      st t when poll reach   delay   offset jitter
============================================================================ ==
xtick.usask.ca   .GPS.            1 u 1003 1024  377   44.954    0.213 480.149
+sanrail.com      2 u  993 1024  377    1.486  -479.03 479.917
+raptor.tera-byt    2 u  322 1024  377   17.295  -480.35 0.766
*zeus.yocum.org    2 u  390 1024  377   70.415  -481.02 1.230
 SHM(0)          .PPS.            0 l 1415   16    0    0.000   -0.002 0.001

Now I believe the tick.usask.ca result, since all of the machines which use
mine as a source suddenly noticed a .48 second jump when my GPS failed. But
why in the world would three systems all suddenly be out by .48 sec? 
Doing a peers on them, one has a GPS as its source, one a .WWVB. and one an
.ACTS. Why should all three suddenly be out by half a second?

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