[ntp:questions] have you seen this before, 3 ms jumps every 6 hours

RAK306 rkellog1 at twcny.rr.com
Sun Oct 29 22:23:10 UTC 2006

I'm seeing some funny behavior with NTP.

My setup:  I have an IRIG card feeding time source to a Symmetricon XLi time 
& frequency system box.  The XLi is intended to be the NTP server for the 
rest of my servers.

The IRIG card is in one of the servers running Linux.  As a test I had this 
server use the XLi as the NTP server, and they in a small program on the 
Linux box I compared the system time to the time on the IRIG card, to see 
how close the NTP can get to the IRIG reference.

What I saw was very good performance of generally less than 1 ms match, 
however, at approximately 6 hour intervals, there was a 3 ms jump lasting 
about 10 minutes.

I have a plot at  http://home.twcny.rr.com/rkellog1/ntp5.jpg

Does anyone have an explanation for this behavior?

In this setup, the XLi is directly connected to the Linux server, and no one 
else is logged onto this isolated server.

Thanks in advance.


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