On Sep 9, 2013, at 10:02 PM, David Taylor wrote: > On 09/09/2013 23:10, E-Mail Sent to this address will be added to the > BlackLists wrote: >> Jared Watkins wrote: >>> ... >>> In pretty much all cases though when graphing the offsets >>> I'm seeing sine wave patterns. >>> The period is usually about 10 hours and the amplitude >>> can vary by +-25ms for the 'closer' ones and as much >>> as +-100ms for the more distant ones. >>> ... >>> Any ideas on what would cause it? >> >> Temperature? > > Plotting with MRTG might show that - I can see peaks in the Winter when the > heating turns on in the morning. >
I've had a chance to try a few things since I posted this.. I don't think it's temperature. I have plots of that and it's very stable. I think it's a combination of network latency to the upstream peer combined with varying system jitter. I plotted the jitter and saw that it's a sawtooth pattern that varies over the same interval with peaks and valleys lining up with the offset swings. On 'good' hosts it fluctuates between about .5 and a max of 1ms and on bad hosts it's more like 1-4ms of jitter. A really good host had jitter swings of between about .2 to .5 ms and a corresponding offset swing of about +- 8ms. I don't know for certain this is cause and effect but I've not been able to find anything else. -J _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
