[ntp:hackers] A stop-gap authenticated time service

Greg Dowd Greg.Dowd at microsemi.com
Wed Nov 11 15:22:55 UTC 2015

Jitter isn't the best metric for analyzing this data if you are looking at performance over time.  Some type of variance metric like tdev is good.  Jitter is more white.  A millisecond of jitter on measurements a day apart is far different than the same measurement 1s apart.  For those who find statistical analysis of the type interesting, maybe we could pull some of these datasets together and see if we can extract some useful conclusions.  The open source ntp does move the Allan intercept around based on jitter and variance.  I tend to not like staying in the pll mode as it steers the clock pretty aggressively in quiet networks and gets trapped in network path changes since it keeps the poll interval smaller.

On Nov 11, 2015 7:09 AM, brian utterback <brian.utterback at oracle.com> wrote:

On 11/11/2015 3:32 AM, Poul-Henning Kamp wrote:
> --------
> In message <20151111065510.GT11550 at localhost>, Miroslav Lichvar writes:
>> What has changed significantly since the old days is the network
>> jitter. It went down by orders of magnitude, so the Allan intercept is
>> much shorter than before and ntpd is too slow now.
> Do you have measurements to back this up, and if so, are they
> representative of the median network paths rather than one particular
> installation ?

I'm with PHK on this. The minimum RTT has fallen and with it the minimum
jitter, but my experience is that jitter across longer network paths has
gone up if anything. I don't have any generally applicable data to back
that up and your mileage may vary, but I haven't seen a decrease of
jitter on my networks.

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