[time-nuts] Network jitter with NTP

Sarah White kuzetsa at gmail.com
Tue Feb 12 20:41:55 EST 2013


Thanks for posting that. I'm currently doing some testing over wifi
links myself, and found that page very useful. You do a really good job
documenting your experiences with GPS-based NTP refclocks, and I
appreciate all the hard work.

I just wanted to ask though, are you compiling your own NTP now or what?


but then under http://support.ntp.org/people/hart/win/x86/

... most recent seems to be ntp-4.2.7p310

^Basically, you were previously documenting use of dave hart's builds
(overlaid over a meinberg ntp install or otherwise)

Sorry rob, I don't have any experience with powerline adapters, but I'm
treating your experiences (which don't seem to be promising) as a data
point showing that they're no better for timing than using wifi...

I'm getting high & unpredictable jitter with NTP over wifi as well
(compared to cat 6 RJ-45 crossover cable directly between NTP servers)

1-20ms jitter for 5ghz band, 802.11n connection running with bitrate
manually limited to 6mbit/s

5-70ms jitter for the 2.4ghz band, 802.11g connection running with
bitrate auto-negotiation (up to 54mbit/s)

... My best case scenario for NTP jitter is about 0-5ms between a
stratum 1 and a stratum 2 server directly connected via gigabit ethernet
crossover (and the stratum 1 itself with a connected refclock seems to
be at a baseline of 0-1ms most of the time, and rarely higher than 2ms)

Those are just rough estimates based on casual observation, and I
haven't done any long-term measurements yet like David Taylor's work...
I'm "getting there" though it's coming slowly because of my trouble with
learning curve in this area.


P.S. I renamed this post. The title "Possibly off topic - Jitter on
Ethernet over poweradapters" seemed silly.

> Rob,
> It's not quite clear which direction you are measuring.  I take it your
> Meinberg servers are "perfect" in NTP terms, and you are monitoring from
> the house?  Or vice-versa?  Anyway, my first guess is that jitter might
> be not dissimilar to Wi-Fi, in which case my lightly-loaded Wi-Fi
> results might be a starting point:
>  http://www.satsignal.eu/mrtg/performance_ntp_wifi.php
> Note the improvement with Windows-8 and the latest NTP (top graph, PC
> Bergen), and the others are somewhat variable.
> Cheers,
> David

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