[time-nuts] Network jitter with NTP
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.
> 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:
> Note the improvement with Windows-8 and the latest NTP (top graph, PC
> Bergen), and the others are somewhat variable.
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