[time-nuts] Network jitter with NTP

Rob Kimberley robkimberley at btinternet.com
Wed Feb 13 05:46:47 EST 2013

Sarah, David,

I've changed my Minpoll and Maxpoll settings as suggested by David and now
getting much better results (1 - 2 mS) when settled for the Meinberg Stratum
1 units. I'm also using Meinberg's version of NTP (6.2.6).

I'm still experimenting with settings, but it looks like my original post
regarding the Ethernet over Power adapters might have been a red herring.


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Sarah White
Sent: 13 February 2013 01:42
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] Network jitter with NTP


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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