[ntp:questions] Clock and Network Simulator

Miroslav Lichvar mlichvar at redhat.com
Wed Jun 30 21:53:23 UTC 2010


On Wed, Jun 30, 2010 at 09:43:26PM +0100, David Woolley wrote:
> Miroslav Lichvar wrote:
> 
> >and is using the LOCAL driver, the rest have clocks with 1ppb/s
> >wander. Between all nodes is network delay with exponential
> >distribution and a constant jitter. The simulations are repeated with
> 
> Real world NTP networks don't behave like that, and most of the
> things that annoy people relate to the real world behaviour.  Real
> networks are subject to diurnal and near step changes in frequency.

In clknetsim, each clock frequency and each network connection can be
configured to any combination of noises (uniform, normal, poisson or
exponential distribution), waveforms (pulse, triangle, sine) and data
stored in file (e.g. if you have measured the clock frequency with a
reference clock).

If you can create a clknetsim expression (as described in README)
which you think describes a real world clock, I'll be happy to rerun
the simulations.

>From what I've seen so far, the ratio between jitter in network delay
and clock frequency is by the most important factor, the character of
the noise doesn't seem to matter much. So, during day you only move to
left and right on the x-axis in the plots I have posted, as the ratio
changes.

-- 
Miroslav Lichvar




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