[ntp:questions] frequency adjusting only

maxime louvel m.louvel at gmail.com
Tue Apr 29 07:21:50 UTC 2008

On Mon, Apr 28, 2008 at 7:14 PM, Unruh <unruh-spam at physics.ubc.ca> wrote:

> hal-usenet at ip-64-139-1-69.sjc.megapath.net (Hal Murray) writes:
> >>Sorry it's actually difficult for me to precise this topic for
> >>confidentiality reason of course and also because I'm an intern and thus
> >>there for a short period. Hence I don't know exactly why myself. This is
> >>just one of the requirement of my project.
> >Keeping a handful of machines synchronized to within 10 microseconds
> >might be possible.  It won't be easy.  It's unlikely to be the cheapest
> >overall solution to some problem.
> >I suggest you tell your boss that he has given you a hard to impossible
> >problem.  You are not likely to get 10 uS by just poking a few magic
> >parameters into your ntp.conf.  Your target is not a reasonable intern
> >project.
> Actually he only wanted 50us from what I recall. And it will depend on the
> state of the switches, of the network cards, of the temp cycling of the
> system, etc. chrony will quite easily achieve 50us. ntp is more difficult,
> a) because it throws away 7/8 of the data (which could of course be
> compensated by just querying more often) and b) throwing away the data one
> it has once been plugged into the feedback loop. (Ie, the system is
> essentially markovian) But even with ntp, I think 50us is possible.
> But all this speculation is a bit pointless. Do the experiment.
> And if you really want to do it properly, get a gps or two and hook it up
> to the machines to measure the actual deviation from true UTC of various
> of
> the machines, including the server. Then you can subtract the two (
> machine
> -server) offsets to see what the relative accuracy is.
> In a situation like this, experiment is always better than theory.
> (Note, I am a theoretical physicists)
I agree with you on this point. The theory here doesn't seem to be of any
help, I'll try as many solution as I can an see which give me the best

I would like to thank everyone for your answers.


> >[That's just my opinion.  I could be way off.]
> >--
> >These are my opinions, not necessarily my employer's.  I hate spam.
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Maxime Louvel
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