[ntp:questions] NTP vs chrony comparison (Was: oscillations in ntp clock synchronization)
unruh-spam at physics.ubc.ca
Thu Jan 24 23:33:58 UTC 2008
"David L. Mills" <mills at udel.edu> writes:
>Sure, I'm stubborn as a bull. The laws of physics make me so.
I happen to be a physicist.
>I am dismissing any comparisons between ntpd and crony or any other
>vehicle unless the comparison includes substantially all the scenarios
>that ntpd is designed to work with. The protocol is specifically
That is fair enough. As I have said, these are one set of experiments.
>designed to work over a wide spectrum including lightly loaded LANs and
>highly congested WANs. The choice of parameters, specifically the time
>constant and operating range, was chosen as a compromise to maximize
>accuracy and minimize network loads under typical and extreme conditions.
>As for the SNTP restrictsions, please, please read the draft
>specification, which explains exactly what SNTP should and should not
>do. At the crux of the matter is the impulse response of a cascade of
>intervening servers each with its own idiosyncratic impulse response.
>The NTP impulse response has a controlled risetime and overshoot over a
>wide range of time constants. Each server in the cascade must have the
>same impulse response to avoid instabilities and possible whip effects.
???? If there were a feedback effect-- A synced to B synced to C synced to
A I could see this. I have no idea what these instabilities would be
otherwise unless you did not really want to use the term instability.
>We could have simply specified the transfer function in polynomial form
>(it's in RFC 1305 and das Buch) and told the implementor to use that. A
>student of digital signal processing would know how to use that
>directly. But, we thought there would be folks like you that would not
>believe the principles and do something evil like bring up a pool server
>running openntp or crony and synchronized via a flaky circuit to Indonesia.
Like me? Do you really want to start ad hominem attacks? What evidence do
you have that I wanted to do anything like that? Or is libel and slander
part of your tools of argument?
It would also be useful if you actually gave a reference as to where in the
article you are refering to.
>It is easy to detect that a particular server has or has not the current
>reference implementation. There are a number of features intrinsic to
>the protocol design and others fiendishly crafted to do that, but I'm
>not going to reveal them here.
Ooooooo. And do they include sacrificing goats on some altar at midnight on
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