Miroslav Lichvar wrote:
On Tue, Jan 18, 2011 at 09:48:08PM +0000, David Woolley wrote:
That was my point. Unruh's main issue is that, on modern LANs, the
dominant low frequency error is in the local clock, rather than the
measurements.
That's the theory behind NTP.
I should probably have said mid frequency. The specific problem with
NTP that he complains about is that it sets it loop time constant too
long (or more precisely fails to adapt it down fast enough) such that
mid-frequency clock errors are removed from the error measurement by the
loop filter and the time drifts badly in response to them. This is the
behaviour you would want in respect of mid-frequency network delay
variations, e.g. the sort of problem I was describing where the delay
jumps up for a couple of ours around 1pm when everyone is browsing
during their lunch break.
(As the temperature variations (and network delay variations) often have
squarish shapes, they actually have a broad spectrum.)
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