"Michael J. Tubby B.Sc. (Hons) G8TIC" wrote:
> NTP is indeed a good solution. On unix the program is run as a service and
> called 'ntpd' or 'xntpd' for Windows users, Windows-2000 and Windows-XP
> have the client-only side of NTP built in to the operating system, M$ don't
> publicise this though.
>
> So, if you have an always on connection (xDSL or whatever) then you can
> configure NTP on your 2000/XP box as follows:
> Don't run NTP from a dialup account unless you want to remain online
> forever...
I can't talk too much for Microsoft Windoze software, but under Unix at
least it is quite possible to arrange the ntp software to either:
1) Get and set the time when you dial up only. This has the slight (but
perhaps not significant) side effect that it makes an immediate and
abrupt change to the computer's clock, rather than a very gradual change
taking into account the calculated drift in your clock. (For example,
ntp has calculated my clock drifts at
2) Do it occasionally (via cron) whether or not you intend to dial up.
This again makes an abrupt change.
3) Do it via the xntpd deamon. This option is normally the prefered one,
as it makes small gradual changes (it skews the clock), rather than an
abrupt change now and again.
I have a dialup account that I pay a flat fee for. I keep the machine
logged in for a large part of the day, hence I use option 3, but I did
before use option 1 with no problems - although I only did this to keep
the clock 'reasonably' accurate, not for a specific purpose where I
needed it sub-second accurarcy.
With brain-dead Windoze, it might not be possible to have this
flexability, but I would not dismiss the use of NTP even with a dialup
account. Certainly on Unix systems it would be possible to use without
remaining on all the time.
The theoretical accuracy of NTP is somwhere between 200 and 300 ps (232
I think), but you wont get that accuracy with current network
technology. However, use of option 3 would be better than 1 or 2.
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Dr. David Kirkby,
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