David J Taylor wrote:
Richard B. Gilbert wrote:
David J Taylor wrote:
[]
As far as I can recall, the default W32time only sets the clock once
a week, so whilst the initial setting may be within 50msec, the
keeping will almost certainly not be within 50msec. When I used to
use an SNTP client, I believe the same was true, as the setting
could be hours apart. David
According to the Brandolini and Green White Paper I cited, W32Time
tries every 45 minutes until it thinks the clocks are synchronized and
then every eight hours.
If W32Time is not good enough, and it may not be, I did point out the
alternatives. If it works, W32Time is by far the easiest way to do
the job; the software is installed with Windows 2000 or Windows XP,
and the configuration is easy.
The reference implementation's version of SNTP would require that he
build from source, install, and configure. Pre-built versions of NTP
are available for Windows and could be downloaded, installed, and
configured..
Richard,
Thanks for that. According to:
http://www.microsoft.com/technet/prodtechnol/winxppro/maintain/intmgmt/26_xpwts.mspx
the default poll interval is 604800 seconds for PCs in a workgroup, that's
7 days. This article:
http://support.microsoft.com/kb/q216734/
has more information, but I am unsure of its relevancy. It seems that how
the PC is configured for function (workgroup or domain) may affect the
update interval.
50ms in 8 hours would be a clock accuracy of 1.7 part per million - very
good for a PC clock.
A pre-built NTP would be my normal choice and recommendation, but
certainly if W32time does the job well enough at least it's "standard OS"
software.
Cheers,
David
The Brandolin and Green paper I was quoting freely from was talking
about systems in a domain. I'm not sure the paper even mentions workgroups.
A large part of the motivation behind W32Time seems to have been
Kerberos authentication. If the systems using Kerberos are not in
reasonably close synchronization (a minute or two) Kerberos doesn't
work. I believe the limit is adjustable but setting it too high allows
"replay attacks" and other nastiness.
Given the problems that Windows seems to have with losing clock
interrupts under load it would not surprise me if ntpd did not work very
much better than W32Time.
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