On 2007-03-01, edouard funke wrote:

> I am not trying to have the exact time on clients but rather, that all
> clients have the same time.

NTP synchronizes a group of computer clocks to a common timebase; the
most commonly used timebase is UTC traceable to NIST.

A good timebase allows you to achieve better synchronization between
systems because the clients will not be chasing a drifing master clock.
An accurate timebase also ensures that one second is consistantly one
second.

> I must run NTP daemon on Windows Server 2003 SP1 and it almost sure
> that, in the end, NTP servers wont be able to have internet connection
> or even GPS

Clock stability is affected by many interrelated factors including the
host OS and application software, hardware, system load, and ambient
temperature. Some combinations of factors produce better results than
others.

One important question you need to answer is what clock accuracy,
precision, and stability, are needed for your application. Without
a clear set of requirements you won't have a valid metric to use in
evaluating the test results.

Your tests should include running ntpd with the Windows Server in its
production configuration so that you can determine if that server will
fulfill your requirements.

--
Steve Kostecke
NTP Public Services Project - http://ntp.isc.org/

edouard funke wrote:
> Hi,
>
> I am running some tests on the NTP protocol for my company : I need to
> achieve (if possible) in LAN a precision (for clients) of about 1
> millisecond (or less :-))

To get that kind of precision you need to have the system directly
connected to a refclock. You'll rarely get that kind of precision over a
network.

>
> 1. the following properties are studied :
>
> - the time for a client to "calibrate" its clock
> o with/without iburst mode
> o with/without drift file
> o with fixed drift

There is no such think.

> o with different values for max polling
>

It will calibrate without ever reaching maxpoll.

> - the maximum precision achievable for clients :
> o with different values for max polling

You will get surprising results if you change maxpoll. The algorithms
are designed to give you the best results without touching maxpoll. You
really need to understand the engineering and algorithms used before you
can draw any conclusions on the best value for maxpoll.

> o with huff n'puff filter

Are you expecting asymmetric paths?

> o with all clients in « peer » mode or at least some of them
>
> the NTP server clock reference will be :
> o undisciplined local clock

Then forget precision here.

> o internet stratum 1 or 2
> o GPS (i have a meinberg lantime M300 and PCI card + GPS receiver on loan)
>
> I am trying to know here which configuration parameters can improve
> the "calibration" speed and maximum precision of clients clock.
> I am not trying to have the exact time on clients but rather, that all
> clients have the same time.
>
You are better of reading Dave's research reports on how all of this
works and his analyses of the data.

> I must run NTP daemon on Windows Server 2003 SP1 and it almost sure
> that, in the end, NTP servers wont be able to have internet connection
> or even GPS : they are included in tests because i want to determine
> the impact of the server precision on the client precision.
>

Well in such a case your server has no precision since it's not
connected to anything and is just drifting.

> For the GPS, i know there is some hardware solution that can run in
> free-run mode after 24h calibration (meinberg).
>
> I am sure it is a commun problem but i couldn't find any good reports
> on it : if you have some that might interest me, that would be great
> :-))
>

Did you try http://www.eecis.udel.edu/~mills/ntp.html

> 2. I just checked the ntpd 4.2.4 changelog : is the windows multimedia
> timer enabled by default ? Where can i find some informations on it ?
>

You need to add -M to the command line or the service to enable it. It's
not enabled by default.

Danny
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Steve Kostecke wrote:

> Your tests should include running ntpd with the Windows Server in its
> production configuration so that you can determine if that server will
> fulfill your requirements.
>

And environment of course, since things like air conditioning,
temperature, diurnal variations affect the clock.

Danny
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