[ntp:questions] LAN synch question

Steve Kostecke kostecke at ntp.org
Thu Sep 11 21:05:35 UTC 2008


On 2008-09-11, rochertov at gmail.com <rochertov at gmail.com> wrote:

> I am conducting research with TDMA on a wired emulated network. I want
> all of the machines in the experiment to have the same time.

[snip]

> Additionally, I don't care about the correctness of the clock compared
> to global time.

This is a common misunderstanding of NTP.

NTP synchronizes clocks to a common time-base across a network.

UTC is ubiquitous and easily acquired via a network or a radio clock
(e.g. a sub $70 timing GPS). It is the time-base customarily used by
NTP. You may, of course, substitute your own time-base.

> I am curious what is he best way to set this up. I was thinking to
> have on dedicated ntp server that operated in broadcast mode, and
> also configure the clients to poll it every 16 seconds. Additionally,
> there are two planes: experimental and control. Since the experimental
> traffic is separated from the control traffic, there should be little
> variance in delay for ntp packets.

You need to discipline the clock in your reference server so that it is
stable (i.e. each tick has exactly the same duration). Otherwise the
client systems will be chasing a moving target and you will be hard
pressed to meet your stated offset requirement of 100us.

-- 
Steve Kostecke <kostecke at ntp.org>
NTP Public Services Project - http://support.ntp.org/




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