[6164] in RedHat Linux List
Re: computer clock error
daemon@ATHENA.MIT.EDU (Piete Brooks)
Tue Nov 26 04:28:26 1996
To: redhat-list@redhat.com
In-reply-to: Your message of Mon, 25 Nov 1996 23:22:01 -0800.
<Pine.LNX.3.95.961125232101.707D-100000@inspire.olympus.net>
Date: Tue, 26 Nov 1996 09:25:06 +0000
From: Piete Brooks <Piete.Brooks@cl.cam.ac.uk>
Resent-From: redhat-list@redhat.com
Reply-To: redhat-list@redhat.com
>> Why not ? I have over 200 machines which sync to a couple of US atomic
clocks
>> every 64 seconds ...
>
>> You don't mention whether you are internet connected.
>> If you are, my preferred package is NTP. Ask your ISP for their provision.
>
> How do you corrrect for the amount of time it takes the signal to get
> to you?
In normal mode, NTP assumes that the paths out and back are symmetric, and
allocates half the Round Trip Time to getting to the remote system, and half
the time to get back. It does lots of stats on the data (weighting low RTT
packets more than high RTT, as the max absolute error is reduced) and watches
multiple clocks to look for "false tickers".
With Multicast, as I said, the accuracy is somewhat less, as the RTT/2 value
is calculated when the clock is first seen, before entering "listen only" mode.
--
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