[ntp:questions] NTP, no external time source, peering "Undisciplined Local Clocks" ?

Brad Knowles brad at stop.mail-abuse.org
Wed Oct 19 11:36:49 UTC 2005


At 4:19 PM +0200 2005-10-18, Marco Molteni wrote:

>  Can I configure A,B,C to peer with each other in a meshed fashion, so
>  to have each clock influenced by all the others?

	Okay, let's analyze this a bit.  You've got three guys on a 
desert island, and they each have wristwatches.  But no one knows 
whose watch is more accurate.  What time is it and how do you choose?

	The answer is that you either choose arbitrarily, or you can't 
choose.  At least, not with the NTP algorithms.


	The concept of NTP is to have an external source of "The One True 
Time", and to always try to work to get your clock to more closely 
agree with that.  There are plenty of algorithms for doing that, but 
everything operates on the fundamental assumption that everyone has 
the same goal, that of always trying to move closer to "The One True 
Time".

	When you violate that most basic assumption, everything else goes 
out the window.


	I don't think that NTP is the right solution here.

-- 
Brad Knowles, <brad at stop.mail-abuse.org>

"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."

     -- Benjamin Franklin (1706-1790), reply of the Pennsylvania
     Assembly to the Governor, November 11, 1755

   SAGE member since 1995.  See <http://www.sage.org/> for more info.



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