[ntp:questions] Tiime Sync solution

Brad Knowles brad at stop.mail-abuse.org
Tue May 31 19:04:53 UTC 2005

At 8:16 PM +0200 2005-05-31, Adrian 'Dagurashibanipal' von Bidder wrote:

>>  relatively slow ADSL line, I'm usually down in the low single-digit
>>  *microsecond* region.
>  You sure?

	I was.  I was quite certain that the column displays in ntpq were 
measured in microseconds, but going back to the documentation at 
<http://www.eecis.udel.edu/~mills/ntp/html/ntpq.html>, I see they are 
actually in milliseconds.  My bad.

>  Hmmm. Eric: Scrap the '10ms or better is pure luck' - I see that my
>  server is below 5ms offset, with hand-picked off-site servers, this is
>  over a little used ADSL connection.

	Agreed.  Looking at my stats again, and I see that my estimated 
offset is currently just over 3ms, with a stability of 0.008.

	Pick some good time servers that are nearby, and you should be 
able to fairly easily get down into the single-digit millisecond 
range, even on lower-end hardware with less than ideal networking -- 
such as my several year-old PowerBook G3/400 running MacOS X 10.3.9, 
running on an 802.11b wireless network which is connected to a fairly 
slow ADSL line.

	However, to get down to 1ms or below, you're going to have to do 
a lot of hard work, and the most important parts are choosing the 
right hardware platform, choosing the right OS on which to serve that 
data, and choosing the right refclocks (e.g., a good GPS device which 
is used to discipline a thermally stabilized oscillator).

	With lots of hard work, and some luck in finding used Rubidium 
clocks at reasonable prices, Poul-Henning Kamp was able to put 
together some devices that achieved sub-millisecond accuracy.  But 
that's a lot of hard work.

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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