[ntp:questions] Query about NTP accuracy
Hal Murray
hal-usenet at ip-64-139-1-69.sjc.megapath.net
Fri May 22 17:22:09 UTC 2009
In article <4a15e001$0$18238$da0feed9 at news.zen.co.uk>,
Andy Yates <andyy1234 at gmail.com> writes:
>Does anybody have any figures that shows the effect on accuracy of an
>NTP v3 client using a stratum 1 server rather than a stratum 2 or 3
>server? It's all in a GE LAN based scenario, commercial stratum 1
>servers connected to GPS and stratum 2 and 3 servers are typically
>dedicated Linux boxes.
>However I'm been pressed to supply an SLA for accuracy. My argument is
>that although you can get your stratum one server to synchronize to
>microseconds of UTP, as soon as the client uses NTP v3 over the LAN,
>even a GE LAN, then the accuracy degrades and putting well designed well
>specified stratum between the boxes is not going to decrease accuracy
>sufficiently to warrant purchasing many stratum one appliances.
What sort of accuracy are you interested in? 1 ms? 10 ms? 100 ms?
How stable is your temperature? (Both the room and the CPU load.)
What is the load on the LAN between the clients and servers?
(Delay is not a problem. Variation in delay is a problem.)
I suggest you measure it. Start with your current system.
Setup a box as a ntpd system and tell it to use several target boxes
as servers and turn on logging. peerstats will tell you the difference
between your local clock and the target system.
--
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