[ntp:questions] Query about NTP accuracy

Unruh unruh-spam at physics.ubc.ca
Fri May 22 18:43:06 UTC 2009

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.

>The reasons is that I would rather scale by adding strata - its a very
>big data center with thousands of clients and has several "zones" that
>are isolated. However some opinion is suggesting we run IRIG-B between
>the GPS receiver and a bunch of stratum 1 servers and clients access
>these directly. Much more expensive and any increase in accuracy from a
>client experience may be negligible.

>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.

I think you need some specifications. What accuracy do you really need?
Without that you are simply wasting your, and everyones time and money.
 Direct GPS connection can give you
1 usec. Lan connection to those can give you 20usec average. Then each
stratum will loose about 20-50 usec (my experience). Do you need better than msec



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