[ntp:questions] Query about NTP accuracy

David J Taylor david-taylor at blueyonder.not-this-part.nor-this.co.uk.invalid
Fri May 22 06:16:44 UTC 2009


Andy Yates wrote:
> 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.
>
> Thoughts?
>
> Regards
> Andy

Andy, I think your approach is correct - no extra stratum-1 boxes.  As 
Richard implies, the load on the network to the clients is perhaps the 
most important factor in accuracy.

Questions:

- why are you still using NTP v3?  Isn't that rather old now?

- what accuracy do your clients actually need?  Are they Windows PCs or 
some other OS?

Cheers,
David 




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