[ntp:questions] help in evaluating NTP servers performance

Danny Mayer mayer at ntp.isc.org
Tue May 15 03:32:52 UTC 2007


Dennis Hilberg Jr wrote:
>> Now, I know that performance is quite a subjective matter. All we need
>> is to keep lan servers and clients in sync, with most timestamps
>> having 1 sec resolution. Currently I see offsets of about +/- 10ms on
>> ours main NTP servers, with occasional peaks, so let's say performance
>> is "good enough" for us.
>>
>> But sometimes I wonder how good is that on an absolute scale, just out
>> of curiosity.

There is no such thing as an absolute scale. As Einstein said, all
things are relative.

 And of course if it can be somehow improved. I've
>> plotted graphs from peerstats of the three main servers (ntp1, ntp2,
>> ntp3), and what really surprises me is that the three servers show
>> quite different patterns (hardware _is_ quite different tho).
>>

That's to be expected. Clocks in computers are the cheapest that the
manufacturers can buy and they don't worry to much about consistency.

> 
> I got the graphs finalized about a month ago, and after watching the plots I 
> was slightly disappointed at their performance initially.  Based on what I 
> read I assumed millisecond to sub-millisecond accuracy, consistently. 
> However, both server's internet connections are asymmetric, the room's 
> temperature can range ± 5°F or more throughout the day, both run a Linux OS, 
> and are PC based.  From what I've read/heard that's about as good as it's 
> going to get, considering the environment.
> 

Millisecond range is about the best you can do. Even temperature
variations of your computer affect this. If you need better accuracy you
need to implement other strategies and you will certainly never get it
over a network where you are subject to things like network congestion,
dropped packets, bandwidth, etc.

Danny



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