[ntp:questions] Query about NTP accuracy

Hans Jørgen Jakobsen hjj at wheel.dk
Mon May 25 19:49:14 UTC 2009

On Fri, 22 May 2009 23:47:35 GMT, Unruh wrote:
> Note also that it can depend on the network harware. When we ran 100Mb/s
> switches, the delay time was astonishingly regular and repeatable. Now
> that we have switched to Gb  switches it is not. It much worse. There
> seems to be a one way "quantization" It used to be that the round trip
> time from the machines to the ntp stratum 1 source was consistantly
> 140-160usec. Now it varies, with one level still at the 140usec, but
> other round trip times of 280 or even longer (on the same machine).
>  And they seem to be one
> way delays ( the worst kind). Ie, you really need to select the switches
> between your stratum 1 sources and your machines carefully to get the
> best behaviour. 

There could be interrupt coalescing going on in one or more network cards.

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