[ntp:questions] NTP absolute accuracy?

David J Taylor david-taylor at blueyonder.not-this-bit.nor-this.co.uk.invalid
Sun Nov 1 07:18:28 UTC 2009


"Unruh" <> wrote in message news:rl5Hm.50089$Db2.40967 at edtnps83...
[]
> As I tried to emphasise, if the round trip is not symmetric, then 
> neither ntp not
> chrony can compensate for that lack of symmetry, and the absolute time 
> will be
> out. If occasionally it has an assymetric round trip, then ntp will 
> probably
> elimate it, and chrony may or may not, depending on how you set up 
> chrony, but
> typically chrony will be more sensitive to that asymmetry.
> Eb, say on exactly every 5th query, an extra .3ms is added to the return 
> trip, and
> lets say that the minimum round trip is .15ms plus or minus .1 ntp will 
> always
> throw out those fifth cases. but will have an error around .05 ms. 
> chrony will
> not, and without them would have an error of .02ms but with them would 
> have an
> error of about .05ms, just as would ntp. Ie, in this case the chrony 
> advantage
> would be more or less erased by those asymmetric round trips.
>
> There is no definative answer.
> It depends on the situation.

Many thanks - that's clearer.

David 




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