[ntp:questions] A question abouth the Allan Intercept

Mauro Fiacco Mauro.Fiacco at ipaccess.com
Thu Nov 24 12:51:00 UTC 2005

Hi to All,

I have a question about the Allan Intercept. I understand how it is used
in the NTP code (i.e. tuning the NHPFL) and I also understand it's use
on characterise oscillators (wander-jitter threshold... basically, its

However I do not understand, if the value of CLOCK_ALLAN, used in the
NTP, represents an approximation of the intercept of the oscillator (the
component under the hood) or more generally of the time discipline
system (which includes processor interrupt latencies, network cards
jitter, clock jitter... temperature variations... platform resolution
and precision... more?)

In the first case, to measure it, I would need a (e.g.) frequency counter,
in the second case, I would need a pretty accurate NTP server and
analysing the NTP rawstats to derive the Allan Intercept.

I believe that the Allan Intercept tries to model the time discipline
system not of the oscillator... am I correct?

Thank you,



Mauro Fiacco 

ip.access Ltd                      
URL: www.ipaccess.com  

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