[ntp:questions] Clock and Network Simulator
David L. Mills
mills at udel.edu
Wed Jun 30 22:10:24 UTC 2010
The ntpdsim simulator uses the real system clock, which is modeled as
the Allan variance. However, the server clock is modeled as a
random-walk process computed as the integral of a Gaussian process. The
network is modeled as an exponential distribution, although provisions
have been made to model transients in the form of step changes.
>On 2010-06-30, David Woolley <david at ex.djwhome.demon.invalid> wrote:
>>Miroslav Lichvar wrote:
>>>and is using the LOCAL driver, the rest have clocks with 1ppb/s
>>>wander. Between all nodes is network delay with exponential
>>>distribution and a constant jitter. The simulations are repeated with
>>Real world NTP networks don't behave like that, and most of the things
>>that annoy people relate to the real world behaviour. Real networks are
>>subject to diurnal and near step changes in frequency.
>? It seems you are discussing the behaviour of the clocks, not of the
>network. (the network has no frequency). His simulator works with real
>clocks which have exactly the behaviour you describe. Now it may be that
>the network model is not the best ( random "long" delays in one way trip
>time due to network overload).
>>Dr Mills modelling also has this problem.
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