[ntp:questions] Clock and Network Simulator

David L. Mills mills at udel.edu
Wed Jun 30 23:28:28 UTC 2010


Guys,

Mercy me! I lied through my incisors. Upon review, the NTP simulator 
simulates the system interfaces to set, adjust and read the hardware 
system clock, so the actual hardware is not involved. It's been several 
years since I used the simulator and it has been updated since then.

Dave

David L. Mills wrote:

> Bill,
>
> 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.
>
> Dave
>
> unruh wrote:
>
>> 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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>>  
>>
>
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