[ntp:questions] Query about NTP accuracy

Brian Utterback brian.utterback at sun.com
Tue Jun 2 13:31:12 UTC 2009


David Woolley wrote:
> smithmikek at googlemail.com wrote:
> 
>> In the case below, will server 3 be treated as a falseticker because
>> its offset lies outside the dispersion interval of the other two
>> servers even though there is some intersection between its dispersion
>> and that of server 2.
> 
> That's basically why I won't be convinced by the four server argument 
> until I've checked the actual code.  I seem to remember that there is an 
> additional constraint, namely that the actual measurement must fall 
> within the intersection.
> 
>> 1
>>           |--------+--------|
>> 2
>>               |----------+----------|
>> 3                              |------------+------------|
>>

It's the other way around. The interval is expanded to include the 
mid-points. So, even though the overlap between server 2 and 3 is that 
small section, the interval actually used must include their 
mid-points (i.e. their offsets) so the interval used in the downstream 
calculations is the offset of server 2 through the offset of server 3.




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