[ntp:questions] Keeping NTP Honest Redux

Unruh unruh-spam at physics.ubc.ca
Mon Nov 9 21:53:05 UTC 2009


Evandro Menezes <evandro at mailinator.com> writes:

>On Nov 9, 9:21=A0am, "David J Taylor" <david-tay... at blueyonder.not-this-
>bit.nor-this.co.uk.invalid> wrote:
>>
>> Here's the offset:
>> =A0http://www.satsignal.eu/ntp/2009-11-07-08-09-Narvik_offset-tod.png
>>
>> and here's the rate:
>> =A0http://www.satsignal.eu/ntp/2009-11-07-08-09-Narvik_frequency-tod.png
>>
>> where values for the last two and half days have been overlaid against
>> time-of-day.

>I think that we can all agree that these charts indicate that the
>variation is due to temperature variations.  Given that, they also
>indicate that NTP, as is, is too slow to react to temperature
>variations, taking something like 8 to 10h to compensate for them,
>even at 64s sampling period, it seems.  The reference stratum 1
>server, Feenix, seems to suffer from the same temperature-induced
>daily accuracy variations.

>Unfortunately, Mills will probably deny that this is an issue and will
>probably refuse revisions to his algorithm.  If this is the case,
>perhaps it's time to add another algorithm alongside Mill's and let to
>the user whether he prefers Mill's algorithm or an alternative.  Which
>alternative I have no idea, but I'd sure like to decide what's good
>for me, not Mills.

Well, you do have that choice, only in different names. chrony uses an entirely
different algorithm (directly estimating the rate and the offset from a sequence
of measurments). Of course you do not have that choice under Windows ( but
perhaps someone could port chrony to windows). There are also other places where
they are not equivalent, but it is at least an option.




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