[ntp:questions] Keeping NTP Honest Redux

Todd Glassey tglassey at earthlink.net
Mon Nov 9 22:15:24 UTC 2009


Unruh wrote:
> 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.  
I think it more that there was no design for NTP to compensate for local 
loading of any kind. For instance if the system is over a set load NTP 
should create alarms for the logging to notice when it is more likely 
that time-slippage or drift may occur.

As to performance specifications - if you want to create a 
temperature/loading type report I would support that but its not part of 
the core protocol per se but rather the reference implementation thereof.
>> 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.
>>     
So you want a seamless application which takes into account all of the 
myriad of HW, Memory, and I/O performance constraints? - Thats not NTP 
as we know it today and would take a total rewrite of the drafts to 
support that use control.
>
> 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). 
>   
But it doesnt support Autokey and has no security capabilities so its 
pretty much unusable as a source of evidence if there are smart lawyers 
involved.
> 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.
>   
The problem with time (MS-SNTP) from the Windows world is how it 
controls the selection of the 'most correct' time and how it doesn't 
allow for the evidence-trappings of NTP to be promulgated into the A-D 
W32TIME.DLL control models.

Todd

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