[time-nuts] clock-block any need ?

Magnus Danielson magnus at rubidium.dyndns.org
Fri Dec 28 00:29:57 UTC 2012


On 12/28/2012 12:31 AM, bg at lysator.liu.se wrote:
> Magnus,
>> Doing ~200 us for a non-trival network with real data on it sound about
>> right.
>> What kills many assumptions is that the noise-forms fail most of the
>> normal assumptions about "noise". It's not zero mean, it does not have a
>> static mean, it does not have a static variance, it is not symmetric, it
>> is not independent of other traffic, it is not "just another service".
>> Cheers,
>> Magnus
> But NTP is very much aware of the measurements coming from a complicated
> statistical source. Look for 'wedge scattergram'.
>     http://www.eecis.udel.edu/~mills/database/brief/algor/algor.pdf
>     http://www.eecis.udel.edu/~mills/database/brief/distlec/distlec.ppt

I am fully aware of it.

NTP has many treatments to the measurements to combat these issues, but 
it can't cut down the noise all the way down as you would like to do 1 
us or so over large scale networks.

My comment above was to point out that you do need to look hard at the 
topic to grasp all the details of it. There are many subtleties and the 
wedge scattergram is one of several methods to approach it.

NTP only come that far, given some of the design constraints it has. It 
does a good job within those limits.


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