[time-nuts] NTP Time Server Ping Timing Stability

[Brooke Clarke]

Hi Hal:

I'm in Califoria on the other side of the country from Atlanta, GA where the 
big dish is located.

Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.precisionclock.com


Hal Murray wrote:
> ); SAEximRunCond expanded to false
> Errors-To: time-nuts-bounces+brooke=pacific.net at febo.com RETRY
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>>I'm curious about the stability of Ping timing between high quality
>>NTP  servers.  Is it the case that a histogram will show different
>>times because the  path may be different between the two servers but
>>the spread for any given path  would be quite small because of the
>>quality of the timing? 
> 
> 
> NTP measures the transit time in both directions.  It assumes symmetry and 
> calculates the offset as half the difference and uses that to adjust the 
> local clock.
> 
> Assuming you have good clocks on both ends:
> 
> If you plot the offset vs round trip time, you get an arrow pointing left.  
> The point (blob) of the arrow is the best case.  The edges of the arrow are 
> due to queuing delays in one direction or the other.  You also get some 
> scattered points trying to fill in the arrow from queuing delays in both 
> directions.
> 
> If you plot round-trip time vs time of day, you can see occasional jumps 
> where the network path changes, or somebody starts a big download that fills 
> up one side of a pipe for a while.
> 
> 
> 
>>Or if I was pinged would the wander of the satellite in the link show
>>up or is  my stock PC so crude it swamps the satellite wander?
>>148.78.32.98 or 148.78.32.97 not sure if those are visible on the net.
> 
> 
> ping just gives you the round trip time.  I'm not sure where ntp fits in.
> 
> It's reasonable to get ntp with a GPS clock running in the few microsecond 
> range.  I'd guess you might see satellite wander if that covers a few miles.  
> It might be hard to see in all the other network noise.
> 
> Where are you located (packet hops, not crow fiies) relative to the satellite 
> ground stations?
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