[ntp:questions] high precision tracking: trying to understand sudden jumps

Unruh unruh-spam at physics.ubc.ca
Tue Apr 1 16:39:57 UTC 2008


hal-usenet at ip-64-139-1-69.sjc.megapath.net (Hal Murray) writes:


>>>probably have make use of PTP (precision timing protocol).
>>
>>No idea what that is. If you had wanted super precision you would have put
>>a GPS onto each machine, I hope. 
>>
>>From the Wikipedia entry on PTP it looks absolutely no different from ntp.
>>I have no idea what the idea is. 

>The basic idea is to do the time stamping in hardware deep in
>the network adaper.  That avoids lots and lots of jitter.

It avoids some jitter. Does that mean that you have to have special
hardware (special network cards, or special network card drivers?)
It does nothing for the 300us jitter I see on my ADSL connected computer.
It might do something for the 10us jitter I see on my ethernet connected
lan-- probably take it down to 8us or something (has anyone tested where
the jitter is-- in the network cards or in the switches?)
 


>-- 
>These are my opinions, not necessarily my employer's.  I hate spam.




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