[ntp:questions] Sub-millisecond NTP synchronization for local network

Unruh unruh-spam at physics.ubc.ca
Sat Dec 6 16:53:06 UTC 2008


>"Unruh" <unruh-spam at physics.ubc.ca> wrote in message
>news:43e_k.3033$si6.762 at edtnps83...

>> [...] Getting 20microseconds over a local net is easy. On a local
>> net, the delay should only be about 100microseconds, certainly not
>> milliseconds. ...

>I must be doing something horribly, horribly wrong then. Delay is
>on the order of 1 millisecond (0.6-1.3) and offsets are currently
>*very* good, all between -1 and 1 millisecond.

OK, strange. YOu can look at www.theory.physics.ubc.ca/chrony.html to see
the delays on my network-- it is local to a university building, but all
over the building. And I see essentially no difference between computers on
one side or the other. The delays on the 100Mbs parts of the network are on
the .15ms level with offsets at the .02ms level. However, the gigabit
machines are much much worse. I had not looked recently, and an a bit
perturbed now with how bad they are in comparison with previous levels (
from 6 months ago).

>What should I be doing to get 20 us? Buy all new computers with
>gigabit Ethernet?

I suspect buying better switches. And it looks to me like you should
definitely NOT go to gigabit Ethernet if you want good timing.
 

>Groetjes,
>Maarten Wiltink





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