[ntp:questions] What is the "best" synchronization possible over the network?

Unruh unruh-spam at physics.ubc.ca
Wed Feb 11 23:45:51 UTC 2009


ntp at tla.org (John Ioannidis) writes:

>The problem setup: two locations, both within the United States, neither 
>has roof access so no GPS reception is possible.  How do you synchronize 

What about window access?  And since you have money, I am sure that your
building does have a roof. Stick a cheap computer near the roof and run a
GPS18 onto the roof and a cable down to that computer. (Nota that you can
extend the line beyond the 5M that the GPS18 comes with -- to get really
best results with an amplifier and matched lines, and run the wires down to
the computers. 

Ie, set up fast amps connected with cat 5 cable and 100ohm termnation on
each end.

>them with better than 50-microsecond accuracy?  Straight NTP over the 
>Internet doesn't do the trick.  They don't need to actually be 

Sure it does. have one of them as a client of the other and on a local
ethernet you should be able to get 50usec agreement. 

>synchronized to "real" time, they only need to be synchronized to each 
>other.  Assume reasonably unlimited resources (running a private fiber 
>plant across the continent *is* unreasonable).

Is running a single Cat5 to the roof unreasonable?


>I've looked into slaving something off a voice-carrier time base, but 
>that's not accurate enough.  Maybe something over raw SONET would do the 
>trick?

>Thanks

>/ji




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