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

John Ioannidis ntp at tla.org
Tue Feb 10 23:30:31 UTC 2009

The problem setup: two locations, both within the United States, neither 
has roof access so no GPS reception is possible.  How do you synchronize 
them with better than 50-microsecond accuracy?  Straight NTP over the 
Internet doesn't do the trick.  They don't need to actually be 
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).

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 



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