[ntp:questions] Two servers, one client : one problem

David Woolley david at ex.djwhome.demon.invalid
Wed May 4 06:49:49 UTC 2011

Richard B. Gilbert wrote:

> NTP is hierarchical!  It expects to get time from an external source 
> such as NTP servers on the internet.  The hierarchy starts with an 
> "atomic clock"  such as those operated by NIST or equivalent.  These are 

There is nothing that prevents an atomic clock (no quotes) being used at 
any level in the hierarchy.  Good means much better than the estimated 
error contributions between the standard and the ntp client.

The key requirement, that is being violated here, is that the top 
stratum sources should be good approximations to the same time scale.

"atomic clock" in quotes is marketing hype for devices that may coast 
with un-temperature controlled crystal accuracy for 24 hours, but then 
be resynchronised, within about 100ms to a radio transmission derived 
from an atomic clock calibrated to a national standard, which is in turn 
calibrated (after the fact) to UTC.


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