[ntp:questions] The libntp resumee...

Richard B. Gilbert rgilbert88 at comcast.net
Tue Sep 9 19:52:30 UTC 2008

Unruh wrote:
> Uwe Klein <uwe_klein_habertwedt at t-online.de> writes:
>> Unruh wrote:
>>> Yes, that is with reference to the road. Car three should thus completely
>>> ignore the other two cars and use his speedometer. 
>>> Ie, put up a GPS receiver with a PPS and use that as your time source, and
>>> ignore all the other ntp time sources, except perhaps as sanity checks (eg
>>> if you r speedometer breaks you should get to know about it by occasionally
>>> looking at the other cars)
>> A)One GPS to each box or
>> B) a single GPS with PPS line to all boxes?
> Whichever you want. Up to you.
>> A:
>> Doesn't that impact reliability?
>> You add the failure probability of a GPS-unit to each Box
>> where one failure will make the whole system fail.
> So, that is why ntp has backup servers. You have a single failure point
> anyway-- the network. It goes down, and nothing can get the time. 

If the possibility of failure of your network or your internet 
connection worries you, you can use a modem and a telephone line as a 
backup!  Or you can get a GPS receiver, WWV/WWVH/WWVB receiver or an 
atomic clock of your very own.  Most sites don't bother because their 
requirements are not that tight.  FWIW, a system that has been 
synchronized by NTP will tend to stay close to the correct time for a 
reasonable period of time as long as the environment does not change 
significantly.  If the network fails AND the air conditioning fails you 
are in trouble!

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