[ntp:questions] NTP architecture recommendation

David J Taylor david-taylor at blueyonder.not-this-bit.nor-this-bit.co.uk
Sun Aug 19 05:39:47 UTC 2007


Richard B. Gilbert wrote:
[]
> Making GPS unreliable for navigation would be shooting ourselves in
> the foot!  Remember that commercial aircraft use GPS for navigation
> as well as private aircraft, military aircraft, ships, motor vehicles
> and lord knows what else.  I'm inclined to doubt that any country's
> weapons systems rely solely on GPS for navigation or targeting.

SA allows different classes of users to achieve different accuracies.  At 
the moment, SA is disabled, meaning that all users can get the same 
accuracy.  Re-introducing SA would simply make commercial and domestic use 
of GPS slightly less accurate.  According to this reference:

  http://www.effective-solutions.co.uk/sa.html

accuracies are about 100m with SA enabled and 20m without.  See also:

  http://en.wikipedia.org/wiki/Global_Positioning_System#Selective_availability

The effect on timekeeping can probably only be seen if you compare with an 
atomic clock.

David 





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