On Fri, 22 Apr 2011 15:19:31 GMT, unruh <[email protected]> wrote:
>On 2011-04-22, Roger <[email protected]> wrote: >> On Thu, 21 Apr 2011 09:32:21 -0400, "Richard B. Gilbert" >><[email protected]> wrote: >> >>>One server: if it fails you have nothing! >>>Two servers: If the two differ, which one do you believe? >>>Three servers: degenerates too easily to the two server case. >>>Four servers: Allows the failure of one server. >>>Five servers: Allows the failure of two. >>>Seven servers: Allows the failure of three. >> >> I've seen these number quoted before and I don't understand >> the last one. Why doesn't 6 allow for the failure of 3? Why > >Because 3-3 is a tie and the system cannot decide which is best. Ie by >failure, read "bad timekeepers". If 3 fail-- ie stop responding to >packets, 6 is pleanty. 4 would be enough. But if they fail by delivering >the wrong time, and all three deliver the same wrong time (say because >all three are in Chicago and all three used a cell phone system to set >the time and .... ) then you have a tie. >It starts to get a bit absurd, I know. Thank you, and David and Dave. I hadn't thought about a 3-3 tie. I hadn't even considered that that might happen. But if that is possible then so is a 2-2 tie with 4 servers. Ho hum, nothing is perfect in this life. -- Roger _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
