[ntp:questions] Re: NTP adjustment mechanism

Johan Swenker J.B.Swenker at KPN.com
Tue Sep 2 11:10:06 UTC 2003


In article <de98eac0.0308310524.75ee06c2 at posting.google.com>, 
ryandrk at hotmail.com says...
>
>If clock adjustment is limited by tickadj/ticksize eg 4/10000 = +-400
>ppm , will this essentially mean that for a +100 ppm clock drift, NTP
>will run at -400 ppm for the first 0.25 of each second making
>adjustments each tick => accumulate an error (relative to actual
>clock) of -100 usec and then over that second the actual clock will
>gain +100 => balance out ..=> this means that worst case scenario NTP
>error will be at 0.25 sec in each sec interval and will be -100 (due
>to adj mechanism) +25 (accumulated error at thsi stage due to inherent
>error) = -75 msec...is this correct?
No, in your example NTP will adjust the clock for the error of 100 ppm. The 
limiting means that NTP cannot discipline the clock outside the limits. Within 
the limits it can do nearly everything.

Regards, Johan




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