[ntp:questions] Root Dispersion and other parameter's effect

Bob Payment bpayment at hotmail.com
Thu Nov 13 19:01:52 UTC 2003


Folks,

My customer asked me what the "maximum" values are for the NTP quality
parameters that can be displayed on his Cisco routers.

I believe that it "depends" but can anyone give some general guide
lines as to what ballpark these values should be in if you wanted to
maintain 1 msec, 5 msec or 10 msec time difference between two devices
that sync back to the same master?

Here is my customer's question.......

Problem Description:  Hello
Previous tac cases have shown how important good NTP synch is. However
it is unclear what are the performance characteristics of NTP (or
better said performance specifications) for support of SAA jitter
measurements.  for example when one runs the cmd " Show NTP Status"
what are the maximum values permitted for each of the four principle
categories:
clock offset 
root delay 
root dispersion 
peer dispersion 


I had NTP synch on my three test boxes but was still not able to see
OW
delay values. Again I had synch. When I switched to a different clock
with
improved NTP values (show NTP status) things worked much better. So
why if I
have synch (thus one assumes that all is hunky dory) do I not get good
OW
delay results with SAA. The answer is that the root and peer
dispersion
values were crap. OK so what are the thresholds one should obey with
NTP to
consider the NTP status good enough to support SAA jitter tests with a
focus
on OW delay values?





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