[ntp:questions] Effect of Root Dispersion and other Parameters on Accuracy

Bob Payment bpayment at cisco.com
Thu Nov 13 19:25:58 UTC 2003


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

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

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?


Bob Payment

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