[ntp:questions] NTP and asymetric delay

mills at udel.edu mills at udel.edu
Thu May 3 14:11:01 UTC 2007


Emmanuel,

No matter how you mangle the equations, there is no way you can account 
for asymmetric delays. You either have to measure these delays by means 
other than NTP or to determine the actual clock offset by means other 
than NTP.

Dave

emmanuel.python at bluewin.ch wrote:
> Hello
> 
> I use the version 3 of NTP on cisco routers and I see that if the 
> delay between the NTP server and the client (my cisco router) is not 
> symetrical (like for example 20ms in one direction and 40ms in the 
> other direction) then the time is not very well synchronized on the 
> router => There is an error of 10ms ((40-20)/2). After reading the 
> NTP algorithm, I see that it uses the round trip time to compute the 
> clock offset. So my question is the following: How to configure or 
> use NTP if there are asymetrical delays or jitter?
> 
> Thank you for your help
> 
> Emmanuel Python
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