[ntp:questions] NTP tunning for OWD measurements

pret3nder at gmail.com pret3nder at gmail.com
Fri Oct 26 22:47:37 UTC 2012


I'm sorry, I'm not following you. What delay asymmetry are you refering to?

OWAMP does rely on accurate time stamps, see http://www.internet2.edu/performance/owamp/index.html

If I have S1 and X1 synching to the same time reference (in this case,
the same stratum 1 server), and I do one-way delay tests between S1 and X1,
I'm expecting to find a valid measurement of the one-way delay, no?

If you're talking about the asymmetry caused by NTP assuming the one-way delay
to/from the clients is RTT/2, I'm aware of that error. And I will try to minimize it,
e.g., using tunnels.


On Friday, October 26, 2012 11:19:26 PM UTC+1, David Woolley wrote:
> pret3nder at gmail.com wrote:
> 
> 
> 
> > 
> 
> > Also, I don't want to use NTP to directly measure the one-way delay, I have OWAMP
> 
> 
> 
> You can't stop it measuring the delay asymmetry!  The trouble is you 
> 
> will not have any way to obtain that value, which will tend to cancel 
> 
> out the asymmetry measured by your primary tool, assuming it depends on 
> 
> accurate time stamps!
> 
> 
> 
> > (more specifically perfSonar - http://www.internet2.edu/performance/pS-PS/)
> 
> > to do that for me.
> 
> > 
> 
> The page is a commercial type hype, not a technical overview of the 
> 
> algorithms used, but the only way I know of measuring one way delay is 
> 
> synchronise the clocks somewhat better than the acceptable measurement 
> 
> error, which you can't do if the synchronisation process is vulnerable 
> 
> to the effects of the same delay asymmetry.



On Friday, October 26, 2012 11:19:26 PM UTC+1, David Woolley wrote:
> pret3nder at gmail.com wrote:
> 
> 
> 
> > 
> 
> > Also, I don't want to use NTP to directly measure the one-way delay, I have OWAMP
> 
> 
> 
> You can't stop it measuring the delay asymmetry!  The trouble is you 
> 
> will not have any way to obtain that value, which will tend to cancel 
> 
> out the asymmetry measured by your primary tool, assuming it depends on 
> 
> accurate time stamps!
> 
> 
> 
> > (more specifically perfSonar - http://www.internet2.edu/performance/pS-PS/)
> 
> > to do that for me.
> 
> > 
> 
> The page is a commercial type hype, not a technical overview of the 
> 
> algorithms used, but the only way I know of measuring one way delay is 
> 
> synchronise the clocks somewhat better than the acceptable measurement 
> 
> error, which you can't do if the synchronisation process is vulnerable 
> 
> to the effects of the same delay asymmetry.



On Friday, October 26, 2012 11:19:26 PM UTC+1, David Woolley wrote:
> pret3nder at gmail.com wrote:
> 
> 
> 
> > 
> 
> > Also, I don't want to use NTP to directly measure the one-way delay, I have OWAMP
> 
> 
> 
> You can't stop it measuring the delay asymmetry!  The trouble is you 
> 
> will not have any way to obtain that value, which will tend to cancel 
> 
> out the asymmetry measured by your primary tool, assuming it depends on 
> 
> accurate time stamps!
> 
> 
> 
> > (more specifically perfSonar - http://www.internet2.edu/performance/pS-PS/)
> 
> > to do that for me.
> 
> > 
> 
> The page is a commercial type hype, not a technical overview of the 
> 
> algorithms used, but the only way I know of measuring one way delay is 
> 
> synchronise the clocks somewhat better than the acceptable measurement 
> 
> error, which you can't do if the synchronisation process is vulnerable 
> 
> to the effects of the same delay asymmetry.



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