[ntp:questions] NTP tunning for OWD measurements

Richard B. Gilbert rgilbert88 at comcast.net
Sat Oct 27 16:22:43 UTC 2012


On 10/26/2012 6:47 PM, pret3nder at gmail.com wrote:
> 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

What is OWAMP?
<snip>



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