[ntp:questions] frequency adjusting only

Unruh unruh-spam at physics.ubc.ca
Wed Apr 23 00:48:14 UTC 2008


m.louvel at gmail.com (maxime louvel) writes:

>Hi

>thanks every body,
>I am looking at the other solution and see what's the best for me.

>- My switches shouldn't be overloaded but I have to check that.
>Any idea of how ? Network sniffing ? theory ?

Look at the ntp roundtrip times and see how they fluctuate. (peerstats)


>- I think I have a problem with the temperature, indeed I have let only ntpd
>run on the node for a week-end and the offset between the two cards was
>quite good. Then I have run my 24H script which has obviously increased the
>temperature.

ntp is designed to take hours to respond to frequency changes. Clearly if
your machine's temp fluctuates on the time scale of hours that will be
problematic. 


>- I have understood that ntp should be able to manage what I want, but you
>seem divided on this issue ;)

I think from my own experiments that it should. 

As I said chrony will give you a factor of 2 better control (30us rather
than 60us say) if the computers have temp fluctuations. If the rates of all
computers never changes,  chrony will  average out the random "phase
fluctutions" better as well .
But either should work.




>Maxime


>On Tue, Apr 22, 2008 at 5:04 PM, Unruh <unruh-spam at physics.ubc.ca> wrote:

>> m.louvel at gmail.com (maxime louvel) writes:
>>
>> >On Tue, Apr 22, 2008 at 2:42 PM, Steve Kostecke <kostecke at ntp.org> wrote:
>>
>> >> On 2008-04-22, maxime louvel <m.louvel at gmail.com> wrote:
>> >>
>> >> > My goal is to achieve a synchronisation between the nodes (not
>> >> > with the public NTP server) within 50 usec.
>> >>
>> >> You may want to explore other synchronization options such as IRIG,
>> >> distributed PPS, or a distributed 10MHz clock.
>>
>>
>> >Thanks I'm gonna look at some other synchronisation solution.
>>
>> >>
>> >>
>> >> >I don't care if the synchronisation to the public NTP is accurate
>> >> >around half a second.
>> >>
>> >> You're displaying a common misconception about NTP.
>> >>
>> >> The goal of NTP is not explictly to synchronize clocks to "the one
>> >> true time". Rather, NTP synchronizes clocks to a common time base. A
>> >> "better" time base, and a "better" distribution method, allows tighter
>> >> synchronization between nodes.
>> >>
>> >> It so happens that UTC (via GPS or HF Radio or UDP) is a ubiquitous,
>> >> stable, and relatively inexpensive time base. A side effect of using
>> UTC
>> >> as your time base is that your clocks are synchronized to the correct
>> >> time.
>>
>>
>> >Sorry I haven't express myself correctly. What I meant is that I want an
>> >accuracy of 50 usec within my subnet and I want my whole subnet to be
>> >synchronised to UTC with an accuracy of 1 second or less if possible.
>>
>>
>> He is saying that ntp is designed to do the former, and if you include an
>> external reference you get the latter for free. How badly overloaded are
>> your switches?
>>
>>
>> >>
>> >>
>> >> --
>> >> Steve Kostecke <kostecke at ntp.org>
>> >> NTP Public Services Project - http://support.ntp.org/
>> >>
>> >> _______________________________________________
>> >> questions mailing list
>> >> questions at lists.ntp.org
>> >> https://lists.ntp.org/mailman/listinfo/questions
>> >>
>>
>>
>>
>> >--
>> >Maxime Louvel
>> >0044 7964 5555 80
>> >43 Allen road
>> >Whitemore reans
>> >WV60AW Wolverhampton
>> >United Kingdom
>>
>> _______________________________________________
>> questions mailing list
>> questions at lists.ntp.org
>> https://lists.ntp.org/mailman/listinfo/questions
>>



>-- 
>Maxime Louvel
>0044 7964 5555 80
>43 Allen road
>Whitemore reans
>WV60AW Wolverhampton
>United Kingdom




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