[ntp:questions] frequency adjusting only
unruh-spam at physics.ubc.ca
Wed Apr 23 17:31:06 UTC 2008
m.louvel at gmail.com (maxime louvel) writes:
>I am thinking that NTP should behave correctly if the activity on the nodes
>(small temperature, hence frequency variation) and on the network (small
>latency of the switch) are roughly constant.
>But if not it will have some trouble, either to compensate the frequency
>change or to deal with the network delay latency.
ntp always behaves correctly. It is a stable system. It is not optimised to
get the very best behaviour is all. Part of its stability is its long
integration times ( and its throwing away 80% of the data in the clock
filter to try to beat down transport noise.)
Even if the frequencies change, it works well, just not as well as it
could. (Or perhaps the chrony philosopy has some situations where it fails.
I do not know)
>what do you think ?
>On Wed, Apr 23, 2008 at 7:12 AM, maxime louvel <m.louvel at gmail.com> wrote:
>> - my network contains only one switch, and all the node are in the same
>> Thus I don't think cabling is a problem. I still have to check the latency
>> of the switch.
>> - I can't use a GPS or other material. I though I wouldn't need any
>> because I don't won't a great accuracy with the real time, just between my
>> nodes. I also think it would have been easier and better to have a common
>> high precision time source (GPS)... But I can't afford that ;)
>> Do you have an explanation of the so different performances observed in
>> your NTP synchronisations ?
>> - I'm going to look at chrony, which at first glance seems usable in my
>> - I am already using the -x option, to be certain to avoid any step.
>> On Wed, Apr 23, 2008 at 2:10 AM, Unruh <unruh-spam at physics.ubc.ca> wrote:
>> > Steve Kostecke <kostecke at ntp.org> writes:
>> > >On 2008-04-22, Unruh <unruh-spam at physics.ubc.ca> wrote:
>> > >> Steve Kostecke <kostecke at ntp.org> writes:
>> > >>
>> > >> ??? In my experience, on a Lan ntpd shows an internode offset of
>> > about
>> > >> 5-15 usec, and on the internet (ADSL) an offset of about 200usec.
>> > >Here's an aggregated plot of the node offsets on my LAN over the last
>> > 24
>> > >hours. I see +3/-5 milliseconds, not anything near 5-15 microseconds.
>> > >
>> > http://support.ntp.org/bin/viewfile/Users/SteveKostecke?rev=1;filename=typical_aggregate_lan_offsets.png
>> > I agree those are pretty bad. HOw are they hooked up? It looks like one
>> > of
>> > the hops is via a telephone modem!
>> > See www.theory.physics/chrony/chrony.html
>> > Mind you those are running with maxpoll 7 not maxpoll 10 (Its my lan and
>> > ntp server, and I'll do what I want to.)
>> > >--
>> > >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
>0044 7964 5555 80
>43 Allen road
More information about the questions