Is this a new problem or has it being happening since day 1? Jim Palfreyman
On Fri, 8 Jan 2021 at 5:42 pm, Steven Sommars <[email protected]> wrote: > At the end of November a question > <https://lists.ntp.org/pipermail/questions/2020-November/041883.html>was > posed to the ntp.org list concerning NTP problems on the International > Space Station. > With William's permission I'm following up on the time-nuts list. > > I analyzed NTP/IP packet captures provided by William and reported on > external visible behaviors. The much simplified diagram is > 2 x Ground NTP(strat 1) --------------- ISS NTP server(strat 2) > -----(gigastor)------- ISS NTP clients(strat 3) > There is a ~600-700 msec RTT between the ground NTP servers and the ISS NTP > server. > > As William describes, the clients are having trouble synchronizing with the > stratum 2 ISS NTP server. > This server is not working well. Here is the UTC time offset seen from an > external packet capture device (Gigastor) > [The Gigastor is only approximately sync'd to UTC, hence the 4 second > offset] > [image: image.png] > The y-axis scale is seconds. > Note also that after each step the initial error is about -500 ppm. When > the server is in alarm the error stays at -500ppm. > When not in alarm the server's clock frequency is changing in the wrong > direction with a resulting error of up to ~ -1500ppm. > Could this be an example of the Integral Windup problem mentioned recently > by PHK and Magnus? > Have others seen this behavior in NTP? > > Getting additional diagnostic information from the ISS is quite difficult. > Even simple changes (e.g., remove ntp.drift) require much planning. > > Steve Sommars > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
