[time-nuts] ISS NTP operation problems.

[Steven Sommars]

Responses to several comments.

Opportunities to collect critical NTP debugging data on the ISS will be
limited.
Specific suggestions sent to me off-list would be appreciated.

Earth station to ISS delays: I inferred the 600-700 msec RTT using the
reported root distance
[I've seen much higher delays on some terrestrial NTP paths.  ]
To really understand RTT / RTT stability NTP server diagnostic data is
needed.

GPS/GNSS, PPS distribution:     seems like a good idea, but this is outside
the area I'm helping with

NTP (4.2.8) algorithmic changes are probably out of scope for the near
future.
If a real-world PLL problem can be documented, the ntp daemon maintainers
might be motivated to investigate.

So far I haven't been able to reproduce on my home Rpi some key features of
the offset graph I showed.

   - pll error begins at -500 ppm
   - pll error grows to -1000 or even -1500 ppm
   - After step pll error is again -500 ppm
   - Does not self correct within 24 hours

By placing large positive or negative values into the NTP drift file I can
produce offset charts with a series of steps, but eventually the steps stop
and the offset is small.

Thanks for all the replies.