[time-nuts] ISS NTP operation problems.

[Poul-Henning Kamp]

--------
Hal Murray writes:

> There is a huff-puff filter, I think it's optional. 

I think it is more likely that the median-filter is causing trouble.

If you let the poll-rate ramp all the way up to 1024 seconds, the
median filter can get "stuck" for almost an hour before it notices
that something is horribly wrong[1].

These days there are almost no circumstances under which you should not
clamp your poll-rate to one minute "server bla maxpoll 6"

On a strange path like the ISS, I would clamp it to the minimum
16 seconds ('maxpoll 4').

When the backbone of the ARPAnet was 56kbit/s, being able to ramp
up to 1024 seconds poll rate made sense.  It never makes sense now.

Poul-Henning


[1] The median filter should be automatically disabled and the most
recent sample used, if the samples in the shift register are
mononotonic or spread too much.  That's another change I never
managed to "sell" to Dave Mills.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.