[ntp:hackers] A stop-gap authenticated time service

Miroslav Lichvar mlichvar at redhat.com
Wed Nov 11 17:39:59 UTC 2015

On Wed, Nov 11, 2015 at 11:42:54AM -0500, Majdi S. Abbas wrote:
> 	What do you think a cellular connection looks like today?
> Or bad airport WiFi?

I think the distribution of the delay there is very different from
ordinary networks and only a small part of the measurements is good
for synchronization. The NTP implementation should be able to drop a
large number of consecutive samples. In the ntpd design it seems
that's not possible. The clock filter can drop only a limited number
of samples before the PLL becames unstable.

> 	I'm not so sure I'd write off some of those assumptions
> just yet, at least not without some hard data around it.  The
> implementation has to be prepared to handle anything out there,
> not just the common case.

I fully agree. That's why I prefer a more adaptive approach, even
when it can't always work better than something optimized for more
specific conditions.

Miroslav Lichvar

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