Re: [Ntp] NTPv5 draft

[Warner Losh <[e-mail]>]

Magnus,

On Tue, Dec 8, 2020 at 8:53 AM Magnus Danielson <[e-mail]> wrote:

> Agree fully. You bring up a point which I think not all is appreciating.
> While we may develop protocols for the Internet, does not mean that they
> actually have access to the network, or that such access is open in any
> normal sense. For such air-gaped networks update cycles can also be long
> enough that for instance leap-second file cannot be sent along each
> upgrade to ensure correct leap-second list that way.
>

When I implemented the LORAN-C timing system refresh at Timing Solutions,
this issue was the biggest issue we had. We could get leap seconds from the
GPS, and had to resort to a number of ad-hoc methods to distribute from
there. Especially since we needed to cope with the scenario where a
computer fails and is replaced by a spare that had been on the shelf for 5
years, but still had the requirement it couldn't get setting the UTC time
of the atomic clock wrong (since LORAN TOC was timed vs UTC time scale, so
a wrong time meant wrong timing signals to the LORAN transmitter), nor wait
for a full GPS almanac to download.... We used a number of ad-hoc methods
to do this since there was nothing standard and in practice they proved to
be less robust than one would have liked. These machines were networked,
but on a private network that existed at each LORAN station only with only
minimal connectivity to the outside world (if any).

Leap seconds sound easy and simple, but the logistical issues surrounding
them are legend, especially when one must engineer for discontinuous use
cases.

Leap seconds are trivial if you have perfect knowledge. Sadly, history has
shown that this knowledge to be somewhat less than perfect...

Warner