Re: [Ntp] CLOCK_TAI (was NTPv5: big picture)

[Miroslav Lichvar <[e-mail]>]

On Tue, Jan 05, 2021 at 04:45:44AM -0800, Hal Murray wrote:
> 
> [e-mail] said:
> > NTP is used for synchronization of various clocks. Most of them are based on
> > UTC. NTPv5 cannot support only TAI. 
> 
> This is a tangled area.

I'd say it's fairly simple.

> I think that a TAI only NTPv5 protocol would be much cleaner and easier to 
> document.  Yes, I agree that we need a story for UTC, but the answer doesn't 
> have to clutter up an RFC for NTPv5.

Much cleaner? It's just a single field needed to negotiate the
timescale.

> All the kernel and/or libc need to convert TAI to/from UTC is the TAI-UTC 
> offset (a small integer) and the date of the next leap second, a flag for 
> insert/delete/none, and the valid-until date of the info.

Even if the kernel+libc fully supported TAI (they currently don't), it
cannot work when the TAI-UTC is unknown, e.g. in an isolated network
with a reference clock which doesn't provide this information. It
doesn't matter how it is called or specified, but NTP has to support
synchronization of UTC clocks when the TAI-UTC offset is unknown.
Otherwise, it would be just an academic project of very limited value.

-- 
Miroslav Lichvar