Re: [Ntp] Suggested improvements to the Roughtime draft (draft-ietf-ntp-roughtime-00)

On Mon, Feb 17, 2020 at 12:23 PM Tony Finch <dot@dotat.at> wrote:
>
> Marcus Dansarie <marcus@dansarie.se> wrote:
>
> > * Adding the DUT1 and DTAI tags for transfer of offsets between UTC and
> > UT1, and UTC and TAI.
> > * Adding the LEAP tag to transfer information on future and past leap
> > second events.
>
> The TF.460 requirements are largely about radio signals for celestial
> navigation, so it's questionable that those aspects are relevant for
> distributing civil time over computer networks. TF.460 also only requires
> DUT1 to 100ms precision, so where does your 1ms precision requirement come
> from? GPS provides DUT1 to sub-microsecond precision, for example.
> (IS-GPS-200 table 30-VII, https://www.gps.gov/technical/icwg/)

If you are designing your own receiver electronics, then this is feasible.
The problem is that standards like NMEA don't provide a field for the
information, so it's a challenge to integrate with GPS clock drivers on
commodity OS's. Our current setup at Cloudflare is fed by NTP, so that's
even less likely to get these fields.

>
> There is no need to distribute both DTAI and a leap second list. (DTAI can
> be derived from the list.) I think a new time protocol should just
> transmit the entire list, because it can easily be compresed to less than
> 20 bytes - the current list is 16 bytes and we're unlikely to pass 20
> bytes within the next 10 years.

What's the point of distributing far past or far future leap seconds via
Roughtime? It can go into the tz database.

>
> I distribute cryptographically signed lists of leap seconds in various
> formats over the DNS, e.g.
>
> leapsecond.dotat.at.    TYPE65432 \# 16 00111111121134312112229D565285FA
> leapsecond.dotat.at.    RRSIG   TYPE65432 13 3 3600 (
>                                 20200227094640 20200215162742 53798
dotat.at.
>
 EWKpYcQOqnbnkMmf9+jQAHpBmqrHGpVOht9O8JzMPHUZ
>
 E95u/cuNWEMlIe8uTSkSfQRX3ZT/OZJIdIlkE9LkXA== )
>
> Sketchy description of the format at
> https://dotat.at/cgi/git/leapseconds.git/blob/HEAD:/syntax.md
>
> (Leap seconds as currently specified will stop working between 1000 and
> 2000 years in the future, when DTAI is about 2h, and the leap second list
> is about 4KB. https://www.ucolick.org/~sla/leapsecs/dutc.html)
>
> Tony.
> --
> f.anthony.n.finch  <dot@dotat.at>  http://dotat.at/
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>
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