Re: [LEAPSECS] An immodest proposal

From: M. Warner Losh <imp_at_BSDIMP.COM>
Date: Tue, 14 Feb 2006 14:18:53 -0700 (MST)

In message: <20060214165529.GW8989_at_feynman>
            Neal McBurnett <neal_at_BCN.BOULDER.CO.US> writes:
: On Mon, Feb 06, 2006 at 10:37:37AM -0700, Rob Seaman wrote:
: > 1) TAI can be recovered from UTC given a table of DTAI.
: > 2) NTP can convey TAI as simply as UTC.
: > 3) Deploy a small network of NTP servers to keep TAI, not UTC.
: > 4) NTP client machines could therefore trivially select between TAI and
: > UTC by subscribing to different servers.
: > 5) This would provide an unbiased experimental sandbox for civil
: > timekeeping issues.
:
: Since TAI can be recovered from UTC, and hosts that use NTP know UTC,
: those hosts can serve any time they want to clients on that host. I
: see little reason to change the particular timestamps that are used in
: the NTP protocol, an less reason to have two different timestamps
: within NTP, or to require users on ntp-using hosts to switch their
: ntp servers just to get a different timescale.

ntp time stampes are ambiguous at leap seconds (the leap indicator
bits aren't part of the time stamp, exactly), which is a good reason
to change them. However, the cost to change them could be quite high
if done in an incompatible manner.

: That's why I support the "Fixing POSIX time" proposal from
: Poul-Henning Kamp. This can be implemented with the latest NTP
: daemons. The operating systems would seem to just need the right sort
: of CLOCK_NTP definition for /usr/include/linux/time.h or equivalent,
: and the appropriate conversion routines as he outlined.

Agreed.

: I'd like to see a standard for NTP that includes the TAI information
: that is now passed in non-standard formats, but that is a separable
: issue.

I believe that the new draft standard of ntp uses TAI time for its
time exchange, and explicitly includes DTAI information in a standard
format. Since the protocol version changes, there's no ambiguity and
that's a good time to change things like this. However, I've not read
the latest ntpng drafts to confirm this.

Warner
Received on Tue Feb 14 2006 - 13:19:53 PST