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Re: ITC copped out on UTC again

2012-01-20 09:19:33
On Fri, Jan 20, 2012 at 10:13 AM, Tim Bray <tbray(_at_)textuality(_dot_)com> 
wrote:
One consequence of your proposal, if adopted, is that there will need
to be a specification of the canonical Internet-time-to-Sidereal-time
function, so that in the long run, the time that your computer says it
is will correspond with what you observe looking out the window. The
Internet will be around long enough that this will indeed become a
problem.

I'd want to look at that specification before getting passionate pro
or contra in this argument. -T

The people who really care about this (i.e., astronomers) already use
TAI to do it.

I have written such code (more than once), the first thing you do is
to find UT1 - TAI, then proceed with various rotations from
there.

50 years ago, using UTC as an approximation to UT1 when you didn't
happen to have a multi-million dollar, multi-ton, mainframe in your
pocket made sense. Today, when that same power (or, actually, more) is
in your smart phone (if not your toaster), it doesn't.

Regards
Marshall


On Fri, Jan 20, 2012 at 6:20 AM, Phillip Hallam-Baker 
<hallam(_at_)gmail(_dot_)com> wrote:
If we are ever going to get a handle on Internet time we need to get rid of
the arbitrary correction factors introduced by leap seconds.

The problems caused by leap seconds are that they make it impossible for two
machines to know if they are referring to the same point in future time and
quite often introduce errors in the present.

1) No machine can determine the number of seconds between two arbitrary UTC
dates in the future since there may be a leap second announced.

2) If Machine A is attempting to synchronize with machine B on a future
point in time, they cannot do so unless they know that they have the same
view of leap seconds. If a leap second is announced and only one makes the
correction, an error is introduced.

3) In practice computer systems rarely apply leap seconds at the correct
time in any case. There is thus a jitter introduced around the introduction
of leap seconds as different machines get an NTP fix at different points in
time.

4) Even though it is possible to represent leap seconds correctly in
standard formats, doing so is almost certain to exercise code paths that
should be avoided.


Since the ITU does not look like sorting this out, I suggest we do so in the
IETF. There is no functional reason that Internet protocols should need leap
seconds.

I suggest that the IETF plan to move to Internet Time in 2015, immediately
after the next ITU meeting. Internet time would be TAI plus the number of
leap seconds that have accumulated up to the next ITU decision point. So if
UTC drops leap seconds at the next meeting the two series will be in sync,
otherwise there will be a divergence.



--
Website: http://hallambaker.com/


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