Re: ITC copped out on UTC again

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On Fri, Jan 20, 2012 at 10:13 AM, Tim Bray <tbray@xxxxxxxxxxxxxx> 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@xxxxxxxxx> 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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>>
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