Re: Predictable Internet Time

Joe Touch <touch@isi.edu> Fri, 21 April 2017 18:42 UTC

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Subject: Re: Predictable Internet Time
To: Phillip Hallam-Baker <phill@hallambaker.com>
Cc: Nico Williams <nico@cryptonector.com>, Paul Eggert <eggert@cs.ucla.edu>, IETF Discussion Mailing List <ietf@ietf.org>, =?UTF-8?B?UGF0cmlrIEbDpGx0c3Ryw7Zt?= <paf@frobbit.se>
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From: Joe Touch <touch@isi.edu>
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Date: Fri, 21 Apr 2017 11:41:43 -0700
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On 4/21/2017 11:35 AM, Phillip Hallam-Baker wrote:
>
>
> On Fri, Apr 21, 2017 at 1:57 PM, Joe Touch <touch@isi.edu
> <mailto:touch@isi.edu>> wrote:
>
>
>
>     On 4/21/2017 10:26 AM, Nico Williams wrote:
>     > "Internet time" (that which we use in [new] Internet protocols)
>     should
>     > just be TAI.  And every existing Internet protocol should be
>     updated to
>     > indicate which time is used in practice, UTC or TAI, regardless
>     of what
>     > was originally specified.
>     I would be very glad of we defined Internet Time as TAI, but also
>     expect
>     all protocols to understand both TAI and UTC if possible.
>
>     Joe
>
>
> ​To answer the issues raised:
>
> 1) POSIX already has this pretty much covered
>
> http://pubs.opengroup.org/onlinepubs/009695399/functions/clock_getres.html​
>
> ​int clock_gettime(clockid_t /clock_id/, struct timespec */tp/);​
>  
> ​So all that is required is to define clock identifiers for:
>
> TAI (The total number of seconds elapsed since the start of the epoch)
> UTC (The TAI value adjusted for UTC leap seconds, i.e. number of non
> leap second seconds since the start of the epoch)
If these aren't already included, I'm surprised (at least UTC).

> PIT (The TAI value adjusted for PIT leap seconds)

We don't need PIT.

> POSIX already defines constants
> for CLOCK_PROCESS_CPUTIME_ID, CLOCK_REALTIME 
>
> All that is needed is to define the additional ones. 
>
>
> ​2) No I did not move the goalposts. My original proposal was to solve
> the needless chaos caused be the idiotic notion of changing the
> definition of time at six months notice. The stupidity of that notion
> should be apparent to all.

There is no getting around the fact that the rest of the planet accepts
leap seconds. If that's not something you want to track, then use TAI
and be off-sync with the rest of the world when they use UTC.

PIT does nothing helpful except add yet another level of indirection and
confusion here.

> 3) Screw the astronomers. Pluto is to a planet.​

IMO, this issue is sufficently driven by "rough consensus and running
code" of the entire planet right now - where all governments already use
UTC.

Joe