Re: Predictable Internet Time

Stewart Bryant <stewart.bryant@gmail.com> Wed, 04 January 2017 09:21 UTC

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Subject: Re: Predictable Internet Time
To: Cyrus Daboo <cyrus@daboo.name>, Ted Lemon <mellon@fugue.com>
References: <CAMm+LwgfQJ8aG5wB=d3fRbbeje3J9o7Z4_DCuP8DL88ouDeKzw@mail.gmail.com> <504e2cea0d1668c31486b05fec0a967a4446aefe@webmail.weijax.net> <CAMm+Lwi_jU6gjdtdM6a2n_9_89tUvWBNXxnMtSjTEA++h1D4Ew@mail.gmail.com> <e0a43370-751f-808c-3719-9716f9cd57d1@isi.edu> <alpine.DEB.2.11.1701031348430.7102@grey.csi.cam.ac.uk> <0bbfcd7c-11a7-0e7f-56f7-eee959b7a947@gmail.com> <CAMm+Lwi0sQyRE_2dMCkwTk7xTiK2JbHhHSPYMkdG2FeBw_6CNA@mail.gmail.com> <7BDE58D23ADF3BC046F8942D@caldav.corp.apple.com> <b27515e2-a36a-7bf2-0ca4-1fae31a9dc21@gmail.com> <04DD5DFCB528DCD404C81F78@caldav.corp.apple.com> <A193D619-7B59-4EFB-A773-B6F6E4FD5884@fugue.com> <C93A4EFBD3E91F4F714DF948@caldav.corp.apple.com>
From: Stewart Bryant <stewart.bryant@gmail.com>
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Date: Wed, 4 Jan 2017 09:21:29 +0000
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Cc: Phillip Hallam-Baker <phill@hallambaker.com>, IETF Discussion Mailing List <ietf@ietf.org>
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On 03/01/2017 19:54, Cyrus Daboo wrote:
> Hi Ted,
>
> --On January 3, 2017 at 1:51:54 PM -0500 Ted Lemon <mellon@fugue.com>; 
> wrote:
>
>>> No that simply does not work. Repeating events or alarms may not 
>>> involve
>>> any UI at all, but the device may need to trigger those at a specific
>>> local time - that means time zone information has to be taken into
>>> account somewhere. This is a crucial fact of any calendaring and
>>> scheduling system that those of us who have been using iCalendar
>>> (RFC5545) fully appreciate.
>>
>> This is true, but any specific local time will always occur at a 
>> specific
>> universal time, so this isn't actually a problem.
>
> No! That is not true because a future local time is not guaranteed to 
> be at a specific universal time because local government can change 
> their time zone (or more likely) their daylight savings time 
> transition at any time between now and said future time. i.e., you 
> cannot "pre-cache" all the local time -> UTC mappings for a future 
> recurring event and then just use the UTC values, because the time 
> zone definition may change.
>

So an application sensitive to that needs to specify its timing in terms 
of local time, but that should not force the fundamental time 
distribution system to operate in that mode.

Maybe we need two time distribution systems, one that accurately does 
the ranging and flywheel management and distributes precision time for 
technical purposes, and a separate one that manages the offsets and 
jumps relative to the underlying precision continuous time distribution 
system.

Stewart