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Re: Document Action: 'BinaryTime: An alternate format for representing date and time in ASN.1' to Experimental RFC

2004-11-15 05:57:58
At 13:13 12/11/04 -0500, you wrote:
The IESG has approved the following document:

- 'BinaryTime: An alternate format for representing date and time in ASN.1 '
   <draft-housley-binarytime-02.txt> as an Experimental RFC

This document has been reviewed in the IETF but is not the product of an
IETF Working Group.

The IESG contact person is Steve Bellovin.

Technical Summary
  This protocol provides a means to represent time in ASN.1 as an integral
number of seconds since the epoch (00:00:00 UTC, January 1, 1970). This avoids
the well-known problems with comparison of timestamps that are given with
respect to some particular timezone.

Protocol Quality

 Steve Bellovin has reviewed this document for the IESG.

RFC Editor Note:

Section 2, old text:
      BinaryTime ::= INTEGER

New text:
       BinaryTime ::= INTEGER (0..MAX)
OLD:

    The integer value is the number of seconds after midnight UTC,
    January 1, 1970.

NEW:

    The integer value is the number of seconds, ignoring leap seconds,
    after midnight UTC, January 1, 1970.

This slipped under my radar until this announcement.

Has there been detailed discussion of leap second issues? What exactly does the revised text "ignoring leap seconds" actually mean (I think I can guess, but I also think there's some room for misinterpretation here)? Has any consideration been given to conversion between the integer timestamp and more conventional representations involving dates and times; if so, is that documented?

My view is that leap seconds are a small detail which have great potential for causing confusion. I've been involved in some discussion of a date-time library for a programming language (Haskell) [1], which discussion is currently stalled because of unresolved leap second issues.

A particular concern of mine is that if a simple count of elapsed seconds is used, then there is no way to define an algorithm for accurately determining the correspondence between this binary timestamp and (say) ISO 8601 date-time representations. Leap second occurrences are not known very far in advance.

My own preference [2] for a binary time representation is to use a pair of numbers: a day count and a second (or sub-second) count. I feel this adequately handles the vast majority of use-cases for timestamps in applications that do not care or know about leap-seconds (i.e. where the inaccuracies of not considering leap-seconds are not considered significant), or when the intervals concerned are generally much less than a day and hence are measured it terms of time only, but still allows specialized applications that do know about such things to make the appropriate adjustments when working with timestamps and time intervals.

I submit these as considerations for when the experimental status of this specification is reviewed, and request that the resolutions be documented if the specification moves from experimental to standards-track status.

#g
--

[1] Approximate locus of Haskell library discussion:
  http://www.haskell.org/pipermail/libraries/2003-June/001093.html
  http://www.haskell.org/pipermail/libraries/2003-June/001157.html

[2] Pretty much my own current view in that debate...
  http://www.haskell.org/pipermail/libraries/2003-June/001211.html
  http://www.haskell.org/pipermail/libraries/2003-November/001541.html
(but there are other views "nearby")



------------
Graham Klyne
For email:
http://www.ninebynine.org/#Contact


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