[AVTCORE] Fwd: POSIX time in draft-ietf-avtcore-leap-second-04

Kevin Gross <kevin.gross@avanw.com> Tue, 01 October 2013 15:58 UTC

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Date: Tue, 1 Oct 2013 09:58:39 -0600
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From: Kevin Gross <kevin.gross@avanw.com>
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Cc: Paul Eggert <eggert@cs.ucla.edu>
Subject: [AVTCORE] Fwd: POSIX time in draft-ietf-avtcore-leap-second-04
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I received some comments on my leap seconds draft from Paul Eggart. I am
submittig a new revision which adds three new references, brings the POSIX
discussion in line with IEEE 1003.1 and mentions the warping techniques.

Are there any other last-call comments from the group?

Kevin Gross
+1-303-447-0517
Media Network Consultant
AVA Networks - www.AVAnw.com <http://www.avanw.com/>


---------- Forwarded message ----------
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Wed, Sep 11, 2013 at 1:59 PM
Subject: POSIX time in draft-ietf-avtcore-leap-second-04
To: Kevin Gross <kevin.gross@avanw.com>
Cc: Ray van Brandenburg <ray.vanbrandenburg@tno.nl>


The topic of POSIX time came up recently on the IANA tz list
and draft-ietf-avtcore-leap-second-04 was mentioned
<http://mm.icann.org/pipermail/tz/2013-September/020156.html>
<http://mm.icann.org/pipermail/tz/2013-September/020158.html>.
I think it'd be helpful to cover the newly-raised points in the draft.
Perhaps something like the following?

--- draft-ietf-avtcore-leap-second-04.txt    2013-08-27
08:31:12.000000000 -0700
+++ new.txt    2013-09-11 12:56:46.328133398 -0700
@@ -157,12 +157,18 @@ Internet-Draft              RTP Leap Sec

 3.3.  POSIX behavior during positive leap second

-   Most POSIX systems insert the positive leap second at the end of the
+   Strictly speaking, POSIX systems are supposed to insert the
+   positive leap second at the end of the
    last second of the day.  This results in repetition of the last
    second.  A timestamp within the last second of the day is therefore
    ambiguous in that it can refer to a moment in time in either of the
    last two seconds of a day containing a leap second.

+   In practice, many POSIX systems ignore this requirement, and
+   instead use a monotone-definite-increasing approximation to POSIX
+   time, e.g., by adding infinitesimal amounts to the POSIX clock
+   whenever the time is requested during a leap second,[9] or by
+   smearing the POSIX clock linearly near the transition.[10,11]


 Gross & van Brandenburg Expires February 28, 2014               [Page 3]
@@ -181,7 +187,7 @@ Internet-Draft              RTP Leap Sec
    second intervals.

    +-------+--------------+--------------+--------------+--------------+
-   |  RTP  |     TAI      |     UTC      |    POSIX     |     NTP      |
+   |  RTP  |     TAI      |     UTC      |    POSIX*    |     NTP      |
    +-------+--------------+--------------+--------------+--------------+
    |  8000 | 00:00:32.500 | 23:59:58.500 | 23:59:58.500 | 23:59:58.500 |
    | 12000 | 00:00:33.000 | 23:59:59.000 | 23:59:59.000 | 23:59:59.000 |
@@ -194,15 +200,21 @@ Internet-Draft              RTP Leap Sec

                                   Table 1

-   NOTE- Some NTP implementations do not entirely freeze the clock while
+   NOTE 1- Some NTP implementations do not entirely freeze the clock while
    the leap second is inserted.  Successive calls to retrieve system
    time return infinitesimally larger (e.g. 1 microsecond or 1
    nanosecond larger) time values.  This behavior is designed to satisfy
-   assumptions applications may make that time increases monotonically.
+   assumptions applications may make that time increases monotonically.[9]
    This behavior occurs in the least-significant bits of the time value
    and so is not typically visible in the human-readable format shown in
    the table.

+   NOTE 2- Some other implementations use a linear smearing near the
+   transition.  This lessens interval-length error as well as
+   satisfying monotonicity.[10,11]  This behavior may affect the
+   low-order human-readable bits of the POSIX time values shown
+   in Table 1.
+
 4.  Receiver behavior during leap second

    Timestamps generated during a leap second may be ambiguous or
@@ -380,6 +392,19 @@ Internet-Draft              RTP Leap Sec

    [8]        BIPM, "Circular T", May 2012.

+   [9]        Mills, D., "The NTP Timescale and Leap Seconds",
+              <http://www.eecis.udel.edu/~mills/leap.html>,
+              12 May 2012 23:43 UTC, retrieved 11 September 2013.
+
+   [10]       Kuhn, M., "Coordinated Universal Time with Smoothed Leap
+              Seconds (UTC-SLS)", January 2006, Internet Draft,
+              <http://tools.ietf.org/html/draft-kuhn-leapsecond-00>.
+
+   [11]       Pascoe, C., "Time, technology and leaping seconds",
+              15 September 2011, Google Official Blog,
+
<
http://googleblog.blogspot.com/2011/09/time-technology-and-leaping-seconds.html
>,
+              retrieved 11 September 2013.
+
 Authors' Addresses