[ntp:questions] Number of Stratum 1 & Stratum 2 Peers

Harlan Stenn stenn at ntp.org
Wed Dec 17 11:39:47 UTC 2014

Phil W Lee writes:
> Leap seconds seem to be a real mess in the IT world.
> It would be useful if the way of inserting a leap-second was set in a
> standard, in such a way that time continued at a set rate (maybe by
> slewing at a set percentage or PPM).  If that could be achieved, it
> would remove many of the objections to leap-seconds.
> It might be difficult to thrash out in practice though.

NTF's General Timestamp API is ready to address this.  We just need to
get enough support to get the ball rolling.

Some timescales have leapseconds, some do not.  If a timescale has leap
seconds, there are different ways it can be applied.  As long as these
choices are "defined" it's possible to usefully 'map' a timestamp taken
in one (version of one) timescale to a timestamp in a different (version
of a) timescale.

> I know that officially at present there is an additional second
> between 23:59:60 and 00:00:00, but no time recording system that I
> know of has the ability to record times between 23:59:60 and 00:00:00
> correctly (despite such times existing since 1st Jan 1961, which must
> surely pre-date any software currently in use), which is a necessary
> requirement if the second is to be inserted exactly as currently
> specified and time continued forward (so that events are recorded in
> the correct order).  
> Does anyone know of any software which will record times during that
> additional second accurately, e.g. as 23:59:60.789?

There are implementations of this that can make it impossible.  Nothing
much can be done about things that occur during that extra second.  If
the implementation does something more ... accommodating, it is possible
to track and map these events.  Some systems will "slow time" by half,
so the leap second occurs over 2 seconds.  Some will slew it over 2

Google's "leap smear" does it unevenly over a 24-hour period.

> Is there any realistic prospect of forcing software to comply with a
> time standard which includes times between 23:59:60 and 00:00:00?

I think so.  And folks can always choose to track time using TAI and
then map those events to the appropriate UTC.

> Now, you can either stipulate that all software including operation
> systems recognise times during that additional second - which would
> require re-writing the time functions of most of the worlds software
> to recognise and record times >23:59:60 < 00:00:00 (but only if a leap
> second has been legally notified), or you can agree to insert the
> additional second more gradually by clock slewing (but at what rate
> would have to be agreed).
> Clock slewing would require much more change to international
> agreements, but would require far less work on re-writing software,
> and would actually relate better to the real world, which is
> annoyingly both analogue AND irregular:-)
> Or the second itself could be redefined to take account of the actual
> speed the earth rotates - but that might be problematic for the
> scientists, as we'd likely have to keep doing it as the earth slows.
> I certainly think we need to deal with the problem better than we do
> at the moment.

Please support/participate in NTF's GTSAPI Consortium.
Harlan Stenn <stenn at ntp.org>
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