Hi John,
On 2016-10-09 12:41 PM, John Sauter wrote:
On Sat, 2016-10-08 at 15:58 -0600, Warner Losh wrote:
On Sat, Oct 8, 2016 at 2:43 PM, Steve Allen <s...@ucolick.org> wrote:
On Fri 2016-10-07T11:48:25 -0600, Warner Losh hath writ:
Accurate, Traceable, and Verifiable Time Synchronization for
World
Financial Markets
http://nvlpubs.nist.gov/nistpubs/jres/121/jres.121.023.pdf
Market synchronization requirements today are 1s. However, in
August
2017 they become 50ms. Good thing normal market hours on the US
exchanges avoids the leap second...
Notably missing in this document is any mention of the term leap
second.
More surprising is no mention of TAI, despite the numerous
references
to the use of IEEE 1588 PTP for the timing systems.
It's like getting a tour map that describes the route but fails to
mention that along the way there's a bridge out.
Yes, it's like all the other systems I worked on that required
external UTC to be correct at all times, even when the GPS receiver
doesn't yet know the current number of leap seconds. I'll have to
pass
the leap second comment along to the author...
Warner
I took the lack of mention of leap seconds to mean that leap seconds
ere not a problem. The output of the NISTDC units is an astonishingly
accurate 1 pulse per second. That feeds NTP, which handles leap
seconds using a table. As long as the table is kept up to date,
everyone agrees on each second's name.
Except the one to be called YYYY-MM-DDT23:59:60.
There are 86401 pegs in the (positive) Leap Second UTC day. There are
86400 holes in traditional timescales in which to put them. Something
has to to go missing - the mapping is indeterminate. Common practice of
introducing Leap Seconds on local timescales simultaneous with its
introduction at UTC places these indeterminate labels at different
time-of-day points along each local timescale. Non standardized and
politically driven Daylight Savings rules further complicates when these
indeterminate moments occur. Meantime there is no standardized way to
keep the Leap Second tables automatically updated to begin with.
-Brooks
John Sauter (john_sau...@systemeyescomputerstore.com)
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