[ntp:questions] Re: HOWTO prepare ntpd to the leap of a second

Serge Bets serge.bets at NOSPAM.laposte.invalid
Fri Dec 30 07:00:11 UTC 2005


 On Thursday, December 29, 2005 at 22:54:20 +0000, David L. Mills wrote:

> You really should read the commentary in the NIST leapsecond file

Thanks for the hint. Latest leap-seconds.3331497600 comments:

| The following entry specifies the expiration date of the data in this
| file in units of seconds since 1900.0. This expiration date will be
| changed at least twice per year whether or not a new leap second is
| announced.

And the important dates in order are:

| Last Update of leap second values:	28 July 2005
| [latest positive leap in table]	 1 Jan  2006
| File expires on:			28 June 2006


> The file does not expire when the leap is inserted; it remains valid
> as a record of past TAI offsets until the next edition is issued.

Better than that: An issue remains completely valid until just before
next still uncertain event opportunity.


> When multiple valid sources display conflicting leap bits, the logical
> OR of these bits is used.

Currently one leap=01 source wins the consensus over any number of
leap=00 sources. That's fine, because many sources don't carry leap bits
at all. But that can be fooled, if the leap=01 source is wrong. Seen
here reports of this HP Zsomething, or that Truetime GPS, anouncing leap
or leaping themselves at a wrong date.

The NIST file could win consensus until expiration, making sure no
spurious leap second announcement is done.


Serge.
-- 
Serge point Bets arobase laposte point net




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