[LEAPSECS] Crunching Bulletin B numbers (POSIX time)

[Warner Losh]

On 02/23/2011 03:53, Ian Batten wrote:

>> Having a known list of leap seconds let one recover TAI time from a cold GPS receiver in a few seconds to a minute, rather than waiting ~20 minutes for the almanac to download.  Many systems have their internal clocks in TAI, but also have requirements to report time in UTC to users.  Such a table would ensure these systems could come back online quickly without having to pay the 20 minute penalty.  While the system may have already been down a little while when the swap is made, an extra 20 minutes can kill reliability targets for the system.

> Hang on.  Let's unpick that scenario.  How long would a machine have to be down such that a cached copy of the almanac no longer contained already applied leap seconds?

The computer and GPS receiver are co-packaged in one tin-can.  This 
tin-can is swapped out as a unit, as the operational personal lack the 
skills, tools and/or training to diagnose any problems to a smaller 
failure unit.

Warner