[LEAPSECS] leap second and DUT1 database

[Warner Losh]

> On Jan 28, 2015, at 5:25 AM, Tom Van Baak <tvb at LeapSecond.com> wrote:
> 
> Hi Warner,
>  
> Keeping cold spares is a good example. I can see that having to acquire GPS lock and waiting up to 12.5 minutes for current leap second information would be a problem. There must be a way to cache that state so rapid failover is possible, in both the hot and cold spare case.

It is possible to keep this state in the general case, but there are some failure modes that this couldn’t be relied upon. And rather than the “happy path” that most people think of, most of the failure analysis was along the lines of “what happens if these components fail at the same time, or in this or that order” which leads to crazy workarounds to avoid the worst case situation where possible, but also knowing that sometimes we have to recover that way.

> I know radio stations like WWV and WWVB that broadcast leap second and UT1 corrections face a very similar problem.
>  
> With all the PhD's and technology at their disposal, NIST has developed a cost-effective, highly reliable solution. Note that their communication infrastructure and UT1 database is compatible with all versions of Linux and Windows, does not require access to the internet, and the storage system is protected from power failures and floods. It provides rapid access in case of emergency and maintains both current and historical values of leap seconds and DUT1. Redundant copies of the database can be placed in an iPhone, as seen below. I was very impressed and plan to implement their solution in my own lab.
>  
> For details, see: http://leapsecond.com/pages/wwvb/

That solution is too high tech for LORAN stations :) We’re dealing with folks that don’t have PhD’s running the show.
 
> On close inspection this NIST system, as currently designed, will fail if DUT1 were allowed to exceed its current range of 0.7 seconds; perhaps another reason to keep leap seconds.

If that’s the only think keeping leap seconds around, I’ll drive up to Fort Collins and neatly paint more white lines on the chalkboards.

Warner

P.S. I know LORAN has shut down in the US, and my experience is a few years old, but the fundamental nature of the problem hasn’t changed.