[time-nuts] [LEAPSECS] Leap second to be introduced at midnight UTC December 31 this year

[Bob Camp]

Hi

The practical problem with any change to leap seconds is transition from what we have
to the “new system”. Anything other than dropping them altogether involves a *lot* of 
coordination. You pretty much have to pick a date and bring everything onto the new
standard then. For testing purposes your time sources should “advertise” the new 
information ahead of that date. As a practical point, that means a new field in the data. 
In the case of GPS and other space based systems, that’s not going to happen. 

The alternative is to have a “magic date” and a pre-defined set of dither bits for the 
next year or two after that. Yes that’s a mess on top of a mess. It does allow people to
roll out a patch that can be tested ahead of time. They can then transition to the full
blown approach. If you think about the amount of time needed to do this … two years
may not be enough …

This indirectly gets into the systems question of: How early *do* you announce the dither
bit for a given month? There are systems that *do not* get their leap second information 
from broadcast or live network sources. You would have to put out the pattern early 
enough to accommodate their “pipeline”. If that involves manually loading files … yikes. 

Bob


> On Jul 22, 2016, at 4:44 AM, Martin Burnicki <martin.burnicki at burnicki.net> wrote:
> 
> Tom Van Baak wrote:
>> Time to mention this again...
>> 
>> If we adopted the LSEM (Leap Second Every Month) model then none of
>> this would be a problem. The idea is not to decide *if* there will be
>> leap second, but to force every month to have a leap second. The IERS
>> decision is then what the *sign* of the leap second should be this
>> month.
> 
> Although this approach sound good, it would cause major problems for
> users of the German longwave transmitter DCF-77. The data format only
> has a "leap second pending flag", which means a leap second is to be
> inserted. AFAIK there is no spec to announce a negative leap second via
> DCF-77.
> 
> Martin
> 
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