Craig.Everhart%CMU-CS-A@sri-unix.UUCP (02/23/84)
Here's some background information on ``atomic time'' and some broadcast
formats.
Date: 23-Jul-83 05:10:28-UT
From: Mills@dcn6 (Dave Mills)
Subject: Time-server leaps and bounds
I have done a little digging on the leap-second problem. The broadcast
standards on which our network time-distribution system is based provide
time-of-day, day-of-year and certain corrections and offset information.
The NBS broadcast formats are described in "NBS Special Publication 432,
Time and Frequency Dissemination Services (1979)." . . . . There are two
time scales of interest: UTC, commonly called "atomic time" and UT1,
commonly called "astronomical time." The broadcast time is UTC; however,
UT1 corrections up to a maximum of about one second are encoded in the
data stream. When the correction exceeds this a leap-second is inserted
or deleted; however, the times when such a correction can be incorporated
are known in advance and coordinated throughout the world by the Bureau
des Heure. . . . . Since UT1, which drives the diddle in the first
place, is determined by observation and the precision necessary to
determine it to the accuracy required has only recently been achieved, it
would seem uninteresting to establish a Network Standard Time based on
UT1. I suspect all existing IEN-142 servers, like ours, simply
brute-force the calculation assuming no corrections were ever made.
This results in our losing about a second a year, on average.