Using the Network Time Protocol (NTP) to Transmit International Atomic Time (TAI)

Judah Levine, David Mills

Abstract:	Although Coordinated Universal Time (UTC) is the time scale that is transmitted by almost all time services, this scale is awkward to use in the vicinity of a leap second. Many computer systems cannot represent the epoch corresponding to a positive leap second (23:59:60), and remain synchronized to UTC by stopping the clock at 23.5959 for I extra second whenever a leap second is to be added. This makes it impossible to assign unambiguous time tags to events that happen during this period. In addition, computing the length of a time interval that includes a leap second of either sign is difficult because simply subtracting the two UTC time stamps at the end-points of the interval does not account for the time interval occupied by the leap second itself; To address these issues, we have augmented the Network Time Protocol to allow a client system to reconstruct TAI from UTC and a table of leap seconds. This time scale has no discontinuity during the leap second. Intervals computed using TAI are unaffected by the additional time occupied by the UTC leap second, and the TAI time scale provides an unambiguous time tag to any event -- even one that happens during a UTC leap second. Although our solution is unique to servers that support the Network Time Protocol, it could be adapted to other time services and formats. Such systems could support time tags using either UTC or TM, and would significantly reduce the problems that result from using UTC alone.
Published in:	Proceedings of the 32th Annual Precise Time and Time Interval Systems and Applications Meeting November 28 - 30, 2000 Hyatt Regency Reston Town Center Reston, Virginia
Pages:	431 - 440
Cite this article:	Levine, Judah, Mills, David, "Using the Network Time Protocol (NTP) to Transmit International Atomic Time (TAI)," Proceedings of the 32th Annual Precise Time and Time Interval Systems and Applications Meeting, Reston, Virginia, November 2000, pp. 431-440.
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