1. APG15-4 Inf. Session 기반표준본부 시간센터 UTC and Leap Second in Rep. of Korea UTC and Leap Second in Rep. of Korea Dai-Hyuk Yu Center for Time and Frequency Division of Physical Metrology Korea Research Institute of Standards and Science

2. Generation of UTC NMIs in the World Time Scale UTC(k) Commercial clocks Time transfer Time Scale UTC(k) Commercial clocks Time transfer Primary Frequency Standards BIPM Free Atomic Scale (EAL) International Atomic Time (TAI) Coordinated Universal Time (UTC) Universal Time (UT1) BIPM Circular T UTC – UTC(k) BIPM Circular T UTC – UTC(k) Weighted Average of ~400 atomic clocks over 70 Labs. Accuracy Evaluation Leap Second |UTC- UT1| < 0.9 s

3. UTC(k) traceable to UTC 9 atomic clocks: 5 Cs clocks + 4 H-masers Circular T issued monthly

4. Dissemination of the Korea Standard Time 5 MHz, 5 kW  Broadcasting of Time Signal (call sign: HLA)  Time service through internet NTP time server at KRISS 260 million/day

5. Survey(2013)  Purpose  Current status of Time Sync. in civil area  Opinions on the “Leap Second” issue  Possible failure experiences during the “Leap Second” insertion  Statistics  Period: August ~ September in 2013  Target: TV stations, Research Institutes, Companies, Banks etc.  17 responses from 22

6. Survey(2013)

7.  GPS: 76.5%  NTP: 23.6%  HF station: 5.9% No problem reported so far can be attributed to the well functioning of GPS and receivers - expect some support in case needed

8. Survey(2013)  Indifference - no problem so far - expect some support in case needed

9. Survey(2013)  Yes - troublesome to care for the insertion of “Leap Second” - avoid possible future catastrophe and the correction is possible with higher accuracy by using other method - need to carefully guide some equipment users to use “GPS Time” not “UTC” to avoid possible malfunction - transaction can be in a mess due to “causality problem”  Cessation of Leap Second  No - no problem so far - need to do extra work to the existing well functioning system

10. Possible problems Judah Levine, NIST, ITU-leapsec, 2013.7

11. Possible problems Judah Levine, NIST, ITU-leapsec, 2013.7

12. Possible problems Judah Levine, NIST, ITU-leapsec, 2013.7

13. NTP time server at KRISS ~3000/s 260 million/day ~3000/s 260 million/day  Impact - KRISS servers transmit ~2x3000 times messages with a time equivalent to 23:59:59 UTC - Some systems do not recognize advance notice parameter and do nothing at leap second (1 s error until next request) - system can request repeatedly - some system can crashes” - increasing number of users for NTP Possible problems

14. Continue to do…  Current status - There are pros and cons for the cessation of “Leap Second” - There are no unanimous agreement in Korea - Direction : continue to study to “prevent possible future repetitive occurrence of catastrophe when the “Leap Second” is maintained