APG15-4 Inf. Session

기반표준본부 시간센터

UTC and Leap Secondin Rep. of Korea

UTC and Leap Secondin Rep. of Korea

Dai-Hyuk Yu

Center for Time and FrequencyDivision of Physical Metrology

Korea Research Institute of Standards and Science

Generation of UTC

NMIs in the World

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 TUTC – UTC(k)

Weighted Average of ~400 atomic clocks over 70 Labs.

Accuracy Evaluation

Leap Second|UTC- UT1| < 0.9 s

UTC(k) traceable to UTC

TA(k)

Atomic Clock 1

t1

t2

t3

tn

BIPMAtomic Clock 2

Atomic Clock 3

Atomic Clock n

UTC(k)

GPS receiver

Clock Comparison

9 atomic clocks: 5 Cs clocks + 4 H-masers

Circular Tissued monthly

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

Survey(2013)

Purpose

Current status of Time Sync. in civil area Opinions on the “Leap Second” issue Possible failure experiences during the “Leap Sec-

ond” insertion

Statistics

Period: August ~ September in 2013 Target: TV stations, Research Institutes, Companies,

Banks etc. 17 responses from 22

Survey(2013)

Quite Well47%Well

47%

No6%

Recognition of Leap Second

Survey(2013)

GPS58.8%

GPS/NTP11.8%

GPS/HF sta-tion

5.9%

NTP11.8%

Other5.9%

No resp.5.9%

Sources of Time Sync.

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

Survey(2013)

Yes29.4%

No17.6%

Indif-ference47.1%

No resp.5.9%

Cessation of Leap Second

Indifference - no problem so far - expect some support in case needed

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

Possible problems

Judah Levine, NIST, ITU-leapsec, 2013.7

Possible problems

Judah Levine, NIST, ITU-leapsec, 2013.7

Possible problems

Judah Levine, NIST, ITU-leapsec, 2013.7

NTP time server at KRISS

~3000/s260 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

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