Tsukasa Iwama

Experiences of leap second adjustment operations and questionnaires in Japan

National Institute of Information and Communications Technology (NICT) in Japan has responsibilities to generate and to maintain Japan Standard Time (JST), and to disseminate the JST throughout the country. For these purposes, NICT is operating multiple sets of Cesium frequency standard systems and Hydrogen maser systems to generate stable and reliable time scale. JST is generated and maintained from the ensemble of the signals from these frequency standards. NICT operates the satellite communication link for TWSTFT (Two-Way Satellite Time and Frequency Transfer) link between Asian region and Physikalisch-Technische Bundesanstalt (PTB) in Germany through the collaborations with the National Metrological Institutes in the Asian region to contribute clock data in the region to establish Coordinated Universal Time (UTC). NICT is also participating in the GNSS (Global Navigation Satellite Systems) time link network and both TWSTFT and GNSS data are used for UTC establishment.

Exponential degrading of NTP synchronization with number of network hops

Time synchronization using the Network Time Protocol (NTP) has increased with the growth of the Internet. There are hundreds of public NTP servers in the world. Conventional client software selects a peer/server using packet delay jitter statistics for some manually listed servers, even though it is commonly understood that the nearest NTP server should be used. We demonstrate that NTP synchronization degrades with the number of network hops. The hop count indicates the number of routers on the network path, which is where most jitter and packet loss occur. The accuracy of client time synchronization degrades exponentially with hop count. We propose a round-trip hop-counts-capable NTP server response for the accurate selection of the nearest server.