NTP: Network Time Protocol
NICT distributes Japan Standard Time to users over the internet by the Network Time Protocol (NTP). The NTP server (or simply time server) is available at
ntp.nict.jp
This server is directly connected to NICT’s Japan Standard Time signal, but the internet environment between the server and the user can greatly affect the received timing information. It is therefore not possible to guarantee the accuracy. Depending on the configuration and traffic over the user’s link to the server, the obtained time may differ from Japan Standard Time by a few to several hundred milliseconds.
For more information on how to set up your operating system to use NICT’s time server, please see the Frequently Asked Questions, where you can also find our contact information.
Service Overview
NTP is the most widely used method for network time transmission and is used by the majority of internet-connected systems and devices that need to synchronize their clocks to an accurate reference. The original version was developed before 1985, making it one of the oldest internet protocols. Network Time Protocol Version 4 is the latest version, standardized in 2010. NICT’s NTP service currently supports version 2 and all newer versions.
As we live in a society with ubiquitous information and communications technology, where many devices now connect to the internet, NICT’s NTP servers need to handle a large number of requests. In 2019, the number reached up to 50,000 requests per second, and seven billion per day [1].
Load and attack resistant server with high precision and reliability
To handle this demand, NICT uses a proprietary server developed in house. To provide a reliable source of Japan Standard Time, the system is configured for redundancy, and operates in a similarly controlled environment as the reference clocks themselves. In addition to the server installed at NICT’s Koganei headquarters, an additional server operates at the Kobe sub-station since 2020. This server will automatically be used as an alternative time source by simply setting the NTP server name to ntp.nict.jp as before.
The NTP server is entirely implemented by an FPGA so that the accuracy does not decrease with growing load [2]. The latest, stand-alone version includes self-monitoring functions referenced to multiple time sources, and it can perform automatic initialization without requiring a host PC to operate. As single-function hardware, it is impossible to break into by hacking or software exploits.
The time server is installed inside NICT's facilities and is directly connected to Japan Standard Time. In the terminology of NTP, this makes it a stratum 1 system. The processing capacity is over 1 million requests per second. Its time accuracy is within 10 nanoseconds of Japan Standard Time, such that the client accuracy is only limited by network effects. While symmetric delays in the round-trip from client to server and back are removed by the network time protocol, other effects like queuing delays and asymmetric round-trip routes cannot completely be corrected for.
References
1) H. Saito, T. Iwama, K. Imamura, N. Kotake, H. Usui and H. Narita Standard Time Services for the Internet Society 情報通信研究機構研究報告 (NICT Research Report) 65(2): 時空標準技術特集 39-44 (2019)
2) A. Machizawa, NICT Public NTP Service — The Highest Throughput Capacity in the World — NICT News 2006(10) 3-4 (2006)
Further reading
A. Machizawa, T. Iwama and H. Toriyama Packet Arrival Interval (PAI)-Based Time Synchronization Electronics and Communications in Japan, Part I, Vol.90(11) (2007)
町澤朗彦、岩間司、鳥山裕史 ネットワーク時空情報サーバと動的ユーザランド時刻クライアントの開発 電子情 報通信学会論文誌, vol.J90-D(6) 1394-1402 (2007)
岩間司、金子明弘、町澤朗彦、鳥山裕史
高速ネットワークを利用した高精度時刻比較 - Precise Estimation of High-Speed Network Time-Transfer
電子情報通信学会論文誌, vol.J89-D(12) 2553-2563 (2006)
©2006 IEICE 許諾番号:07RB0120
鳥山裕史、町澤朗彦、岩間司
ハードウエアSNTPサーバの開発 - Development of a Hardware SNTP Server
電子情報通信学会論文誌, vol.J89-B(10) 1867-1873 (2006)
©2006 IEICE 許諾番号:07RB0121
町澤朗彦、岩間司、鳥山裕史
毎正秒パケット到着間隔(PAI)に基づいた時刻同期方式 - Packet Arrival Interval (PAI) Based Time Synchronization
電子情報通信学会論文誌, vol.J89-B(10) 1855-1866 (2006)
©2006 IEICE 許諾番号:07RB0122
町澤朗彦、鳥山裕史、岩間司、金子明弘
通過型高精度UDPタイムスタンパの開発 - Development of a Cascadable Passing Through Precision UDP Time-Stamping
Device
電子情報通信学会論文誌, vol.J88-B(10) 2002-2011 (2005)
©2005 IEICE 許諾番号:07RB0123
北口善明、町澤朗彦、鶴正人、尾家祐二、箱崎勝也 パケット自己消滅手法によるネットワーク時刻同期精度の向上 - The Advanced Network Time Synchronous System by Self-discarding Packet Technique 情報処理学会論文誌, 46(4) 1017-1024 (2005)
北口善明、町澤朗彦、箱崎勝也、中川晋一
高精度時刻 PC による片道遅延時間によるネットワーク帯域推定手法 - The Network Bandwidth Measurement Based on One-Way Delay Using
a High-Precicion PC
電子情報通信学会論文誌, vol.J87-B(10), 1696-1703 (2004)
©2004 IEICE 許諾番号:07RB0124
町澤朗彦、北口善明
割込みハンドラと高精度PCによるソフトウェアタイムスタンプの精度改善 - Improvement of Software Timestamp Accuracy with Interrupt Handler and
High Precision PC
電子情報通信学会論文誌, vol.J87-B(10), 1678-1685 (2004)
©2004 IEICE 許諾番号:07RB0125
T. Iwama, A. Kaneko, A. Machizawa and H. Toriyama Real-Time Measurement of One-Way Delay in the Internet Environment Proc. ATF2004, No.TD-5 (2004)
Y. Kitaguchi, A. Machizawa, M. Tsuru, H. Fukuoka and K. Hakozaki Research of advanced time synchronous system with network support Proc. 2003 IEEE Pacific Rim Conference on Communications, Computers and Signal Processing (PACRIM'03) 1036-1039, Victoria (2003)
今村國康, 後藤忠広, 金子明弘, 今江理人, 栗原則幸 ネットワークによる日本標準時供給システム 第1回情報科学技術フォーラム (FIT2002)
T. Gotoh, K. Imamura and A. Kaneko Improvement of NTP Time Offset under the Asymmetric Network with Double Packet Method Conf. Precision Electromagnetic Measurements, Ottawa (2002)
H. Okazawa, A. Machizawa, S. Nakagawa, Y. Kitaguchi, T. Asami and A. Ito
Advanced NTP Synchronization Device for Internet Monitoring Tools
Proc. INET2001, Stockholm (2001)
via web.archive.org
A. Machizawa, K. Sugiura, T. Komine, H. Okazawa, S. Nakagawa and S. Uetsuki On the Delay and Quality of DV Transmissions Systems using ATM Networks Proc. 15th International Conference on Information Networking (ICOIN-15), 709-713, Beppu (2001)
後藤忠広, 今村國康, 金子明弘, 関戸衛, 川合英治 NTP 高精度化のためのネットワーク遅延補正 - Compensation of Network Round Trip Delay for High Precision NTP 2001年信学会総合全国大会 (2001)
K. Imamura, A. Kaneko, M. Imae, N. Kurihara and T. Gotoh The UTC(CRL) time dissemination server by Network Time Protocol (NTP) Proc. of the ATF 2000, Tokyo, p. 263 (2000)
後藤忠広, 今村國康, 森川容雄, 深瀬弘恭 NTP Stratum 1 Server の性能評価 1996年信学会総合全国大会, no.B-194 (1996)
後藤忠広, 今村國康, 森川容雄, 深瀬弘恭 NTPによる時刻の供給 1995年信学会総合全国大会, no.D-240 (1995)
T. Gotoh and K. Imamura Development of the UTC(CRL) time dissemination server for the computer network Proc. of the 9th European Frequency and Time Forum (EFTF), Besancon, p. 314 (1995)
後藤忠広, 今村國康 ネットワーク計算機の協定世界時(UTC)への同期 - UTC Time Distribution via Network Time Protocol 1993年信学会総合全国大会, no. B-722 (1993)