Time synchronization in North America
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Time synchronization in North America can be achieved with many different methods, some of which require only a telephone, while others require expensive, sensitive, and rare electronic equipment. In the United States, the United States Naval Observatory provides the standard of time, called UTC(USNO), for the United States military and the Global Positioning System,{{Cite web|url=http://tycho.usno.navy.mil/|title=US Naval Observatory Precise Time Department|access-date=2018-01-15|archive-date=2019-08-26|archive-url=https://web.archive.org/web/20190826164130/https://tycho.usno.navy.mil/|url-status=dead}} while the National Institute of Standards and Technology provides the standard of time for civil purposes in the United States, called UTC(NIST).
ITU-R Standard Frequency and Time Signals
A standard frequency and time signal service is a station that operates on or immediately adjacent to 2.5 MHz, 5 MHz, 10 MHz, 15 MHz, 20 MHz, and 25 MHz, as specified by Article 5 of the ITU Radio Regulations (edition 2012).ITU Radio Regulations, CHAPTER II – Frequencies, ARTICLE 5 Frequency allocations, Section IV – Table of Frequency Allocations The US service is provided by radio stations WWV (Colorado) and WWVH (Hawaii).
The methods below provide either Coordinated Universal Time (UTC), which is defined by Recommendation ITU-R TF.460,{{Cite web|url=https://www.itu.int/rec/R-REC-TF.460/en|title=TF.460 : Standard-frequency and time-signal emissions|website=www.itu.int|access-date=2018-01-11|archive-date=2018-03-04|archive-url=https://web.archive.org/web/20180304074112/http://www.itu.int/rec/R-REC-TF.460/en|url-status=live}} or the official U.S. implementation of UTC, officially labeled UTC (NIST).
Internet time sources
Several different time synchronization protocols exist on the Internet, including:
| class="wikitable"
|+ !Protocol !RFCs !Accuracy !Ports !Time servers |
| Daytime Protocol
|RFC 868 |Nearest second |TCP port 13 | |
| Time Protocol (a.k.a. NETDATE)
|RFC 868 |Nearest second |TCP/UPD part 37 | |
| NTP
|RFC 1305, RFC 5905 | | | |
| SNTP
|RFC 1769, RFC 2030 | | | |
| ICMP TIMESTAMP
|RFC 0792, page 16 | | | |
| IP TIMESTAMP option
|RFC 0791, 3.1, page 16 | | | |
GPS time synchronization
GPS receiver requirements
- Minimum: GPS receiver that works with user chosen software; this requires some combination of GPGGA, GPRMC, GPZDA, GPGSA, and GPGSV sentences. This provides accuracy of between 1 and 2 seconds, and includes most, but not all modern GPS receivers.
- Better: USB GPS receiver with the NMEA 0183 GPZDA sentence sent at least once a second. The developer of the Windows software NMEATime2 recommends GPS units with the U-blox 7 receiver,{{Cite web |url=http://www.visualgps.net/NMEATime2/MoreInfo.html |title=NMEATime2 |website=www.visualgps.net |access-date=2018-01-15 |archive-date=2018-01-16 |archive-url=https://web.archive.org/web/20180116081105/http://www.visualgps.net/NMEATime2/MoreInfo.html |url-status=live }} and this software uses a control loop to analyze the text of the GPS timing sentence, and claims to achieve 1 ms accuracy with the technique.
- Better yet: RS-232 GPS receiver with the NMEA 0183 GPZDA sentence sent at least once a second, plus a 1PPS signal on DCD (1 μs accuracy possible with a real RS-232 port not on the USB bus; 1 ms possible with a RS-232 to USB adapter{{Cite web|url=https://gpsd.gitlab.io/gpsd/hardware.html|title=Compatible GPSes|website=gpsd.gitlab.io|access-date=2021-10-27|archive-date=2021-10-23|archive-url=https://web.archive.org/web/20211023231637/https://gpsd.gitlab.io/gpsd/hardware.html|url-status=live}}). The Garmin GPS 18x LVC{{Cite web|url=https://buy.garmin.com/en-US/US/p/27594|title=Garmin GPS 18x OEM™ | Sensor|access-date=2018-01-11|archive-date=2018-01-12|archive-url=https://web.archive.org/web/20180112044112/https://buy.garmin.com/en-US/US/p/27594|url-status=live}}{{Cite web|url=https://www.lammertbies.nl/comm/info/gps-time|title=GPS time synchronization tutorial|first=Lammert|last=Bies © 1997-2021|access-date=2021-10-27|archive-date=2021-05-02|archive-url=https://web.archive.org/web/20210502023643/https://www.lammertbies.nl/comm/info/gps-time|url-status=live}}{{Cite web|url=http://www.satsignal.eu/ntp/NTP-on-Windows-serial-port.html|title=An NTP Stratum-1 clock usng a GPS 18 LVC and Windows 2000/XP/Windows-7|website=www.satsignal.eu|access-date=2018-01-11|archive-date=2018-01-07|archive-url=https://web.archive.org/web/20180107201221/http://www.satsignal.eu/ntp/NTP-on-Windows-serial-port.html|url-status=live}} appears to be the only such device that is generally available to consumers, but this then needs an external 5 V DC power source.
- Best: Higher accuracy is possible with a high-end GPS receiver designed for time signal use, but these are very expensive (around $1000), feature OCXOs (oven-controlled crystal oscillators), and often require special software and physical RS-232 ports not connected via a USB bus to achieve that accuracy.
Utility frequency
In 2009 the Federal Energy Regulatory Commission made time error correction (TEC) of the power grid frequency mandatory.{{cite web |title=Western Electricity Coordinating Council Regional Reliability Standard Regarding Automatic Time Error Correction |date=May 21, 2009 |publisher=Federal Energy Regulatory Commission |url=http://www.ferc.gov/whats-new/comm-meet/2009/052109/E-14.pdf |access-date=June 23, 2016 |archive-date=December 21, 2016 |archive-url=https://web.archive.org/web/20161221015250/https://ferc.gov/whats-new/comm-meet/2009/052109/E-14.pdf |url-status=dead }} While TEC does not provide full synchronization (date and time) and synchronization is lost in case of a power outage it provides an inexpensive way to maintain high long term accuracy of synchronous clocks found in most household appliances. Once the initial time is set the power grid will typically maintain the accuracy within 10 seconds relative to UTC by adjusting frequency.{{cite web|url=http://www.naesb.org/pdf2/weq_bklet_011505_tec_mc.pdf|title=Manual Time Error Correction|website=naesb.org|access-date=4 April 2018}}
All time sources
Several different organizations provide publicly accessible recorded voice time sources, including the NIST Telephone Time of Day Service, see speaking clock. Other sources include GPS, terrestrial radio time signals, and internet services, as listed below.
See also
- Time signal
- Atomic clock
- Network Time Protocol
- Radio clock
- List of radio time signal stations
- WWV (radio station)
- WWVH
- WWVB
- Extended Data Services (XDS "Time-of-Day Packet")
- Standard frequency and time signal service
- Coordinated Universal Time
- List of UTC timing centers
- Time and frequency transfer
- Synchronization
- Time synchronization over radio
References
{{Reflist}}
External links
- [https://www.itu.int/rec/R-REC-TF.768/en Recommendation ITU-R TF.768, Standard Frequencies and Time Signals]
{{Americas topic|Time synchronization in}}