GPS time synchronization server, Beidou time meter-jingzhun electronic technology
GPS time synchronization server, Beidou time meter-jingzhun electronic technology
Jingzhan Electronic Technology Officer Weiahjzsz
Foreword
In recent years, with the improvement of the level of computer automation systems, it has been widely used in major computer monitoring systems, microcomputer protection devices, microcomputer fault recorders and various data management machines, and the cooperation of these automatic devices needs to have A precise and uniform time. When the system fails, it can not only realize the operation monitoring and post-accident failure analysis of each system of the entire station under a unified time base, but also analyze the cause and process of the accident through the sequence of each protection action, the switching of the switch and the accurate time , It is convenient to analyze and trace the various events that occur during operation, which improves the automation level of the system.
An overview of
the field of communication, "synchronization" refers to a concept of synchronization frequency, i.e., the clock frequency and phase synchronization of each node in the network, the error should comply with the relevant standards. At present, in the communication network, the problem of frequency and phase synchronization has been basically solved, but the synchronization of time has not been solved well. Time synchronization refers to the time and time interval of the clocks of each node of the network and the clocks of various application interfaces connected through the network are synchronized with Coordinated Universal Time (UTC), at least in a local or metropolitan network to be synchronized with Beijing time. The time synchronization network is the basis for ensuring time synchronization. The time synchronization network can be wired or wireless. Here we mainly introduce Internet time synchronization technology and products, that is, network time synchronization through a network time server that supports the NTP protocol.
The basic unit of time is seconds, which is one of the seven basic units of the International System of Units (SI unit system). In 1967, the International Conference on Metrology (CGDM) gave a new definition of seconds: "Seconds are 9 192 631 770 cycles of radiation corresponding to the transition between two superfine energy levels of the cesium 133 (133Cs) atom at 0K temperature ground state "Duration", or "Atomic Second" (TAI). The commonly used coordinated universal time is actually an atomic second adjusted for leap seconds.
At present, the cesium atomic clock is mainly used in the international and national benchmarks. The cold atom fountain cesium atomic clock established by the Chinese Academy of Metrology has a frequency reproducibility of 5 × 10-15, which is close to the international advanced level. In fact, at the application level, the high time and frequency accuracy of the national benchmark is not required. Different applications have different requirements for accuracy. Table 1 lists some typical applications that require time accuracy (error of application interface time relative to UTC time).
Table 1: Some typical applications for time accuracy
| application |
Time accuracy requirements |
| Computers and servers for banking, securities, stock and futures trading |
1 second |
| Power line fault diagnosis |
1 microsecond |
| Switch and billing system |
1 second |
| CDMA2000 and TD-SCDMA |
10 ms |
| Network management system |
500 ms |
| No. 7 signaling monitoring system |
1 millisecond |
2. Network time synchronization technology
There are currently a variety of time synchronization technologies, each of which has its own characteristics. The time synchronization accuracy of different technologies also varies greatly, as shown in Table 2:
Table 2: Various commonly used time synchronization techniques
| Time synchronization technology |
Accuracy |
Coverage |
| Shortwave timing |
1 ～ 10ms |
global |
| Long wave timing |
1 millisecond |
region |
| GPS |
5 ～ 500ns |
global |
| Telephone dialing |
100 ms |
global |
| Internet Time Service (NTP) |
1 ～ 50ms |
global |
| SDH transmission network timing |
100 nanoseconds |
long haul |
1. Time synchronization technology of long and short wave timing
Timing using radio signals has a history of more than 80 years. The international long wave timing mainly uses the Roland-C system. The domestic launch station is located in the coastal area, mainly used for military and navigation, and is not yet civilian.
2. Phone dialing time synchronization technology
The equipment used for telephone dialing and timing (ACTS) is relatively simple, requiring only a telephone line, analog modem, PC and client software. At present, this kind of computer is mainly used to calibrate the time of the home personal computer, and it does not have real-time performance.
3. GPS time synchronization technology
GPS time synchronization technology is a relatively mature and widely used time synchronization technology in the world. At present, in addition to the GPS of the United States, there are the GLANASS system of the former Soviet Union and the "Beidou" system of our country. Due to economic reasons, the GLANASS system has a limited number of health stars, and its stability and reliability cannot be guaranteed. The "Beidou" system has not been used by civilians, and it cannot be covered in real time. GPS is currently a relatively mature and reliable system.
4. Internet time synchronization technology
It is very convenient to use the Internet to synchronize the time of the computer. At present, this method is widely used in the local area network. Microsoft has embedded the Network Time Protocol (NTP) into the Windows XP system. As long as the computer can be connected to the Internet, it can perform computer time calibration within the LAN or WAN. The standard NTP protocol uses the RFC 1350 standard, and the simplified network time protocol (SNTP) uses the RFC 1769 standard. The NTP protocol includes a 64-bit Coordinated Universal Time (UTC) time stamp with a time resolution of 200 ps, and can provide a time accuracy of 1 to 50 ms (depending on network load). But experiments have shown that the calibration accuracy of this technology in intercontinental can only reach hundreds of milliseconds or even seconds. Therefore, primary and secondary time servers should be set up in a huge network to solve the accuracy problem.
In addition, there are two relatively simple, low-precision Internet time protocols: Time protocol (RFC868) and Daytime protocol (RFC867), which can provide WAN time synchronization with 1s calibration accuracy.
3. GPS network time server
The network time server is a combination of GPS time synchronization technology and Internet time synchronization technology. Adopt 19-inch 1U rack design, built-in GPS receiver, take GPS satellite time as standard time source, support NTP protocol (V2.0 / V3.0 / V4.0) and SNTP protocol. It can provide time calibration for hundreds of computers and routers in the local area network. The following figure shows the application scheme of GPS network time server:
In the above solution, from the provincial central network to the local municipal network, it is necessary to keep the time of the application interface synchronized. If only one network time server is set up in the provincial network, then the clients in the prefecture-level network cannot guarantee the required accuracy due to network delays, etc., then it can be solved by setting up a network time server in the prefecture-level network. This problem, but if the network conditions are good, this error can be automatically compensated when NTP protocol;