Time synchronization is a process of providing a unified time scale for distributed systems through some operations on local clocks. In a centralized system, because all processes or modules can get the time from the unique global clock of the system, any two events in the system have a clear order.
In a distributed system, due to physical dispersion, the system cannot provide a unified global clock for independent modules, but each process or module maintains its own local clock. Because the timing rate of these local clocks is inconsistent with the running environment, even if all local clocks are calibrated at a certain time,
After a period of time, these local clocks will also be inconsistent. In order to make these local clocks reach the same time value again, time synchronization operation must be performed.
Extended data:
The main classification of time synchronization
radio wave
Another time synchronization method is to transmit time information through radio waves. That is to say, the time standard of radio wave transmission is passed, and then the comparison between the time signal and the local clock is restored by the timing receiver, and the delay on the propagation path and the influence of various error factors are deducted to realize clock synchronization.
With the increasing demand for clock synchronization accuracy, radio wave time service method is used. Timing (millisecond precision), because the propagation path of short wave is affected by ionospheric change, sky wave has one or more sky waves, and the propagation distance of ground wave is close, so the timing accuracy can only reach millisecond level.
Later, it was developed to use ultra-long waves, that is, Omega, to time, and its timing accuracy was about10 μ s. Later, long waves, that is, Roland C chain, were used to time, and its timing accuracy could reach μ s. Even if Roland C chain was networked, it would be difficult to achieve global coverage. Later, it was developed to use satellite clocks as mobile clocks. Time signals are transmitted by ultrashort waves. By receiving a satellite, the user can make its timing accuracy better than that of the moving clock, and the accuracy can reach 10ns.
satellite
It seems that satellite timing is a good way to achieve accurate global clock synchronization. Only by using satellites can time signals be transmitted to all parts of the world by ultrashort waves. Using ultrashort wave to transmit time signal not only has high transmission accuracy, but also can improve the clock comparison accuracy.
By the method of * * observation, the satellite clock can be used as the portable clock, and the timing accuracy can be higher than that of the direct-acting clock, so it is difficult for the clocks in the two places to look at each other. * * * Vision can eliminate many systematic errors and errors that change slowly with time, and fast random errors can be eliminated by accumulation smoothing.
network
First of all, we should know what NTP protocol is: NTP protocol is the full name of network time protocol. Its purpose is to deliver a unified standard time on the Internet. The specific implementation scheme is to specify several clock source websites on the network to provide time service for users, and these websites should be able to compare with each other to improve accuracy.
NTP was first designed and implemented by Professor Mills of the University of Delaware. It has been nearly 20 years since 1982 was first put forward, and the accuracy of 200 1 the latest NTPv4 has reached 200 milliseconds.
NTP synchronization refers to time calibration with time source through NTP protocol of network. Prerequisites: the output of time source must pass through the network interface, and the data output format must conform to NTP protocol.
All PCs, servers and other devices in the local area network keep synchronization with the time server through the network. NTP protocol automatically judges the network delay and makes time compensation for the obtained data. So as to keep that time of LAN equipment uniform and accurate.
Baidu Encyclopedia-Time Synchronization