Clock synchronization

In a centralized system, time is unambiguous. When a process wants to know the time, it simply makes a call to the operating system. If process A asks for the time, and then a little later process B asks for the time, the value that B gets will be higher than (or possibly equal to) the value A got. It will certainly not be lower. In a distributed system, achieving agreement on time is not trivial.

The global standard for a clock is known as Coordinated Universal Time (UTC). Sometimes UTC and Greenwich Mean Time (GMT) are used interchangeably to refer to the global standard for a clock. However, GMT is British summer time, which is one hour ahead of UTC [Howse 1980]. UTC was officially adopted in 1960 [Arias and Guinot 2004]. It is based on the average observations of the time reported by atomic clocks.

An atomic clock is based on the state transition of electrons in atoms as it keep moving from one energy level to the other. The electrons in atoms emit microwave signals when they change their energy levels on transitions. The definition of one atomic second is as follows.

So What is Clock synchronization?

Clock synchronization in distributed systems refers to the process of coordinating the clocks of individual nodes or machines so that they maintain a consistent time reference across the system. This ensures that all participants in the distributed environment have a uniform understanding of time, which is crucial for the correct ordering of events, coordination, and communication between nodes.