TDM Full Form is Time Division Multiplexing. This is one of the most widely used methods of transmitting signals, especially in telephony. The GSM network of telephones uses TDM. In TDM, all the signals use the same frequency but at different times. In this technique, the same link or fiber is used to transmit signals belonging to multiple users. The users take turns to use the link / fiber to transmit signals. So each user is allocated fixed time slots where his data is either received or sent.
Both the multiplexer and the demultiplexer work in sync so that both switch over to the next user simultaneously. A timely synchronizing signal or distinguishing identifier is usually required so that the receiver can tell which user’s data is currently being transmitted or received in the shared common line. The time slots can be divided into asynchronous way or a synchronized way depending on the requirement.
In synchronous TDM, all users’ clocks are necessary to be aligned with some reference clock, which could be provided by one of the involved systems. In a synchronous TDM, the timeslots are random. They are assigned dynamically as needed. Generally for digital signals use TDM. But more recently, techniques are developed to transmit analog signals using TDM.