Time Division Multiplexing or TDM is the digital process that allows several connections to share the high bandwidth of a link. Instead of sharing the portion of the bandwidth like FDM, time is shared here in TDM. Each connection occupies a portion of time in link. In TDM, data rate of link that carries data from 'n' connections must be 'n' times the data rate of a connection to guarantee the flow of data. Therefore, the duration of unit in a connection is 'n' times the duration of a time slot in frame. TDM can be visualized as two fast rotating switches, one on the multiplexing side and other on the de-multiplexing side. The switches are synchronized and rotate at the same speed, but in opposite direction. On multiplexing side, as the switch opens in front of a connection, that connection has the opportunity to send a unit on to the path. This process is termed as interleaving. On the de-multiplexing side, as the switch opens in front of a connection, that connection has the opportunity to receive a unit from the path. Implementation of TDM is not as easy and simple as that of the FDM. Synchronization between the multiplexer and the de-multiplexer is a major issue.
