Multiplexing schemes can be divided into three basic categories, Frequency Division Multiplexing (FDM), Time Division Multiplexing (TDM), and Code Division Multiplexing (CDM), depending on how users share the available transmission medium
Time division multiplexing (TDM) is the timeinterleavingof samples from several sources so that the Information from these sources can be transmitted serially over a single communication channel.In Other way,
Time division multiplexing (TDM) is a digital process that can be applied when the data rate capacity of a transmission medium is much greater than the data rate required by individual sending and receiving devices. In such case, multiple transmissions can occupy a single link by subdividing them and interleaving the portions. This subdivision can vary from one bit forbit-interleaved multiplexers,trough a few bits forcharacter-interleaved multiplexers,to a few thousand bits in the latest types of high bit-rate multiplexers, theSynchronous Time Division Multiplexers (STDM)designed for the synchronous transfer mode.