Multiplexing: To combine multiple signals (analog or digital) for transmission over a single line or media.

Multiplexing is done by using a device called multiplexer (MUX) that combines n input lines to generate one output line i.e. (many to one). Therefore multiplexer (MUX) has several inputs and one output.

At the receiving end, a device called De-multiplexer (DEMUX) is used that separates signal into its component signals. So DEMUX has one input and several outputs.

The multiplexing techniques can be broadly classified into two categories namely analog and digital.

Analog multiplexing can be either FDM or WDM and digital multiplexing is TDM.

Generally the FDM and WDM systems are used to deal with the analog information whereas the TDM systems are used to handle the digital information.

In FDM many signals are transmitted simultaneously where each signal occupies a different frequency slot within a common bandwidth.

In TDM the signals are not transmitted at a time, instead they are transmitted in different time slots.