FDM is possible when bandwidth of signal to be transmitted. The number of signal can be carry simultaneously if reach signal is modulated to a different frequency six signal sources are fed in to a multiplexing, which each signal on to a different frequency.
The input signal fed to the multiplexing are may be analog or digital. If the input is digital signal, the signal will be converted in to analog using modem or vice versa.
Of FDM is Radio or Television.
TDM is also known as synchronous TDM, use for multiplexing digitized voice stream and data stream. We can improve the efficient of synchronous. TDM by adding complexity to the multiplexer.