The two ways to allocate the capacity of transmission media are with baseband and broadband transmissions.
Baseband devotes the entire capacity of the medium to one communication channel.
Broadband enables two or more communication channels to share the bandwidth of the communications medium.
Baseband is the most common mode of operation. Most LANs function in baseband mode, for example. Baseband signaling can be accomplished with both analog and digital signals.
Although you might not realize it, you have a great deal of experience with broadband transmissions. Consider, for example, that the TV cable coming into your house from an antenna or a cable provider is a broadband medium.
Many television signals can share the bandwidth of the cable because each signal is modulated using a separately assigned frequency. You can use the television tuner to choose the channel you want to watch by selecting its frequency.
This technique of dividing bandwidth into frequency bands is called ‘Frequency-division Multiplexing’ (FDM) and works only with analog signals. Another technique, called ‘Time-division Multiplexing’ (TDM), supports digital signals.