Multiplexing is essentially the means of permitting multiple signals on one transmission on one data link. Many users can use the same path and medium at the same time without interruption or need for use intervention. Terms used in the Multiplexing environment are multiplexer and demultiplexer. The multiplexer combines the singles and the demultiplexer is the inverse. Essentially this is the sending and receiving ends.
There are several categories of multiplexing, and they include analog and digital. Analog has Frequency-Division Multiplexing and Wave-Division Multiplexing and digital has Time-Division Multiplexing. The need for different frequency bands ensures noise is filtered out and avoids overlapping.
Frequency-Division Multiplexing was initially used with telephone exchange networks. With Frequency-Division Multiplexing, analog signals are combined. A high frequency signal is the basis for the signal and this signal is called the carrier signal. With Frequency-Division Multiplexing, all signals are transmitted simultaneously with non-overlapping frequency bands. Frequency-Division Multiplexing must have sufficient bandwidth. Signal overlapping is separated by guard bands. Frequency-Division Multiplexing divides single bandwidths into different frequencies. With digital, information is modulated; modifying its amplitude, frequency or phase, and this is called the modulating signal.
With Wave-Division Multiplexing, it is really the same as Frequency-Division Multiplexing however; it involves signals through fiber-optic channels. In this scenario, light is separated by a prism. Colors (light beams) are essential to sending and receiving with Wave-Division Multiplexing.
Time-Division Multiplexing allows many signals to be used in the same channel, but different time slots can be used. With Time-Division Multiplexing, it is a digital process that handles data rate capacity if greater than required by sending and receiving devices. Essentially, Time-Division Multiplexing is a digital multiplexing that combines data by collecting and storing transmissions and allocating and sending it, as appropriate.
Time-Division Multiplexing can be used both synchronous and asynchronous.