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When we want to transmit multiple messages, the goal is maximum reuse of the given resources: time and frequency. . It involves grouping manyseparate wires into a common cable enclosure. A cable that has, for example, 50 twisted pairs inside it can support 50 channels. There is therefore a one-to-one correspondence between physical and logical channels.

SDM has the unique advantage of not requiring any multiplexing equipment. It isusually combined with other multiplexing techniques to better utilize the individual physical channels.

For example If there are six people in the office and they all want to talk at the same time, there obviously will be some interference between the conversations taking place. To reduce the interference they may divide themselves into three groups of two, such that the conversation is between each pair of people. If the pairs continue talking whilst sitting next to each other, the interference would still be present.

The best way for each pair to converse with minimal interference would be to sit a few feet away from the other pairs (within the same room) and converse. They would still be sharing the same medium for their conversations but the physical space in the room would be divided for each conversation. This is an example of SPACE DIVISION MULTIPLEXING