Whenever the transmission capacity of a medium linking two devices is greater than the transmission needs of the devices, the link can be shared, much as a large water pipe can carry water to several separate house at once
Multiplexing allows several transmission sources to share a larger transmission capacity
In traffic problem that occurs in data communication (number of users increase), we can solve the problem by install higher capacity links (high bandwidth media such as coaxial cable, optical fiber, and satellite, microwaves) and use each to carry multiple signals instead of add individual line each time a new channel is needed