[1] Carrier systems typically transmit multiple channels of communication simultaneously over the shared medium using various forms of multiplexing.
Many television programs are carried simultaneously on the same coaxial cable by sending each at a different frequency.
For long-distance calls several of these channels may be sent over a communications satellite link by frequency-division multiplexing.
Capacity of these systems increased in the middle of the century, while in the 1950s researchers began to take seriously the possibility of saving money on the terminal equipment by using time-division multiplexing.
Due to the shorter repeater spacings required by digital systems, long-distance still used FDM until the late 1970s when optical fiber was improved to the point that digital connections became the cheapest ones for all distances, short and long.