Just to elaborate on Pedro's writeup, the Multiplex technology was invented around the end of the 19th century, by a fellow by the name of Alexander Graham Bell. It was based on a system of separate electrical pulse frequencies that ran along one telegraph wire, allowing for many communications at once. It was multiplexing technology that made the invention of things like the phone and then the internet possible. Otherwise, at most about 4 people (that is, after the invention of the quadruplex telegraph by Edison) could use one cable (and by Morse code only), which would terribly impractical given maintenance costs.