NBC set up the first permanent coast-to-coast radio network in the United States by 1928, using dedicated telephone line technology. The network physically linked individual radio stations, nearly all of which were independently owned and operated, in a vast chain, NBC's audio signal thus transmitted from station to station to listeners across the United States. Other companies, including CBS and the Mutual Broadcasting System, soon followed suit, each network signed hundreds of individual stations on as affiliates: stations which agreed to broadcast programs from one of the networks.
