A US law which forbade the attachment to the public telephone network of any device not furnished by official network provider AT&T gave Western Electric, a wholly-owned subsidiary of AT&T, an almost total monopoly in the US modem market. The market was only opened up to competition in June 1968 following a legal ruling known as the Carterfone Decision which permitted non-AT&T equipment to be connected to the telephone network providing that the equipment passed a series of stringent Federal Communications Commission (FCC) tests.
