g the software for its new "System 12" digital switches competitive in the American market. Alcatel continued ITT's customer-premise equipment business under the Cortelco name but exited the American central office space until some years later, when it acquired DSC Communications. By the early 1990s, then, the wireline central office switch business had been narrowed down considerably. AT&T Technologies and Northern Tele- com split the lion's share. Siemens was the token third vendor for most RBOCs, with Sweden's L.M. Ericsson having a tiny presence in a few states. (Ericsson, however, was far more successful selling to cellular providers.) Two 1980s-era start-ups had established niche markets for themselves. Digital Switch Corp., later called DSC Communications, was strong in the long distance field, selling primarily to IXCs. Redcom Laboratories specialized in smaller, ruggedized Divestiture: Equal Access and Chinese Walls switches, which were sold to both military applications and the smallest rural telephone companies, especially in difficult environments such as the Arctic and tropics. But a wave of new switch vendors did not arise until the Telecom Act created new local competitors. Digitization of the Transmission Network During the 1970s, the bulk of the AT&T Long Lines network consisted of ana- log microwave radio links, with analog coaxial cable along high-traffic routes. But short-haul links, those under 50 miles, were most often carried over T1 digital carrier systems. T1 carrier was the original digital transmission system. It oper- ated at a speed of 1.544 Mbps and ran over ordinary twisted-pair copper cable. T1 carrier required a repeater every 6,000 feet, which was the same spacing used for putting loading coils on long local loops, making it easy to deploy. At the end of each T1 carrier system was a channel bank (multiplexor), which converted it to analog in order to meet the still-analog switches. Analog was mapped onto digital at a rate of 64,000 bps per channel; the mapping used by the Western