elecom had a proprietary electronic telephone instrument, called the P-set (as in "proprietary"), for its DMS-100 Centrex and SL-100 PBX (the latter being basically the same product but sold to an end user instead of a common carrier). FCC regulations prohibited local exchange carriers from sup- porting any new service whose interface specifications had not been published ahead of time, SO the P-set was eventually documented and registered. But it was still proprietary, a one-vendor solution. AT&T Technologies, as Western Elec- tric had been renamed after divestiture, did not have a corresponding product for the 5ESS Centrex. Instead, it devoted its effort to supporting an emerging worldwide standard, Integrated Services Digital Network (ISDN), that would serve the same purpose. With a digital telephone set on a digital switch with digital trunks, the network would finally be digital from end to end. Centrex remained an important market for the RBOCs. It provided them with an impetus to support ISDN and the digitization of the network. Unfortu- nately, it may have blinded some Bell executives from seeing the other possibili- ties made possible by a digital network. Digital Switching Becomes the Norm During the late 1970s, the PBX industry had moved from analog to digital switching for all but the smallest line sizes. AT&T's Dimension was a holdout, but only because it was waiting for 1983's deregulation before rolling out the 1979 Antelope. Yet at the same time, the Bell networks were themselves almost entirely analog. Western Electric was a Johnny-come-lately to digital switching in the central office, too. All of the Bell System's central office switches were electromechanical until the mid-1960s. Their first production "electronic" switch was the 1ESS, first placed in service in 1965. This combined stored-program control with electro- mechanical reed-relay switching. New step-by-step and crossbar switches were Divestiture: Equal Access and Chinese Walls discontinued a few years later. In the 1970s, the 2BESS w