a networks based on CCITT Recommendation [27] X.25. Designed primarily for terminal-to-host connec- tivity using low-speed modems and analog transmission, X.25 was not nearly as popular in the United States as it was elsewhere. Some PTTs also built circuit- switched data networks, which were faster than the day's modems, based on Recommendation X.21. ISDN could provide circuit-switched and packet- Divestiture: Equal Access and Chinese Walls switched data, as well as voice telephone service. Many network operators con- sidered this to be compelling. The American perspective was a bit different. For one thing, the market dynamics were different. In Europe, each PTT was both a monopoly for tele- phone service and a monopsony for telephone network components. If British Telecom wanted GEC or Plessey to build to a precisely given specification, they had little choice. (The CCITT specifications had room for some national varia- tion, necessary because of historical differences between national networks.) Divestiture, however, resulted in seven large RBOCs and numerous independ- ents facing two major switch vendors, AT&T and Northern Telecom. This gave the latter companies more market power. Another issue was the RBOCs' rather slow perceptions. The integrated voice-data PBX boom had fizzled out prior to divestiture; the idea of using the telephone system as a local area data network was as dated as last month's lunchmeat. Yet the predominant RBOC view of ISDN seemed to be that it was designed to offer integrated voice and data (IVD) desktop connections. ISDN's lower-speed connection, the basic rate interface (BRI), had two 64 Kbps bearer (B) channels. Either one could be used for voice or data. But in the common American viewpoint of the day, it was one voice, one data-just like the IVD PBXs with which Centrex was competing. ISDN's higher-speed connection, the primary rate interface (PRI), ran over good old T1 facilities and typically offered 23 B channels (plus the signaling "D" channel) [28]. It made a good PBX trunk,