 as well as a useful link for higher-speed applica- tions such as video teleconferencing. But while most PBX trunks in Europe were converted to PRI by the mid-1990s, analog and non-ISDN channelized T1 trunks remained the domestic norm. To a considerable extent, this was driven by the RBOCs' newfound devo- tion to Centrex. ISDN was just what Centrex needed, at least in their eyes. It allowed for standardized multibutton feature-rich telephone sets, to compete with PBX systems' proprietary instruments, and it offered integrated voice and data to the desktop. If ISDN had lived up to its early promise, then by 1988 or so, Centrex would have been feature-competitive with the digital PBX systems of 1980! In fact, while domestic ISDN trials began in 1987, Centrex-driven rollout was slow, though a number of installations were made by the end of the 1980s. RBOC marketing material featured IVD and local area data applica- tions. Non-Centrex ISDN was even slower to appear. When, by the early 1990s, most major European and Japanese central offices had been upgraded to ISDN and service was readily available at little price premium over analog rates, the RBOCs were dragging their heels, typically treating non-Centrex ISDN as a super-premium service. The early ISDN push spawned a minor industry of its own, but vendors faced a more difficult road than most expected. Bellcore was actively promoting ISDN, albeit with little marketing savvy. Dozens of companies introduced The Great Telecom Meltdown ISDN terminal equipment, not to mention the extensive test equipment needed to actually make it work: Although ISDN was conceived as a standardization project, the American implementation was somewhat different. AT&T created its own ISDN specification for the 5ESS, known as AT&T Custom. Northern Telecom created its own specification for the DMS-100, known as Nortel Custom. Needless to say, these were not nearly compatible; terminal vendors usually had to implement both formats. (There were, after all, more RBOCs than equipment vendors.) 