st what ISDN is, because it has meant SO many different things to SO many people [25]. The telephone network had been built out of analog subsystems, which were being replaced by digital ones. Before ISDN, digital switches and digital transmission facilities were inter- connected using protocols, such as multifrequency tone signaling, designed for the analog world: Digital islands in an analog sea. ISDN was to be the digital glue to bind them together, removing the obsolete analog artifacts, with digital local loops to extend this network to the subscriber. ISDN development began in 1978 at the CCITT (this stands for the International Telephone and Telegraph Consultative Committee, with the ini- tials coming from the French), which was then the International Telecommuni- cations Union's worldwide telecom standardization branch. (It is now known as the ITU Telecommunications Standardization Sector, or ITU-T for short.) CCITT projects ("study questions") were planned based on four-year study periods, each of which culminated in a new set of published standards [26]. The CCITT began a serious study of ISDN in the 1980-1984 time frame, culminat- ing in a preliminary set of draft standards in the 1984 "Red Book" and a much more developed set of standards in the 1988 "Blue Book." ISDN was especially important to the European telephone monopolies of the day, most of whom at that time were still known as the PTTs. Because each country's analog network had evolved separately, with dissimilar standards, equipment had to be built to a given national standard. This was particularly troublesome at the subscriber end. In an era of increasing free trade, especially among the European states, ISDN promised a single worldwide digital telecom standard, and thus "terminal port- ability," as well as a more globalized market for network gear. ISDN also promised to integrate both voice and data onto one network, saving on capital and operational costs. During the late 1970s, many of the PTTs had invested heavily in packet-switched dat