ISDN started to become available in 1980, around the same period that SONET was beginning to be deployed in major population centers in the United States. It was believed that ISDN would meet the increasing demand for reasonably affordable small office/home office (SOHO) digital telephony, enhanced voice and data services, and flexible digital transport for dedicated data and video services. However, the dream of ISDN, as it turned out, was long in coming. In the United States, starting in the 1970s, an effort had been underway by AT&T and the BOCs to convert the original electromechanical switch-based FDM telephone system to a TDM-based infrastructure. The TDM system provided better transport facilities for voice and accommodated data ...

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