ISDN Basic Rate Interface Interoperability with Key and Hybrid Systems

Abstract

More than one million AT&T small business customers have invested billions of dollars in MERLIN® II and MERLIN LEGEND® telecommunications equipment, typical small customer premises equipment (CPE) switches. Many of these customers want to be able to use applications such as video conferencing and high-speed data, available only with digital facilities, such as integrated services digital network (ISDN), either through ISDN primary rate interface (PRI) lines or ISDN basic rate interface (BRI) lines. Before the fourth quarter of 1994, the MERLIN LEGEND control unit supported only PRI connectivity. Unfortunately, PRI lines are beyond the price range of many customers because of the large number of channels they require and their associated costs. On the other hand, customers who want ISDN BRI lines must change their service features and replace most of their existing MERLIN II and MERLIN LEGEND equipment. This paper describes a BRI solution — based on a software-emulated terminal (SET) model — for customers who want the capabilities that ISDN offers, as a natural extension of the digital architecture of the MERLIN Communications System. Its system architecture and infrastructure now support basic rate access from MERLIN Communications Systems to a central office (CO). The SET model that resides within the MERLIN LEGEND control unit supports both the ISDN B-channel transport service and access to CO-based supplementary services. The SET appears to the central office as one or two physical terminals, complete with handset, keypad, and feature buttons. Combining the emulated terminals with the internal architecture of the MERLIN LEGEND produces a seamless user interface, regardless of network connectivity. With this design, customers can continue to use their embedded base of equipment, while gaining access to digital transport and advanced services accessible through BRI.