Nortel Meridian is a private branch exchange telephone switching system. It provides advanced voice features, data connectivity, LAN communications, computer telephony integration (CTI), and information services for communication applications ranging from 60 to 80,000 lines. History Exploratory development on digital technology, common for the SL-1 (PBX) and the DMS (public switch) product lines, began in 1969 at Northern Telecom, while R&D activities related to the SL-1 started in 1971. SL stands for Stored Logic. The original products were developed in a Bell-Northern Research developed proprietary toolset and language, similar to Pascal called Protel, and ran without a specific operating system. In the 1990s it was evolved onto VxWorks, a commercial real time embedded operating system, at which time the model numbers were evolved to add the letter C to the end of the option numbers. It was introduced by Northern Telecom in December 1975, with an original capacity from 100 to 7,600 lines, and became the first fully digital PBX announced on the global market aimed at the smaller PBX market. In the early 1970s, most PBXs were either electromechanical (e.g. cross-bar) or based on a hybrid technology (e.g. switching matrix made from a two-dimensional array of contacts but control performed by an electronic logic). For this reason, the SL-1 enjoyed a great success on the enterprise market both in North-America and globally. Its success went on to power the company into a leadership position in the telephony world, and led to expanded designs "up and down" to provide products at all sizes, including the DMS series high-end machines, and the Meridian Norstar for smaller installations up to 200 users. The SL-1 was gradually enhanced (peripheral hardware, packaging, etc.) and renamed Meridian-1 in the late 1980s. The Meridian-1 has evolved to support IP telephony and other next generation IP services. Impact The Meridian has 43 million installed users worldwide, making it the most widely used PBX. The Meridian was one of the few PBXs still available from a major communications supplier that can be configured as non-VOIP PBX and could be upgraded to a hybrid system with VoIP added. Models The Meridian 1 range currently consists of several models: Meridian 1 Option 11C (60-800 lines) Meridian 1 Option 11C Mini (60-128 lines) Meridian 1 Option 61C (600-2000 lines) Meridian 1 Option 81C (200-16,000 lines) Additionally, other products have been sold using the Meridian brand: The Norstar key telephone system was