Digital Multiplexing

Digital Multiplex System (DMS) is the name shared among several different telephony product lines from Nortel Networks for wire line and wireless operators. Among them are the DMS-1 Rural/Urban digital loop carrier, DMS-10 telephone switch, the DMS Super Node family of telephone switches (DMS-100, DMS-200, DMS-250, DMS-300, DMS-500, DMS-GSP, DMS-MSC, DMS-MTX), and the S/DMS optical transmission system.

Exploratory development on the technology began in 1971. The first toll switch entered service in 1976 and the first Class 5 switch began service in 1979. DMS was the first commercially successful digital switch and revolutionized the industry. Previously technology entered the telecom industry only slowly with the telephone companies amortizing equipment over periods as long as forty years. AT&T was intending to delay the introduction of digital switching until the 1990s. The success of DMS changed the industry by creating a technological imperative that has lasted until this day. DMS, with its massive introduction of digital technology, was one of the antecedents that encouraged the Internet to grow large.


The DMS name arose from a designation for a switching matrix design that was developed in the exploratory phase of the project. The Digital Multiplexed Switch was selected as the basic switching design for the project. The product was intended as a successor for Nortel's first electronic switch the SP1 and was to be called the SP2.

However the DMS acronym was mellifluous and was eventually (1975) adopted as the designation for the DMS-100 family of products with the 'S' standing for 'system' rather than 'switch.' It was then applied to the entire digital switching family.

DMS is favoured by many European cable operators as the switching platform for their voice networks. The DMS-10 is widely used by rural wireline providers as well as the US Military. DMS-100 and 200 switches are widely deployed throughout the U.S. by RBOC and independent telcos. The DMS-250 is the backbone of the long distance network and the DMS-500 is commonly deployed by CLECs because it combines DMS-100 and 250 capabilities.