Xbar (CROSSbar)

Electromagnetic, common control circuit switches that replaced the electro-

mechanical step-by-step (SxS) switches. AT&T Bell Telephone Laboratories accomplished most of the conceptual work on the Xbar, but the Ericsson company (Sweden) was responsible for much of the early practical development. The first Xbar switch installed in the United States was a central office (CO) exchange in Brooklyn, New York in 1938. Xbar technology quickly became preferred over that of the electromechanical SxS switch, which dates to 1891. In an Xbar switch, a marker recognizes a request for dial tone, directs a sender to store the dialed digits, and directs a translator to route the call, reserving a path through a switching matrix. Once the call connects, these various components become available to serve other calls. Compared to the SxS switch, the Xbar has relatively few moving parts. Xbar switches offer the advantages of increased intelligence, common control, faster connection speed, smaller physical footprint, lower maintenance costs, and greater traffic capacity. Xbar switches were considered state of the art for nearly 30 years, until the appearance of the electronic common control (ECC) switch in 1965. See also ECC, switch matrix, and SxS.

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