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4ESS switch
From Wikipedia, the free encyclopedia
The 4ESS switch is a Class 4 telephone Electronic Switching System that was the first digital electronic toll switch introduced by Western Electric for long distance switching. Early versions used the same 1A processor as the contemporaneous improved 1ESS switch. It was introduced in 1976 in Chicago to replace the 4a crossbar switch and the last of 145 in the AT&T network was installed in 1999 in Atlanta. Over 100 4ESS switches remained in service in the United States in 2006.
Early Automatic & Crossbar Switches
Strowger Switch • Panel Switch • Western Electric 1XB • Western Electric 5XB
Electronic Switching Systems
Western Electric 1ESS • Western Electric 1AESS • Western Electric 5ESS • Northern Electric SP1 • Northern Telecom DMS-100 • Stromberg-Carlson/Siemens DCO • Automatic Electric GTD-5 EAX