History
The 5ESS Class 5 Switch first appeared in Seneca, Illinois (815 Area Code) in 1982, and slowly replaced the 1ESS switch and other electromechanical and analog systems in the 1980s and 1990s. The 5ESS was also used as a Class 4 telephone switch or as a mixed Class 4/5 in markets too small for a 4ESS switch. Approximately half of all US telephone exchanges are serviced by 5ESS switches. The 5ESS is also exported internationally, and manufactured outside of the US under license.
The development effort for 5ESS required 5000 employees, producing 100 million lines of code, with 100 million lines of header and makefiles. Evolution of the system took place over 20 years, while three releases were often being developed simultaneously (each taking about 3 years to develop).
A 5ESS-2000 version, introduced in the 1990s, increased the capacity of the switching module (SM), with more peripheral modules and more optical links per SM to the communications module (CM; see below). A follow-on version, the 5ESS-R/E, was in development during the late 1990s but did not reach market.
Lucent Technologies (now part of Alcatel-Lucent) was formerly the AT&T Network Systems division of AT&T, which in turn was formerly known as Western Electric. The 5ESS came to market as the Western Electric No. 5 ESS, later 5ESS, 5ESS-2000, 5E-XC and is currently marketed as the Alcatel-Lucent 5ESS.
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