5ESS Switch is a telephone switching system first introduced in 1982 by Lucent Technologies ( formerly AT&T).
It has evolved into a truly universal digital switch that meets all the telecommunications needs of the modern information age. 5ESS has a wide variety of applications. It can serve as a local, toll or international gateway exchange, or a combination of these functions. It provides the following major applications: Local exchange, tandem exchange, Toll or transit exchange, Operator Services Position System (OSPS), Signal Transfer Point (STP) for a common channel signaling system, International gateway exchange, Wireless (cellular) switch (Mobile Switching Center/Mobile Telephone Switching Office; MSC/MTSO), Remote (switching) operations.
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The 5ESS Switch is the Class 5 telephone electronic switching system sold by Alcatel-Lucent. This digital central office telephone circuit switching system is used by many telecommunications service providers.