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ESS(1) (Electronic Switching System) A large-scale computer used to route telephone calls in a telephone company office. The 5ESS is a Class 5 central office switch, and the 4ESS is a Class 4 tandem office switch. The ESS designation originated with AT&T when it manufactured the machines and was the only telephone company in the U.S. See SS7, Class 4 switch, Class 5 switch and digital cross-connect.
(2) (Enterprise Storage Server) A family of SAN devices for mainframes and Unix servers from IBM. ESS units are built with a high degree of fault tolerance and connect via Fibre Channel, SCSI, ESCON and FICON interfaces. See SAN.
(3) (Executive Support System) See EIS.
(4) (Electronic SpreadSheet) See spreadsheet.
(5) (Extended Service Set) Two or more Wi-Fi access points in the same subnet. See BSS and 802.11.