The Picturephone System: No. 101 ESS

1.1 General1-8 The No. 101 Electronic Switching System (ESS), an electronic private branch exchange (PBX), has been providing customers with Centrex and other specialized services since the first commercial installation was made in Cocoa Beach, Florida, in November 1963. The system, consisting basically of a control unit (CU) and one or more switch units (SU), effects the actual interconnections between lines, trunks, and service circuits on a time division switched basis as described in the February 1969 issue of the B.S.T.J. 4 The SUs are connected by means of data links to the CU a common, centrally located, special purpose computer which processes calls in the system by means of a stored program technique.0,6 Although practical for the handling of voiceband frequencies, the time division circuitry in the No. 101 ESS switch units is not capable of handling the higher frequencies required for transmission of video signals. In order to provide video switching capability, a wideband switch unit (WSU) utilizing space division switching has been designed for use in parallel with the 2A, 3A, and 4A switch units. 7-9 1.2 Objectives The design objectives for the WSU were based upon the expected low demand for Picturephone service during the initial years. It was 605