The Picturephone System: Central Office Switching

Although devices have been developed to switch megahertz bandwidth signals, they have been limited to a small number of inputs and outputs. Also, the logical controls for these devices have been relatively simple. The development described in this article is the first automated, large-scale switching system designed to switch large numbers of wideband signals on an analog basis. We discuss the network and controls added to the No. 5 crossbar switching system that enable an existing switching system to process calls from Picturephone stations as well as telephones. l.i Design Philosophy Picturephone service is intended to be an extension of basic telephone service rather than a separate communication package. This fact has important implications in all of the Bell System, particularly in the design of switching systems. As such, the wideband switching system developed for Picturephone service utilizes the existing telephone plant as much as possible. Clearly this design method is reasonable from an economic standpoint since a large number of existing telephone switching functions--registration of dial digits, charging, call supervision, signaling--are also needed for Picturephone 533