Loop Plant Electronics: The Loop Switching System

The Loop Switching System By N. G. AVANEAS and J. M. BROWN (Manuscript received October 26, 1977) A new system for achieving more efficient use of cable pairs, the Loop Switching System (LSS), has been developed which uses a microcomputer to control the call processing, traffic measurement and display, system maintenance, and manual testing. The LSS, which works with any central office, switches 96 subscriber lines onto 32 voice frequency trunk pairs by means of a graded multiple space division switching network at the remote terminal (RT) and expands the trunks back into the individual line appearances at the central office terminal (COT) located within a central office. An additional 96 lines and 32 trunks can be added to the LSS, either at the same RT or a second RT on a different cable route, using the same COT common control equipment. Control of the RT is via two standard voice-frequency pairs used for a fullduplex data link. This four-wire data link, operating at 1250 bits per second, is used to transmit concentrator connection orders from the COT to the RT, service request information from the RT to the COT, and other information pertaining to LSS maintenance and alarms. This paper describes the system features, operational characteristics, and circuit designs used in the LSS system.