A Digital Carrier-Concentrator System with Elastic Traffic Capacity

Delta modulation is used with a unique method of selective time-division multiplexing (TDM) to obtain concentration switching and digital transmission of telephone subscriber traffic. The switching function is nonblocking and the system can accept traffic without limit. There is, however, a tradeoff between instantaneous traffic load and system transmission quality. A switchsettable blocking limit is provided to prevent excessive degradation. Realistic traffic limits are determined by consideration of messagechannel degradations which may occur for a small fraction of the busy hour. With nominal traffic loading, the system provides telephone service to 256 subscriber lines connected to one or more remote terminals separately located along a single two-way digital line. This paper is the first of three which deal with different aspects of the system. It describes the system organization, the switching function, supervision and control, and the reframing procedure. A second paper describes traffic engineering considerations for the system [1]. A third paper describes the subscriber line equipment, delta codecs, line signaling functions, and an in-service line test facility [2].