Digital Data System: Local Distribution System

The local distribution portion of the Digital Data System is discussed in this paper. Baseband, bipolar transmission over telephone cable pairs is used to extend the digital channel from the serving central office to the customer's location. The performance and requirements of these local channels are presented. The design and performance of the local distribution hardware are examined. Design features include (i) automatic equalization by means of an automatic line-build-out network and (ii) control mode indication by means of bipolar format violations.