Digital Data System: System Overview

The Digital Data System (DDS) is a new data communications network that is integrated into the nationwide telecommunications system. With this network, Dataphone® digital services are available. Point-topoint and multipoint private line services are provided. The first allows digital communication between two subscriber terminals, while the latter allows several terminals at different locations to share a common transmission channel. Data rates of 2.4, 4.8, 9.6, and 56.0 kb/s are offered. These services are similar to those which have been available for the past decade using analog telephone channels of various bandwidths. The new system, however, utilizes station-to-station digital transmission techniques as contrasted to modulation and demodulation of digital signals to and from analog form for transmission over telephone channels. Existing business machine terminals are directly usable on the system through industry standard interfaces or, if the customers prefer, 811 connection may be made at a four-wire channel service interface. Data transmission is synchronous; timing signals are always supplied from the network. The DDS has become practical and desirable through the large-scale deployment of digital transmission systems in metropolitan areas, the development of long-haul digital transmission systems, progress in technology, and the development of a sufficient market for the services. It offers economies in the cost of transmission and, by taking advantage of the regeneration, monitoring, and protection approaches applicable to digital signals, it promises a higher-quality service than has been realized in using analog telephone systems for data communication.