Digital Data System: Physical Design

Communications systems developed to serve a young and growing market and to provide service to a broad geographical area have always presented challenges. Not the least of these challenges is the physical partitioning and packaging of the various subsystems that make up a total service. For the DDS, the task has been to provide private-line data service at several customer bit rates for a changing cross section of users, and to introduce such service into many large cities initially, with a capability of expanding to serve small towns all over the country. Like most systems faced with interconnecting stations scattered so diversely, the basic DDS layout comprises a hierarchical structure beginning with interconnected hub offices located in large metropolitan areas. Fanning out from these hubs are local offices and the individual subscribers to the service. Equipment in the DDS offices performs the general functions of terminating loops to the customer, multiplexing and demultiplexing data streams, and monitoring and testing the integrity of the system. Station apparatus located at the customer's premises provides the interface between the customer's data terminal and the DDS. Hub offices are partitioned into four functional sections each of which may be located in separate areas of a central office building or all may be grouped together in one dedicated DDS area. Local offices have, in general, less equipment and, although they function similarly to hub offices, the integrated nature of their design 943