Guest Editor's Prologue: The Thrust of Electronic Systems in the Subscriber Loop Plant

In the closing years of the 1970s, two complementary technological trends emerged which are on the verge of bringing the electronic loop network to fruition as the prescription of choice for growth in the suburban and urban loop plant: highly integrated digital telecommunications networks, and intelligent electronic systems. Digital subscriber carrier systems, experiencing significant cost reductions from dramatic advances in digital LSI technology, were introduced in the mid 1970s, and by 1979 were functionally integrated with new local digital switches. At the same time, the economics of digital carrier were challenged by emerging intelligent electronic range-extender systems which provided automatic voice and signaling gain as well as increasingly lower per-channel cost. Integrated with large stored-program-control analog switches, such range extenders could be concentrated behind the first stages of switching and automatically adjust themselves to provide optimal transmission treatment to whatever subscriber they served based on measurements made instantaneously at time of call setup. Both of these approaches to lower cost loop systems are being complemented by increasingly intelligent automatic maintenance diagnostic systems which enhance their value to the operating companies. It is from this vantage point that the first paper in this special section unveils the scenario for the continued development of the electronic loop network. In considerable detail, the next three papers reveal the latest integrated range extension system plan based on intelligent interaction with the host office and customer plant and its implementation in the Bell System. The final three papers - from Japan, France, and Canada - project into the future and examine the strategies by which advanced digital technology and fiber optic facilities will be merged with operating system overlays to provide new telecommunication services that promise to provide customer services and conveniences undreamed of but 15 years before.