The evolution of transmission and switching for integrated services digital networks

This paper reviews the evolution of digital transmission and switching in a telecommunication network, and emphasizes the importance of integration of networks and services. The concept of an Integrated Digital Network and an Integrated Services Digital Network are introduced and a brief review is given of the repertoire of transmission systems available in the United Kingdom to realize such networks. The objective of this introductory paper is to provide general background information supporting the companion papers in these special issues.