Integrated services digital networks: Narrowband networks

Abstract This paper deals with the deployment of the narrowband Integrated Services Digital Network, which is conceived as a significant rationalization of the existing public telecommunication networks, which include at present a number of different structures devoted to the various kinds of services. The main guidelines of ISDN evolution are depicted, starting with a short analysis of the expected wide range of TLC services, as this market is the main driving force for the deployment of new network architectures providing a powerful integrated access, a rapid service introduction and a high flexibility. The resulting reference network architecture is then described, highlighting the maximum possible integration of techniques and services, the unified access for the whole range of TLC services, the significant improvement of the user‐network signalling capabilities, the provision of high level network capabilities and the efficient communication among the various network entities. Some interworking and network dimensioning aspects, related to the gradual deployment of this new network architecture, are also examined, together with some consideration about further evolutionary steps. A second part of the paper is devoted to an analysis of ISDN functionalities, starting with a short survey of ISDN protocols (X.31 network access protocol, higher layers protocols, CCITT N. 7 network signalling for ISDN), which are the international standards on which this evolution is based. Circuit and packet ISDN switching facilities are then briefly examined, focusing on ISDN access functions, which are very important for both the access integration and the hardware cost reduction. A further important point examined concerns ISDN protocol testing and validation (for both terminals and switching offices), together with the performance evaluation of ISDN switching officies. The last part of the paper is devoted to a short survey of the present status of ISDN world development (pilot services, start of commercial services), starting from the European situation (France, Germany, United Kingdom, Italy etc.), examining the ISDN development in other Countries (United States, Japan, Canada and others) and giving finally some indications about the expected future plans.