Trends in the development of public telecommunication networks

Abstract

Abstract By applying digital techniques not only to interexchange transmission and switching but also to the subscriber access, public telephone networks are evolving into end-to-end digital networks. The 64 kbit/s digital channels needed for carrying PCM encoded speech can also be used to convey non-voice information. This leads to the concept of the Integrated Services Digital Network (ISDN) offering access to a wide range of services over a single subscriber line. By using optical fibers at the subscriber access and by adding high-speed switching networks capable of handling channels at speeds up to 135 Mbit/s, the 64 kbit/s ISDN will be upgraded towards the Broadband ISDN (B-ISDN). Additional services offered in B-ISDN include video conferencing, video telephony and TV distribution and high-speed data transmission. The adaptation of X.25 to ISDN will be the standard method for packet switching (PS) in ISDN for many years. Additional packet mode bearer services refer to closer integration of PS into ISDN by employing the ISDN signalling procedures designed for circuit switching (CS) also for controlling virtual connections. The ultimate step will be a new type of fast PS technique in B-ISDN combining the advantages of PS and CS: Asynchronous Transfer Mode (ATM). Public telecommunication networks are being enhanced to offer Value-added Services (VAS), i.e. high layer capabilities beyond pure transport of information.