ex: Telecommunications Infrastructure History Fixed line telephony and data - current infrastructure state and its evolution Developments and modernisation Over the past 130 years, since the inception of the Bell System in the United States in 1875, the main infrastructure stock in telecommunications has traditionally been in fixed line technologies, originally analogue* voice telephony. This consisted of three major elements, the local loop, the switches and a trunk or long distance network. From the 1970s onwards, most OECD countries transferred to digitised voice with codecs (coder decoders) SO that two main signalling systems were in operation in the local loop - the original analogue and also the new digitised voice, using pulse code modulation (PCM) according to CCITT/ITU standards and with dual tone multifrequency (DTMF) dialing. Digitalisation of the infrastructure 1973-95 Renewal of the technology stock over the period 1973-95, led by OECD countries, moved the infrastructure of most of the world from analogue signalling and control to digital switching and transmission. The benefits of digitalisation included expanded line capacity with advanced multiplexing, a higher complexity of switching, improved speed of call set up end to end, and above all far higher network reliability. A richer set of features could also be added via programmability to customer premises equipment - the handset instrument and the PABXs and key systems. Digitalisation meant the exchange switch effectively became a routing computer and part of a software defined network whose topology could be dynamically adapted to traffic levels M.D. Fagen, ed., A History of the Engineering and Science in the Bell System: the Early Years (1875-1925), Bell Telephone Laboratories, New York, 1975. INFRASTRUCTURE TO 2030: TELECOM, LAND TRANSPORT, WATER AND ELECTRICITY - ISBN 92-64-02398-4 - © OECD 2006 2. TELECOMS INFRASTRUCTURE TO 2030 and abnormal events. This led to lower cost/line, capacity, speed and reliability. Using digital techniques allowe