 the telecom- Vail in 1838. The electrical current was carried through wire sus- munications management networks (TMN). Wireless and optical pended between poles, a system which could only be used when applications have grown rapidly. Mobile communications, from crossing a relatively narrow expanse of water. Invention of a suit- personal communication networks (PCN) through to wireless able cable insulation in 1847, by Werner Siemens, solved this PABX, cellular, telepoint and paging, are in increasing use. The problem; the English Channel was crossed in 1850 and the Atlantic trend is a change from accessing locations (e.g. a person's office in 1866. desk) to accessing the person directly by a personal number. Satel- Since then there has been rapid progress in international com- lite based telephony services have provided global coverage, and munications, driven first by a demand for the service and followed have introduced a new phase into the traveller's vocabulary: phon- by the enabling technology. The first transatlantic telephone cable ing and non-phoning airline seats! was laid in 1956 (TAT-1); the first transatlantic fibre optic cable, capable of carrying 40000 simultaneous telephone conversations, was laid in 1988 (TAT-8); and the first international communica- 11.5.2.1 The local loop tions satellite (Intelsat I, also called Early Bird) was launched in 1965, followed by many others world-wide. The local loop can act as a monopoly and a technology bottleneck. It is freely available to the user, although the user may not have a 11.5.2 Core and application technologies choice to which carrier he is connected. However the loop is restricted to service providers, and therefore acts as a barrier be- Technologies may be considered to be of two types: core and tween them and their customers. application, a few of these being illustrated in Figure 11.9. Core The original local loop was one wire, and used the earth for the technologies are primarily of four types: return path. This was too noisy and so two copper wi