, in the 300Hz to 3.4kHz frequency range. This arose out of the conver- sion of voice into an electrical signal and is still the vital component for all voice telephony. Frequency Division Multiplexing provided the means of grouping a number of 300kHz to 3.4kHz signals into single group by multiplexing them on to a higher and higher fre- quency carrier. Figure 56.3 Distributed computing over an analogue It allowed PTTs to build multiple groups of analogue circuits network. (CC = Cluster controller; FEP = Front end throughout their network with immediate consolidation of the raw processor.) transport mechanism, which at the time on the trunk network was coaxial cable. The heart of the service were analogue leased lines, as supplied by In the late 1960s users began to build computer systems to assist the monopolistic PTTs. As these networks increased and expanded in the management of their business. Initially these systems were better technology was developed to improve the speed at which data centralised into one facility with clusters of user terminals and could be transmitted, with more sophisticated modems such as V.29 peripherals located around a large mainframe system such as IBM and now V.32 and V.42, and to optimise the manner in which the 3000 range. The benefits of computing applications were realised analogue service was presented using such techniques as multidrop by such businesses as airlines, banking and insurance companies, SO and multiport. These had two goals, speed of information to the user, the pressure to remotely connect some of the user community from and to attempt to save money from the high PTT tariffing cost the mainframe became paramount. associated with such networks. 56/4 Local and Wide Area Networking Throughout this period of growth other means were developed for devices became the work horse for many asynchronous based anal- the delivery of computer sources to the user which at first seemed a ogue networks. good alternative to the large analogue based networks. The most notable was