An experimental public service telephone exchange is to be installed at Highgate Wood in North London. It has been developed in order to gain experience of the problems posed by introducing electronic exchanges into the public network. It meets a full and flexible facility schedule, and will test a variety of electronic time-sharing and commoncontrol techniques in the field.Speech and other signals are transmitted over unidirectional highways carrying 100 time-division-multiplex pulse channels. Each connection uses a pair of antiphase channels and is set up through line and inter-highway switches by storing channel pulses in magnetostriction delay lines. Delay lines also form the central feature of common register and supervisory equipments which, by operating with the channel pulses, control the setting up and progress of all calls. Common apparatus selects the channels to be used on all connections which are set up one at a time using information stored on magneticdrum tracks. Such information includes the directory number, meter record, state, class of service and type of each line, together with a library of translations required to route calls over junctions.A diversity of circuit techniques is included in the Highgate Wood exchange, which also incorporates security arrangements and maintenance aids to safeguard service to the subscriber, and to ease maintenance problems. The experience gained during the design, development, manufacture and trials of the system is expected to prove invaluable in progressing towards the telephone system of the future.