Interexchange Tandem Trunking in the Los Angeles Metropolitan Area

Twenty-four years have elapsed since the first large-scale machine switching tandem system was designed and installed for service in Los Angeles. As an intermediate switching center, the tandem office enabled operators to use the dial method of operation for establishing interexchange telephone connections over the associated trunking network. During the intervening Years, it has facilitated the rapid handling of telephone calls between the various communities in and around the city. Step-by-step tandem equipment was employed and as the volume of calls grew, the trunk capacity was increased by installing additional switching equipment. In 1946 it became evident that the abnormal rate of growth required additions substantially beyond the practical size limit of the step-by-step tandem unit. To solve the resulting problem, it became necessary to reorganize the tandem trunking system and select a multiunit tandem switching plan. It also provided an opportunity to consider the application of the more recently developed crossbar tandem switching system. This paper reviews the factors affecting the general problem of interexchange trunking which have led to the development of the present tandem network in the Los Angeles elements of a system which now employs a total of five tandem switching units, three of which are crossbar tandem offices.