Abridgment of tandem system of handling short-haul toll calls in and about Los Angeles

IN telephone practise there are, broadly considered, two distinct methods of completing telephone calls between central offices, one by means of direct trunking and the other by means of tandem trunking. The fundamental difference between these two methods may be best obtained by referring to Fig. 1. It will be noted that direct trunking, as the name implies, requires a separate group of trunks from any one office to every other office, whereas tandem trunking provides for a single group of trunks from each office to a centralized point, known as the tandem center or office, at which are means for switching together any desired amount of tandem switching is done automatically. The first tandem trunking system to employ on a large scale, apparatus for switching which is under the control of dials located at the various operators' positions tributary to the tandem office, was recently installed at Los Angeles to handle the short-haul toll traffic within a radius of approximately 40 mi. This system is known as a dial tandem system.