Some very long telephone circuits of the Bell System

Recent papers¹ have discussed at length the use of toll cables for the handling of certain long distance traffic. These cables, which are being used in areas of dense traffic, have been made possible by many developments in cable design, repeaters and loading coils. Coincident with these developments have gone others which are finding their application in the extensive establishment of improved open wire circuits for use over very long distances. The purpose of the present paper is to discuss some of the considerations involved in the overall design and maintenance of these very long open wire circuits. These circuits are often referred to as “backbone” circuits and supply a network of trunk lines for the entire Bell System. The most important of these routes are shown in Fig. 1.