The Type-O Carrier System

While the sight of an open-wire toll line is a rarity in many parts of the East, considerable use is made of open-wire facilities in other sections of the country to provide toll and exchange service. At the present time there are about 170,000-route-miles of open-wire in the Bell System which carry some 1,400,000 pair-miles of wire used for toll service. It is estimated that about 60 per cent of this pair-mileage is used for carrier, although only about 10 per cent carries the full fifteen carrier channels, which is possible by employing type-0 and type-J carrier systems. It is obvious that some of the remaining line pairs are available for additional carrier growth, provided, of course, the demand for additional circuits exists, and there are carrier systems which can meet these demands economically. Type O is a multi-channel, open-wire carrier system which has been designed to provide, economically, additional circuits in the range from a minimum of about 15 up to a maximum of 150 miles, or more. The type-0 system is the open-wire counterpart of the type N short-haul cable system. Present open-wire toll lines vary from a single-arm line, with one or two pairs of wires, up to lines with five or six arms carrying thirty pairs. These lines may carry long-haul toll circuits up to about 1000 miles in length, short-haul toll circuits up to 150 miles, as well as tributary trunks and exchange circuits. Growth in the past of toll and tributary circuits on these lines has been provided by the addition of single-channel D or H systems, three-channel C systems, twelve-channel J systems or by other similar carrier systems.