evenly between the operators. Since each operator will occupy a position at the switchboard, and since two positions are
required to accommodate two operators, a switchboard so designed is referred to as a two-position switchboard. In many
instances, switchboards reach to 30 or more positions.
A telephone system with one central office consists of a number of telephone stations connected by lines to
the central office, so that any two telephones of the system may be interconnected for two-way conversation. Such a
system may serve a few or thousands of stations; it may have more than one central office. A system includes the
individual telephone stations, the outside plant equipment for connecting each telephone station to a central office and for
interconnecting central offices, and all the central-office equipment required for making connections between the
telephones and switchboards. Whatever the size and extent of the system, and however many switchboards, and central
offices are a part of it, any telephone station can be connected with any other telephone station. The telephone stations,
central office, and connecting lines shown in figure 26B constitute a telephone system with a single central office.
A telephone system which provides telephone communication within a particular local area, such as an Army
post, maneuver area, town, village, or city, is a telephone exchange. It may have one or more central offices, depending
on the extent of the telephone service and traffic that is handled.
a. The switchboard and eight telephone stations of figure 25A would be called an exchange, although an
exchange usually includes hundreds of telephone stations and their associated lines, switching facilities, and accessory
b. By interconnecting telephone exchanges, service can be provided between telephone stations served by
two or more exchanges. The transmission lines interconnecting the central offices of different exchanges are
called trunk lines, or trunks. When a person at station A in exchange I (fig. 27) wishes to call a person at station
B in exchange II, the procedure is only a little more extended than the procedure within a single exchange. The caller