at station A signals (attracts the attention of) the switchboard operator in exchange I and asks to be connected to station B
in exchange II. The operator responds by relaying the number of the called station over the trunk to the switchboard
operator in exchange II, who then signals station B and completes the connection. The figure shows the connecting cords
and completed connection between station A and station B through the trunk connecting exchange I and exchange II.
FIGURE 27. Telephone Exchanges
Connected by Trunks.
a. One-way communication can be effected with a transmitter at one telephone station, a receiver at the other, a
battery, and connecting lines.
b. Two-way communication requires at each telephone station at least a transmitter, a receiver, and a means for
signaling the called station.
c. For economy and efficiency, telephone stations usually are connected to a switchboard or other switching
device in a central office, and intercommunication is effected through it.