ringer at station B. The sounding of the ringer attracts the attention of someone, who thereupon answers the call. The
transmission line connecting the two stations conducts connecting the two stations conducts both the voice currents and
the signaling current; also, although a ringer has been mentioned as the signaling device and a hand generator as the
source of signaling current, other devices may be used for the generation of signaling current and the signaling itself.
These will be considered later in detail.
a. A telephone system frequently consists of hundreds, even thousands, of telephone stations. In operation, the
system permits voice communication between any of the telephone stations which are part of it. The simple circuit of
figure 25 can be used in a telephone system if each station is connected by a similar circuit to all the other stations in the
system. Such an arrangement would require the use of two wires and a switch from each station to every one of the other
stations. It would be impractical for serving a large number of telephone stations; for even a few, the system would be a
maze of wires. The block diagram of figure 26A shows the wiring required to interconnect eight stations.
b. An important saving in line wire is obtained by including in the system a centrally located switchboard. Each
telephone station then is connected directly to the switchboard, not to each of the others. The connecting wires and their
attachments constitute a transmission line. Conversation between any two stations is made possible by interconnecting
their transmission lines at the switchboard. The connections are made by a switchboard operator or attendant by means
either of switches or, more frequently, cords with plugs for insertion in jacks connected to the ends of the lines from the
two telephones. The block diagram of figure 26A shows the eight telephone stations of figure 26B connected to a