City of Light: The Story of Fiber Optics

78 CITY OF LIGHT
phone, and asking for the phone number being called. Then the operator
plugged the proper wires into the corresponding holes on the switchboard
and listened to see if the person on the other end picked up the phone. This
worked for a town with only a few phones, but it didn’t scale very well. Think
of it as a manual system, like making calculations by writing numbers on
pieces of paper.
As the number of phones grew, phone companies added more operators
and switchboards. They also set up extra offices or switching centers to serve
different parts of larger cities. To complete calls from one part of town to
another, the operator would patch a call through to a second central office,
where another operator would make the connection. The same principle
worked for long distance.
The more phones, the more complex the network grew and the more
operators were needed. Eventually, telephone engineers started to replace operators
with mechanical switches that moved in response to electrical signals,
making and breaking connections. A simple switch might rotate to one of ten
positions (the digits on a dial) and stay in that position while the next switch
in line rotated to the proper position. One of the most popular switches was
designed by a Kansas City undertaker, Almon B. Strowger, who wanted to
automate the phone system because he feared that operators were routing
business elsewhere. 2 Dial phones automated the system, the click of each digit
of rotation telling the mechanical switch to take another step. Think of mechanical
switches as adding machines, clanking, chattering, and clunking
away to route phone signals.
Expansion of the phone system meant more people could be calling from
one town to the next at the same time. That required ever bigger ‘‘pipes’’ to
carry more and more signals between local switching offices. The more traffic,
the bigger the pipe was needed. Switches were expensive, so they were used
only where traffic was heavy and the task not too complex. All long-distance
calls had to be placed through operators until long-distance direct dialing was
introduced in the 1950s, 3 and for many years afterward smaller towns still
routed long-distance calls through operators.
At the same time, phone companies were developing all-electronic switches
that routed signals without mechanical motion. Mechanical switches had simply
reached their own limits; solid ranks of them filled brick buildings in town
after town across the country, and they couldn’t keep up with system growth.
The search for all-electronic switches led Bell Laboratories to develop the transistor,
which not only could amplify signals, but also could turn them ‘‘off’’
and ‘‘on’’ in response to a control input. That let transistor circuits serve the
same function as electromechanical switches. Put enough circuits together
and you have a special-purpose computer that decodes the numbers you dial
and routes your phone signals accordingly. These electronic switches are indeed
computers, far more powerful than the electromechanical switches that
were the adding machines of the telephone world.