A network more than a device
The twentieth century is when the telephone changed from a promising invention into infrastructure. The handset on a desk at the end of the century looked recognizably similar to the one from 1900, but almost everything behind it changed. This article follows four themes: dialing, distance, oceans and digitization.
Dialing
At the start of the century, a typical call began with a request to an operator. Automatic exchanges using the Strowger system had existed since 1892, and a dial for the caller had come in the mid-1890s, but manual service still dominated in big cities. Over the following decades, automatic equipment spread, first in smaller cities and then in larger ones. In many places the final manual exchanges closed only in the middle of the century, and in rural areas even later.
Dialing changed how people thought about telephone numbers. A subscriber now needed to know exactly what to dial, and numbering plans became important. In North America, telephone companies designed an area-code system in the 1940s, and the first area codes were introduced in 1947. This arrangement made it possible for customers to dial long distance themselves. In 1951, direct dialing of long-distance calls by customers started in Englewood, New Jersey, and was extended to more cities over the following years. Push-button dialing using paired tones, marketed as Touch-Tone, was introduced in 1963 and gradually replaced rotary dials.
Distance
Early telephone lines had a limited range because the signal weakened and became distorted over distance. A first improvement was the loading coil, which added inductance to the line and improved transmission quality, and its use began around the start of the century. A larger step was the electronic amplifier, using vacuum tubes, which could repeat and strengthen a signal at intervals along the line. With these devices the Bell System opened a transcontinental line between New York and San Francisco in 1915. The ceremonial call is remembered because Alexander Graham Bell in New York repeated words he had said in 1876 to Thomas Watson, who this time was in San Francisco.
Later improvements allowed many conversations to share a single pair of wires or a coaxial cable by multiplexing, which puts each call on its own frequency band. That reduced the cost of long-distance calls and made them more routine, although they remained expensive for ordinary callers for many years.
Across oceans
Telegraph cables had crossed the Atlantic since 1866, but telephone cables were harder because voice signals needed more bandwidth and amplification. For that reason, the first transatlantic telephone link was by radio. A radiotelephone service between New York and London opened in 1927. It was costly, sometimes of poor quality, and subject to atmospheric interference, and for a while it was used mainly by businesses and governments.
The first transatlantic telephone cable, TAT-1, was inaugurated in 1956, between Scotland and Newfoundland, with repeater amplifiers set along the seabed. It initially carried several dozen simultaneous calls, and it was a major improvement in quality and reliability. Capacity grew with later cables, and in 1988 TAT-8 became the first transatlantic cable to use optical fibers, an early large-scale use of fibre optic communications, which carry far more traffic per cable than copper.
Satellites joined the picture in the 1960s, a few years after the first artificial satellites were launched. Telstar in 1962 was an experimental satellite that carried telephone and television signals across the Atlantic, and communications satellites such as Early Bird, launched in 1965, offered a commercial telephone service. Satellite links had a noticeable delay because of the long path up to a satellite and back, and many international calls shifted to fiber cables as these became widely available.
Going digital
In the 1960s, telephone engineers began converting speech to digital form for transmission between exchanges. In a technique called pulse-code modulation, the voice signal is sampled thousands of times per second and each sample is converted to a number. Digital signals can be regenerated, not just amplified, so noise does not build up along a line. The approach was first used in links between exchanges, and by the 1980s digital transmission and digital switching were becoming the norm in many countries.
Electronic switching, beginning with the Bell System’s No. 1 ESS in 1965, allowed computers to control exchanges, and made new services possible, such as call forwarding and call waiting. The home telephone line itself remained analog for years in most places, converting to digital at the exchange. Services such as ISDN, introduced in some countries in the 1980s and 1990s, extended digital to the customer, and broadband services like DSL later reused the copper line for data. These developments connected the telephone network to the history of the internet, which in its early years depended on telephone lines for dial-up access.
Competition and change
The structure of the business also changed. In the United States, the Bell System was broken up in 1984 as a result of an antitrust settlement. Competition in long-distance service followed, and similar liberalizations took place in many other countries, often with a shift from state monopolies to private operators. Prices for long-distance and international calls fell sharply over the following decades.
Mobile service
The last decades of the century also saw mobile telephony turn from a niche into a mass market. Cellular networks began operating commercially in Japan in 1979 and in the United States in 1983. By the end of the century, many countries had more mobile subscriptions than could be explained by business use alone.
The century in short
In 1900, a telephone call meant a request to an operator, a local circuit, and a short distance. By 2000, it meant dialing a number, crossing automatic exchanges, traveling by fiber or satellite, and often being carried digitally for most of the route. The device people held changed little by comparison. The transformation was in the network, and it happened gradually enough that most users never noticed.