Alexander Graham Bell's invention of the telephone in 1876 rang in the era of talking at a distance. Innovators in the 20th century expanded the telephone's reach across continents and oceans, figuratively shrinking the world and connecting its citizens. Electronic switching systems and other technological advances helped customers place calls without the help of operators. By the year 2000, more than a billion people all over the world had gone wireless—using cellular technology to talk and deliver text and photos on super-lightweight telephones smaller than a deck of cards.
| 1900 |
Telephone transmission extends across and between major cities As telephone transmission extends across and between major cities, "loading coils" or inductors are placed along the lines to reduce distortion and attenuation or the loss of a signal's power. Independently invented by the American Telephone and Telegraph Company's (AT&T) George Campbell and Michael Pupin of Columbia University, the loading coils are first used commercially in New York and Boston, nearly doubling the transmission distance of open lines. Pupin is awarded the patent for the device in 1904, and AT&T pays him for its use. |
| 1904 |
Fleming invents the vacuum diode British engineer Sir John Ambrose Fleming invents the two-electrode radio rectifier; or vacuum diode, which he calls an oscillation valve. Based on Edison's lightbulbs, the valve reliably detects radio waves. Transcontinental telephone service becomes possible with Lee De Forest's 1907 patent of the triode, or three-element vacuum tube, which electronically amplifies signals. |
| 1915 |
First transcontinental telephone call Alexander Graham Bell makes the first transcontinental telephone call to Thomas Watson-from New York to San Francisco-after trials using De Forest’s triodes successfully boost the long-distance signal. What is the world’s longest telephone line consists of 2,500 tons of copper wire, 130,000 poles, three vacuum-tube repeaters, and countless numbers of loading coils. |
| 1919 |
Switching systems and rotary-dial telephones Bell System companies begin installing switching systems and rotary-dial telephones, though dial phones have been around since just before the turn of the century. The dial makes it easier for customers to place calls without an operator. The finger wheel of the dial interrupts the current in the phone line, creating pulses that correspond to the digits of the number being called. |
| 1920 |
Frequency multiplexing concept AT&T develops the frequency multiplexing concept, in which frequencies of speech are shifted electronically among various frequency bands to allow several telephone calls at the same time. Metal coaxial cable eventually is used to carry a wide range of frequencies. |
| 1947 |
North American Numbering Plan With the rapidly growing number of telephone customers, AT&T and Bell Labs develop the North American Numbering Plan, a system that assigns telephone numbers to customers in the United States and its territories as well as Canada and many Caribbean nations. The first three digits of a typical number identify the area being called; the next three, called the prefix, locate the closest central or switching office; and the last four digits represent the line number. Bell Labs conceives the idea of reusing radio frequencies among hexagonal "cells"—the beginning of the drive toward cellular communications. Mobile phones become an even more realistic dream with the invention of the transistor, which eventually makes them possible. |
| 1948 |
A Mathematical Theory of Communication Bell Labs’s Claude Shannon publishes the landmark paper "A Mathematical Theory of Communication," which provides mathematicians and engineers with the foundation of information theory. The paper seeks to answer questions about how quickly and reliably information can be transmitted. |
| 1949 |
First phone to combine a ringer and handset AT&T introduces the Model 500 telephone, the first that combines a ringer and handset. The classic black rotary phone, featuring an adjustable volume control for the bell and later a variety of colors, becomes a cultural icon. |
| 1951 |
Direct longdistance calling first available In a test in Englewood, New Jersey, customers are able to make long-distance calls within the United States directly, without the assistance of an operator. But it takes another decade for direct long-distance dialing to be available nationwide. |
| 1956 |
First transatlantic telephone cable The first transatlantic telephone cable—the TAT-1—is installed from Scotland to Nova Scotia, providing telephone service between North America and the United Kingdom. Additional circuitry through London links Western European countries such as Germany, France, and the Netherlands. A joint project of the United States, Canada, and Britain, the TAT-1 takes 3 years and $42 million to plan and install, using 1,500 nautical miles of specially insulated coaxial cable. It handles up to 36 simultaneous calls and supplements existing telegraph and radiophone links. The first TAT-1 call is placed on September 25 by the U.K. postmaster to the chairman of AT&T and the Canadian Minister of Transport. |
| 1962 |
First commercial digital transmission system Illinois Bell turns on the first commercial digital transmission system, known as the T1 (Transmission One), which eventually replaces analog lines. The multiplexed system carrying voice signals has a total capacity of 1.5 million bits (or binary digits) per second and is less susceptible to electrical interference from high-tension wires. The T1 quickly becomes the main transmission system for long-distance telephone service and, eventually, local calls. Bell Systems demonstrates the first paging system at the Seattle World’s Fair. Called Bellboy, the personal pager is one of the first consumer applications for the transistor. An audible signal alerts customers, who then call their offices or homes from a regular phone to retrieve their messages. |
| 1962 |
Telstar 1 Communications satellite Telstar 1 is launched by a NASA Delta rocket on July 10, transmitting the first live transatlantic telecast as well as telephone and data signals. At a cost of $6 million provided by AT&T, Bell Telephone Laboratories designs and builds Telstar, a faceted sphere 34 inches in diameter and weighing 171 pounds. The first international television broadcasts shows images of the American flag flying over Andover, Maine to the sound of "The Star-Spangled Banner." Later that day AT&T chairman Fred Kappel makes the first long-distance telephone call via satellite to Vice President Lyndon Johnson. Telstar I remains in orbit for seven months, relaying live baseball games, images from the Seattle World's Fair, and a presidential news conference. |
| 1963 |
Touch-tone telephone is introduced The touch-tone telephone is introduced, with the first commercial service available in Carnegie and Greensburg, Pennsylvania, for an extra charge. The Western Electric 1500 model features 10 push buttons that replace the standard rotary dial. A 12-button model featuring the * and # keys comes out soon afterward and replaces the 10-button model. |
| 1965 |
First electronic central office switching system The first electronic central office switching system, the 1 ESS, is installed in Succasunna, New Jersey, after years of research and planning and at a cost of $500 million. Switching systems switch telephone traffic through local central offices that also house transmission equipment and other support systems. The 1 ESS has the capacity to store programs and allows such features as call forwarding and speed dialing. The 4 ESS, developed by Western Electric in 1976, is the first digital switch and will remain the workhorse system for several decades before increases in the transmission of data, as well as voice signals, spur new advances. |
| 1968 |
First 911 call is made On February 16 the first 911 call is made in Haleyville, Alabama. Legislation calling for a single nationwide phone number for citizens to use to report fires and medical emergencies was passed by Congress in 1967, and in January 1968 AT&T announced plans to put such a system into place. An independent company, Alabama Telephone, scrambled to build its own system and succeeded in beating AT&T to the punch. The numbers 911 were chosen because they were easy to remember and did not include three digits already in use in a U.S. or Canadian area code. In Britain a national emergency number—999—had been in place since the late 1930s. |
| 1973 |
First portable cell phone call is made The first portable cell phone call is made by Martin Cooper of Motorola to his research rival at Bell Labs, Joel Engel. Although mobile phones had been used in cars since the mid-1940s, Cooper’s was the first one invented for truly portable use. He and his team are awarded a patent in 1975. |
| 1975 |
U.S. military begins using fiber optics The U.S. military begins using fiber optics to improve communications systems when the navy installs a fiber-optic telephone link on the USS Little Rock. Used to transmit data modulated into light waves, the specially designed bundles of transparent glass fibers are thinner and lighter than metal cables, have greater bandwidth, and can transmit data digitally while being less susceptible to interference. The first commercial applications come in 1977 when AT&T and GTE install fiber-optic telephone systems in Chicago and Boston. By 1988 and 1989, fiber-optic cables are carrying telephone calls across the Atlantic and Pacific Oceans. |
| 1976 |
Common channel interoffice signaling AT&T introduces common channel interoffice signaling, a protocol that allows software-controlled, networked computers or switches to communicate with each other using a band other than those used for voice traffic. Basically a dedicated trunk, the network separates signaling functions from the voice path, checks the continuity of the circuit, and then relays the information. |
| 1978 |
Public tests of a new cellular phone system Public tests of a new cellular phone system begin in Chicago, with more than 2,000 trial customers and mobile phone sets. The system, constructed by AT&T and Bell Labs, includes a group of small, low-powered transmission towers, each covering an area a few miles in radius. That test is followed by a 1981 trial in the Washington-Baltimore area by Motorola and the American Radio Telephone Service. The Federal Communications Commission officially approves commercial cellular phone service in 1982, and by the late 1980s commercial service is available in most of the United States. |
| 1990s (Mid) |
Voice Over Internet Protocols The advent of Voice Over Internet Protocols (VoIP)—methods of allowing people to make voice calls over the Internet on packet-switched routes— starts to gain ground as PC users find they can lower the cost of their long-distance calls. VoIP technology is also useful as a platform that enables voice interactions on devices such as PCs, mobile handhelds, and other devices where voice communication is an important feature |
| 2000 |
100 million cellular telephone subscribers The number of cellular telephone subscribers in the United States grows to 100 million, from 25,000 in 1984. Similar growth occurs in other countries as well, and as phones shrink to the size of a deck of cards, an increasingly mobile society uses them not only for calling but also to access the Internet, organize schedules, take photographs, and record moving images. |
It was indeed conceivable. The enterprise he helped launch that year—the forerunner of the American Telephone and Telegraph Company—would grow into one of the biggest corporations ever seen. At its peak in the early 1980s, just before it was split apart to settle an antitrust suit by the Justice Department, AT&T owned and operated hundreds of billions of dollars worth of equipment, harvested annual revenues amounting to almost 2 percent of the gross domestic product of the United States, and employed about a million people. AT&T's breakup altered the business landscape drastically, but the telephone's primacy in personal communications has only deepened since then, with technology giving Bell's invention a host of new powers.
Linked not just by wires but also by microwaves, communications satellites, optical fibers, networks of cellular towers, and computerized switching systems that can connect any two callers on the planet almost instantaneously, the telephone now mediates billions of distance—dissolving conversations every day-eight per person, on average, in the United States. As Bell foresaw in his prospectus, it is "utilized for nearly every purpose for which speech is employed," from idle chat to emergency calls. In addition, streams of digital data such as text messages and pictures now often travel the same routes as talk. Modern life and the telephone are inextricably intertwined.
At the outset, people weren't quite sure how to use this newfangled device, but they knew they wanted one—or more accurately, two, because telephones were initially sold in pairs. (The first customer, a Boston banker, leased a pair for his office and home, plus a private line to join them.) Telephony quickly found a more flexible form, however. The year 1878 saw the creation of the first commercial exchange, a manual switching device that could form pathways between any of 21 subscribers. Soon that exchange was handling 50 subscribers, and bigger exchanges, with operators handling a maze of plugs and cords to open and close circuits, quickly began popping up in communities all across America. Although the Bell system would stick with operators and plugboards for a while, an automated switchboard became available in the 1890s, invented by an Indiana undertaker named Almon Strowger, who suspected that local telephone operators were favoring his competitors. His apparatus made a connection when a caller pressed two buttons on a telephone a certain number of times to specify the other party. Soon, a 10-digit dialing wheel replaced the buttons, and it would hold sway until Touch-Tone dialing—a faster method that expressed numbers as combinations of two single—frequency tones-arrived on the scene in the 1960s.
At the start of the 20th century, many basic features of telephone technology were in place. By then, the human voice was captured by a method that would remain standard for many decades: In the microphone, sound waves pressed carbon granules together, changing their electrical resistance and imposing an analogous pattern of variations on a current passing through them. The signal was carried by a pair of copper wires rather than the single iron or steel wire of the dawn years. Copper's electrical resistance was only a tenth as much, and random noise was dramatically reduced by using two wires instead of completing the circuit through the ground, as telegraphy did. In cities, unsightly webs of wires were minimized by gathering lines in lead pipes about 2 inches in diameter. The early cables, as such bundles were called, held a few dozen pairs; by 1940 about 2,000 could be packed into the pipe.
As other countries caught the telephone contagion, their governments frequently claimed ownership, but the private enterprise model prevailed in the United States, and a multitude of competitors leaped into the business as the original Bell patents expired. At the turn of the 20th century, the Bell system accounted for 856,000 phones, and the so-called independents had 600,000. Corporate warfare raged, with AT&T buying up as many of the upstarts as possible and attempting to derail the rest by refusing to connect their lines to its system. Two decades later AT&T secured its supremacy when the U.S. Senate declared it a "natural monopoly"—one that would have to accept tight governmental regulation.
During these years, all the contenders experimented with sales gimmicks such as wake-up calls and telephone-delivered sermons. Price was a major marketing issue, of course, and it dropped steadily. At the beginning of the century, the Bell system charged $99 per thousand calls in New York City; by the early 1920s a flat monthly residential rate of $3 was typical. As the habit of talking at a distance spread, some social commentators worried that community ties and old forms of civility were fraying, but the telephone had unstoppable momentum. By 1920 more than a third of all U.S. households were connected. Most had party lines, which generally put two to four households on the same circuit and signaled them with distinctive rings. Phone company publications urged party line customers to keep calls brief and not to eavesdrop on their neighbors, but such rules were often honored only in the breach.
Extending the range of telephone calls was a key engineering challenge, much tougher than for telegraphy because the higher frequency of voice-based signals caused them to fade faster as they traveled along a wire. Early on, a device called a loading coil offered a partial cure. Independently invented in 1899 by Michael Pupin of Columbia University and George Campbell of AT&T, it basically consisted of a coil of wire that was placed along a line every 6,000 feet or so, greatly diminishing attenuation in the range of frequencies suitable for voice transmission. Two years later commercial service began between Philadelphia and Chicago, and by 1911 a long-distance line stretched all the way from New York to Denver. But transcontinental service remained out of reach until Bell engineers began experimenting with the triode vacuum tube, patented in 1907 by the radio pioneer Lee De Forest as "A Device for Amplifying Feeble Electrical Currents."
De Forest's tube used a small, varying voltage on a gridlike element to impose matching variations, even at high frequencies, on a much larger flow of electrons between a heated filament and a plate. The inventor's understanding of his device was imperfect, however. He thought that ionized gas in the tube was somehow involved. In 1913 a Bell physicist named H. D. Arnold showed that, on the contrary, the completeness of the vacuum dictated the performance. Arnold and his colleagues designed superior tubes and related circuitry to amplify long-distance telephone transmissions, and service was opened between New York and San Francisco in 1915. Alexander Graham Bell made the first call, speaking to Thomas Watson, who had helped him develop a working telephone four decades earlier. The transcontinental path had 130,000 telephone poles, 2,500 tons of copper wire, and three vacuum-tube devices to strengthen the signals. A 3-minute conversation that year cost $20.70.
By the mid-1920s long distance lines connected every part of the United States. Their capacity was expanded by a technique called frequency multiplexing, which involves electronically shifting the frequencies of speech (about 200 to 3,400 cycles per second) to other frequency bands so that several calls could be sent along a wire simultaneously. After World War II, the Bell system began to use coaxial cable for this kind of multiplexing. Its design—basically a tube of electrically conducting material surrounding an insulated central wire—enabled it to carry a wide range of frequencies.
Stretching coaxial cable beneath oceans posed difficulties so daunting that the first transatlantic link, capable of carrying 36 calls at a time, wasn't established until 1956. But radio had been filling the oceanic gaps for several decades by then while also connecting ships, planes, and cars to the main telephone system or to each other. After mid-century, a previously unexploited form of radio—the microwave frequencies above a billion cycles per second—took over much of the landbased long-distance traffic. Microwaves travel in a straight line rather than following the curvature of the earth like ordinary radio waves, which means that the beam has to be relayed along a chain of towers positioned 26 miles apart on average. But their high frequency permits small antenna size and high volume. Thousands of two-way voice circuits can be crammed into a single microwave channel.
The never-ending need for more capacity brought steady strides in switching technology as well. A simple architecture had been developed early on. Some switching stations handled local circuits, others connected clusters of these local centers, and still others dealt with long-distance traffic. Whenever congestion occurred, the routing was changed according to strict rules. By the 1970s Bell engineers had devised electromechanical switches that could serve more than 30,000 circuits at a time, but an emerging breed of computer-like electronic switches promised speed and flexibility that no electromechanical device could match.
The move to electronic switching began in the 1960s and led to all-digital systems a decade later. Such systems work by converting voice signals into on-off binary pulses and assigning each call to a time slot in a data stream; switching is achieved by simply changing time slot assignments. This so-called time division approach also boosts capacity by packing many signals into the same flow, an efficient vehicle for transmission to and from communications satellites. Today's big digital switches can handle 100,000 or more circuits at a time, maintaining a remarkably clear signal. And like any computer, the digital circuits are versatile. In addition to making connections and generating billing information, their software enables them to provide customers with a whole menu of special services—automatically forwarding calls, identifying a caller before the phone is answered, interrupting one call with an alert of another, providing voice mail, and more.
In recent decades, long-distance transmission has undergone a revolution, with such calls migrating from microwave and coaxial cable to threadlike optical fibers that channel laser light. Because light waves have extremely high frequencies, they can be encoded with huge amounts of digital information, a job done by tiny semiconductor lasers that are able to turn on and off billions of times a second. The first fiber-optic telephone links were created in the late 1970s. The latest versions, transmitting several independently encoded streams of light on separate frequencies, are theoretically capable of carrying millions of calls at a time or vast volumes of Internet or video traffic. Today, the world is wrapped in these amazing light pipes, and worries about long-distance capacity are a thing of the past (see Lasers and Fiber Optics).
Another technological triumph is the cell phone, a radio-linked device that is taking the world by storm. Old-style mobile telephones received their signals from a single powerful transmitter that covered an area about 50 miles in diameter, an interference-prone method that provided enough channels to connect only a couple of dozen customers at a time. Cellular technology, by contrast, uses low-powered base stations that serve "cells" just a few square miles in area. As a customer moves from one cell to another, the phone switches from a weakening signal to a stronger one on a different frequency, thus maintaining a clear connection. Because transmissions are low powered, frequencies can be reused in nonadjacent cells, accommodating thousands of callers in the same general area.
Although the principles of cellular telephony were worked out at Bell Labs in the 1940s, building such systems had to await the arrival of integrated circuits and other microelectronic components in the 1970s. In the United States, hundreds of companies saw the promise of the business, but government regulators were very slow in making a sufficiently broad band of frequencies available, delaying deployment considerably. As a result, Japan and the Scandinavian countries created the first cellular systems and have remained leaders in the technology. At the start there was plenty of room for improvement. Early cell phones were mainly installed in cars; handheld versions were as big as a brick, cost over a thousand dollars, and had a battery life measured in minutes. But in the 1990s the magic of the microchip drove prices down, shrank the phones to pocket size, reduced their energy needs, and packed them with computational powers.
By the year 2000, 100 million people in the United States and a billion worldwide were using cell phones—not just talking on them but also playing games, getting information off the Internet, and using the keyboard to send short text messages, a favorite pastime of Japanese teenagers in particular. In countries where most households still lack a telephone— China and India, for example—the first and only phone for many people is likely to be wireless. Ultimately, Alexander Graham Bell's vision of a wired world may yield to a future in which, for everyone, personal communication is totally portable.
Ian M. Ross
President Emeritus
AT&T Bell Laboratories
Shortly after arriving from England to join Bill Shockley's organization at Bell Labs in March 1952, I was asked to arrange a laboratory session for an April symposium on transistor technology. In 1947, Shockley's team had invented the transistor in an effort to replace relays and vacuum tubes in the telephone network with faster, more reliable solid-state devices. My lab session was meant to allow the attendees, most of whom had never seen a transistor, to measure the characteristics of the device touted as having no failure mechanisms and nothing to wear out.
AT&T had long prided itself on its stringent requirements for network reliability. For example, switching machines were to have no more than 2 hours of downtime in 40 years—a policy statement that has had a powerful impact over the years. The requirement may seem somewhat quaint today: Why not 1 hour of downtime in 20 years or 3 minutes per year? I believe the intent was to specify two things—first, the minuscule percentage of time it was acceptable for a machine to be down, and second, that the switch should be designed to serve for 40 years. Two days before the start of the symposium, New Jersey experienced its typical one-day transition from winter directly to the heat and humidity of summer. In those days Bell Labs was not air-conditioned, and when I got to the lab that morning I found that my transistors for the session had lost all their electrical characteristics—the CRT traces were flat! I had discovered for myself what many people already knew: The transistor was sensitive to its environment and particularly to humidity.
The lack of reliability of early transistors was a huge setback and embarrassment to the semiconductor community. The transistor had been lauded as a device with no failure mechanisms, with nothing to wear out. Instead, we had a severe reliability problem—and it took another 14 years to solve the problem completely. Given AT&T's reliability specification, the delay effectively paced the large-scale introduction of semiconductor devices into the telephone network.
Two decades later I was put in charge of the Network Planning Division at Bell Labs. About this time the technology was at hand to permit the conversion of the networks to all-digital operation. Here again AT&T's reliability specification strongly governed the design. The new electronic switching machines were to be controlled by a stored-program processor—in effect a special-purpose computer. The only way we at Bell Labs knew how to meet the downtime requirement was to use dual processors, simultaneously running identical programs. Fortunately, the machines that were introduced in the early 1970s are still providing service today. So far so good!