Telephone Technology and Networks

Summary

A country without a solid telecommunications infrastructure faces insurmountable obstacles. Telephones and their networks are an essential part of telecommunications. The ability to connect individuals and government agencies by telephone is necessary to allow nations and economies to flourish. Technological advances have developed telephones from large wooden boxes fixed to walls to small, handheld portable devices that can do much more than simply enable people to talk at a distance.

Definition and Basic Principles

Any communication between two parties—people or machines—requires an originator and a receiver, as well as a network connecting the two. The simplest network tying these two parties together is a simple wire (in electrical terms) or a pair of wires. However, as the number of parties increases to three, three hundred, or three thousand, the required network becomes impossibly large. In the legacy telephone network, a hierarchy of switching systems has been developed to allow communications from any user to any other user.

As technology has advanced, other means of communication have developed. In many cases, the pair of wires connecting the transmitting party and the receiving party has been replaced with radio transmission systems (such as satellite communications, cell phones, microwave systems), coaxial cables (a physical structure that permits high-speed transmission), or fiber optics (which converts electrical signals to light).

Just as the technology used for telecommunications has advanced, so has the structure of the telephone network. The Internet is rapidly replacing the circuit-switched network (the public switched telephone network) that has been in use for more than a century for the transmission of not only data but also sound.

Background and History

The telephone industry began on February 14, 1876, when Alexander Graham Bell filed his first patent for a telephone. One month later, on March 10, 1876, he and his assistant Thomas Augustus Watson produced a model that worked, and the immortal words “Mr. Watson, come here, I want you,” were spoken over the device.

In the years that followed, numerous technological advances were made, and the telephone became a practical device. Telephone companies sprang up by the thousands, frequently two or more firms in the same city. Connections among these companies were the exception rather than the rule, and competition became ruthless.

By the middle of the twentieth century, the industry had reached some degree of stability. The Bell System, the largest of the country's telephone companies, had managed to capture about 80 percent of the telephone service in the country.

The Bell System survived a number of government-initiated lawsuits over the years, but in 1982, it agreed to split itself up into two major entities, the telephone operating companies and the parent company, AT&T, which brought with it the long-distance arm, manufacturing facility, and research and development units.

Once again, the industry became highly competitive, with new companies appearing and disappearing each year.

The new technologies embraced by the many startups caused the industry to change dramatically. Advances in radio technology permitted satellite communications, microwave transmissions, and cellular radio. The development of fiber optics allowed data to be transmitted almost at the speed of light and increased the capacity of the country's network. Advances in electronics changed the way information was transmitted. Digital signals replaced analog. In the 1960s, packet switching between computer networks, or internet, changed communication dramatically.

How It Works

The modern telephone has four major components: the transmitter (which converts sound waves into electrical signals), the receiver (which converts received electrical signals into audio signals), an alerting device (generally called a ringer, although the alerting signal is usually some sort of tone), and a signaling device (either a rotary dial or a set of push-buttons).

The ringer rides the telephone line whenever the telephone is on-hook and is removed from the line when the telephone is in use. The ringing signal for most telephones is 90 volts, alternating current.

A major part of the telephone's circuitry deals with sidetone. Because the telephone typically operates on a two-wire circuit, sounds spoken into a telephone tend to be heard at the distance end of the circuit and in the local receiver. The circuitry used to combat this reduces the volume of the conversation fed back to the local receiver. Interestingly, this fed-back conversation is not entirely electronically eliminated, lest the user think the telephone is not operating.

A call is initiated by removing the handset from the cradle. This action removes the ringer from the circuit and connects the telephone's electronic apparatus. A circuit is established through this apparatus, which the central office detects. Equipment at the central office sends a dial tone to the subscriber. Hearing this dial tone, the subscriber dials a number—either with a true dial interrupting the two-wire circuit the indicated number of times or a keypad, which transmits two tones to the central office.

The Transmission Medium. Modern transmission mediums are a far cry from the two-wire connections of yesteryear. Copper still predominates, but coaxial cable, fiber optics, and radio communications are increasingly used.

Coaxial cable has a greater capacity than twisted-pair copper and is still the prime transmission medium for cable television. The cable is, in fact, coaxial. A single strand of copper is surrounded by insulation, which is encased in metallic sheathing. This configuration keeps desired signals in and undesirable signals out.

Fiber optics has become the transmission medium of choice. A hair-thin strand of ultrapure glass carries pulses of light at gigabit rates. By using electronic techniques, thousands of conversations can be multiplexed onto a single strand of fiber.

Several forms of radio communications—satellites, cellular radio, and Wi-Fi—are commonly in use. Satellite communications can be used for voice, television, or data. When used for voice, satellites often result in undesirable confusion because the time required to bounce a signal off a satellite (parked at an altitude of about 22,300 miles (35,888 kilometers) in geostationary orbit) is 0.125 seconds each way. Therefore, there is a built-in 0.25-second delay in any conversation.

A more talked-about use of radio is the wireless communication provided by cellular radio. The wireless segment of a cell phone conversation is remarkably short; simply the two- or three-mile segment from the cell phone to the cell phone tower. At this point, the signal travels down the tower through copper or fiber optics and goes to the local telephone central office.

A third use of radio transmissions is in local area networks. A radio transmission connects a device attached to a telephone line and a computer. Frequently, this is identified as Wi-Fi. Although the technology is different, a cordless telephone operates in much the same way.

Transmission Path Selection. Some sort of a selection device—for instance, a telephone dial—is required to select the destination of whatever message is being sent. The method of transmitting this address to the network and the network's ability to establish a connection are equally important.

Commonly used transmission devices are telephones, which increasingly are cell phones, smartphones, or handheld computers. The dial is usually a set of push-buttons (the keypad). The system converts the analog signals of the unit to a digital signal (a series of ones and zeros).

Since its establishment, the hierarchy of switching systems has served its function well. A transmission path is established from a local switching office to a higher class office and then (if required) to a still higher class office. Then the path is extended downward to finally reach the called party. Thus, a total circuit is established, and the overall process is logically called circuit switching.

In many cases, circuit-switching networks have been replaced with packet-switching networks. Instead of establishing and holding a total circuit for the duration of a call (a wasteful process), a message (voice or data) is digitized and then broken into small chunks (called packets). Each packet of this digitized data is preceded with supervisory material that indicates the importance of the packet, its destination, and other information. Then the switch (which of course bears a remarkable resemblance to a computer) establishes a connection to a distant switch and transmits its packet. Each packet, therefore, can travel a different path to the ultimate destination. It is left for the final switch to reassemble the packets in the appropriate sequence.

Applications and Products

The technologies used in the first hundred years of the telephone industry were primarily mechanical and electromechanical. Massive amounts of equipment were necessary, a great deal of space was required for central offices, and the speed of transmission was limited. The advent of electronics—primarily the transistor—changed all this, and new technologies continue to be developed. Some of the technologies that have made major differences in most people's lives are the transistor, the integrated circuit, and central office switching.

The Transistor. In 1947, three scientists from Bell Telephone Laboratories, Walter Brattain, John Bardeen, and William Shockley, invented the transistor, a solid-state device that would replace the vacuum tube. The tiny device was a solid and did not employ a vacuum or special gas. It consumed very little power and could perform amplification or switching just as the vacuum tube could. Furthermore, its life was almost unlimited. Over the years, it also became very inexpensive.

Clearly, the transistor could be used to replace the vacuum tubes used in amplifiers in the telephone network. Also, a rethinking of the switching function in the telephone central offices made possible a new device, the digital-switch, and, in later years, the internet and packet-switching.

Although the invention of the transistor was important (it has been called the invention of the century), it by no means ended technological advances in electronics. Transistor technology advanced, and devices were made both smaller and faster, and the result was called the integrated circuit. These advances have continued, and there is no evidence that they will stop. In 1965, Gordon E. Moore, director of engineering at Fairchild Semiconductor, analyzed the advances being made in transistor technology and determined that the capability of the solid-state device would most likely double every eighteen months. This doubling of capacity is called Moore's law.

Central Office Switching. In the conventional telephone switching system, many telephone lines enter the central office. The switch, based on input instructions (the dialed number), connects one of those lines to another, thus establishing a circuit, a process called circuit switching. Such a circuit is maintained between the two parties (calling and called) for the duration of the telephone call.

Digital switching takes a different approach. The analog voice signal is sampled very rapidly and converted into a series of ones and zeros. These ones and zeros trigger electronics within the switch, and the identical signal is transmitted from the central office to the next office. Such a switch is more efficient than the legacy analog switch.

The transistor, the integrated circuit, and the technology of digital switching were immensely valuable to the telecommunications industry. Of equal importance, however, was the change that took place in the use of the network itself.

Packet Switching. Circuit switching is inherently inefficient because the dedicated circuit is idle about half the time. A better method, although orders of magnitude more complicated, is packet switching. With packet switching, little bundles, or packets, of ones and zeros are transmitted from computer to computer across the country. Supervisory information preceding each packet of data identifies its priority, its destination, and other pertinent information.

Each packet of information follows its own path to the destination. Because of traffic on the network and the number of stops along the way, a packet sent earlier than another packet may arrive later. If the packets are chunks of digitized voice, the order matters, and it is left to the computer at the receiving point to put the packets in the proper order before delivering them to the recipient.

Two points are extremely important in such a process. The first has to do with the speed of transmission through the network and the time that each packet takes to pass through a node (this is called latency). In actual use, latency has been reduced to about one millisecond. The second point demonstrates the improvement in network efficiency. Each time a packet passes through a node, headed for a transmission link to the next node, the previous link is released. In telephone terms, the computer hangs up. Except for the supervisory information attached to each packet, the system's efficiency is approaching 100 percent.

Wireless Communications. One technology, wireless communications, has become critically important for telephones. The process of operating telephones over radio is not new, nor is it complicated. Radio transmitting stations, whether public or private, simply mount a very tall antenna on the highest piece of land available and apply enough power to reach all potential users (such as the fire department, police department, radio stations, and taxicab companies). As long as these users stay within range of the antenna, all is well. As many channels as allowed are provided with the system (this number is easily determined with radio and television stations). For a telephone system, however, this poses problems. Just how many channels are required? More important, how many channels are available? Too frequently, few channels are available to satisfy an entire city. The result would be a lengthy wait for dial tone.

What is the solution? A number of organizations and companies in the United States and abroad thought they had an answer. Instead of one large antenna and one set of frequency channels, they would provide a plurality of frequency channels, each assigned to a subset of the geographic community heretofore covered. These geographic subsets would be called cells, and the antenna covering each would be reduced in strength to the point where it would not impinge on nearby cells. This would make it possible to reuse those particular frequency channels in cells somewhat removed from the original cell.

A major problem with this approach was mobility. Would a taxicab driver in one cell, talking on one frequency, have to redial after moving to a different cell? This was not acceptable. By using very sophisticated electronics, the cell phone in use could transfer the call to the cell site antenna it was approaching and drop it from the cell it was leaving. This handoff capability was one of the most important characteristics of the proposed system.

The cell phone has become very popular. About two-thirds of the people in the world—more than five billion people—have access to a cell phone. In the United States, more and more people with cell phones no longer have a conventional land line. The number of subscribers to conventional phone service is dropping each year. In 2004, 90 percent of U.S. households had a landline phone. In 2020, this number dropped to 37 percent, and in 2024, it dropped to 28 percent.

Spectrum. This expansion of wireless communications is making it more difficult to find sufficient electromagnetic spectrum to support it. In the United States, toward the end of the twentieth century, the Federal Communications Commission began auctioning off huge chunks of spectrum. They were to be used “to provide a wide array of innovative wireless services and technologies, including voice, data, video and other wireless broadband services.” The value of such spectrum was not lost on the telecommunications service providers. In one such auction, begun August 9, 2006, there were 161 rounds of bidding. The Federal Government took in more than $13 billion from this auction.

1G, 2G, 3G, 4G, and 5G. Wireless networks are placed into generations known as 1G, 2G, 3G, 4G, and 5G. 1G describes the original, analog cell phone systems. From 2G on, the systems were digital. 3G improved on 2G, and 4G, which began to appear in 2010, is even more powerful. The first 5G phones were introduced in 2019.

Careers and Course Work

The services provided by telephone companies and their suppliers no longer amount to what is called POTS (plain old telephone service) but rather are very sophisticated. Anyone who chooses to work in telecommunications, at least on the technological side, must be very conversant with electrical engineering, computer engineering, and information technology.

New terms for new concepts and advancements are constantly being generated. For example, a webmaster is a person who structures, maintains, and expands a Web site. Also, many companies have created a chief information officer (CIO) position. These positions are evidence of the expanding telephone industry.

Social Context and Future Prospects

Despite the overall move toward digital communication, landline phones remain an important aspect in the safety of citizens. In February 2024, AT&T customers across the U.S. lost all cellular communication for about twelve hours when the network failed. In situations like this, if cellular towers fail or the network is overloaded, landline phones offer a way to communicate, especially during emergencies. Though many U.S. citizens are cord-cutting, or moving toward all aspects of digital communication, in the event cellular service fails, landline communication will likely still work.

However, Moore's law predicts continuing development in computer technology, which is likely to translate to technical advances in the field of telecommunications. In terms of telecommunications, each site on Earth is the same distance from any other site. The cost of transmitting information—voice, data, or video—is extremely low. Communication among people, especially the young, is very frequently through electronic means.

All of this has changed the shape of many companies and institutions. One large computer manufacturer does not have a home office. Dozens of major corporations have offices far removed from their manufacturing facilities. Major universities are offering classes, lesson plans, and other student resources online. Following the 2020 COVID-19 pandemic, many business and schools reverted to in-home work and learning. In the years that followed, many organizations continued the “work-from-home” model and some made it permanent.

The reliance on online communications can come with some danger. Supposedly secure information frequently turns out to be not secure, and important information (such as credit card numbers) ends up in the hands of unscrupulous people. Data leaks, infringements, and the selling of consumer information are constant threats. Systems to avoid problems of this nature have been developed, but so are means to bypass such security measures. However, for most people, the conveniences outweigh the dangers. Because of this, consumers will continue to use a mixture of landlines, cell phones, smart phones, laptops, and desktops to communicate.

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