communication theory: see information theory.

communication, transfer of information, such as thoughts and messages, as contrasted with transportation, the transfer of goods and persons (see information theory). The basic forms of communication are by signs (sight) and by sounds (hearing; see language). The reduction of communication to writing was a fundamental step in the evolution of society for, in addition to being useful in situations where speech is not possible, writing permits the preservation of communications, or records, from the past. It marks the beginning of recorded history. Whereas the rise of book publishing and journalism (see also newspaper and periodical) facilitated the widespread dissemination of information, the invention of the telegraph, the radio, the telephone, and television made possible instantaneous communication over long distances. With the installation of the submarine cable and improvements in short-wave radio technology, international communication was greatly improved and expanded. In 1962 the first active communications satellite was launched; it provided the first live television broadcast between the United States, Europe, Japan, and South America. Today, satellite communications is used extensively for relaying television signals, telephone calls, and special teleconferencing calls that might include two-way video and graphics along with audio (see satellite, artificial). The 20th-century development of mass media has played a major role in changing social, economic, political, and educational institutions. In the United States, radio and television communication is controlled by the Federal Communications Commission. The international phases of transport and communications are under the direction of the Office of Transport and Communications of the Dept. of State. The United Nations maintains an International Telecommunication Union (ITU), which has three functions—to maintain and extend international cooperation for the improvement and rational use of telecommunication, to promote the development and efficient use of technical facilities, and to harmonize the actions of nations. Telecommunication has been defined by international agreement as any emission, transmission, or reception of signs, signals, sounds, and writing. Recent advances in electronics have made mobile personal communications widely available and inexpensive, primarily through cellular telephony. Worldwide computer networks allow computer users to use modems to communicate rapidly and inexpensively through electronic mail. The proliferation of facsimile machines allows users to send printed communications over telephone lines. See broadcasting.

Earth-orbiting system capable of receiving a signal (e.g., data, voice, TV) and relaying it back to the ground. Communications satellites have been a significant part of domestic and global communications since the 1970s. Typically they move in geosynchronous orbits about 22,300 mi (35,900 km) above the earth and operate at frequencies near 4 gigahertz (GHz) for downlinking and 6 GHz for uplinking.

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or confidential communication

In law, communication between parties to a confidential relation such that the communication's recipient is exempted from disclosing it as a witness. Communications between attorney and client are privileged and do not have to be disclosed to the court. The right to privileged communication also exists between husbands and wives, as neither is required to testify against the other in court, and between physicians and patients, though doctors may be required to disclose such information if the right of the defendant to receive a fair trial outweighs the patient's right to confidentiality. Members of the clergy have limited rights to refuse to testify in court, and reporters have been accorded a limited right to privileged communication concerning the sources of their information, though they can be ordered to divulge information in certain circumstances.

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Communication between parties at a distance from one another. Modern telecommunication systems—capable of transmitting telephone, fax, data, radio, or television signals—can transmit large volumes of information over long distances. Digital transmission is employed in order to achieve high reliability with minimal noise, or interference, and because it can transmit any signal type, digital or analog. For digital transmission, analog signals must be subjected to a process of analog-to-digital conversion; most television, radio, and voice communications are analog and must be digitized before transmission. Transmission may occur over cables, wireless radio relay systems, or via satellite links.

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United Nations agency headquartered in Geneva. Its roots can be traced to 1865, when the International Telegraph Union was established to coordinate international development of the telegraph. It acquired its present name in 1934 and became a UN specialized agency in 1947. Its activities include regulating allocation of radio frequencies, setting standards on technical and operational matters, and assisting countries in developing their own telecommunications systems.

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Field of mathematics that studies the problems of signal transmission, reception, and processing. It stems from Claude E. Shannon's mathematical methods for measuring the degree of order (nonrandomness) in a signal, which drew largely on probability theory and stochastic processes and led to techniques for determining a source's rate of information production, a channel's capacity to handle information, and the average amount of information in a given type of message. Crucial to the design of communications systems, these techniques have important applications in linguistics, psychology, and even literary theory.

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Transmission of information from one animal to another by means of sound, visible sign or behaviour, taste or odour, electrical impulse, touch, or a combination of these. Most animal communication uses sound (e.g., birds calling, crickets chirping). Visual communication usually indicates an animal's identity (species, sex, age, etc.) or other information through specific characteristics (e.g., horns, patches of colour) or behaviour (e.g., the bee's “dance” describing a source of food). Chemical communication involves pheromones (chemical signals) produced by the animal's endocrine system. Eels and some other fishes use electrical impulses to communicate.

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