Telecommunication is the extension of communication over a distance. In practice it also recognizes that something may be lost in the process; hence the term 'telecommunication' covers all forms of distance and/or conversion of the original communications, including radio, telegraphy, television, telephony, data communication and computer networking. Communication is the process of exchanging information usually via a common system of symbols. ... Communication is the process of exchanging information usually via a common system of symbols. ... Telegraphy (from the Greek words tele = far away and grapho = write) is the long distance transmission of written messages without physical transport of letters, originally over wire. ... A telephone handset A touch-tone telephone dial Telephone This article is about telephone technology. ... A computer network is a system for communication among two or more computers. ...

The elements of a telecommunication system are a transmitter, a medium (line) and possibly a channel imposed upon the medium (see baseband and broadband as well as multiplexing), and a receiver. The transmitter is a device that transforms or encodes the message into a physical phenomenon; the signal. The transmission medium, by its physical nature, is likely to modify or degrade the signal on its path from the transmitter to the receiver. The receiver has a decoding mechanism capable of recovering the message within certain limits of signal degradation. In some cases, the final "receiver" is the human eye and/or ear (or in some extreme cases other sense organs) and the recovery of the message is done by the brain (see psychoacoustics.) In communications and information processing, a transmitter (sometimes abbreviated XMTR) is an object (source) which sends information to an observer (receiver). ... The word line apparently derives from the Latin linum, meaning flax plant from which linen is produced; at one time, a stretched linen thread was the most reliable way to determine a straight line. ... For the geographical meanings of this word, see channel (geography). ... In telecommunication, the term baseband has the following meanings: 1. ... Broadband in general refers to data transmission where multiple pieces of data are sent simultaneously to increase the effective rate of transmission. ... In telecommunications, multiplexing (MUXing) is the combining of two or more information channels onto a common transmission medium using hardware called a multiplexer or (MUX). ... The word receiver has a number of different meanings: In communications and information processing, a receiver is the recipient (observer) of a message (information), which is sent from a source (object). ... In the anatomy of animals, the brain, or encephalon, is the supervisory center of the nervous system. ... Psychoacoustics is the study of subjective human perception of sounds. ...

Telecommunication can be point-to-point, point-to-multipoint or broadcasting, which is a particular form of point-to-multipoint that goes only from the transmitter to the receivers. Point-to-Point telecommunications is most recently (2003) referenced regarding wireless data communications for Internet or Voice over IP via radio frequencies in the multi-gigahertz range. ... Point-to-multipoint (PT2MP) telecommunications is most typically (2003) used in wireless Internet and IP Telephony via gigahertz radio frequencies. ... Note: broadcasting is also the old term for hand sowing. ...

One of the roles of the telecommunications engineer is to analyse the physical properties of the line or transmission medium, and the statistical properties of the message in order to design the most effective encoding and decoding mechanisms. The word line apparently derives from the Latin linum, meaning flax plant from which linen is produced; at one time, a stretched linen thread was the most reliable way to determine a straight line. ... A transmission medium is any material substance, such as fiber-optic cable, twisted-wire pair, coaxial cable, dielectric-slab waveguide, water, and air, that can be used for the propagation of signals, usually in the form of modulated radio, light, or acoustic waves, from one point to another. ...

When systems are designed to communicate through human sense organs (mainly vision and hearing), physiological and psychological characteristics of human perception will be taken into account. This has important economic implications and engineers will research what defects may be tolerated in the signal yet not affect the viewing or hearing experience too badly. Vision can refer to: Visual perception is one of the senses. ... Hearing is one, the auditory, of the traditional five senses, and refers to the ability to detect sound. ... In psychology and the cognitive sciences, perception is the process of acquiring, interpreting, selecting, and organizing sensory information. ...

Examples of human (tele)communications

In a simplistic example, consider a normal conversation between two people. The message is the sentence that the speaker decides to communicate to the listener. The transmitter is the language areas in the brain, the motor cortex, the vocal cords, the larynx, and the mouth that produce those sounds called speech. The signal is the sound waves (pressure fluctuations in air particles) that can be identified as speech. The channel is the air carrying those sound waves, and all the acoustic properties of the surrounding space: echoes, ambient noise, reverberation. Between the speaker and the listener (the receiver), might be other devices that do or do not introduce their own distortions of the original vocal signal (e.g. telephone, HAM radio, IP phone, etc.) The penultimate receiver is the listener's ear and auditory system, the auditory nerve, and the language areas in the listener's brain that will "decode" the signal into meaningful information and filter out background noise. In the anatomy of animals, the brain, or encephalon, is the supervisory center of the nervous system. ... Early work on motor cortex function Back in the 1940s, Canadian neurosurgeon Wilder Penfield wanted to know which bits of epileptics brains he could suck out without them noticing. ... The vocal cords, also known as vocal folds, are composed of twin infoldings of mucous membrane stretched horizontally across the human larynx. ... The larynx (IPA læɹɪŋks) is an organ in the neck of mammals involved in control of breathing, protection of the trachea and sound production. ... The mouth, also known as the buccal cavity or the oral cavity, is the opening through which an animal or human takes in food. ... A schematic representation of auditory signaling Sound is an alternation in pressure, particle displacement, or particle velocity propagated in an elastic material (Olson 1957) or series of mechanical compressions and rarefactions or longitudinal waves that successively propagate through medium that are at least a little compressible (solid, liquid or gas... Speech: (n. ... This article is about compression waves. ... Echo is: Echo - character in Greek mythology echo - natural phenomenon Echo sounding Forward echo Echo, Minnesota Echo Township, Minnesota Echo Township, Michigan Echo Lake, Washington The rock band Echo & the Bunnymen The 1999 album Echo by Tom Petty the letter E in the NATO phonetic alphabet. ... When sound is produced in an enclosed space multiple reflections build up and blend together creating reverberation or reverb. ... Amateur radio, commonly called ham radio, is a hobby enjoyed by many people throughout the world (as of 2004 about 3 million worldwide, 60,000 in UK, 70,000 in Germany, 5,000 in Norway, 57,000 in Canada, and 700,000 in the USA). ... The auditory nerve is the nerve along which the sensory cells (the hair cells) of the inner ear transmit information to the brain. ...

All channels have noise. Another important aspect of the channel is called the bandwidth. A low bandwidth channel, such as a telephone, cannot carry all of the audio information that is transmitted in normal conversation, causing distortion and irregularities in the speaker's voice, as compared to normal, in-person speech. Analog Bandwidth is the width, usually measured in hertz, of a frequency band f2 − f1. ... A telephone handset A touch-tone telephone dial Telephone This article is about telephone technology. ...

Other Background

Bell Labs scientist Claude E. Shannon published A Mathematical Theory of Communication in 1948. This landmark publication was to set the mathematical models used to describe communication systems called information theory. Information theory enables us to evaluate the capacity of a communication channel according to its bandwidth and signal-to-noise ratio. Original theory on communication principles was provided by Harry Nyquist and Émile Baudot after whom the term Baud was conceived to represent a single piece of transmitted information. Claude Elwood Shannon (April 30, 1916 _ February 24, 2001) has been called the father of information theory, and was the founder of practical digital circuit design theory. ... A Mathematical Theory of Communication, published in 1948 by mathematician and computer scientist Claude Shannon, was one of the founding works of the field of information theory. ... 1948 is a leap year starting on Thursday (link will take you to calendar). ... Information theory is a branch of the mathematical theory of probability and mathematical statistics, that quantifies the concept of information. ... Channel capacity, shown often as C in communication formulas, is the amount of discrete information bits that a defined area or segment in a communications medium can hold. ... The phrase signal-to-noise ratio, often abbreviated SNR or S/N, is an engineering term for the ratio between the magnitude of a signal (meaningful information) and the magnitude of background noise. ... Harry Nyquist (February 7, 1889 - April 4, 1976) was an important contributor to information theory. ... Jean-Maurice-Émile Baudot, ( September 11, 1845 – March 28, 1903), French telegraph engineer and inventor of the Baudot code. ... In telecommunications and electronics, baud (pronounced ) is a measure of the signaling rate which is the number of changes to the transmission media per second in a modulated signal. ...

Early telecommunication systems were predominantly based on analog electronic circuit design and used a single encoding technique. The introduction of mass-produced digital integrated circuits has enabled telecom engineers to take full advantage of information theory and simultaneously use multiple encoding techniques. From the demands of telecom circuitry, a whole specialist area of integrated circuit design has emerged called digital signal processing. An integrated circuit (IC) is a thin chip consisting of at least two interconnected semiconductor devices, mainly transistors, as well as passive components like resistors. ... Digital signal processing (DSP) is the study of signals in a digital representation and the processing methods of these signals. ...

Early phone systems used analog transmission lines between central offices, but in the 1960s digital multiplexed circuits were used to send voice calls over a Time Division Multiplexed (TDM) circuit. This was done at speeds of either 1.544 Mbit/s (a T1), or at 2.04 Mbit/s (an E1). A T1 circuit was capable of carrying 24 voice channels while an E1 was capable of carrying 30 voice channels. Each voice channel uses 64 kbit/s worth of digital bandwidth to convey the analog waveform.

The development of the computer modem from 1980 is a clear testimony of increases in information transfer capability through the use of multiple mechanisms. A modem today uses frequency, phase and data compression techniques to squeeze data through what originally seemed an impossibly small bandwidth. The tower of a personal computer (specifically a Power Mac G5). ... A modem (a portmanteau word constructed from modulator and demodulator) is a device that modulates an analog carrier signal (sound), to encode digital information, and that also demodulates such a carrier signal to decode the transmitted information. ... 1980 is a leap year starting on Tuesday. ...

Possible imperfections in a communication channel are: shot noise, thermal noise, latency, non-linear channel transfer function, sudden signal drops, bandwidth limitations, signal reflections (echos). More recent telecommunications systems take advantage of some of these imperfections to actually improve the quality of the channel. Shot noise consists of random fluctuations of the electric current in an electrical conductor, which are caused by the fact that the current is carried by discrete charges (electrons). ... Johnson-Nyquist noise (sometimes thermal noise, Johnson noise or Nyquist noise) is the noise generated by the equilibrium fluctuations of the electric current inside an electrical conductor, which happens without any applied voltage, due to the random thermal motion of the charge carriers (the electrons). ... Latency is the time a message takes to traverse a system. ... A transfer function is a mathematical representation of the relation between the input and output of a linear time-invariant system. ... Analog Bandwidth is the width, usually measured in hertz, of a frequency band f2 − f1. ... When a signal is transmitted along a transmission medium, such as a copper cable or an optical fibre, there is the possibility that some of the signal power is reflected back to its origin, rather than being carried all the way along the cable to the far end. ...

Modern telecommunication systems often make extensive use of a clock signal which is used to decode a transmitted data stream, synchronization. In order to accumulate and manage such streams a telco always provided the clock signal. With the advent of global communications it became necessary to have a single worldwide standard derived from a master atomic clock, or to secondary clocks synchronised to that clock. Synchronous circuits are often used between routers. Asynchronous Transfer Mode, ATM is a relatively new standard, operating at very high bit rates where synchronization outside of the data stream can result in errors. Synchronization is coordination with respect to time. ... TATA Engineering and Locomotive Company A telephone company (or telco) provides telecommunications services such as telephony and data communications. ... An atomic clock is a type of clock that uses an atomic resonance frequency standard as its counter. ... This article describes the computer networking device. ... Asynchronous Transfer Mode, or ATM for short, is a cell relay network protocol which encodes data traffic into small fixed sized (53 byte) cells instead of variable sized packets as in packet-switched networks (such as the Internet Protocol or Ethernet). ... ATM is an initialism with the following meanings: Adobe Type Manager, font management software from Adobe Systems Advanced Traffic Management and Arterial Traffic Management, terms used in the intelligent transportation system industry. ...

See modulation for examples of techniques for encoding information into analog signals. For the musical use of modulation, see modulation (music). ...

Examples

Examples of digital channel coding systems: Hamming coding, Gray coding, Binary coding, Turbo coding. In digital telecommunications, channel coding is a pre_transmission mapping applied to a digital signal or data file, usually designed to make error-correction possible. ... In telecommunication, a Hamming code is an error-correcting code named after its inventor, Richard Hamming. ... A Gray code is a binary numeral system where two successive values differ in only one digit, originally designed to prevent spurious output from electromechanical switches. ... Binary coding is the term used to describe how information, normally numbers, are stored in binary, radix-2 form. ... Turbo codes are a class of recently-developed high-performance error correction codes finding use in deep-space satellite communications and other applications where designers seek to achieve maximal information transfer over a limited-bandwidth communication link in the presence of data-corrupting noise. ...

Examples of telecommunications systems:

• Semaphore
• Telegraphy
• Radioteletype
• The global telephone network (also known as the Public Switched Telephone Network or PSTN)
• Radio
• Television
• Communications satellites
• Ethernet
• Predictive Dialers
• The Internet

The semaphore line was a signalling system invented by the Chappe brothers in France. ... Telegraphy (from the Greek words tele = far away and grapho = write) is the long distance transmission of written messages without physical transport of letters, originally over wire. ... Radioteletype (RTTY) is a telecommunications system consisting of two teleprinters linked by a radio link. ... The public switched telephone network (PSTN) is the concatenation of the worlds public circuit-switched telephone networks, in much the same way that the Internet is the concatenation of the worlds public IP-based packet-switched networks. ... U.S. military MILSTAR communications satellite A communications satellite (sometimes abbreviated to comsat) is an artificial satellite stationed in space for the purposes of telecommunications or reconnaisance using radio at microwave frequencies. ... Ethernet is a frame-based computer networking technology for local area networks (LANs). ... A predictive dialer is generally a computerized system that automatically dials batches of telephone numbers, and developed from the autodialer. ...

See also

• ITU
• Federal Standard 1037C for a glossary of telecommuncations terms
• Public utility
• Lists of public utilities

The International Telecommunication Union (ITU) is an international organization established to standardize and regulate international radio and telecommunications. ... Federal Standard 1037C entitled Telecommunications: Glossary of Telecommunication Terms is a U.S. Federal Standard, issued by the General Services Administration pursuant to the Federal Property and Administrative Services Act of 1949, as amended. ... A public utility is a company that maintains the infrastructure for a public service. ... These are lists of public utilities. ...

External links

• Ericsson's Understanding Telecommunications (http://www.ericsson.com/support/telecom)
• Intec Telecom Systems' Telecom Dictionary (http://www.carrieraccessbilling.com/telecommunications-glossary-a.asp)
• Mobile Phone Directory Telecommunications Glossary (http://www.mobile-phone-directory.org/Glossary/)
• Doc-Telecom  (http://doc-telecom.enst-bretagne.fr/doc-telecom/)

History

• Aronsson's Telecom History Timeline (http://www.aronsson.se/hist.html)