Baird's device relied upon the Nipkow disk and thus became known as the mechanical television. It formed the basis of experimental broadcasts done by the British Broadcasting Corporation beginning 30 September The first version of such a television to show promise was produced by Philo Farnsworth and demonstrated to his family on 7 September The development of transistor technology has been fundamental to modern electronic telecommunication. According Edholm's law , the bandwidth of telecommunication networks has been doubling every 18 months.
However, already in the s, researchers started to investigate packet switching , a technology that sends a message in portions to its destination asynchronously without passing it through a centralized mainframe. While Internet development was a focus of the Internet Engineering Task Force IETF who published a series of Request for Comment documents, other networking advancements occurred in industrial laboratories , such as the local area network LAN developments of Ethernet and the token ring protocol [ citation needed ].
The wireless revolution began in the s,    with the advent of digital wireless networks leading to a social revolution, and a paradigm shift from wired to wireless technology,  including the proliferation of commercial wireless technologies such as cell phones , mobile telephony , pagers , wireless computer networks ,  cellular networks , the wireless Internet , and laptop and handheld computers with wireless connections.
Realization and demonstration, on 29 October , of the first digital cinema transmission by satellite in Europe    of a feature film by Bernard Pauchon,  Alain Lorentz, Raymond Melwig  and Philippe Binant. Modern telecommunication is founded on a series of key concepts that experienced progressive development and refinement in a period of well over a century. Telecommunication technologies may primarily be divided into wired and wireless methods.
Overall though, a basic telecommunication system consists of three main parts that are always present in some form or another:. For example, in a radio broadcasting station the station's large power amplifier is the transmitter; and the broadcasting antenna is the interface between the power amplifier and the "free space channel". The free space channel is the transmission medium; and the receiver's antenna is the interface between the free space channel and the receiver.
Next, the radio receiver is the destination of the radio signal, and this is where it is converted from electricity to sound for people to listen to. Sometimes, telecommunication systems are "duplex" two-way systems with a single box of electronics working as both the transmitter and a receiver, or a transceiver. For example, a cellular telephone is a transceiver. This can be readily explained by the fact that radio transmitters contain power amplifiers that operate with electrical powers measured in watts or kilowatts , but radio receivers deal with radio powers that are measured in the microwatts or nanowatts.
Hence, transceivers have to be carefully designed and built to isolate their high-power circuitry and their low-power circuitry from each other, as to not cause interference. Telecommunication over fixed lines is called point-to-point communication because it is between one transmitter and one receiver. Telecommunication through radio broadcasts is called broadcast communication because it is between one powerful transmitter and numerous low-power but sensitive radio receivers. Telecommunications in which multiple transmitters and multiple receivers have been designed to cooperate and to share the same physical channel are called multiplex systems.
The sharing of physical channels using multiplexing often gives very large reductions in costs. Multiplexed systems are laid out in telecommunication networks, and the multiplexed signals are switched at nodes through to the correct destination terminal receiver. Communications signals can be sent either by analog signals or digital signals. There are analog communication systems and digital communication systems. For an analog signal, the signal is varied continuously with respect to the information. In a digital signal, the information is encoded as a set of discrete values for example, a set of ones and zeros.
During the propagation and reception, the information contained in analog signals will inevitably be degraded by undesirable physical noise. The output of a transmitter is noise-free for all practical purposes. Commonly, the noise in a communication system can be expressed as adding or subtracting from the desirable signal in a completely random way.
This form of noise is called additive noise , with the understanding that the noise can be negative or positive at different instants of time. Noise that is not additive noise is a much more difficult situation to describe or analyze, and these other kinds of noise will be omitted here. On the other hand, unless the additive noise disturbance exceeds a certain threshold, the information contained in digital signals will remain intact.
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Their resistance to noise represents a key advantage of digital signals over analog signals. A telecommunications network is a collection of transmitters, receivers, and communications channels that send messages to one another. Some digital communications networks contain one or more routers that work together to transmit information to the correct user.
An analog communications network consists of one or more switches that establish a connection between two or more users. For both types of network, repeaters may be necessary to amplify or recreate the signal when it is being transmitted over long distances. This is to combat attenuation that can render the signal indistinguishable from the noise. The term "channel" has two different meanings.
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In one meaning, a channel is the physical medium that carries a signal between the transmitter and the receiver. Examples of this include the atmosphere for sound communications, glass optical fibers for some kinds of optical communications , coaxial cables for communications by way of the voltages and electric currents in them, and free space for communications using visible light , infrared waves , ultraviolet light , and radio waves.
The various RG designations are used to classify the specific signal transmission applications. The sending of radio waves from one place to another has nothing to do with the presence or absence of an atmosphere between the two. Radio waves travel through a perfect vacuum just as easily as they travel through air, fog, clouds, or any other kind of gas. The other meaning of the term "channel" in telecommunications is seen in the phrase communications channel , which is a subdivision of a transmission medium so that it can be used to send multiple streams of information simultaneously.
For example, one radio station can broadcast radio waves into free space at frequencies in the neighborhood of In the example above, the "free space channel" has been divided into communications channels according to frequencies , and each channel is assigned a separate frequency bandwidth in which to broadcast radio waves. This system of dividing the medium into channels according to frequency is called " frequency-division multiplexing ". Another term for the same concept is " wavelength-division multiplexing ", which is more commonly used in optical communications when multiple transmitters share the same physical medium.
Another way of dividing a communications medium into channels is to allocate each sender a recurring segment of time a "time slot", for example, 20 milliseconds out of each second , and to allow each sender to send messages only within its own time slot. This method of dividing the medium into communication channels is called " time-division multiplexing " TDM , and is used in optical fiber communication.
The shaping of a signal to convey information is known as modulation. Modulation can be used to represent a digital message as an analog waveform. This is commonly called "keying" —a term derived from the older use of Morse Code in telecommunications—and several keying techniques exist these include phase-shift keying , frequency-shift keying , and amplitude-shift keying.
The " Bluetooth " system, for example, uses phase-shift keying to exchange information between various devices. Modulation can also be used to transmit the information of low-frequency analog signals at higher frequencies. This is helpful because low-frequency analog signals cannot be effectively transmitted over free space.
Hence the information from a low-frequency analog signal must be impressed into a higher-frequency signal known as the " carrier wave " before transmission. There are several different modulation schemes available to achieve this [two of the most basic being amplitude modulation AM and frequency modulation FM ].
Telecommunication has a significant social, cultural and economic impact on modern society. On the microeconomic scale, companies have used telecommunications to help build global business empires. This is self-evident in the case of online retailer Amazon.
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Even relatively poor communities have been noted to use telecommunication to their advantage. In Bangladesh 's Narshingdi district, isolated villagers use cellular phones to speak directly to wholesalers and arrange a better price for their goods. Because of the economic benefits of good telecommunication infrastructure, there is increasing worry about the inequitable access to telecommunication services amongst various countries of the world—this is known as the digital divide.
A survey by the International Telecommunication Union ITU revealed that roughly a third of countries have fewer than one mobile subscription for every 20 people and one-third of countries have fewer than one land-line telephone subscription for every 20 people.
In terms of Internet access, roughly half of all countries have fewer than one out of 20 people with Internet access. From this information, as well as educational data, the ITU was able to compile an index that measures the overall ability of citizens to access and use information and communication technologies.
Telecommunication has played a significant role in social relationships. Nevertheless, devices like the telephone system were originally advertised with an emphasis on the practical dimensions of the device such as the ability to conduct business or order home services as opposed to the social dimensions. It was not until the late s and s that the social dimensions of the device became a prominent theme in telephone advertisements. New promotions started appealing to consumers' emotions, stressing the importance of social conversations and staying connected to family and friends.
Since then the role that telecommunications has played in social relations has become increasingly important. In recent years, the popularity of social networking sites has increased dramatically. These sites allow users to communicate with each other as well as post photographs, events and profiles for others to see. The profiles can list a person's age, interests, sexual preference and relationship status.
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In this way, these sites can play important role in everything from organising social engagements to courtship. Prior to social networking sites, technologies like short message service SMS and the telephone also had a significant impact on social interactions. In cultural terms, telecommunication has increased the public's ability to access music and film. With television, people can watch films they have not seen before in their own home without having to travel to the video store or cinema.
With radio and the Internet, people can listen to music they have not heard before without having to travel to the music store. Telecommunication has also transformed the way people receive their news. A survey right table of slightly more than 3, Americans by the non-profit Pew Internet and American Life Project in the United States the majority specified television or radio over newspapers.
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Telecommunication has had an equally significant impact on advertising. Many countries have enacted legislation which conforms to the International Telecommunication Regulations established by the International Telecommunication Union ITU , which is the "leading UN agency for information and communication technology issues". According to the ITU's Radio Regulations adopted in Atlantic City, all frequencies referenced in the International Frequency Registration Board , examined by the board and registered on the International Frequency List "shall have the right to international protection from harmful interference".
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From a global perspective, there have been political debates and legislation regarding the management of telecommunication and broadcasting. The history of broadcasting discusses some debates in relation to balancing conventional communication such as printing and telecommunication such as radio broadcasting. In , the BBC broadcast propaganda to the Arab World to partly counter similar broadcasts from Italy, which also had colonial interests in North Africa. Modern insurgents, such as those in the latest Iraq War , often use intimidating telephone calls, SMSs and the distribution of sophisticated videos of an attack on coalition troops within hours of the operation.