Wired communication refer to transmission over a wire communication channel like fiber optic. On the other hand, communication technologies that don't use wire like wifi is known as wireless.
Early signaling and Telegraphy
Semaphore - a type of signaling, in which visual cues represent letters or words. Morse code - the transmission of a series of short and long pulses (dots and dashes) that represented characters. Duplexing - simultaneously transmitting a signal in both directions along the same wire. Multiplexing - simultaneously transmitting an indeterminate number of multiple signals over one circuit. 1856 - Western Union Telegraph Company was founded. 1861 – Over two thousand telegraph offices operated across the United States.
Telephone technology
1878- The first telephone exchange opened in New Haven, Connecticut. Connected 21 separate lines.
In 1913, N.J. Reynolds, a Western Electric engineer, developed a better automatic switch, the crossbar switch. It used a grid of horizontal and vertical bars, with electromagnets at their ends. The horizontal bars could rotate up and down to connect to specific vertical bars and thus complete circuits. Original version could complete 10 simultaneous connections. By the 1970 a single crossbar could connect 35,000 connections.
In the mid-20th century AT&T integrated electronics into crossbar switches l1965 – first electronic switching system was used to handle up to 65,000 two-way voice circuits. Until 1970 all telephone switches depended on a continuous physical connection to complete and maintain the call.
1976 – New electronic switching device was put into service. Time division switching - a transmission technique in which samples from multiple incoming lines are digitized, then each sample is issued to the same circuit, in a predetermined sequence, before finally being transmitted to the correct outbound line.
Space division switching - manipulating the physical space between two lines, thereby closing a circuit to connect a call. Local switching center (often called a local office) - a place where multiple phone lines from homes and businesses in one geographic area converge and terminate. Tandem switching center - an exchange where lines from multiple local offices converge and terminate. Toll switching center - an exchange where lines from multiple tandem switching centers converge and terminate.
Wireless Technology
Telegraphs and telephones are examples of wireline, or wire-bound technology, because they rely on physically connected wires to transmit and receive signals. Wireless technology - relies on the atmosphere to transmit and receive signals.
Examples of wireless technology are Phones, Radios, Televisions, Satellite communications.
1894- Italian physicist Guglielmo Marconi a method of transmitting electromagnetic signals through the air. His invention relied on an induction coil.
Induction coil is made by winding wire in a either one or multiple layers around a metal rod to form a coil then applying a charge. Charged wire induces an electromagnetic field that generates voltage Marconi connected an induction coil to a telegraph key. Each time the key was pressed the coil discharged a voltage through the air between to brass surfaces. Metal filings in a glass cylinder became charged and cohered. The length of time they cohered translated into short and long pulses. Pulses were relayed to a Morse code printer. Marconi invention used the same type of signals sent and received by a telegraph.
Vacuum tube - a sealed container made of glass, metal, or ceramic, that contains, in a vacuum, a charged plate that transmits current to a filament. Audion - patented in 1907 by DeForest, is a type of vacuum tube that contains an additional electrode in the middle of the positive and negative electrodes. Boosts or amplifies a signal. First instants of signal amplification and it formed the basis for all subsequent radio and television advances. 1912- Edwin Armstrong improved the Audion. He discovered that by feeding the signal back the tube the power of the Audion could be increased.
Continued experimentation resulted in the invention of Frequency modulation. Frequency modulation is technology used in FM radio and other forms of wireless technology. In Frequency modulation one wave containing the information to be transmitted (for example, on a classical FM radio station, a violin concerto) is combined with another wave, called a carrier wave, whose frequency is constant. Frequency is the number of times each second that a sine wave completes a full cycle.
The advent of FM radio afforded the best clarity of all wireless technologies then available. Walkie-Talkies use frequency modulation 1946- Bell Laboratories connect the first wireless car phone to the St. Louis network. 1962- Telstar Satellite successfully transmitted television and telephone conversation across the Atlantic for the first time.
Geosynchronous - means that satellites orbit the earth at the same rate as the earth turns. Uplink - a broadcast from an earth-based transmitter to an orbiting satellite. At the satellite, a transponder receives the uplink, then transmits the signals to another earth-based location in a downlink.
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