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Data transmission

"Data transfer" redirects here. For sharing data between different programs or schemas, see Data exchange.

Data transmission also data communicationor digital communications is the transfer ofdata (a digital bitstream or a digitized analog signal^[1]) over a point-to-point or point-to-multipoint communication channel. Examples of such channels are copper wires, optical fibers, wireless communication channels,storage media and computer buses. The data are represented as an electromagnetic signal, such as an electrical voltage, radiowave,microwave, or infrared signal.

Analog or analogue transmission is a transmission method of conveying voice, data, image, signal or video information using a continuous signal which varies in amplitude, phase, or some other property in proportion to that of a variable. The messages are either represented by a sequence of pulses by means of a line code (basebandtransmission), or by a limited set of continuously varying wave forms (passbandtransmission), using a digital modulationmethod. The passband modulation and corresponding demodulation (also known as detection) is carried out by modemequipment. According to the most common definition of digital signal, both baseband and passband signals representing bit-streams are considered as digital transmission, while an alternative definition only considers the baseband signal as digital, and passband transmission of digital data as a form ofdigital-to-analog conversion.

Data transmitted may be digital messages originating from a data source, for example a computer or a keyboard. It may also be an analog signal such as a phone call or a video signal, digitized into a bit-stream for example using pulse-code modulation (PCM) or more advanced source coding (analog-to-digital conversion and data compression) schemes. This source coding and decoding is carried out by codec equipment.

Distinction between related subjects

Protocol layers and sub-topics

Applications and history

Serial and parallel transmission

Types of communication channels (Network topologies)

Asynchronous and synchronous data transmissionEdit

Main article: comparison of synchronous and asynchronous signalling

Asynchronous start-stop transmission uses start and stop bits to signify the beginning bit^{[citation needed]} ASCII character would actually be transmitted using 10 bits. For example, "0100 0001" would become "1 0100 0001 0". The extra one (or zero, depending on parity bit) at the start and end of the transmission tells the receiver first that a character is coming and secondly that the character has ended. This method of transmission is used when data are sent intermittently as opposed to in a solid stream. In the previous example the start and stop bits are in bold. The start and stop bits must be of opposite polarity.^{[citation needed]} This allows the receiver to recognize when the second packet of information is being sent.

Synchronous transmission uses no start and stop bits, but instead synchronizes transmission speeds at both the receiving and sending end of the transmission using clocksignal(s) built into each component.^[vague] A continual stream of data is then sent between the two nodes. Due to there being no start and stop bits the data transfer rate is quicker although more errors will occur, as the clocks will eventually get out of sync, and the receiving device would have the wrong time that had been agreed in the protocol for sending/receiving data, so some bytes could become corrupted (by losingbits).^{[citation needed]} Ways to get around this problem include re-synchronization of the clocks and use of check digits to ensure thebyte is correctly interpreted and received

See alsoEdit

• Computer networking
• Data migration
• Information theory
• Media (communication)
• Network security
• Signal processing
• Telecommunication
• Transmission (disambiguation)

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networked computing devicesexchange data with each other using a data link. The connections between nodes are established using either cable omputers, phones, serversas well as networking hardware. Two such devices can be said to be networked together when one device is able to exchange information with the other device, whether or not they have a direct connection to each other. In most cases, application-specific communications protocols are layered (i.e. carried as payload) over other more general communications protocols. This formidable collection of information technology requires skilled network management to keep it allrunning reliably.

Computer networks support an enormous number of applications and services such as access to the World Wide Web, digital video,digital audio, shared use of application and storage servers, printers, and fax machines, and use of email and instant messagingapplications as well as many others. Computer networks differ in the transmission medium used to carry their signals,communications protocols to organize network traffic, the network's size, topologyand organizational intent. The best-known computer network is the Internet.