 | It has been suggested thatData in transit bemerged into this article. (Discuss) Proposed since March 2025. |
Data communication, includingdata transmission anddata reception, is the transfer ofdata,transmitted and received over apoint-to-point orpoint-to-multipoint communication channel. Examples of such channels arecopper wires,optical fibers,wireless communication usingradio spectrum,storage media andcomputer buses. The data are represented as anelectromagnetic signal, such as anelectrical voltage,radiowave,microwave, orinfrared signal.
Analog transmission is a method of conveying voice, data, image, signal or video information using a continuous signal that 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 aline code (baseband transmission), or by a limited set of continuously varying waveforms (passband transmission), using a digitalmodulation method. The passband modulation and correspondingdemodulation is carried out bymodem equipment.
Digital communications, includingdigital transmission anddigital reception, is the transfer of either adigitized analog signal or aborn-digitalbitstream.[1] According to the most common definition, both baseband and passband bit-stream components are considered part of adigital signal; an alternative definition considers only the baseband signal as digital, and passband transmission of digital data as a form ofdigital-to-analog conversion.
Courses and textbooks in the field ofdata transmission[1] as well asdigital transmission[2][3] anddigital communications[4][5] have similar content.
Digital transmission or data transmission traditionally belongs totelecommunications andelectrical engineering. Basic principles of data transmission may also be covered within thecomputer science orcomputer engineering topic of data communications, which also includescomputer networking applications andcommunication protocols, for example routing, switching andinter-process communication. Although theTransmission Control Protocol (TCP) involves transmission, TCP and other transport layer protocols are covered in computer networking butnot discussed in a textbook or course about data transmission.
In most textbooks, the termanalog transmission only refers to the transmission of an analog message signal (without digitization) by means of an analog signal, either as a non-modulated baseband signal or as a passband signal using ananalog modulation method such asAM orFM. It may also include analog-over-analogpulse modulated baseband signals such as pulse-width modulation. In a few books within the computer networking tradition,analog transmission also refers to passband transmission of bit-streams usingdigital modulation methods such asFSK,PSK andASK.[1]
The theoretical aspects of data transmission are covered byinformation theory andcoding theory.
| OSI model bylayer |
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Courses and textbooks in the field of data transmission typically deal with the followingOSI model protocol layers and topics:
It is also common to deal with the cross-layer design of those three layers.[7]
Data (mainly but not exclusivelyinformational) has been sent via non-electronic (e.g.optical,acoustic,mechanical) means since the advent ofcommunication.Analog signal data has been sent electronically since theadvent of the telephone. However, the first data electromagnetic transmission applications in modern time wereelectrical telegraphy (1809) andteletypewriters (1906), which are bothdigital signals. The fundamental theoretical work in data transmission and information theory byHarry Nyquist,Ralph Hartley,Claude Shannon and others during the early 20th century, was done with these applications in mind.
In the early 1960s,Paul Baran inventeddistributed adaptive message block switching for digital communication of voice messages using switches that were low-cost electronics.[8][9]Donald Davies invented and implemented modern data communication during 1965-7, includingpacket switching, high-speedrouters,communication protocols, hierarchicalcomputer networks and the essence of theend-to-end principle.[10][11][12][13] Baran's work did not include routers with software switches and communication protocols, nor the idea that users, rather than the network itself, would provide thereliability.[14][15][16] Both were seminal contributions that influenced the development ofcomputer networks.[17][18]
Data transmission is utilized incomputers incomputer buses and for communication withperipheral equipment viaparallel ports andserial ports such asRS-232 (1969),FireWire (1995) andUSB (1996). The principles of data transmission are also utilized in storage media forerror detection and correction since 1951. The first practical method to overcome the problem of receiving data accurately by the receiver using digital code was theBarker code invented byRonald Hugh Barker in 1952 and published in 1953.[19] Data transmission is utilized incomputer networking equipment such asmodems (1940),local area network (LAN) adapters (1964),repeaters,repeater hubs,microwave links,wireless network access points (1997), etc.
In telephone networks, digital communication is utilized for transferring many phone calls over the same copper cable or fiber cable by means ofpulse-code modulation (PCM) in combination withtime-division multiplexing (TDM) (1962).Telephone exchanges have become digital and software controlled, facilitating many value-added services. For example, the firstAXE telephone exchange was presented in 1976. Digital communication to the end user usingIntegrated Services Digital Network (ISDN) services became available in the late 1980s. Since the end of the 1990s, broadband access techniques such asADSL,Cable modems,fiber-to-the-building (FTTB) andfiber-to-the-home (FTTH) have become widespread to small offices and homes. The current tendency is to replace traditional telecommunication services withpacket mode communication such asIP telephony andIPTV.
Transmitting analog signals digitally allows for greatersignal processing capability. The ability to process a communications signal means that errors caused by random processes can be detected and corrected. Digital signals can also besampled instead of continuously monitored. Themultiplexing of multiple digital signals is much simpler compared to the multiplexing of analog signals. Because of all these advantages, because of the vast demand to transmit computer data and the ability of digital communications to do so and because recent advances inwidebandcommunication channels andsolid-state electronics have allowed engineers to realize these advantages fully, digital communications have grown quickly.
The digital revolution has also resulted in many digital telecommunication applications where the principles of data transmission are applied. Examples includesecond-generation (1991) and latercellular telephony,video conferencing,digital TV (1998),digital radio (1999), andtelemetry.
Data transmission, digital transmission or digital communications is the transfer of data over a point-to-point or point-to-multipoint communication channel. Examples of such channels include copper wires, optical fibers, wireless communication channels, storage media and computer buses. The data are represented as anelectromagnetic signal, such as an electrical voltage, radio wave, microwave, or infrared light.
While analog transmission is the transfer of a continuously varying analog signal over an analog channel, digital communication is the transfer of discrete messages over a digital or an analog channel. The messages are either represented by a sequence of pulses by means of a line code (baseband transmission), or by a limited set of continuously varying wave forms (passband transmission), using a digital modulation method. The passband modulation and corresponding demodulation (also known as detection) is carried out by modem equipment. According to the most common definition of a 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 of digital-to-analog conversion.[citation needed]
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.
In telecommunications,serial transmission is the sequential transmission ofsignal elements of a group representing acharacter or other entity ofdata. Digital serial transmissions are bits sent over a single wire, frequency or optical path sequentially. Because it requires lesssignal processing and less chances for error than parallel transmission, thetransfer rate of each individual path may be faster. This can be used over longer distances and a check digit orparity bit can be sent along with the data easily.
Parallel transmission is the simultaneous transmission of related signal elements over two or more separate paths. Multiple electrical wires are used that can transmit multiple bits simultaneously, which allows for higher data transfer rates than can be achieved with serial transmission. This method is typically used internally within the computer, for example, the internal buses, and sometimes externally for such things as printers.Timing skew can be a significant issue in these systems because the wires in parallel data transmission unavoidably have slightly different properties so some bits may arrive before others, which may corrupt the message. This issue tends to worsen with distance making parallel data transmission less reliable for long distances.
Some communications channel types include:
Asynchronous serial communication uses start and stop bits to signify the beginning and end of transmission.[20] This method of transmission is used when data are sent intermittently as opposed to in a solid stream.
Synchronous transmission synchronizes transmission speeds at both the receiving and sending end of the transmission usingclock signals. The clock may be a separate signal orembedded in the data. 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 may be more efficient.
Essentially all the work was defined by 1961, and fleshed out and put into formal written form in 1962. The idea of hot potato routing dates from late 1960.
Davies's invention of packet switching and design of computer communication networks ... were a cornerstone of the development which led to the Internet
the first occurrence in print of the term protocol in a data communications context ... the next hardware tasks were the detailed design of the interface between the terminal devices and the switching computer, and the arrangements to secure reliable transmission of packets of data over the high-speed lines
Paul Baran ... focused on the routing procedures and on the survivability of distributed communication systems in a hostile environment, but did not concentrate on the need for resource sharing in its form as we now understand it; indeed, the concept of a software switch was not present in his work.
As Kahn recalls: ... Paul Baran's contributions ... I also think Paul was motivated almost entirely by voice considerations. If you look at what he wrote, he was talking about switches that were low-cost electronics. The idea of putting powerful computers in these locations hadn't quite occurred to him as being cost effective. So the idea of computer switches was missing. The whole notion of protocols didn't exist at that time. And the idea of computer-to-computer communications was really a secondary concern.
Baran had put more emphasis on digital voice communications than on computer communications.
Historians credit seminal insights to Welsh scientist Donald W. Davies and American engineer Paul Baran
Aside from the technical problems of interconnecting computers with communications circuits, the notion of computer networks had been considered in a number of places from a theoretical point of view. Of particular note was work done by Paul Baran and others at the Rand Corporation in a study "On Distributed Communications" in the early 1960's. Also of note was work done by Donald Davies and others at the National Physical Laboratory in England in the mid-1960's. ... Another early major network development which affected development of the ARPANET was undertaken at the National Physical Laboratory in Middlesex, England, under the leadership of D. W. Davies.
