Editing Data communication (section)

==Applications and history==
Data (mainly but not exclusively [[information]]al) has been sent via non-electronic (e.g. [[optical]], [[acoustics|acoustic]], [[Classical mechanics|mechanical]]) means since the advent of [[communication]]. [[Analog signal]] data has been sent electronically since the [[History of the telephone|advent of the telephone]]. However, the first data electromagnetic transmission applications in modern time were [[electrical telegraphy]] (1809) and [[teletypewriter]]s (1906), which are both [[digital signal]]s. The fundamental theoretical work in data transmission and information theory by [[Harry 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]] invented ''distributed adaptive message block switching'' for digital communication of voice messages using switches that were low-cost electronics.<ref name=":17">{{Cite journal |last=Baran |first=Paul |date=2002 |title=The beginnings of packet switching: some underlying concepts |url=http://web.cs.ucla.edu/~lixia/papers/Baran2002.pdf |url-status=live |journal=IEEE Communications Magazine |language=en |volume=40 |issue=7 |pages=42–48 |doi=10.1109/MCOM.2002.1018006 |issn=0163-6804 |archive-url=https://ghostarchive.org/archive/20221010/http://web.cs.ucla.edu/~lixia/papers/Baran2002.pdf |archive-date=2022-10-10 |quote=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.}}</ref><ref>{{Cite web |title=Paul Baran and the Origins of the Internet |url=https://www.rand.org/about/history/baran.html |access-date=2020-02-15 |website=RAND Corporation |language=en}}</ref> [[Donald Davies]] invented and implemented modern data communication during 1965-7, including [[packet switching]], high-speed [[Router (computing)|routers]], [[communication protocol]]s, hierarchical [[computer network]]s and the essence of the [[end-to-end principle]].<ref name=":6">{{Cite book |last=Yates |first=David M. |url=https://books.google.com/books?id=ToMfAQAAIAAJ&q=packet+switch |title=Turing's Legacy: A History of Computing at the National Physical Laboratory 1945-1995 |date=1997 |publisher=National Museum of Science and Industry |isbn=978-0-901805-94-2 |pages=132–4 |language=en |quote=Davies's invention of packet switching and design of computer communication networks ... were a cornerstone of the development which led to the Internet}}</ref><ref>{{Cite book |last=Naughton |first=John |author-link=John Naughton |url=https://archive.org/details/briefhistoryoffu0000naug/page/292/mode/2up |title=A Brief History of the Future |date=2000 |publisher=Phoenix |isbn=9780753810934 |page=292 |language=en |orig-date=1999}}</ref><ref name=":3">{{Cite journal |last=Campbell-Kelly |first=Martin |date=1987 |title=Data Communications at the National Physical Laboratory (1965-1975) |url=https://archive.org/details/DataCommunicationsAtTheNationalPhysicalLaboratory |journal=Annals of the History of Computing |language=en |volume=9 |issue=3/4 |pages=221–247 |doi=10.1109/MAHC.1987.10023 |s2cid=8172150 |quote=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}}</ref><ref name=":5">{{cite conference |last1=Davies |first1=Donald |last2=Bartlett |first2=Keith |last3=Scantlebury |first3=Roger |last4=Wilkinson |first4=Peter |date=October 1967 |title=A Digital Communication Network for Computers Giving Rapid Response at remote Terminals |url=https://people.mpi-sws.org/~gummadi/teaching/sp07/sys_seminar/how_did_erope_blow_this_vision.pdf |conference=ACM Symposium on Operating Systems Principles |archive-url=https://ghostarchive.org/archive/20221010/https://people.mpi-sws.org/~gummadi/teaching/sp07/sys_seminar/how_did_erope_blow_this_vision.pdf |archive-date=2022-10-10 |access-date=2020-09-15 |url-status=live}} "all users of the network will provide themselves with some kind of error control"</ref> 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 the [[Reliability (computer networking)|reliability]].<ref>{{Cite journal |last=Kleinrock |first=L. |date=1978 |title=Principles and lessons in packet communications |url=https://ieeexplore.ieee.org/document/1455412 |journal=Proceedings of the IEEE |volume=66 |issue=11 |pages=1320–1329 |doi=10.1109/PROC.1978.11143 |issn=0018-9219 |quote=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.|url-access=subscription }}</ref><ref name="Pelkey6.1a">{{Cite book |last=Pelkey |first=James L. |title=Entrepreneurial Capitalism and Innovation: A History of Computer Communications 1968–1988 |chapter=6.1 The Communications Subnet: BBN 1969 |quote=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. |chapter-url=https://historyofcomputercommunications.info/section/6.1/the-communications-subnet-bbn-1969/}}</ref><ref name=":5a">{{Cite book |last=Waldrop |first=M. Mitchell |url=https://books.google.com/books?id=eRnBEAAAQBAJ&pg=PT285 |title=The Dream Machine |date=2018 |publisher=Stripe Press |isbn=978-1-953953-36-0 |pages=286 |language=en |quote=Baran had put more emphasis on digital voice communications than on computer communications.}}</ref> Both were seminal contributions that influenced the development of [[computer network]]s.<ref name=":16">{{Cite news |title=The real story of how the Internet became so vulnerable |url=http://www.washingtonpost.com/sf/business/2015/05/30/net-of-insecurity-part-1/ |url-status=dead |archive-url=https://web.archive.org/web/20150530231409/http://www.washingtonpost.com/sf/business/2015/05/30/net-of-insecurity-part-1/ |archive-date=2015-05-30 |access-date=2020-02-18 |newspaper=Washington Post |language=en-US |quote=Historians credit seminal insights to Welsh scientist Donald W. Davies and American engineer Paul Baran}}</ref><ref>{{cite report |url=https://apps.dtic.mil/sti/pdfs/ADA115440.pdf |title=A History of the ARPANET: The First Decade |date=1 April 1981 |publisher=Bolt, Beranek & Newman Inc. |pages=13, 53 of 183 (III-11 on the printed copy) |quote=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. |archive-url=https://web.archive.org/web/20121201013642/http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA115440 |archive-date=1 December 2012 |url-status=live}}</ref>

Data transmission is utilized in [[computers]] in [[computer bus]]es and for communication with [[peripheral equipment]] via [[parallel port]]s and [[serial port]]s such as [[RS-232]] (1969), [[FireWire]] (1995) and [[USB]] (1996). The principles of data transmission are also utilized in storage media for [[Error detection and correction#Data storage|error detection and correction]] since 1951. The first practical method to overcome the problem of receiving data accurately by the receiver using digital code was the [[Barker code]] invented by [[Ronald Hugh Barker]] in 1952 and published in 1953.<ref>{{cite book |title=Group Synchronisation of Binary Digital Systems | last=Barker| first= RH| date=1953 |publisher=Butterworth |location=Communication Theory |pages=273–287}}</ref> Data transmission is utilized in [[computer networking]] equipment such as [[modems]] (1940), [[local area network]] (LAN) adapters (1964), [[repeater]]s, [[repeater hub]]s, [[microwave link]]s, [[wireless access point|wireless network access point]]s (1997), etc.

In telephone networks, digital communication is utilized for transferring many phone calls over the same copper cable or fiber cable by means of [[pulse-code modulation]] (PCM) in combination with [[time-division multiplexing]] (TDM) (1962). [[Telephone exchange]]s have become digital and software controlled, facilitating many value-added services. For example, the first [[AXE telephone exchange]] was presented in 1976. Digital communication to the end user using [[Integrated Services Digital Network]] (ISDN) services became available in the late 1980s. Since the end of the 1990s, broadband access techniques such as [[ADSL]], [[Cable modem]]s, [[fiber-to-the-building]] (FTTB) and [[fiber-to-the-home]] (FTTH) have become widespread to small offices and homes. The current tendency is to replace traditional telecommunication services with [[packet mode communication]] such as [[IP telephony]] and [[IPTV]].

Transmitting analog signals digitally allows for greater [[signal 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 be [[sampling (signal processing)|sampled]] instead of continuously monitored. The [[multiplexing]] 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 in [[wideband]] [[communication channel]]s and [[solid-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 include [[2G|second-generation]] (1991) and later [[cellular telephony]], [[video conferencing]], [[digital TV]] (1998), [[digital radio]] (1999), and [[telemetry]].

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 an [[electromagnetic 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.{{cn|date=September 2022}}

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.