Data transmission - Wikipedia Data transmission `` Data transfer '' redirects here. For sharing data between different programs or schemas, see Data exchange. Data transmission ( also data communication or digital communications ) is the transfer of data ( a digital bitstream or a digitized analog signal ) 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 ( 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 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. 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. Contents 1 Distinction between related subjects 2 Protocol layers and sub-topics 3 Applications and history 4 Serial and parallel transmission 5 Types of communication channels ( Network topologies ) 6 Asynchronous and synchronous data transmission 7 See also 8 Notes Distinction between related subjects Courses and textbooks in the field of data transmission as well as digital transmission and digital communications have similar content. Digital transmission or data transmission traditionally belongs to telecommunications and electrical engineering. Basic principles of data transmission may also be covered within the computer science or computer engineering topic of data communications, which also includes computer networking applications and networking protocols, for example routing, switching and inter-process communication. Although the Transmission Control Protocol ( TCP ) involves transmission, TCP and other transport layer protocols are covered in computer networking but not discussed in a textbook or course about data transmission. The term tele transmission involves the analog as well as digital communication. In most textbooks, the term analog 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 an analog modulation method such as AM or FM. It may also include analog - over-analog pulse modulatated 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 using digital modulation methods such as FSK, PSK and ASK. Note that these methods are covered in textbooks named digital transmission or data transmission, for example. The theoretical aspects of data transmission are covered by information theory and coding theory. Protocol layers and sub-topics OSI model by layer 7. Application layer NNTP SIP SSI DNS FTP Gopher HTTP NFS NTP SMPP SMTP SNMP Telnet DHCP Netconf more... 6. Presentation layer MIME XDR ASN. 1 5. Session layer Named pipe NetBIOS SAP PPTP RTP SOCKS SPDY 4. Transport layer TCP UDP SCTP DCCP SPX 3. Network layer IP IPv4 IPv6 ICMP IPsec IGMP IPX AppleTalk X. 25 PLP 2. Data link layer ATM ARP IS - IS SDLC HDLC CSLIP SLIP GFP PLIP IEEE 802.2 LLC MAC L2TP IEEE 802.3 Frame Relay ITU - T G.hn DLL PPP X. 25 LAPB Q. 921 LAPD Q. 922 LAPF 1. Physical layer EIA / TIA - 232 EIA / TIA - 449 ITU - T V - Series I. 430 I. 431 PDH SONET / SDH PON OTN DSL IEEE 802.3 IEEE 802.11 IEEE 802.15 IEEE 802.16 IEEE 1394 ITU - T G.hn PHY USB Bluetooth RS - 232 RS - 449 Courses and textbooks in the field of data transmission typically deal with the following OSI model protocol layers and topics : Layer 1, the physical layer : Channel coding including Digital modulation schemes Line coding schemes Forward error correction ( FEC ) codes Bit synchronization Multiplexing Equalization Channel models Layer 2, the data link layer : Channel access schemes, media access control ( MAC ) Packet mode communication and Frame synchronization Error detection and automatic repeat request ( ARQ ) Flow control Layer 6, the presentation layer : Source coding ( digitization and data compression ), and information theory. Cryptography ( may occur at any layer ) Applications and history Data ( mainly but not exclusively informational ) has been sent via non-electronic ( e.g. optical, acoustic, mechanical ) means since the advent of communication. Analog signal data has been sent electronically since the advent of the telephone. However, the first data electromagnetic transmission applications in modern time were telegraphy ( 1809 ) and teletypewriters ( 1906 ), which are both digital signals. 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. Data transmission is utilized in computers in computer buses and for communication with peripheral equipment via parallel ports and serial ports 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 since 1951. Data transmission is utilized in computer networking equipment such as modems ( 1940 ), local area networks ( 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 of Pulse code modulation ( PCM ), i.e. sampling and digitization, in combination with Time division multiplexing ( TDM ) ( 1962 ). Telephone exchanges have become digital and software controlled, facilitating many value added services. For example, the first AXE telephone exchange was presented in 1976. Since the late 1980s, digital communication to the end user has been possible using Integrated Services Digital Network ( ISDN ) services. Since the end of the 1990s, broadband access techniques such as ADSL, Cable modems, 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 by 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 sampled instead of continuously monitored. The multiplexing of multiple digital signals is much simpler to the multiplexing of analog signals. Because of all these advantages, and because recent advances in wideband communication channels and solid - state electronics have allowed scientists to fully realize these advantages, digital communications has grown quickly. Digital communications is quickly edging out analog communication because of the vast demand to transmit computer data and the ability of digital communications to do so. The digital revolution has also resulted in many digital telecommunication applications where the principles of data transmission are applied. Examples are second - generation ( 1991 ) and later cellular telephony, video conferencing, digital TV ( 1998 ), digital radio ( 1999 ), telemetry, etc. Data transmission, digital transmission or digital communications is the physical transfer of data ( a digital bit stream 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. While analog transmission is the transfer of a continuously varying analog signal over an analog channel, digital communications 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 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. 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. Serial and parallel transmission In telecommunications, serial transmission is the sequential transmission of signal elements of a group representing a character or other entity of data. Digital serial transmissions are bits sent over a single wire, frequency or optical path sequentially. Because it requires less signal processing and less chances for error than parallel transmission, the transfer rate of each individual path may be faster. This can be used over longer distances as a check digit or parity bit can be sent along it easily. In telecommunications, parallel transmission is the simultaneous transmission of the signal elements of a character or other entity of data. In digital communications, parallel transmission is the simultaneous transmission of related signal elements over two or more separate paths. Multiple electrical wires are used which can transmit multiple bits simultaneously, which allows for higher data transfer rates than can be achieved with serial transmission. This method is used internally within the computer, for example the internal buses, and sometimes externally for such things as printers, The major issue with this is `` skewing '' because the wires in parallel data transmission have slightly different properties ( not intentionally ) so some bits may arrive before others, which may corrupt the message. A parity bit can help to reduce this. However, electrical wire parallel data transmission is therefore less reliable for long distances because corrupt transmissions are far more likely. Types of communication channels ( network topologies ) Main article : communication channel Some communications channel types include : Data transmission circuit Full - duplex Half - duplex Multi-drop : Bus network Mesh network Ring network Star network Wireless network Point - to - point Simplex Asynchronous and synchronous data transmission Main article : comparison of synchronous and asynchronous signalling This section may contain misleading parts. Please help clarify this article according to any suggestions provided on the talk page. ( August 2012 ) Asynchronous start - stop transmission uses start and stop bits to signify the beginning bit 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. 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 clock signal ( s ) built into each component. 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 losing bits ). Ways to get around this problem include re-synchronization of the clocks and use of check digits to ensure the byte is correctly interpreted and received See also Computer networking Data migration Information theory Media ( communication ) Network security Node - to - node data transfer Signal processing Telecommunication Transmission ( disambiguation ) Notes ^ Jump up to : A.P. Clark, `` Principles of Digital Data Transmission '', Published by Wiley, 1983 Jump up ^ David R. Smith, `` Digital Transmission Systems '', Kluwer International Publishers, 2003, ISBN 1 - 4020 - 7587 - 1. See table - of - contents. Jump up ^ Sergio Benedetto, Ezio Biglieri, `` Principles of Digital Transmission : With Wireless Applications '', Springer 2008, ISBN 0 - 306 - 45753 - 9, ISBN 978 - 0 - 306 - 45753 - 1. See table - of - contents Jump up ^ Simon Haykin, `` Digital Communications '', John Wiley & Sons, 1988. ISBN 978 - 0 - 471 - 62947 - 4. See table - of - contents. Jump up ^ John Proakis, `` Digital Communications '', 4th edition, McGraw - Hill, 2000. ISBN 0 - 07 - 232111 - 3. See table - of - contents. Jump up ^ `` What is Asynchronous Transmission ? - Definition from Techopedia ''. Techopedia.com. Retrieved 2017 - 12 - 08. Retrieved from `` https://en.wikipedia.org/w/index.php?title=Data_transmission&oldid=863206059 '' Categories : Data transmission Computer networking Media technology Telecommunications Hidden categories : Misleading articles All articles with unsourced statements Articles with unsourced statements from April 2010 All Wikipedia articles needing clarification Wikipedia articles needing clarification from April 2010 Talk Contents About Wikipedia Asturianu Azərbaycanca Bosanski Català Čeština Deutsch Eesti Ελληνικά Español Français 한국어 Hrvatski Bahasa Indonesia Italiano Қазақша Latgaļu Magyar Mirandés မြန်မာဘာသာ Nederlands 日本 語 ਪੰਜਾਬੀ Português Română Русский Suomi Українська Tiếng Việt 吴语 中文 22 more Edit links This page was last edited on 9 October 2018, at 10 : 53 ( UTC ). Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. 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Question: group of wires that transfer data are known as
Answer: communication channel