Duplex ( telecommunications ) - wikipedia Duplex ( telecommunications ) This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. Please help to improve this article by introducing more precise citations. ( September 2015 ) A duplex communication system is a point - to - point system composed of two or more connected parties or devices that can communicate with one another in both directions. Duplex systems are employed in many communications networks, either to allow for a communication `` two - way street '' between two connected parties or to provide a `` reverse path '' for the monitoring and remote adjustment of equipment in the field. There are two types of duplex communication systems : full - duplex ( FDX ) and half - duplex ( HDX ). In a full - duplex system, both parties can communicate with each other simultaneously. An example of a full - duplex device is a telephone ; the parties at both ends of a call can speak and be heard by the other party simultaneously. The earphone reproduces the speech of the remote party as the microphone transmits the speech of the local party, because there is a two - way communication channel between them, or more strictly speaking, because there are two communication channels between them. In a half - duplex system, both parties can communicate with each other, but not simultaneously ; the communication is one direction at a time. An example of a half - duplex device is a walkie - talkie two - way radio that has a `` push - to - talk '' button ; when the local user wants to speak to the remote person they push this button, which turns on the transmitter but turns off the receiver, so they can not hear the remote person. To listen to the other person they release the button, which turns on the receiver but turns off the transmitter. Systems that do not need the duplex capability may instead use simplex communication, in which one device transmits and the others can only `` listen ''. Examples are broadcast radio and television, garage door openers, baby monitors, wireless microphones, and surveillance cameras. In these devices the communication is only in one direction. Contents 1 Half duplex 2 Full duplex 3 Full - duplex emulation 3.1 Time - division duplexing 3.2 Frequency - division duplexing 3.3 Echo cancellation 4 See also 5 References 6 Further reading Half duplex A simple illustration of a half - duplex communication system A half - duplex ( HDX ) system provides communication in both directions, but only one direction at a time ( not simultaneously ). Typically, once a party begins receiving a signal, it must wait for the transmitter to stop transmitting, before replying. An example of a half - duplex system is a two - party system such as a walkie - talkie, wherein one must use `` over '' or another previously designated keyword to indicate the end of transmission, and ensure that only one party transmits at a time, because both parties transmit and receive on the same frequency. A good analogy for a half - duplex system would be a one - lane road with traffic controllers at each end, such as a two - lane bridge under re-construction. Traffic can flow in both directions, but only one direction at a time, regulated by the traffic controllers. Half - duplex systems are usually used to conserve bandwidth, since only a single communication channel is needed, which is shared alternately between the two directions. For example, a walkie - talkie requires only a single frequency for bidirectional communication, while a cell phone, which is a full - duplex device, requires two frequencies to carry the two simultaneous voice channels, one in each direction. In automatically run communications systems, such as two - way data - links, the time allocations for communications in a half - duplex system can be firmly controlled by the hardware. Thus, there is no waste of the channel for switching. For example, station A on one end of the data link could be allowed to transmit for exactly one second, then station B on the other end could be allowed to transmit for exactly one second, and then the cycle repeats. In half - duplex systems, if more than one party transmits at the same time, a collision occurs, resulting in lost messages. Full duplex A simple illustration of a full - duplex communication system. Full - duplex is not common in handheld radios as shown here due to the cost and complexity of common duplexing methods, but is used in telephones, cellphones and cordless phones. A full - duplex ( FDX ) system, or sometimes called double - duplex, allows communication in both directions, and, unlike half - duplex, allows this to happen simultaneously. Land - line telephone networks are full - duplex, since they allow both callers to speak and be heard at the same time, with the transition from four to two wires being achieved by a hybrid coil in a telephone hybrid. Modern cell phones are also full - duplex. A good analogy for a full - duplex system is a two - lane road with one lane for each direction. Moreover, in most full - duplex mode systems carrying computer data, transmitted data does not appear to be sent until it has been received and an acknowledgment is sent back by the other party. In this way, such systems implement reliable transmission methods. Two - way radios can be designed as full - duplex systems, transmitting on one frequency and receiving on another ; this is also called frequency - division duplex. Frequency - division duplex systems can extend their range by using sets of simple repeater stations because the communications transmitted on any single frequency always travel in the same direction. Full - duplex Ethernet connections work by making simultaneous use of two physical twisted pairs inside the same jacket, which are directly connected to each networked device : one pair is for receiving packets, while the other pair is for sending packets. This effectively makes the cable itself a collision - free environment and doubles the maximum total transmission capacity supported by each Ethernet connection. Full - duplex has also several benefits over the use of half - duplex. First, there are no collisions so time is not wasted by having to retransmit frames. Second, full transmission capacity is available in both directions because the send and receive functions are separate. Third, since there is only one transmitter on each twisted pair, stations ( nodes ) do not need to wait for others to complete their transmissions. Some computer - based systems of the 1960s and 1970s required full - duplex facilities, even for half - duplex operation, since their poll - and - response schemes could not tolerate the slight delays in reversing the direction of transmission in a half - duplex line. Full - duplex emulation Where channel access methods are used in point - to - multipoint networks ( such as cellular networks ) for dividing forward and reverse communication channels on the same physical communications medium, they are known as duplexing methods, such as time - division duplexing and frequency - division duplexing. Time - division duplexing Time - division duplexing ( TDD ) is the application of time - division multiplexing to separate outward and return signals. It emulates full duplex communication over a half duplex communication link. Time - division duplexing has a strong advantage in the case where there is asymmetry of the uplink and downlink data rates. As the amount of uplink data increases, more communication capacity can be dynamically allocated, and as the traffic load becomes lighter, capacity can be taken away. The same applies in the downlink direction. For radio systems that are n't moving quickly, another advantage is that the uplink and downlink radio paths are likely to be very similar. This means that techniques such as beamforming work well with TDD systems. Examples of time - division duplexing systems are : UMTS 3G supplementary air interfaces TD - CDMA for indoor mobile telecommunications. The Chinese TD - LTE 4 - G, TD - SCDMA 3 - G mobile communications air interface. DECT wireless telephony Half - duplex packet switched networks based on carrier sense multiple access, for example 2 - wire or hubbed Ethernet, Wireless local area networks and Bluetooth, can be considered as time - division duplexing systems, albeit not TDMA with fixed frame - lengths. IEEE 802.16 WiMAX PACTOR ISDN BRI U interface, variants using the time - compression multiplex ( TCM ) line system G. fast, a digital subscriber line ( DSL ) standard under development by the ITU - T Frequency - division duplexing Frequency - division duplexing ( FDD ) means that the transmitter and receiver operate at different carrier frequencies. The method is frequently used in ham radio operation, where an operator is attempting to use a repeater station. The repeater station must be able to send and receive a transmission at the same time, and does so by slightly altering the frequency at which it sends and receives. This mode of operation is referred to as duplex mode or offset mode. Uplink and downlink sub-bands are said to be separated by the frequency offset. Frequency - division duplexing can be efficient in the case of symmetric traffic. In this case, time - division duplexing tends to waste bandwidth during the switch - over from transmitting to receiving, has greater inherent latency, and may require more complex circuitry. Another advantage of frequency - division duplexing is that it makes radio planning easier and more efficient, since base stations do not `` hear '' each other ( as they transmit and receive in different sub-bands ) and therefore will normally not interfere with each other. Conversely, with time - division duplexing systems, care must be taken to keep guard times between neighboring base stations ( which decreases spectral efficiency ) or to synchronize base stations, so that they will transmit and receive at the same time ( which increases network complexity and therefore cost, and reduces bandwidth allocation flexibility as all base stations and sectors will be forced to use the same uplink / downlink ratio ) Examples of frequency - division duplexing systems are : ADSL and VDSL Most cellular systems, including the UMTS / WCDMA use frequency - division duplexing mode and the cdma2000 system. IEEE 802.16 WiMax also uses frequency - division duplexing mode. Echo cancellation Full - duplex audio systems like telephones can create echo, which needs to be removed. Echo occurs when the sound coming out of the speaker, originating from the far end, re-enters the microphone and is sent back to the far end. The sound then reappears at the original source end, but delayed. This feedback path may be acoustic, through the air, or it may be mechanically coupled, for example in a telephone handset. Echo cancellation is a signal - processing operation that subtracts the far - end signal from the microphone signal before it is sent back over the network. Echo cancellation is important technology allowing modems to achieve good full - duplex performance. The V. 32, V. 34, V. 56, and V. 90 modem standards require echo cancellation. Echo cancelers are available as both software and hardware implementations. They can be independent components in a communications system or integrated into the communication system 's central processing unit. Devices that do not eliminate echo sometimes will not produce good full - duplex performance. See also Duplex mismatch Four - wire circuit Multiplexing Duplexer Communications channel Crossband operation Push to talk Simplex communication Radio resource management Double - track railway References Jump up ^ `` Cell phone Frequencies ''. HowStuffWorks. Jump up ^ Greenstein, Shane ; Stango, Victor ( 2006 ). Standards and Public Policy. Cambridge University Press. pp. 129 -- 132. ISBN 978 - 1 - 139 - 46075 - 0. Further reading Tanenbaum, Andrew S. ( 2003 ). Computer Networks. Prentice Hall. ISBN 0 - 13 - 038488 - 7. Riihonen, Taneli ( 2014 ). Design and Analysis of Duplexing Modes and Forwarding Protocols for OFDM ( A ) Relay Links. Aalto University publication series DOCTORAL DISSERTATIONS, 81 / 2014. ISBN 978 - 952 - 60 - 5715 - 6. Channel access methods and Media access control Channel - based FDMA OFDMA WDMA SC - FDMA TDMA MF - TDMA STDMA CDMA W - CDMA TD - CDMA TD - SCDMA DS - CDMA FH - CDMA MC - CDMA SDMA HC - SDMA PDMA PAMA Packet - based Collision recovery ALOHA Slotted ALOHA R - ALOHA AX. 25 CSMA / CD Collision avoidance MACA MACAW CSMA CSMA / CA DCF PCF HCF CSMA / CARP Collision - free Token ring Token bus MS - ALOHA Delay & disruption tolerant MANET VANET DTN Dynamic Source Routing Duplexing methods TDD FDD Telecommunications History Beacon Broadcasting Cable protection system Cable TV Communications satellite Computer network Drums Electrical telegraph Fax Heliographs Hydraulic telegraph Internet Mass media Mobile phone Optical telecommunication Optical telegraphy Pager Photophone Prepay mobile phone Radio Radiotelephone Satellite communications Semaphore Smartphone Smoke signals Telecommunications history Telautograph Telegraphy Teleprinter ( teletype ) Telephone The Telephone Cases Television Timeline of communication technology Undersea telegraph line Videoconferencing Videophone Videotelephony Whistled language Pioneers Edwin Howard Armstrong John Logie Baird Paul Baran Alexander Graham Bell Tim Berners - Lee Jagadish Chandra Bose Vint Cerf Claude Chappe Donald Davies Lee de Forest Philo Farnsworth Reginald Fessenden Elisha Gray Erna Schneider Hoover Charles K. Kao Hedy Lamarr Innocenzo Manzetti Guglielmo Marconi Antonio Meucci Radia Perlman Alexander Stepanovich Popov Johann Philipp Reis Nikola Tesla Camille Tissot Alfred Vail Charles Wheatstone Vladimir K. Zworykin Transmission media Coaxial cable Fiber - optic communication Optical fiber Free - space optical communication Molecular communication Radio waves Transmission line Network topology and switching Links Nodes Terminal node Network switching ( circuit packet ) Telephone exchange Multiplexing Space - division Frequency - division Time - division Polarization - division Orbital angular - momentum Code - division Networks ARPANET BITNET Cellular network Computer CYCLADES Ethernet FidoNet Internet ISDN LAN Mobile NGN NPL network Public Switched Telephone Radio Telecommunications equipment Television Telex WAN Wireless World Wide Web Portal Retrieved from `` https://en.wikipedia.org/w/index.php?title=Duplex_(telecommunications)&oldid=850527871 '' Categories : Channel access methods Communication circuits Hidden categories : Articles lacking in - text citations from September 2015 All articles lacking in - text citations Talk Contents About Wikipedia Català Čeština Dansk Deutsch Eesti Español فارسی Français Galego 한국어 Bahasa Indonesia Italiano Nederlands 日本 語 Norsk Polski Português Русский Српски / srpski Basa Sunda Suomi Svenska Українська Tiếng Việt 中文 17 more Edit links This page was last edited on 16 July 2018, at 13 : 05 ( UTC ). 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Question: in which mode the communication channel is used in both directions at the same time
Answer: A duplex