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45-416: The LLC sublayer provides multiplexing mechanisms that make it possible for several network protocols (e.g. IP , IPX and DECnet ) to coexist within a multipoint network and to be transported over the same network medium. It can also provide flow control and automatic repeat request (ARQ) error management mechanisms. The LLC sublayer is primarily concerned with multiplexing protocols transmitted over

90-532: A data link layer which is split between LLC (for flow and error control) and MAC (for multiple access) is the ITU-T G.hn standard, which provides high-speed local area networking over existing home wiring (power lines, phone lines and coaxial cables). Multiplexing In telecommunications and computer networking , multiplexing (sometimes contracted to muxing ) is a method by which multiple analog or digital signals are combined into one signal over

135-425: A multiple-input multiple-output communications (MIMO) scheme. In wired communication, space-division multiplexing , also known as space-division multiple access (SDMA) is the use of separate point-to-point electrical conductors for each transmitted channel. Examples include an analog stereo audio cable, with one pair of wires for the left channel and another for the right channel, and a multi-pair telephone cable ,

180-423: A shared medium . The aim is to share a scarce resource – a physical transmission medium . For example, in telecommunications, several telephone calls may be carried using one wire. Multiplexing originated in telegraphy in the 1870s, and is now widely applied in communications. In telephony , George Owen Squier is credited with the development of telephone carrier multiplexing in 1910. The multiplexed signal

225-408: A time-multiplexing system of multiple Hughes machines in the 1870s. In 1874, the quadruplex telegraph developed by Thomas Edison transmitted two messages in each direction simultaneously, for a total of four messages transiting the same wire at the same time. Several researchers were investigating acoustic telegraphy , a frequency-division multiplexing technique, which led to the invention of

270-510: A transport layer protocol such as TCP or by some application layer protocol. These higher layer protocols work in an end-to-end fashion, i.e. re-transmission is done from the original source to the final destination, rather than on individual physical segments. For these protocol stacks only the multiplexing capabilities of the LLC sublayer are used. An LLC sublayer was a key component in early packet switching networks such as X.25 networks with

315-495: A LLC protocol, providing multiplexing, but it does not provide flow control and error management. In a telephone network, bit errors might be common, meaning that error management is crucial, but that is today provided by modern protocols. Today's modem protocols have inherited LLC features from the older LAPM link layer protocol, made for modem communication in old X.25 networks. The GPRS LLC layer also does ciphering and deciphering of SN-PDU ( SNDCP ) packets. Another example of

360-412: A customer's residential area, but the service provider can send multiple television channels or signals simultaneously over that cable to all subscribers without interference. Receivers must tune to the appropriate frequency (channel) to access the desired signal. A variant technology, called wavelength-division multiplexing (WDM) is used in optical communications . Time-division multiplexing (TDM)

405-486: A peak bit rate of 54 Mbit/s, thus increasing the total peak bit rate by the factor k . Different antennas would give different multi-path propagation (echo) signatures, making it possible for digital signal processing techniques to separate different signals from each other. These techniques may also be utilized for space diversity (improved robustness to fading) or beamforming (improved selectivity) rather than multiplexing. Frequency-division multiplexing (FDM)

450-814: A single event loop , with system calls like poll and select (Unix) . Multiple variable bit rate digital bit streams may be transferred efficiently over a single fixed bandwidth channel by means of statistical multiplexing . This is an asynchronous mode time-domain multiplexing which is a form of time-division multiplexing. Digital bit streams can be transferred over an analog channel by means of code-division multiplexing techniques such as frequency-hopping spread spectrum (FHSS) and direct-sequence spread spectrum (DSSS). In wireless communications , multiplexing can also be accomplished through alternating polarization ( horizontal / vertical or clockwise / counterclockwise ) on each adjacent channel and satellite, or through phased multi-antenna array combined with

495-539: A switched star network such as a telephone access network, a switched Ethernet network, and a mesh network . In wireless communication, space-division multiplexing is achieved with multiple antenna elements forming a phased array antenna . Examples are multiple-input and multiple-output (MIMO), single-input and multiple-output (SIMO) and multiple-input and single-output (MISO) multiplexing. An IEEE 802.11g wireless router with k antennas makes it in principle possible to communicate with k multiplexed channels, each with

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540-481: A transport stream and/or container is commonly called a multiplexer or muxer . A demuxer is software that extracts or otherwise makes available for separate processing the components of such a stream or container. In digital television systems, several variable bit-rate data streams are multiplexed together to a fixed bit-rate transport stream by means of statistical multiplexing . This makes it possible to transfer several video and audio channels simultaneously over

585-412: Is a class of techniques where several channels simultaneously share the same frequency spectrum , and this spectral bandwidth is much higher than the bit rate or symbol rate . One form is frequency hopping, another is direct sequence spread spectrum. In the latter case, each channel transmits its bits as a coded channel-specific sequence of pulses called chips. Number of chips per bit, or chips per symbol,

630-405: Is a digital (or in rare cases, analog) technology that uses time, instead of space or frequency, to separate the different data streams. TDM involves sequencing groups of a few bits or bytes from each individual input stream, one after the other, and in such a way that they can be associated with the appropriate receiver. If done sufficiently quickly, the receiving devices will not detect that some of

675-439: Is a novel method for polarized antenna transmission utilizing a differential technique. Orbital angular momentum multiplexing is a relatively new and experimental technique for multiplexing multiple channels of signals carried using electromagnetic radiation over a single path. It can potentially be used in addition to other physical multiplexing methods to greatly expand the transmission capacity of such systems. As of 2012 it

720-811: Is a technique in which each channel transmits its bits as a coded channel-specific sequence of pulses. This coded transmission is typically accomplished by transmitting a unique time-dependent series of short pulses, which are placed within chip times within the larger bit time. All channels, each with a different code, can be transmitted on the same fiber and asynchronously demultiplexed. Other widely used multiple access techniques are time-division multiple access (TDMA) and frequency-division multiple access (FDMA). Code-division multiplex techniques are used as an access technology, namely code-division multiple access (CDMA), in Universal Mobile Telecommunications System (UMTS) standard for

765-405: Is inherently an analog technology. FDM achieves the combining of several signals into one medium by sending signals in several distinct frequency ranges over a single medium. In FDM the signals are electrical signals. One of the most common applications for FDM is traditional radio and television broadcasting from terrestrial, mobile or satellite stations, or cable television. Only one cable reaches

810-523: Is likewise also true for digital subscriber lines (DSL). Fiber in the loop (FITL) is a common method of multiplexing, which uses optical fiber as the backbone . It not only connects POTS phone lines with the rest of the PSTN , but also replaces DSL by connecting directly to Ethernet wired into the home . Asynchronous Transfer Mode is often the communications protocol used. Cable TV has long carried multiplexed television channels , and late in

855-461: Is not practical (such as where there are different sources using a single transponder ), single channel per carrier mode is used. In FM broadcasting and other analog radio media, multiplexing is a term commonly given to the process of adding subcarriers to the audio signal before it enters the transmitter , where modulation occurs. (In fact, the stereo multiplex signal can be generated using time-division multiplexing, by switching between

900-524: Is not used), IEEE 802.5 , and IEEE 802.11 . IEEE 802.2 is also used in some non-IEEE 802 networks such as FDDI . Since bit errors are very rare in wired networks, Ethernet does not provide flow control or automatic repeat request (ARQ), meaning that incorrect packets are detected but only cancelled, not retransmitted (except in case of collisions detected by the CSMA/CD MAC layer protocol). Instead, retransmissions rely on higher-layer protocols. As

945-558: Is one in which members share a number of ties stemming from more than one social context, such as workmates, neighbors, or relatives. SNDCP SNDCP , Sub Network Dependent Convergence Protocol, is part of layer 3 of a GPRS protocol specification. SNDCP interfaces to the Internet Protocol at the top, and to the GPRS-specific Logical Link Control (LLC) protocol at the bottom. In

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990-718: Is part of the CSMA/CA MAC protocol, and not part of the LLC layer. The LLC sublayer follows the IEEE 802.2 standard. Some non-IEEE 802 protocols can be thought of as being split into MAC and LLC layers. For example, while HDLC specifies both MAC functions (framing of packets) and LLC functions (protocol multiplexing, flow control, detection, and error control through retransmission of dropped packets when indicated), some protocols such as Cisco HDLC can use HDLC-like packet framing and their own LLC protocol. Over telephone network modems , PPP link layer protocols can be considered as

1035-728: Is possible (just as in statistical multiplexing ), that the wide bandwidth allows poor signal-to-noise ratio according to Shannon–Hartley theorem , and that multi-path propagation in wireless communication can be combated by rake receivers . A significant application of CDMA is the Global Positioning System (GPS). A multiplexing technique may be further extended into a multiple access method or channel access method , for example, TDM into time-division multiple access (TDMA) and statistical multiplexing into carrier-sense multiple access (CSMA). A multiple-access method makes it possible for several transmitters connected to

1080-420: Is still in its early research phase, with small-scale laboratory demonstrations of bandwidths of up to 2.5 Tbit/s over a single light path. This is a controversial subject in the academic community, with many claiming it is not a new method of multiplexing, but rather a special case of space-division multiplexing. Code-division multiplexing (CDM), code-division multiple access (CDMA) or spread spectrum

1125-418: Is the spreading factor . This coded transmission typically is accomplished by transmitting a unique time-dependent series of short pulses, which are placed within chip times within the larger bit time. All channels, each with a different code, can be transmitted on the same fiber or radio channel or other medium, and asynchronously demultiplexed. Advantages over conventional techniques are that variable bandwidth

1170-418: Is transmitted over a communication channel such as a cable. The multiplexing divides the capacity of the communication channel into several logical channels, one for each message signal or data stream to be transferred. A reverse process, known as demultiplexing, extracts the original channels on the receiver end. A device that performs the multiplexing is called a multiplexer (MUX), and a device that performs

1215-692: The EtherType in an Ethernet frame using Ethernet II framing is used to multiplex different protocols on top of the Ethernet MAC header it can be seen as an LLC identifier. However, Ethernet frames lacking an EtherType have no LLC identifier in the Ethernet header, and, instead, use an IEEE 802.2 LLC header after the Ethernet header to provide the protocol multiplexing function. In wireless communications, bit errors are very common. In wireless networks such as IEEE 802.11, flow control and error management

1260-458: The Fourier transform principle. In computer programming , it may refer to using a single in-memory resource (such as a file handle) to handle multiple external resources (such as on-disk files). Some electrical multiplexing techniques do not require a physical " multiplexer " device, they refer to a " keyboard matrix " or " Charlieplexing " design style: In high-throughput DNA sequencing ,

1305-510: The LAPB data link layer protocol, where flow control and error management were carried out in a node-to-node fashion, meaning that if an error was detected in a frame, the frame was retransmitted from one switch to next instead. This extensive handshaking between the nodes made the networks slow. The IEEE 802.2 standard specifies the LLC sublayer for all IEEE 802 local area networks, such as IEEE 802.3 / Ethernet (when Ethernet II frame format

1350-531: The SGSN , and works when a PDP Context is established and the quality of service has been negotiated. The SNDCP layer primarily converts, encapsulates and segments external network formats (like Internet Protocol Datagrams) into sub-network formats (called SNPDUs). It also performs compression of NPDUs to make for efficient Data transmission. It performs the multiple PDP Context PDU transfers and it also ensures that NPDUs from each PDP Context are transmitted to

1395-504: The 20th century began offering the same services as telephone companies . IPTV also depends on multiplexing. In video editing and processing systems, multiplexing refers to the process of interleaving audio and video into one coherent data stream. In digital video , such a transport stream is normally a feature of a container format which may include metadata and other information, such as subtitles . The audio and video streams may have variable bit rate. Software that produces such

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1440-569: The MAC layer (when transmitting) and demultiplexing them (when receiving). It can also provide node-to-node flow control and error management. The flow control and error management capabilities of the LLC sublayer are used by protocols such as the NetBIOS Frames protocol. However, most protocol stacks running atop 802.2 do not use LLC sublayer flow control and error management. In these cases flow control and error management are taken care of by

1485-462: The airport ticket desk back to the airline data center are also installed. Some web proxy servers (e.g. polipo ) use TDM in HTTP pipelining of multiple HTTP transactions onto the same TCP/IP connection . Carrier-sense multiple access and multidrop communication methods are similar to time-division multiplexing in that multiple data streams are separated by time on the same medium, but because

1530-446: The capacity to carry several HDTV channels in one multiplex. In digital radio , a multiplex (also known as an ensemble) is a number of radio stations that are grouped together. A multiplex is a stream of digital information that includes audio and other data. On communications satellites which carry broadcast television networks and radio networks , this is known as multiple channel per carrier or MCPC . Where multiplexing

1575-458: The case of CCITT7 signaling systems and 30 voice channels for customer-connected Q931, DASS2, DPNSS, V5 and CASS signaling systems. Polarization-division multiplexing uses the polarization of electromagnetic radiation to separate orthogonal channels. It is in practical use in both radio and optical communications, particularly in 100 Gbit/s per channel fiber-optic transmission systems . Differential Cross-Polarized Wireless Communications

1620-425: The circuit time was used to serve another logical communication path. Consider an application requiring four terminals at an airport to reach a central computer. Each terminal communicated at 2400 baud , so rather than acquire four individual circuits to carry such a low-speed transmission, the airline has installed a pair of multiplexers. A pair of 9600 baud modems and one dedicated analog communications circuit from

1665-422: The reverse process is called a demultiplexer (DEMUX or DMX). Inverse multiplexing (IMUX) has the opposite aim as multiplexing, namely to break one data stream into several streams, transfer them simultaneously over several communication channels, and recreate the original data stream. In computing , I/O multiplexing can also be used to refer to the concept of processing multiple input/output events from

1710-498: The same frequency channel, together with various services. This may involve several standard-definition television (SDTV) programs (particularly on DVB-T , DVB-S2 , ISDB and ATSC-C), or one HDTV , possibly with a single SDTV companion channel over one 6 to 8 MHz-wide TV channel. The device that accomplishes this is called a statistical multiplexer . In several of these systems, the multiplexing results in an MPEG transport stream . The newer DVB standards DVB-S2 and DVB-T2 has

1755-531: The same physical medium to share their capacity. Multiplexing is provided by the physical layer of the OSI model , while multiple access also involves a media access control protocol, which is part of the data link layer . The Transport layer in the OSI model, as well as TCP/IP model, provides statistical multiplexing of several application layer data flows to/from the same computer. Code-division multiplexing (CDM)

1800-584: The signals have separate origins instead of being combined into a single signal, are best viewed as channel access methods , rather than a form of multiplexing. TD is a legacy multiplexing technology still providing the backbone of most National fixed-line telephony networks in Europe, providing the 2 Mbit/s voice and signaling ports on narrow-band telephone exchanges such as the DMS100. Each E1 or 2 Mbit/s TDM port provides either 30 or 31 speech timeslots in

1845-471: The spirit of the GPRS specifications, there can be many implementations of SNDCP, supporting protocols such as X.25 . However, in reality, IP (Internet Protocol) is such an overwhelming standard that X.25 has become irrelevant for modern applications, so all implementations of SNDCP for GPRS only support IP as the payload type. The SNDCP layer is relevant to the protocol stack of the mobile station and that of

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1890-405: The telephone . In telephony , a customer 's telephone line now typically ends at the remote concentrator box, where it is multiplexed along with other telephone lines for that neighborhood or other similar area. The multiplexed signal is then carried to the central switching office on significantly fewer wires and for much further distances than a customer's line can practically go. This

1935-407: The term is used to indicate that some artificial sequences (often called barcodes or indexes ) have been added to link given sequence reads to a given sample, and thus allow for the sequencing of multiple samples in the same reaction. In sociolinguistics , multiplexity is used to describe the number of distinct connections between individuals who are part of a social network . A multiplex network

1980-482: The third-generation (3G) mobile communication identified by the ITU. The earliest communication technology using electrical wires, and therefore sharing an interest in the economies afforded by multiplexing, was the electric telegraph . Early experiments allowed two separate messages to travel in opposite directions simultaneously, first using an electric battery at both ends, then at only one end. Émile Baudot developed

2025-471: The two (left channel and right channel) input signals at an ultrasonic rate (the subcarrier), and then filtering out the higher harmonics.) Multiplexing in this sense is sometimes known as MPX , which in turn is also an old term for stereophonic FM, seen on stereo systems since the 1960s. In spectroscopy the term is used to indicate that the experiment is performed with a mixture of frequencies at once and their respective response unraveled afterward using

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