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A crossbar switch is one of the principal architectures used to construct switches of many types. Originally the term was used literally, for a matrix switch controlled by a grid of crossing metal bars, and later was broadened to matrix switches in general. Crossbar switches are sometimes referred to as "cross-point switches," "crosspoint switches," or "matrix switches." The other principal switch architectures are that of a memory switch or a crossover switch. A banyan switch is an important type of crossover switch. Electrical switches. ...
Crossover Switches are complex array matrixes to switch any one input path to any one(or more) output path(s). ...
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General properties
Crossbar switches have a characteristic matrix of switches between the inputs to the switch and the output of the switch. If the switch has M inputs and N outputs, then a crossbar has a matrix with M x N cross-points or places where there the "bars" "cross". A given crossbar is a single layer, non-blocking switch. Collections of crossbars can be used to implement multiple layer and/or blocking switches.
Applications Crossbar switches are most famously used in information processing applications such as telephony and packet switching, but they are also used in applications such as mechanical sorting machines with multiple inputs.
Implementations Historically, a crossbar switch consisted of metal bars associated with each input and output, controlling movable contacts at each cross-point. In the later part of the 20th Century these literal crossbar switches declined and the term came to be used figuratively for rectangular array switches in general. Modern "crossbar switches" are usually implemented with semiconductor technology. An important emerging class of optical crossbars are being implemented with MEMS technology. A mite next to a gear set produced using MEMS. Courtesy Sandia National Laboratories, SUMMiTTM Technologies, www. ...
Mechanical A type of late 19th Century telegraph exchange consisted of a grid of vertical and horizontal brass bars with holes at the intersection. The operator inserted a brass pin to connect one telegraph line to another.
Electromechanical / telephony A telephony crossbar switch is an electromechanical device for switching telephone calls. The first design of what is now called a crossbar switch was Western Electric's "coordinate selector" of 1915. It was little used in America, but the LM Ericsson company used an improved version for rural exchanges in Sweden, organized on the selector principle rather than the link principle. The design used in AT&T's 1XB crossbar exchanges, which entered revenue service from 1938, was developed by Bell Telephone Labs, based on the link principle. Delayed by the Second World War, they were widely installed from the 1950s in the United States, and from there quickly spread to the rest of the world. They replaced most earlier designs like the Strowger and Panel systems in larger installations in the U.S., where, graduating from entirely electromechanical control on introduction, they were gradually elaborated to have full electronic control and a large variety of extra services like short-code and speed dialling. In the UK the Plessey Company produced a range of crossbar exchanges, but their widespread rollout by the British Post Office was inhibited by the parallel development of reed relay and electronic exchange systems, and they never achieved a large number of customer connections although they did find some success as tandem exchanges. In engineering, electromechanics combines the sciences of electromagnetism of electrical engineering and mechanics. ...
In the field of telecommunications, a central office houses equipment that is commonly known as simply a switch, which is a piece of equipment that connects phone calls. ...
Look up Telephone in Wiktionary, the free dictionary. ...
Western Electric (sometimes abbreviated WE and WECo) was a US electrical engineering company, the manufacturing arm of AT&T from 1881 to 1995 . ...
Lars Magnus Ericsson Ericsson () NASDAQ: ERIC is a Swedish telecommunications equipment manufacturer, founded in 1876 as a telegraph equipment repair shop by Lars Magnus Ericsson. ...
This article describes the present AT&T Inc. ...
The current logo Bell Laboratories (also known as Bell Labs and formerly known as AT&T Bell Laboratories and Bell Telephone Laboratories) was the main research and development arm of the United States Bell System. ...
The 1950s was the decade spanning from the 1st of January, 1950 to the 31st December, 1959. ...
Almon Brown Strowger (1839 - May 26, 1902) gave his name to the electromechanical telephone exchange technology that his invention and patent inspired. ...
It has been suggested that this article or section be merged into Reed switch. ...
Crossbar switches use switching matrices made from a two-dimensional array of contacts arranged in an x-y format. These switching matrices are operated by a series of horizontal bars arranged over the contacts. Each such "select" bar can be rocked up or down by electromagnets to provide access to two levels of the matrix. A second set of vertical "hold" bars is set at right angles to the first (hence the name, "crossbar") and also operated by electromagnets. The select bars carry spring-loaded wire fingers that operate the contacts beneath the bars. When the select and then the hold electomagnets operate in sequence to move the bars, they trap one of the fingers to close the contacts beneath the point where two bars cross. This then makes the connection through the switch to connect the telephone call. The select magnet is then released, while the hold magnet remains energized for the duration of the call to maintain the connection. The crossbar switching interface was referred to as the TXC switch (Telephone eXchange Crossbar). Crossbar Telephone Switch The copyright status of this work is difficult or impossible to determine. ...
Crossbar Telephone Switch The copyright status of this work is difficult or impossible to determine. ...
Look up Contact in Wiktionary, the free dictionary. ...
An electromagnet is a type of magnet in which the magnetic field is produced by a flow of electric current. ...
A wire is a single, usually cylindrical, elongated strand of drawn metal. ...
A telephone call is a connection over a telephone network between the calling party and the called party. ...
The picture represents a typical Bell System Type B crossbar switch of the 1960s, with twenty verticals and ten levels. Each select bar carried twenty fingers to allow any of the twenty verticals to connect to either of two levels. Each crosspoint connected three wires. Many switches were made to connect six wires; some had fewer verticals or more levels. The Bell System Type C miniature crossbar switch of the 1970s was similar, but the fingers projected forward from the back and the select bars held paddles to move them. Type C usually had twelve levels. The Northern Electric Minibar used in SP1 was similar but even smaller. The ITT Pentaconta Multiswitch of the same era had usually 22 verticals, 26 levels, and six to twelve wires. Ericsson crossbar switches sometimes had only five verticals.
Telephone exchange With the prominent US exception of 5XB switch a crossbar exchange was divided into an originating side and a terminating side. When a user picked up their handset, the resulting line loop operating the user's line relay caused the exchange to connect the user's telephone to an originating sender, which returned the user a dial tone. The sender then recorded the dialed digits and passed them to the originating marker, which selected an outgoing trunk and operated the various crossbar switch stages to connect the calling user to it. The originating marker then passed the trunk call completion requirements (type of pulsing, resistance of the trunk, etc) and the called party's details to the sender and released. The sender then relayed this information to a terminating sender (which could be on either the same or a different exchange). This sender then used a terminating marker to connect the calling user, via the selected incoming trunk, to the called user, and caused the controlling relay set to pass intermittent ring voltage of about 90 VAC at 20 Hz to ring the called user's phone bell, and return ringing tone to the caller. The Number Five Crossbar Switching System, designed by Bell Labs and made by Western Electric was in use in Bell System telephone exchanges from 1948 to the 1980s. ...
The hertz (symbol: Hz) is the SI unit of frequency. ...
The crossbar switch itself was very simple: exchange design moved all the logical decision-making to the common control elements, which as relay sets were themselves very reliable. The design criterion was to have two hours of "downtime" for service every forty years, which was a huge improvement on earlier electromechanical systems. The exchange design concept lent itself to incremental upgrades, as the control elements could be replaced separately from the call switching elements. The minimum size of a crossbar exchange was comparatively large, but in city areas with a large installed line capacity the whole exchange occupied less space than other exchange technologies of equivalent capacity. For this reason they were also typically the first switches to be replaced with digital systems, which were even smaller and more reliable. A digital system is one that uses discrete numbers, especially binary numbers, or non-numeric symbols such as letters or icons, for input, processing, transmission, storage, or display, rather than a continuous spectrum of values (an analog system). ...
Two methods of controlling crossbar switches were used. One early method was based on the selector principle, and used the switches as functional replacement for Strowger switches. Control was distributed to the switches themselves. Call establishment progressed through the exchange stage by stage, as successive digits were dialled. With the selector principle, each switch could only handle its portion of one call at a time. Each moving contact of the array was multipled with corresponding crosspoints on other switches to a selector in the next bank of switches. Thus an exchange with a hundred 10x10 switches in five stages could only have twenty conversations in progress. Distributed control meant there was no common point of failure, but also meant that the setup stage lasted for the ten seconds or so the caller took to dial the required number. In control occupancy terms this comparatively long interval degrades the traffic capacity of a switch.
The later and more common method was based on the link principle, and used the switches as crosspoints. Each moving contact was multipled with the other contacts on the same level by simpler "banjo" wires, to a link on one of the inputs of a switch in the next stage. The switch could handle its portion of as many calls as it had levels or verticals. Thus an exchange with forty 10x10 switches in four stages could have a hundred conversations in progress. The link principle was more efficient, but required a more complex control system to find idle links through the switching fabric.
This meant common control, as described above: all the digits were recorded, then passed to the common control equipment - the marker - to establish the call at all the separate switch stages simultaneously. A marker-controlled crossbar system had in the marker a highly vulnerable central control; this was invariably protected by having duplicate markers. The great advantage was that the control occupancy on the switches was of the order of one second or less, representing the operate and release lags of the X-then-Y armatures of the switches. The only downside of common control was the need to provide digit recorders enough to deal with the greatest forecast originating traffic level on the exchange. A marker is a type of special purpose computer that was used in electromechanical telephone central office switches. ...
The Plessey TXK1 or 5005 design used an intermediate form, in which a clear path was marked through the switching fabric by distributed logic, and then closed through all at once.
In some countries, no crossbar exchanges remain in revenue service. However, crossbar exchanges remain in use in countries like Russia, where some massive city telephone networks have not yet been fully upgraded to digital technology. Preserved installations may be seen in museums like the Science Museum in London. The Louvre Museum in Paris, one of the largest and most famous museums in the world. ...
The National Science Museum in London The Science Museum on Exhibition Road, Kensington, London, is part of the National Museum of Science and Industry. ...
London (pronounced ) is the capital city of England and the United Kingdom. ...
Changing nomenclature can confuse: in current American terminology a 'switch' now frequently refers to a system which is also called a 'telephone exchange' (the usual term in English) - that is, a large collection of selectors of some sort within a building. For most of the twentieth century a 'Strowger switch' or a 'crossbar switch' referred to an individual piece of equipment making up part of an exchange. Hence the picture above shows a 'crossbar switch' using the earlier meaning.
Semiconductor Semiconductor implementations of crossbar switches typically consist of a set of input amplifiers or retimers connected to a series of metalizations or "bars" within a semiconductor device. A similar set of metalizations or "bars" are connected to output amplifiers or retimers. At each cross-point where the "bars" cross, a pass transistor is implemented which connects the bars. When the pass transistor is enabled, the input is connected to the output.
As computer technologies have improved, crossbar switches have found uses in systems such as the multistage interconnection networks that connect the various processing units in a uniform memory access parallel processor to the array of memory elements.
Arbitration A standard problem in using crossbar switches is that of setting the cross-points. In the classic telephony application of cross-bars, the crosspoints are closed and open as the telephone calls come and go. In Asynchronous Transfer Mode or packet switching applications, the crosspoints must be made and broken at each decision interval. In high-speed switches, the settings of all of the cross-points must be determined and then set millions or billions of times per second. One approach for making these decisions quickly is through the use of a wavefront arbiter. Asynchronous Transfer Mode (ATM) is a cell relay network protocol which encodes data traffic into small fixed-sized (53 byte; 48 bytes of data and 5 bytes of header information) cells instead of variable sized packets (sometimes known as frames) as in packet-switched networks (such as the Internet Protocol...
A Wavefront arbiter is a circuit used to make decisions which control the crossbar of a a high capacity switch fabric in parallel. ...
See also A substitute for a 16x16 crossbar switch made from 12 4x4 crossbar switches. ...
External links - 1XB
- 5XB
- 4XB
- XBT
- Ericsson ARF (in Dutch)
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