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58-469: Strowger may refer to: Strowger switch , automatic telephone exchange equipment Strowger Automatic Telephone Exchange Company , the company that manufactured Strowger switches Almon Brown Strowger (1839–1902), who invented the principle of the Strowger switch in 1888 See also [ edit ] Stroger (disambiguation) Topics referred to by

116-525: A balanced pair circuit and a sleeve lead for control. Many connected six wires, either for two distinct circuits or for a four wire circuit or other complex connection. The Bell System Type C miniature crossbar of the 1970s was similar, but the fingers projected forward from the back and the select bars held paddles to move them. The majority of type C had twelve levels; these were the less common ten level ones. The Northern Electric Minibar used in SP1 switch

174-416: A rotary switch , memory switch, and a crossover switch . A crossbar switch is an assembly of individual switches between a set of inputs and a set of outputs. The switches are arranged in a matrix. If the crossbar switch has M inputs and N outputs, then a crossbar has a matrix with M × N cross-points or places where connections can be made. At each crosspoint is a switch; when closed, it connects one of

232-642: A clear path was marked through the switching fabric by distributed logic, and then closed through all at once. Crossbar exchanges remain in revenue service only in a few telephone networks. Preserved installations are maintained in museums , such as the Museum of Communications in Seattle, Washington, and the Science Museum in London . Semiconductor implementations of crossbar switches typically consist of

290-407: A connection may be established by closing a switch located at each intersection, the elements of the matrix. Originally, a crossbar switch consisted literally of crossing metal bars that provided the input and output paths. Later implementations achieved the same switching topology in solid-state electronics . The crossbar switch is one of the principal telephone exchange architectures, together with

348-405: A crossbar switch is also used in some semiconductor memory devices which enables the data transmission. Here the bars are extremely thin metal wires, and the switches are fusible links . The fuses are blown or opened using high voltage and read using low voltage. Such devices are called programmable read-only memory . At the 2008 NSTI Nanotechnology Conference a paper was presented that discussed

406-465: A hole at each intersection ( c.f. top picture). The operator inserted a metal pin to connect one telegraph line to another. A telephony crossbar switch is an electromechanical device for switching telephone calls. The first design of what is now called a crossbar switch was the Bell company Western Electric 's coordinate selector of 1915. To save money on control systems, this system was organized on

464-513: A matrix switch, as it is more commonly called in this application) is used to distribute the output of multiple video appliances simultaneously to every monitor or every room throughout a building. In a typical installation, all the video sources are located on an equipment rack, and are connected as inputs to the matrix switch. Where central control of the matrix is practical, a typical rack-mount matrix switch offers front-panel buttons to allow manual connection of inputs to outputs. An example of such

522-744: A mesh arrangement. This became quadratically more complex as each new customer was added, as each new customer needed a switch to connect to every other customer. In modern terminology, the previous systems were not " scalable ". From 1912, the British General Post Office , which also operated the British telephone system, installed several automatic telephone exchanges from several vendors in trials at Darlington on 10 October 1914 and Dudley on 9 September 1916 ( rotary system ), Fleetwood (relay exchange from Sweden), Grimsby (Siemens), Hereford (Lorimer) and Leeds (Strowger). The GPO selected

580-415: A nanoscale crossbar implementation of an adding circuit used as an alternative to logic gates for computation. Matrix arrays are fundamental to modern flat-panel displays. Thin-film-transistor LCDs have a transistor at each crosspoint, so they could be considered to include a crossbar switch as part of their structure. For video switching in home and professional theater applications, a crossbar switch (or

638-414: A patent for an automatic telephone exchange in 1891. The initial model was made from a round collar box and some straight pins. While Almon Strowger devised the initial concept, he was not alone in his endeavors and sought the assistance of his brother Arnold, nephew William, and others with a knowledge of electricity and financing to realize the concept. The Strowger Automatic Telephone Exchange Company

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696-460: A set of input amplifiers or retimers connected to a series of interconnects within a semiconductor device. A similar set of interconnects 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

754-402: A telephone network, often by a line-finder which searches "backward" for the calling line; so requiring only a few relays (in most cases two, a Line, and a Cut-off relay), for the equipment required for each customer line. Later Strowger (SXS) exchanges often use a subscriber uniselector as part of the line equipment individual to each line, which searches "forward" for a first selector. This

812-424: A telephone set for dialing. Each key requires a separate wire to the exchange. The keys are tapped to step the switch in two stages. The first set of incoming pulses raises the armature of an electromagnet to move a shaft which selects the desired level of contacts, by engaging a pawl with the upper ratchet. Another pawl, pivoting on the frame, holds the shaft at that height as it rotates. The second set of pulses, from

870-495: A terminating marker to connect the calling user, via the selected incoming trunk, to the called user, and caused the controlling relay set to send the ring signal to the called user's phone, and return ringing tone to the caller. The crossbar switch itself was simple: exchange design moved all the logical decision-making to the common control elements, which were very reliable as relay sets. The design criteria specified only two hours of downtime for service every forty years, which

928-455: A terminating side, while the later and prominent Canadian and US SP1 switch and 5XB switch were not. When a user picked up the telephone 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

986-418: A time; thus, an exchange with a hundred 10×10 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. Starting with

1044-474: 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 enable

1102-437: A usage might be a sports bar , where numerous programs are displayed simultaneously. Ordinarily, a sports bar would install a separate desk top box for each display for which independent control is desired. The matrix switch enables the operator to route signals at will, so that only enough set top boxes are needed to cover the total number of unique programs to be viewed, while making it easier to control sound from any program in

1160-712: A variety of calling features including short-code and speed-dialing. In the UK the Plessey Company produced a range of TXK crossbar exchanges, but their widespread rollout by the British Post Office began later than in other countries, and then was inhibited by the parallel development of TXE reed relay and electronic exchange systems, so they never achieved a large number of customer connections although they did find some success as tandem switch exchanges. Crossbar switches use switching matrices made from

1218-402: Is controlled by the current pulses coming from the originating customer's telegraph keys, and later from the rotary dial. The Strowger switch has three banks of contacts. Toward the upper end of each shaft are two ratchets . The upper one has ten grooves, and raises the shaft. The lower one has long vertical teeth (on the other side, hidden). The Strowger switch uses two telegraph-type keys on

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1276-418: Is different from Wikidata All article disambiguation pages All disambiguation pages Strowger switch Strowger, an undertaker , was motivated to invent an automatic telephone exchange after having difficulties with his telephone service. He became convinced that the manual telephone exchange operators were deliberately interfering with his calls, leading to loss of business. According to

1334-507: Is more economical for higher calling-rate domestic or business customers, and has the advantage that access to additional switches can readily be added if the traffic increases (the number of linefinders serving a group is limited by the wiring multiple installed). Hence exchanges with subscriber uniselectors were usually used at British exchanges with a high proportion of business customers, e.g. director exchanges, or in New Zealand where

1392-523: The 1XB switch , the later and more common method was based on the link principle, and used the switches as crosspoints. Each moving contact was multipled to the other contacts on the same level by bare-strip wiring, often nicknamed banjo wiring . 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 10×10 switches in four stages could have one hundred conversations in progress. The link principle

1450-439: The multistage interconnection networks that connect the various processing units in a uniform memory access parallel processor to the array of memory elements. A standard problem in using crossbar switches is that of setting the crosspoints. In the classic telephony application of crossbars, the crosspoints are closed, and open as the telephone calls come and go. In Asynchronous Transfer Mode or packet switching applications,

1508-904: The stepping switch or selector principle rather than the link principle. It was little used in America, but the Televerket Swedish governmental agency manufactured its own design (the Gotthilf Betulander design from 1919, inspired by the Western Electric system), and used it in Sweden from 1926 until the digitization in the 1980s in small and medium-sized A204 model switches. The system design used in AT&;T Corporation 's 1XB crossbar exchanges, which entered revenue service from 1938, developed by Bell Telephone Labs ,

1566-408: The "cascading" enabled connection to many more customers, and to customers at other exchanges. Another requirement for commercial systems was a circuit to detect a busy connection (line) and return a busy signal to the calling subscriber. Instead of dedicating an expensive first-stage selector switch to each customer as in the first exchange, the customer was given access to the first-stage switch of

1624-578: The 1XB and A204 systems for the international market. In the early 1960s, the company's sales of crossbar switches exceeded those of their rotating 500-switching system, as measured in the number of lines. Crossbar switching quickly spread to the rest of the world, replacing most earlier designs like the Strowger (step-by-step) and Panel systems in larger installations in the U.S. Graduating from entirely electromechanical control on introduction, they were gradually elaborated to have full electronic control and

1682-447: The 20th century, the use of mechanical crossbar switches declined and the term described any rectangular array of switches in general. Modern crossbar switches are usually implemented with semiconductor technology. An important emerging class of optical crossbars is implemented with microelectromechanical systems (MEMS) technology. A type of mid-20th-century telegraph exchange consisted of a grid of vertical and horizontal brass bars with

1740-556: The Automatic Electric Company. Strowger sold his patents in 1896 for US$ 1,800 (equivalent to $ 57,000 in 2023) and sold his share in Automatic Electric in 1898 for $ 10,000 (equivalent to $ 310,000 in 2023). His patents subsequently sold for $ 2,500,000 (equivalent to $ 48,000,000 in 2023) in 1916. Company engineers continued development of the Strowger designs and submitted several patents in

1798-460: The Strowger switches for small and medium-sized cities and towns. The selection of switching systems for London and other large cities was not decided until the 1920s, when the Director telephone system was adopted. The Director systems used SXS switches for destination routing and number translation facilities similar to the register used in common-control exchanges. Using similar equipment as in

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1856-435: The digits 1–9, and 0 (which sends 10 pulses). This equipment originally consisted of two telegraph keys engaged by knife switches , and evolved into the rotary dial telephone. The central office switching equipment has a two-motion stepping switch . A contact arm is moved up to select one of ten rows of contacts, and then rotated clockwise to select one of ten contacts in that row, a total of 100 choices. The stepping motion

1914-402: The equipment rack. The special crossbar switches used in distributing satellite TV signals are called multiswitches . Historically, a crossbar switch consisted of metal bars associated with each input and output, together with some means of controlling movable contacts at each cross-point. The first switches used metal pins or plugs to bridge a vertical and horizontal bar. In the later part of

1972-576: The first switches to be replaced with digital systems, which were even smaller and more reliable. Two principles of crossbar switching existed. An early method was based on the selector principle, which used crossbar switches to implement the same switching fabric used with Strowger switches . In this principle, each crossbar switch would receive one dialed digit, corresponding to one of several groups of switches or trunks. The switch would then find an idle switch or trunk among those selected and connect to it. Each crossbar switch could only handle one call at

2030-417: The hold bar keeps them in the active position as long as the connection is up. The horizontal off-normals on the sides of the switch are activated by the horizontal bars when the butterfly magnets rotate them. This only happens while the connection is being set up, since the butterflies are only energized then. The majority of Bell System switches were made to connect three wires including the tip and ring of

2088-461: The hold bars to operate the contacts beneath the bars. When the select and then the hold electromagnets operate in sequence to move the bars, they trap one of the spring fingers to close the contacts beneath the point where two bars cross. This then makes the connection through the switch as part of setting up a calling path through the exchange. Once connected, the select magnet is then released so it can use its other fingers for other connections, while

2146-564: The hold magnet remains energized for the duration of the call to maintain the connection. The crossbar switching interface was referred to as the TXK or TXC (telephone exchange crossbar) switch in the UK. However, the Bell System Type B crossbar switch of the 1960s was made in the largest quantity. The majority were 200-point switches, with twenty verticals and ten levels of three wires. Each select bar carries ten fingers so that any of

2204-624: The inputs to one of the outputs. A given crossbar is a single layer, non-blocking switch. A crossbar switching system is also called a coordinate switching system. Collections of crossbars can be used to implement multiple layer and blocking switches. A blocking switch prevents connecting more than one input. A non-blocking switch allows other concurrent connections from inputs to other outputs. Crossbar switches are commonly used in information processing applications such as telephony and circuit switching , but they are also used in applications such as mechanical sorting machines . The matrix layout of

2262-409: The local Bell Telephone Company manager Herman Ritterhoff, Strowger swore to "get even" with the telephone operators and "put every last one of them out of a job." Ritterhoff claimed that the real cause of Strowger's difficulties was a metal sign hung on his wall over his telephone, causing an intermittent short circuit when blown by the wind. Strowger conceived his invention in 1888, and was awarded

2320-466: The mechanical Boolean AND function of telephony crossbar switches, but other models had individual relays (one coil per crosspoint) in matrix arrays, connecting the relay contacts to [x] and [y] buses. These latter types were equivalent to separate relays; there was no logical AND function built in. Cunningham crossbar switches had precious-metal contacts capable of handling millivolt signals. Early crossbar exchanges were divided into an originating side and

2378-446: The names of its employees. The Strowger system was widely used until the development of the more reliable crossbar switch , an electromechanical switch with a matrix of vertical and horizontal bars and simpler motions. Strowger's patent specifies dialing equipment at the customer location and the switching equipment at the central office. The telegraph keys or telephone dial creates trains of on-off current pulses corresponding to

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2436-538: The new invention the "girl-less, cuss-less, out-of-order-less, wait-less telephone". In 1896 the company patented the finger-wheel dial as an improvement to the existing four-key design. The Strowger Automatic Telephone Exchange Company became the Automatic Electric Company , which Strowger was involved in founding, although Strowger himself seems not to have been involved in further developments. The Strowger patents were exclusively licensed to

2494-440: The overall sound system. Such switches are used in high-end home theater applications. Video sources typically shared include set-top receivers or DVD changers; the same concept applies to audio. The outputs are wired to televisions in individual rooms. The matrix switch is controlled via an Ethernet or RS-232 connection by a whole-house automation controller, such as those made by AMX , Crestron , or Control4 , which provides

2552-438: The provision of local free calling meant that residential customers had a relatively high calling rate. The fundamental modularity of the system combined with its step-by-step (hence the alternative name) selection process and an almost unlimited potential for expansion gives the Strowger system its technical advantage. Previous systems had all been designed for a fixed number of subscribers to be switched directly to each other in

2610-471: The rest of the network was deemed beneficial and the equipment could be manufactured in Britain. Crossbar switch In electronics and telecommunications , a crossbar switch ( cross-point switch , matrix switch ) is a collection of switches arranged in a matrix configuration. A crossbar switch has multiple input and output lines that form a crossed pattern of interconnecting lines between which

2668-412: The same term [REDACTED] This disambiguation page lists articles associated with the title Strowger . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Strowger&oldid=785886901 " Category : Disambiguation pages Hidden categories: Short description

2726-409: The second key, operates another electromagnet. Its pawl engages the (hidden) vertical teeth in the lower ratchet to rotate the shaft to the required position. It is kept there against spring tension by a pawl pivoted on the frame. When the switch returns to its home position, typically when a call is complete, a release magnet disengages the pawls that hold the shaft in position. An interlock ensures that

2784-518: The spring on the shaft rotates it to angular home position before it drops to its home position by gravity. The commercial version of the Strowger switch, as developed by the Strowger Automatic Telephone Exchange Company, used a rotary dial for signalling to the exchange. The original final selector (connector) switch which connected to 100 customers was supplemented by preceding group selector stages, as

2842-402: The ten circuits assigned to the ten verticals can connect to either of two levels. Five select bars, each able to rotate up or down, mean a choice of ten links to the next stage of switching. Each crosspoint in this particular model connected six wires. The vertical off-normal contacts next to the hold magnets are lined up along the bottom of the switch. They perform logic and memory functions, and

2900-418: The third key five times and the final key six times. The company installed and opened the first commercial exchange in his then-home town of La Porte, Indiana on November 3, 1892. The exchange had around 75 subscribers. The installation followed the original patented design, with four keys and four additional line wires connected to the exchange, but not all of the keys were used. Early advertising called

2958-416: The user interface that enables the user in each room to select which appliance to watch. The actual user interface varies by system brand, and might include a combination of on-screen menus, touch-screens, and handheld remote controls. The system is necessary to enable the user to select the program they wish to watch from the same room they will watch it from, otherwise it would be necessary for them to walk to

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3016-399: 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

3074-472: Was a large improvement over 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

3132-415: Was founded in 1891. In the original design patent, four keys were added near the telephone, one each for thousands, hundreds, tens and units, with each key having an additional wire connection to the central exchange. Each key had to be tapped the correct number of times to step the switch and make the desired connection. To connect to number 1256, the user would press the first key once, the second key twice,

3190-725: Was inspired by the Swedish design but was based on the rediscovered link principle. In 1945, a similar design by Swedish Televerket was installed in Sweden, making it possible to increase the capacity of the A204 model switch. Delayed by the Second World War, several millions of urban 1XB lines were installed from the 1950s in the United States. In 1950, the Swedish Ericsson company developed their own versions of

3248-534: 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. The Plessey TXK 1 or 5005 design used an intermediate form, in which

3306-416: Was more efficient, but required a 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

3364-453: 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. For instrumentation use, James Cunningham, Son and Company made high-speed, very-long-life crossbar switches with physically small mechanical parts which permitted faster operation than telephone-type crossbar switches. Many of their switches had

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