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80-431: 5XB was originally intended to bring the benefits of crossbar switching to towns and small cities with only a few thousand telephone lines . The typical starting size was 3000 to 5000 lines, but the system had essentially unlimited growth capacity. The earlier 1XB urban crossbar was impractically expensive in small installations, and had difficulties handling large trunk groups. 5XB was converted to wire spring relays in

160-525: 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

240-445: 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 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

320-474: A channel is called a mismatch and resulted in picking another trunk, or another line, or the use of the ALL where that exists, or giving up and letting the caller try again. As in previous designs, supervision of incoming calls is handled by relay sets known as incoming trunk circuits , which sit at the entry point just outside the switching network. Unlike in previous designs, outgoing trunk circuits are used for

400-642: 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

480-405: 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

560-427: A four-wire version of 5XB, with a more complex marker to implement its nonhierarchical polygrid routing system. Trunk circuits had additional logic and data storage built in, to implement multilevel precedence and preemption . Picturephone arrived in the early 1970s. 1ESS switch was already going into service and provided a more sophisticated basis for advanced services, but was not yet as widely available, so 5XB

640-465: 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

720-412: A line insulation test frame and an automatic trunk test frame. The latter was operated via a Teletype tape reader, and conducted trunk tests based on instructions encoded in 5-level punched tape. An automated AMA translator test frame checked for mis-wiring that could cause billing errors. A non-automated outgoing trunk test panel allows voltmeter, and signaling checks on trunks to distant offices, freeing

800-629: A line link frame appearance, as if it were a line. To avoid expense, incoming trunks were divided into groups, some of them having tandem ability and some not. This complication was avoided in places big enough to pay for a separate tandem switch. Connection of trunks to incoming registers and outgoing senders is not through the four-stage voice fabric. Rather it is through a dedicated single-stage crossbar network known as incoming register link (IRL) or outgoing sender link (OSL) respectively. Registers and senders are in groups of ten, assigned one to each level of as many crossbar switches as are appropriate to

880-400: A line to a trunk consisted of three links of switching fabric: line link, junctor, and trunk link. In a 10x20 or larger office, ten channels, numbered 0 to 9, were available from any line to any trunk. The line junctor switch number and the trunk junctor switch number are the same as the channel number. Logic in the marker compares the ten links of each kind to obtain a clear channel. The lack of

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960-495: A marker, once alerted to a trip condition, picks an OR by the same mechanism it uses to pick a trunk, identifies a clear path between line and OR, loads the OR with any information necessary for later processing (such as line equipment and class of service) and releases itself. The OR then receives the digits (rotary or tone), stores them in reed relay packs, and used the pretranslator to determine how many digits to receive before calling in

1040-513: 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

1120-847: 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 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

1200-415: 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

1280-439: A particular kind of signalling or call metering (see automatic message accounting ) or other peculiarity. Thus a TSPS trunk can give complete control to an operator, while an E and M signaling trunk can do the kind of signaling required of a private long-distance line, while a local outgoing trunk can be simpler. Thanks to this more complex trunk circuit, outgoing trunks are selected by a quicker and more versatile method than

1360-423: A phone number (or 6 when using a separate foreign area translator) to identify the correct outgoing trunks and handling. Connectors , similar in purpose to the data buses inside a computer CPU, connect the markers to the peripheral equipment. each connector is made up of large relays of 30 contacts each, to connect all the leads by which the marker would exchange information and control signals. For example, each of

1440-460: 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

1520-495: 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

1600-455: 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

1680-418: 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

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1760-474: 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

1840-437: 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

1920-712: 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

2000-415: Is feasible because there are only a few markers, and beneficial because their correct function was critical. Digit codes, for instance, are checked to ensure that exactly two out of the five lines are activated. When the built-in self-test circuits of a marker detect an error, a large punch card is produced at the test station recording the failure in order to assist the switchmen in detecting it and diagnosing

2080-422: Is less efficient for coin phones , which need special signalling. In urban areas, they were served by older exchanges that had separate junctors for coin phones. Where the 5XB was the only exchange, a number of work-around methods were devised. Regular and coin phones shared the more complex and expensive coin trunks, or else separate routes were established, or coin trunks connected via tandem switches including

2160-435: Is removed from service. 5XB markers were designed to rotate preferences in such a way that it is highly unlikely that the same circuit elements will be used in the next call. Thus, if a call encounters an equipment problem, a second try will probably succeed. Partly because of this deliberate design decision to help shield users from component failures, the few shared markers contain a great deal of self-checking circuitry. This

2240-470: Is responsible for off-hook , ringing signal , answer, ground start , on-hook unidirectional supervision messaging in each direction from calling party to called party and vice versa. After an off-hook, line signaling initiates register signaling to accomplish the exchange of telephone numbers of called party and in more modern line-signaling protocols, the calling party as well. While register signaling occurs, line signaling remains quiescent unless

2320-478: Is used to detect off-hook from a line being rung, release the RSS hold magnet, and engage the shielded supervision relay so reverse battery answer supervision would be returned to the originating end. Call-back, single-train, and other sophisticated methods require more sophisticated controls, but they increased efficiency and became standard for later designs. 5XB also separates the registers for receiving digits from

2400-523: 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

2480-439: 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,

Number Five Crossbar Switching System - Misplaced Pages Continue

2560-904: 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 ,

2640-408: The 1950s and otherwise upgraded in the 1960s to serve exchanges with tens of thousands of lines. The final 5A Crossbar variant, produced starting in 1972, was available only in sizes of 990 and 1960 lines, and generally delivered on one pallet , rather than assembled on site as usual for larger exchanges. 5XB introduced the call-back principle, in which the initial concentrating switch train from

2720-578: 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

2800-447: 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

2880-433: The 5XB itself acting as its own tandem. In this last case, the call had to use two connections through the switching fabric: one to connect the line to the coin supervision trunk and another to connect that trunk to the outgoing trunk. It was also less efficient for tandem calls, since the fabric is unable to connect a trunk directly to a trunk. Instead, each incoming trunk that has the ability to make tandem calls has to have

2960-537: The ALL were only used in heavy traffic periods. Junctors are wired from LLF through the junctor grouping frame to the levels of trunk junctor switches in the trunk link frame (TLF). Unlike earlier designs, the junctors have no supervisory relays or other active hardware, all such functions being assigned to trunk circuits. The basic design of the TLF has ten junctor switches with their horizontal multiples split in half, hence two hundred junctors, and two hundred trunk links to

3040-707: The MTF from this tedious job. Each outgoing trunk is represented by two jacks: one for test access for the voltmeter and sender circuits, and one for the make-busy operation. The master test frame was able to override a made-busy status when necessary. The first office capable of international direct distance dialing ( IDDD ) in the United States was the LT-1 exchange on the 10th floor of the 435 West 50th Street exchange building in Manhattan, New York. A group of its MF senders

3120-462: The ability of the markers to select different lines to particular trunks. This test facility became more valuable as Centrex , direct distance dialing , and other innovations brought more complications to the tasks of translation and trunk selection. When used for testing lines, the MTF can test translations and conduct voltmeter tests to detect impedance imbalances and other electrical conditions that can impair service. Other test equipment includes

3200-513: The calling party goes on-hook or an abnormal cessation of the call occurs, such as due to equipment malfunction or shutdown or due to network outage upstream in that call-attempt's series of spanned trunks. Line signaling can be conveyed in a single DS0 channel of a trunk . In modern PCM telecommunications, line signaling is represented by the ABCD bits in DS0 #16 of an E1 or a selected DS0 within

3280-413: The crosspoints must be made and broken at each decision interval. In high-speed switches, the settings of all of the crosspoints 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 . Line signaling Line signaling is a class of telecommunications signaling protocols . Line signaling

Number Five Crossbar Switching System - Misplaced Pages Continue

3360-402: 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

3440-483: The equivalent outgoing functions. This means that the junctors , which have the same name as earlier crossbar systems, are simplified, and are now only wires providing links between lines and trunks. The outgoing trunk circuits, which are placed at the outside edge of the switching network, are responsible for originating-side supervision. Since different outgoing trunks are connected to different places and are used for different calls, their relay sets can be specialized for

3520-510: The first bay have their horizontal multiples, or "banjo wires", cut in half, effectively dividing each switch into a line switch and a junctor switch. Each of the ten junctor switches have ten junctors on its ten verticals, and each of its ten levels was wired as a line link, to one of the ten line switches of the LLF. Thus, the line link frame terminates 100 Junctors. Each junctor has full availability to however many hundreds of lines there are, via

3600-576: 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

3680-417: 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

3760-461: 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

3840-564: 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

3920-417: The hundred line links. The number of lines, thus the line concentration ratio (LCR), was engineered for the expected occupancy. Each line switch in this first, mixed bay has nine lines on nine of its verticals, the tenth vertical being reserved for test purposes. In addition to the 90 lines on these switches, each LLF has at least one simple line switch bay, with ten more line switches carrying 200 lines. Thus

4000-404: 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 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

4080-435: The late 1950s multiple trunk junctor switch bays (ETL and SETL) were added to give each TLF access to more junctors. The first expanded version allowed each office to have 20x40, and in the 1960s the maximum reached 30x60. Development stopped at that point because the four-stage layout was becoming progressively less efficient at greater sizes, and because the 1ESS switch with eight stages was under development. A channel from

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4160-431: The line links of an even numbered LLF, and on its verticals, the junctors of the neighboring odd numbered one; the other half is vice versa. By this means, each LLF can use the junctors of its mate, if the marker failed to find an idle path on the first try. Since they are odd and even, their junctors appear on opposite sides of the trunk junctor switches, thus giving access to the mate trunk links as well. Connections through

4240-469: The line or trunk to which the audio portion of the call would be completed, and then set up both the audio switches and the video ones. Wideband remote switches (WBRS) were installed in smaller exchanges, as video concentrators for lines that were beyond video range from a larger exchange that had been given the Picturephone feature. Crossbar switch In electronics and telecommunications ,

4320-514: The line to the digit receiver was entirely dropped during call completion so its links could immediately be reused for this or another call. This is in contrast to earlier crossbar systems where the original switch train was simply built up and expanded as the call was connected, and not dropped in favor of a completely new one. It also uses entirely the same four-stage switching fabric for incoming as for outgoing calls, instead of separate fabric, as had been done in earlier systems. These developments had

4400-412: The marker again to complete the call. Larger 5XB systems were built in the 1960s with more markers. To save money the markers were separated into two kinds: simple dial tone markers (DTM) just to connect the line to the OR, and completing markers (CM), many times more complex and expensive, to complete the call to or from a trunk. CM has, among other features, the ability to translate the first 3 digits of

4480-433: The marker to choose a TLF that has an idle trunk and then connect to that trunk through the trunk link connector (TLC) to choose one of those idle trunks. This two step method, along with the mixing of incoming and outgoing traffic, distributed traffic more evenly, thus alleviating the link congestion problems that often arose with earlier methods that restricted a trunk group to one or two outgoing switch frames. This method

4560-466: 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

4640-429: The minimum size of a LLF is 290 lines for a line concentration ratio of 2.9:1. Optionally it has still another frame, with ten more switches and another 200 lines, and so forth, up to a maximum line concentration ratio of 5.9:1 since they all shared the same hundred line links. The line circuit is much like that in 1XB with a line relay for alerting the exchange to a trip condition, and the vertical off-normal contacts of

4720-507: The oblong reed packs in an OR would have to be connected by five leads through the originating register marker connector to transmit the two-out-of-five code representing one dialed digit. For speed, transfer is entirely parallel, requiring many large relays to connect so many wires. Connectors that respond to a peripheral circuit's request for action are given the name of the requesting circuit and "marker", as in ORMC or IRMC. Connectors whose use

4800-581: The overall effect of simplifying the switch fabric, and using it as a "service" rather than as an immutable part of the call, as was the case in most earlier systems. All lines are terminated on line link frames (LLF) and all trunks and most service circuits on trunk link frames (TLF). Each TLF is connected to all LLF by at least ten junctors . Calls from subscribers originate at line link frames and pass through trunk link frames on their way to their destinations. Line link frames (LLFs) are tiers of 10x20 crossbar switches in two or more bays. The switches in

4880-440: 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

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4960-407: The senders for sending them. This complication necessitates more transmission of data among the control circuits but greatly shortens the holding time of senders and increases general efficiency and versatility without having to put the versatility into large, numerous, and complex senders as in earlier systems . Originating registers (OR) are wired to the trunk link frame (TLF). In the original 5XB,

5040-424: The sleeve test previously used. Each trunk circuit provides a ground on an FT lead to indicate idleness. The FT leads for trunks in a particular group are cross-connected to a FTC (frame test common) lead for the trunk link frame upon which it appears, to indicate that the TLF has one or more idle trunks in that group. The route relay in the completing marker connects sensor relays to all the trunk link frames, allowing

5120-501: The source. The card punch, with some cards, is visible in the lower left of the test frame picture below. To a greater degree than in previous designs, test facilities are centralized into a master test frame (MTF). This complex piece of equipment is wired into all common control equipment, and can, for example, automatically exercise the abilities of digit receivers to operate at different speeds, voltages, and other parameters. The MTF can select particular outgoing trunks, including testing

5200-404: The switch vertical serving as cutoff relay. For control purposes the subscriber lines on the switches of the LLF are divided into vertical groups of fifty, being five line units on each of ten switches. Each vertical group is divided into five vertical files of ten lines, important because class of service, or customer group identification in later Centrex offices, is shared by all ten lines in

5280-402: 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

5360-417: The ten trunk switches. The banjo wiring of the trunk switch was not split, but a discriminator level trick devoted two levels to doubling the use of the other eight, thus allowing each trunk switch to connect sixteen trunks to its twenty trunk links. This results in the TLF having a 0.8:1 trunk concentration ratio (TCR). This degree of deconcentration eventually turned out to provide too few trunk appearances for

5440-680: The traffic they can handle. Different trunks are wired to different IRLs or OSLs depending on what kind of signaling they use; i.e. IRDP, IRRP (see panel switch ), or IRMF . Previous systems use relays in the incoming trunk circuit to control ringing and to return busy tone. 5XB uses a ringing selection switch (RSS): a crossbar switch with ten verticals, serving ten trunks. The various levels provide various tones, and ringing current of various durations and cadences (especially valuable for party lines ). Levels 0 and 1 are used as discriminating levels to set polarity for selective ringing on tip side or ring side . An especially sensitive wire spring RT relay

5520-416: 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

5600-405: The variety of trunk types needed. The final 1970s 5XB offices had type C trunk switches with twelve levels, using two for discrimination, leaving a TCR of unity. The TLF having twice as many links, junctor switches, and junctors as the LLF, there are always twice as many LLFs as TLFs. As first designed, the maximum number was ten TLFs and twenty LLFs, known as 10x20, and at first rarely achieved. In

5680-399: 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

5760-525: The vertical file. Staff in Centrex offices spent much time standing on ladders, rewiring the Class of Service data fields at the top of LLF. Late in the career of 5XB, junctor group size and thus link efficiency of the largest offices was increased by the use of auxiliary line link (ALL) frames. The ALL is a bay with ten junctor switches, divided as usual into left and right halves. One half has on its levels

5840-472: 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

5920-413: Was designated as the switching vehicle. Every Picturephone line has six wires: the old talking pair plus a video transmission pair and a video receiving pair. A new wideband switching fabric was designed using a 6-wire version of Type B crossbar switches, two of the wires being grounded, thus diminishing crosstalk for the two video pairs. When completing a Picturephone call, the completing marker first picked

6000-466: Was equipped for the unique dual outpulse requirements of that service. Most large new urban 5XB in subsequent years had IDDD, and it was retrofitted to some existing ones, but most omitted the dual outpulse capability, that job being handled by TSPS . Also taking advantage of the superior versatility of 5XB, Centrex was invented as a service package. Later stored program control exchanges allowed more extensive service features. Autovon originally used

6080-662: 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

6160-534: 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

6240-416: 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

6320-428: Was requested by a marker are named only for the circuit to which they connect, as in outsender connector, line link connector, and trouble recorder connector. One of the drawbacks of step-by-step and other early systems is that the preference for choosing trunks or selector links is fixed, and the most preferred links are used more often, with the result that the same faulty hardware blocks repeated call attempts until it

6400-453: 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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