Device used to connect telephone circuits to establish calls between users
PBX switchboard, 1975
A telephone switchboard is a device used to connect circuits of telephones to establish telephone calls between users or other switchboards. The switchboard is an essential component of a manual telephone exchange, and is operated by switchboard operators who use electrical cords or switches to establish the connections.
The switchboard saw the peak of its use in the 20th century before wider adoption of the electromechanicalautomatic telephone exchange. The automatic exchange, invented by Almon Strowger in 1888, has replaced most switchboards in central telephone exchanges around the world.
Nevertheless, many manual branch exchanges remained operational into the second half of the 20th century in many enterprises. Some establishments, such as the White House, still operate a switchboard.
Electronic devices and computer technology have given exchange operators more features. For example, a private branch exchange (PBX) in a business usually has an attendant console, or an auto-attendant function, which bypasses the operator.
Following the invention of the telephone in 1876, the first telephones were rented in pairs which were limited to conversation between the parties operating those two instruments. The use of a central exchange was soon found to be even more advantageous than in telegraphy.
In May 1877, the Holmes Burglar Alarm Company in Boston, Massachusetts, established by Edwin T. Holmes, installed the first central office and switchboard that served both as a security service at night for banks and businesses, as well as a telephone system.[1] The switchboard operated telephone instruments manufactured by Charles Williams, a licensee of the Alexander Graham Bell company.
In January 1878 the Boston Telephone Dispatch company had started hiring boys as telephone operators. Boys had been very successful as telegraphy operators, but their attitude, lack of patience, and behavior was unacceptable for live telephone contact,[2] so the company began hiring women operators instead. Thus, on September 1, 1878, Boston Telephone Dispatch hired Emma Nutt as the first woman operator. Small towns typically had the switchboard installed in the operator's home so that he or she could answer calls on a 24-hour basis. In 1894, New England Telephone and Telegraph Company installed the first battery-operated switchboard on January 9 in Lexington, Massachusetts.
Early switchboards in large cities usually were mounted floor to ceiling in order to allow the operators to reach all the lines in the exchange. The operators were boys who would use a ladder to connect to the higher jacks. Late in the 1890s this measure failed to keep up with the increasing number of lines, and Milo G. Kellogg devised the Divided Multiple Switchboard for operators to work together, with a team on the "A board" and another on the "B". These operators were almost always women until the early 1970s, when men were once again hired.[3] Cord switchboards were often referred to as "cordboards" by telephone company personnel. Conversion to panel switch and other automated switching systems first eliminated the "B" operator and then, usually years later, the "A". Rural and suburban switchboards for the most part remained small and simple. In many cases, customers knew their operator by name.
As telephone exchanges converted to automatic (dial) service, switchboards continued to serve specialized purposes. Before the advent of direct-dialed long-distance calls, a subscriber would need to contact the long-distance operator in order to place a toll call. In large cities, there was often a special number, such as 112, which would ring the long-distance operator directly. Elsewhere, the subscriber would ask the local operator to ring the long-distance operator.
The long-distance operator would record the name and city of the person to be called, and the operator would advise the calling party to hang up and wait for the call to be completed. Each toll center had only a limited number of trunks to distant cities, and if those circuits were busy, the operator would try alternate routings through intermediate cities. The operator would plug into a trunk for the destination city, and the inward operator would answer. The inward operator would obtain the number from the local information operator and ring the call. Once the called party answered, the originating operator would advise him or her to stand by for the calling party, whom she'd then ring back, and record the starting time once the conversation began.
A large Bell System international switchboard in 1943
In the 1940s, with the advent of dial pulse and multi-frequency operator dialing, the operator would plug into a tandem trunk and dial the NPA (area code) and operator code for the information operator in the distant city. For instance, the New York City information operator was 212-131. If the customer knew the number, and the point was direct-dialable, the operator would dial the call. If the distant city did not have dialable numbers, the operator would dial the code for the inward operator serving the called party, and ask her to ring the number.
In the 1960s, once most phone subscribers had direct long-distance dialing, a single type of operator began to serve both the local and long-distance functions. A customer might call to request a collect call, a call billed to a third number, or a person-to-person call. All toll calls from coin phones required operator assistance. The operator was also available to help complete a local or long-distance number which did not complete. For example, if a customer encountered a reorder tone (a fast busy signal), it could indicate "all circuits busy," or a problem in the destination exchange. The operator might be able to use a different routing to complete the call. If the operator could not get through by dialing the number, she could call the inward operator in the destination city, and ask her to try the number, or to test a line to see if it was busy or out of order.
Cord switchboards used for these purposes were replaced in the 1970s and 1980s by Traffic Service Position System (TSPS) and similar systems, which greatly reduced operator involvement in calls. The customer would, instead of simply dialing "0" for the operator, dial 1+NPA+7digits, after which an operator would answer and provide the desired service (coin collection, obtaining acceptance on a collect call, etc.), and then release the call to be automatically handled by the TSPS.
Before the late 1970s and early 1980s, it was common for many smaller cities to have their own operators. An NPA (area code) would usually have its largest city as its primary toll center, with smaller toll centers serving the secondary cities scattered throughout the NPA. TSPS allowed telephone companies to close smaller toll centers and consolidate operator services in regional centers which might be hundreds of miles from the subscriber.
In the mid-1980s the Bell Operating Companies (BOCs) opened their own Operator Services offices with a system called TOPS (Traffic Operator Position System) to act as local and intraLATA telephone operators. With this the BOCs took intraLATA call traffic from AT&T as well as services which were once provided on a cordboard (Toll Stations, Mobile and Marine [Ship-to-Shore]). Operators from AT&T returned to work for the BOC as the intraLATA traffic was cut to the BOC.
In the early 1990s AT&T replaced TSPS with OSPS (Operator Service Position System). The OSPS position was a computer terminal which the AT&T operator entered billing information. With the advent of OSPS a feature called Interflow allowed operators on a system to answer calls from anywhere within their region.
As technology changed, so did the application of Interflow. Interflow was implemented nationwide by AT&T. This allowed AT&T to close virtually every operator office throughout the US. As of 2004[update] the only AT&T operator offices remaining were located in Houston, Texas, and Jacksonville, Florida.
The switchboard is usually designed to accommodate the operator, who sits facing it. It has a high back panel, which consists of rows of female jacks, each jack designated and wired as a local extension of the switchboard (which serves an individual subscriber) or as an incoming or outgoing trunk line. The jack is also associated with a lamp.
On the table or desk area in front of the operator are columns of 3-position toggle switches termed "keys", lamps, and cords. Each column consists of a front key and a rear key, a front lamp and a rear lamp, followed by a front cord and a rear cord, making up together a cord circuit. The front key is the "talk" key allowing the operator to speak with that particular cord pair. The rear key on older "manual" boards and PBXs is used to ring a telephone physically. On newer boards, the back key is used to collect (retrieve) money from coin telephones. Each of the keys has three positions: back, normal and forward. When a key is in the normal position an electrical talk path connects the front and rear cords. A key in the forward position (front key) connects the operator to the cord pair, and a key in the back position sends a ring signal out on the cord (on older manual exchanges). Each cord has a three-wire TRS phone connector: tip and ring for testing, ringing and voice; and a sleeve wire for busy signals.
When a call is received, a jack lamp lights on the back panel and the operator responds by placing the rear cord into the corresponding jack and throwing the front key forward. The operator then converses with the caller, who informs the operator to whom he or she would like to speak. If it is another extension, the operator places the front cord in the associated jack and pulls the front key backwards to ring the called party. After connecting, the operator leaves both cords "up" with the keys in the normal position so the parties can converse. The supervision lamps light to alert the operator when the parties finish their conversation and go on-hook. Either party could "flash" the operator's supervision lamps by depressing their switch hook for a second and releasing it, in case they needed assistance with a problem. When the operator pulls down a cord, a pulley weight behind the switchboard pulls it down to prevent it from tangling.
On a trunk, on-hook and off-hook signals must pass in both directions. In a one-way trunk, the originating or A board sends a short for off-hook, and an open for on-hook, while the terminating or B board sends normal polarity or reverse polarity. This "reverse battery" signaling was carried over to later automatic exchanges.
Some areas used specialized switchboards to handle calls from payphones. In North America, these "coin boards" were gradually phased out after the introduction of the Automated Coin Toll System that was provided by the Traffic Service Position System. Dedicated coin boards were primarily used in large, densely populated areas such as New York City where the large local calling area required special billing arrangements to allow the rate for a local call to vary based on the distance called. In less densely populated regions, calls from payphones were handled by normal assistance operators without the use of dedicated coin boards.
Direct distance dialing (DDD) is a telecommunications service feature in North America by which a caller may, without operator assistance, call any other user outside the local calling area. Direct dialing by subscribers typically requires extra digits to be dialed as prefixes to the directory telephone number of the destination. International Direct Distance Dialing (IDDD) extends the system beyond the geographic boundaries of the North American Numbering Plan (NANP).
In telephony, ringdown is a method of signaling an operator in which telephone ringing current is sent over the line to operate a lamp or cause the operation of a self-locking relay known as a drop.
A blue box is an electronic device that produces tones used to generate the in-band signaling tones formerly used within the North American long-distance telephone network to send line status and called number information over voice circuits. During that period, charges associated with long-distance calling were commonplace and could be significant, depending on the time, duration and destination of the call. A blue box device allowed for circumventing these charges by enabling an illicit user, referred to as a "phreaker," to place long-distance calls, without using the network's user facilities, that would be billed to another number or dismissed entirely by the telecom company's billing system as an incomplete call. A number of similar "color boxes" were also created to control other aspects of the phone network.
The North American Numbering Plan (NANP) is a telephone numbering plan for twenty-five regions in twenty countries, primarily in North America and the Caribbean. This group is historically known as World Zone 1 and has the telephone country code 1. Some North American countries, most notably Mexico, do not participate with the NANP.
A telephone call or telephone conversation, also known as a phone call or voice call, is a connection over a telephone network between the called party and the calling party. Telephone calls started in the late 19th century. As technology has improved, a majority of telephone calls are made over a cellular network through mobile phones or over the internet with Voice over IP. Telephone calls are typically used for real-time conversation between two or more parties, especially when the parties cannot meet in person.
Subscriber trunk dialling (STD), also known as subscriber toll dialing, is a telephone numbering plan feature and telecommunications technology in the United Kingdom and various Commonwealth countries for the dialling of trunk calls by telephone subscribers without the assistance of switchboard operators.
In the early days of telephony, companies used manual telephone switchboards, and switchboard operators connected calls by inserting a pair of phone plugs into the appropriate jacks. They were gradually phased out and replaced by automated systems, first those allowing direct dialing within a local area, then for long-distance and international direct dialing.
Routing in the PSTN is the process of forwarding telephone calls between the constituent telephone networks that comprise the public switched telephone network (PSTN).
Seven-digit dialing is a telephone dialing procedure customary in some territories of the North American Numbering Plan (NANP) for dialing telephone numbers in the same numbering plan area (NPA). NANP telephone numbers consist of ten digits, of which the leading three are the area code. In seven-digit dialing it is not necessary to dial the area code. The procedure is also sometimes known as local format or network format.
The Traffic Service Position System (TSPS) was developed by Bell Labs in Columbus, Ohio to replace traditional cord switchboards. The first TSPS was deployed in Morristown, New Jersey in 1969 and used the Stored Program Control-1A CPU, "Piggyback" twistor memory and Insulated Gate Field Effect Transistor solid state memory devices similar to dynamic random access memory.
Trunk and toll calling were two alternative methods of charging customers for long-distance calls in the United Kingdom in the first half of the 20th century. The distinction became obsolete with the introduction of subscriber trunk dialling (STD).
In telecommunications, a long-distance call (U.S.) or trunk call is a telephone call made to a location outside a defined local calling area. Long-distance calls are typically charged a higher billing rate than local calls. The term is not necessarily synonymous with placing calls to another telephone area code.
A telephone exchange name or central office name was a distinguishing and memorable name assigned to a central office. It identified the switching system to which a telephone was connected, and facilitated the connection of telephone calls between switching systems in different localities.
A class-4, or tandem, telephone switch is a U.S. telephone company central office telephone exchange used to interconnect local exchange carrier offices for long distance communications in the public switched telephone network.
A telephone number is a sequence of digits assigned to a landline telephone subscriber station connected to a telephone line or to a wireless electronic telephony device, such as a radio telephone or a mobile telephone, or to other devices for data transmission via the public switched telephone network (PSTN), or other public and private networks. Modern smart phones have added a built-in layer of abstraction whereby individuals or businesses are saved into a contacts application and the numbers no longer have to be written down or memorized.
The original North American area codes were established by the American Telephone and Telegraph Company (AT&T) in 1947, after the demonstration of regional Operator Toll Dialing during the World War II period. The program had the goal of speeding the connecting times for long-distance calling by eliminating intermediary telephone operators. Expanding this technology for national use required a comprehensive and universal, continent-wide telephone numbering plan.
A telephone exchange, also known as a telephone switch or central office, is a crucial component in the public switched telephone network (PSTN) or large enterprise telecommunications systems. It facilitates the interconnection of telephone subscriber lines or digital system virtual circuits, enabling telephone calls between subscribers.
In conventional landline telephony, a non-dialable toll point or toll station was a lone station or line serving a rural subscriber many miles from the nearest central office. As it had no home telephone exchange and therefore no local calling area, no customer could dial its number; all connections to it had to be obtained manually by the long distance operator.
Operator Toll Dialing was a telephone call routing and toll-switching system for the Bell System and the independent telephone companies in the United States and Canada that was developed in the 1940s. It automated the switching and billing of long-distance calls. The concept and technology evolved from the General Toll Switching Plan of 1929, and gained technical merits by the cutover of a new type of crossbar switching system in Philadelphia to commercial service in August 1943. This was the first system of its kind for automated forwarding of calls between toll switching centers, but it served customers only for regional toll traffic. It established initial experience with automatic toll switching for the design of a nationwide effort that was sometimes referred to as Nationwide Operator Toll Dialing.
The Panel Machine Switching System is a type of automatic telephone exchange for urban service that was used in the Bell System in the United States for seven decades. The first semi-mechanical types of this design were installed in 1915 in Newark, New Jersey, and the last were retired in the same city in 1983.
References
↑ G.K. Thompson, R.B. Hill, The First Telephone Switchboard and Its Method of Operation, Bell Telephone Quarterly Volume 9(3), p.205 (July 1930).
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