Telephone switchboard
From Free net encyclopedia
Image:JT Switchboard 770x540.jpg A switchboard (also called a manual branch exchange) is a device used to manually connect a group of telephones from one to another or to an outside connection, within and between telephone exchanges or private branch exchanges (like hotels). The user is typically known as an operator.
The device is usually designed to enable the operator to sit at it. It has a high backpanel 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 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. The front key is associated and wired to the front cord and the rear key is associated with and wired to the rear cord. 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 connects the operator to the cord, and a key in the back position sends a ring signal out on the cord. Each cord has a three-wire TRS 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 up on the back panel and the operator responds by placing the rear cord into the jack and throwing the rear key forward. The operator now converses with the caller and finds out where the caller would like to be connected to. 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 and the parties can converse.
History
Switchboards came into use shortly after the invention of the telephone in 1876. Small towns typically had the operator's switchboard installed in the operator's home so that she could answer calls on a 24 hour basis. In 1894, New England Telephone and Telegraph installed the first battery-operated switchboard on January 9 in Lexington, Massachusetts.
Early switchboards in large cities usually were mounted floor to ceiling. The operators were boys who could scoot up a ladder to connect to the higher jacks. The boys were replaced by women because it was found that boys had little patience and would frequently curse the customers. Operators were almost always women until the mid-1960s when men were once again hired.
As telephone exchanges converted to automatic, or direct-dial, service, switchboards remained in use for 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 call. In large cities, there was often a special number, such as 1-1-2, which would ring the long-distance operator directly . In other cities, the subscriber would ask the local operator to ring the long-distance operator.
When calling long distance, the customer often would not have the phone number available, so would simply ask for the name and city of the person desired. The long distance operator would plug into the trunk for the distant city, and the inward operator in the distant city would answer, obtain the number from their local information operator, and ring the call.
Image:Operadoras-Museo-Telecomunicaciones-Madrid.jpg Later, with the advent of operator dialing, the operator would plug into a trunk line and dial the area code and operator code for the information operator in the distant city. If the customer knew the number, and the point was direct-dialable, the operator could dial the call. If the distant city did not have dialable numbers, the operator would dial the code for the inward operator, and ask her to ring the number.
After most phone subscribers had direct long-distance dialing, one type of operator served both the local and long distance functions. A customer might call to request help getting through on a number that did not ring, or might be out of order, for instance. If the number was in a distant city, the operator would 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.
Manual switchboards have for the most part been replaced by more sophisticated devices or even personal computers, which give the operator access to an abundance of features. In businesses, a key phone system often has an attendant console for the operator, with an auto-attendant often avoiding the operator entirely.
The electromechanical automatic telephone exchange, invented by Almon Strowger in 1888, replaced manual switchboards.
The early "cord" switchboards were often referred to as "cordboards" by telephone company personnel.