In the field of telecommunications Telecommunication is the transmission of messages, over significant distances, for the purpose of communication. In earlier times, telecommunications involved the use of visual signals, such as smoke, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded drumbeats, lung-blown horns, or sent by loud whistles, for, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls. A central office is the physical building used to house inside plant Around the turn of the century, DSLAMs became an important part of telephone company inside plant. Inside plant will also have distribution frames and other equipment including passive optical network equipment including telephone switches, which make telephone calls A telephone call is a connection over a telephone network between the calling party and the called party "work" in the sense of making connections and relaying the speech information.
The term exchange area can be used to refer to an area served by a particular switch, but is typically known as a wire center in the US telecommunications industry. The exchange code or Central Office Code refers to the first three digits of the local number (NXX). It is sometimes confused with the area code A telephone numbering plan is a type of numbering scheme used in telecommunications to allocate and route telephone numbers in a telephone network. A closed numbering plan, such as found in North America, features fixed length area codes and local numbers. An open numbering plan features variance in length of area code or local number, or both (NPA A telephone numbering plan is a type of numbering scheme used in telecommunications to allocate and route telephone numbers in a telephone network. A closed numbering plan, such as found in North America, features fixed length area codes and local numbers. An open numbering plan features variance in length of area code or local number, or both). In the United States ^ b. English is the de facto language of American government and the sole language spoken at home by 80% of Americans age five and older. Spanish is the second most commonly spoken language, local exchange areas together make up a legal entity called local access and transport areas Local access and transport area is a term used in U.S. telecommunications regulation. It represents a geographical area of the United States under the terms of the Modification of Final Judgment (MFJ) that precipitated the breakup of the original AT&T into the "Baby Bells" or created since that time for wireline regulation (LATA Local access and transport area is a term used in U.S. telecommunications regulation. It represents a geographical area of the United States under the terms of the Modification of Final Judgment (MFJ) that precipitated the breakup of the original AT&T into the "Baby Bells" or created since that time for wireline regulation) under the Modification of Final Judgment In United States telecommunication law, Modification of Final Judgment is the 1982 agreement (consent decree) settling United States v. AT&T, a landmark antitrust suit. Entered into between the United States Department of Justice and the American Telephone & Telegraph Company (AT&T) the MFJ, after modification and upon approval of the (MFJ).
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Historic perspective
Tivadar Puskás Tivadar Puskás was a Hungarian inventor, telephone pioneer, and inventor of the telephone exchange He was also the founder of Telefon Hírmondó, the inventor. A Verizon Verizon Communications Inc. is an American broadband and telecommunications company and a component of the Dow Jones Industrial Average. It was formed in 1983 as Bell Atlantic as part of the 1984 AT&T breakup into seven Baby Bells. Prior to its transformation into Verizon, Bell Atlantic had merged with another Regional Bell Operating Company, Central Office in Lakeland, Florida at night. An AT&T AT&T Inc. is the largest provider of fixed telephony in the United States, and also provides broadband and subscription television services. AT&T is the second largest provider of mobile telephony service in the United States, with over 90.1 million wireless customers, and more than 210 million total customers Central Office in Houston, Texas. The imprint of the old Bell System The Bell System was the American Bell Telephone Company and AT&T led organization that provided telephone service in the United States from 1877 to 1984, at various times as a monopoly. In 1984, a Federal mandate broke the company up into separate companies logo is visible.Prior to the telephone, electrical switches were used to switch telegraph lines. One of the first people to build a telephone exchange was Hungarian Hungary /ˈhʌŋɡəri/ (Hungarian: Magyarország [ˈmɒɟɒrorsaːɡ] ( listen)), officially the Republic of Hungary (Magyar Köztársaság listen (help·info)), is a landlocked country in the Carpathian Basin in Central Europe, bordered by Austria, Slovakia, Ukraine, Romania, Serbia, Croatia, and Slovenia. Its capital is Budapest. Hungary is a Tivadar Puskás Tivadar Puskás was a Hungarian inventor, telephone pioneer, and inventor of the telephone exchange He was also the founder of Telefon Hírmondó in 1877 while he was working for Thomas Edison Thomas Alva Edison was an American inventor, scientist, and businessman who developed many devices that greatly influenced life around the world, including the phonograph, the motion picture camera, and a long-lasting, practical electric light bulb. Dubbed "The Wizard of Menlo Park" (now Edison, New Jersey) by a newspaper reporter, he.[1][2][3][4][5] George W. Coy designed and built the first commercial telephone exchange which opened in New Haven, Connecticut New Haven is the second-largest municipality in Connecticut and the sixth-largest municipality in New England with a core population of about 124,000 people. "New Haven" may also refer to the wider Greater New Haven area, which has nearly 600,000 inhabitants in the immediate area. It is located in New Haven County, on New Haven Harbor, in January, 1878. The switchboard was built from "carriage bolts, handles from teapot lids and bustle wire" and could handle two simultaneous conversations .[6]
Later exchanges consisted of one to several hundred plug boards A switchboard was a device used to connect a group of telephones manually to one another or to an outside connection, within and between telephone exchanges or private branch exchanges (PBXs). The user was typically known as an operator. Public manual exchanges disappeared during the last half of the 20th century, leaving a few PBXs working in staffed by telephone operators With the development of computerized telephone dialing systems, many telephone calls which previously required a live operator can be placed automatically by the calling party without additional human intervention. Before the advent of automatic exchanges, an operator's assistance was required for anything other than calling telephones across a. Each operator sat in front of a vertical panel containing banks of ¼-inch tip-ring-sleeve A TRS connector also called an audio jack, phone plug, jack plug, stereo plug, mini-jack, mini-stereo, or headphone jack, is a common analog audio connector. It is cylindrical in shape, typically with three contacts, although sometimes with two (a TS connector) or four (a TRRS connector) (3-conductor) jacks, each of which was the local termination of a subscriber The subscription business model is a business model where a customer must pay a subscription price to have access to the product/service. The model was pioneered by magazines and newspapers, but is now used by many businesses and websites's telephone line A telephone line or telephone circuit is a single-user circuit on a telephone communications system. Typically this refers to the physical wire or other signaling medium connecting the user's telephone apparatus to the telecommunications network, and usually also implies a single telephone number for billing purposes reserved for that user. In front of the jack panel lay a horizontal panel containing two rows of patch cords, each pair connected to a cord circuit. When a calling party The calling party is a person who (or device that) initiates a telephone call over the public switched telephone network, usually by dialing a telephone number lifted the receiver, a signal lamp near the jack would light. The operator would plug one of the cords (the "answering cord") into the subscriber's jack and switch her headset into the circuit to ask, "Number, please?" Depending upon the answer, the operator might plug the other cord of the pair (the "ringing cord") into the called party's local jack and start the ringing cycle, or plug into a trunk circuit to start what might be a long distance call handled by subsequent operators in another bank of boards or in another building miles away. In 1918, the average time to complete the connection for a long-distance call was 15 minutes.[7] In the ringdown 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. Ringdown is used in manual operation, as distinguished from dialing, (b) uses a continuous or pulsed ac signal transmitted over the line, and (c) may method, the originating operator called another intermediate operator who would call the called subscriber, or passed it on to another intermediate operator.[8] This chain of intermediate operators could complete the call only if intermediate trunk lines were available between all the centers at the same time. In 1943 when military calls had priority, a cross-country US call might take as long as 2 hours to request and schedule in cities that used manual switchboards for toll calls.
On March 10, 1891, Almon Brown Strowger Almon Brown Strowger gave his name to the electromechanical telephone exchange technology that his invention and patent inspired, an undertaker in Kansas City, Missouri Kansas City is the largest city in the U.S. state of Missouri. It encompasses 318 square miles in parts of Jackson, county. It is one of two county seats of Jackson County, the other being Independence, just to the city's east. The city also serves as the anchor city of the Kansas City Metropolitan Area, second largest in Missouri, and largest, patented the stepping switch In electrical controls, a stepping switch, also known as a stepping relay, is an electromechanical device which allows an input connection to be connected to one of a number of possible output connections, under the control of a series of electrical pulses. It can step on one axis , or on two axes (a Strowger switch). Stepping switches were, a device which led to the automation of telephone circuit switching. While there were many extensions and adaptations of this initial patent, the one best known consists of 10 levels or banks, each having 10 contacts arranged in a semicircle. When used with a rotary telephone dial The rotary dial is a device mounted on or in a telephone or switchboard that is designed to send interrupted electrical pulses, known as pulse dialing, corresponding to the number dialed. The early form of the rotary dial used lugs on a finger plate instead of holes. A patent was filed on August 20, 1896 by employees of Almon Strowger, namely, A, each pair of digits caused the shaft of the central contact "hand" of the stepping switch to first step (ratchet) up one level for each pulse in the first digit and then to swing horizontally in a contact row with one small rotation for each pulse in the next digit.
Later stepping switches In electrical controls, a stepping switch, also known as a stepping relay, is an electromechanical device which allows an input connection to be connected to one of a number of possible output connections, under the control of a series of electrical pulses. It can step on one axis , or on two axes (a Strowger switch). Stepping switches were were arranged in banks, the first stage of which was a linefinder. If one of up to a hundred subscriber lines had the receiver lifted "off hook", a linefinder connected the subscriber's line to a free first selector, which returned the subscriber a dial tone A dial tone is a telephony signal used to indicate that the telephone exchange is working, has recognized an off-hook, and is ready to accept a call. The tone stops when the first numeral is dialed. If no digits are forthcoming, the permanent signal procedure is invoked, often eliciting a special information tone to show that it was ready to receive dialed digits. The subscriber's dial pulsed at about 10 pulses per second, although the speed depended on the standard of the particular telephone administration.
Exchanges based on the Strowger switch were eventually challenged by other exchange types The panel switching system was an early type of automatic telephone exchange, first put into urban service by the Bell System in the 1920s and removed during the 1970s. The Panel and Rotary systems were developed in parallel by Bell Labs before World War I , and had many features in common, though the Rotary system was used in Europe and later by crossbar In electronics, a crossbar switch is a switch connecting multiple inputs to multiple outputs in a matrix manner. 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. It is one of the principal switch architectures, together with a memory technology. These exchange designs promised faster switching and would accept pulses faster than the Strowger's typical 10 pps—typically about 20 pps. At a later date many also accepted DTMF Dual-tone multi-frequency signaling is used for telecommunication signaling over analog telephone lines in the voice-frequency band between telephone handsets and other communications devices and the switching center. The version of DTMF that is used in push-button telephones for tone dialing is known as Touch-Tone, was first used by AT&T in "touch tones" or other tone signaling systems.
A transitional technology (from pulse to DTMF) had DTMF link finders which converted DTMF to pulse, to feed to older Strowger, panel, or crossbar switches. This technology was used as late as mid 2002.
Number plan details
Technologies
This article will use the terms:
- manual service for a condition where a human operator routes calls inside an exchange and a dial is not used
- dial service for an exchange where calls are routed by a switch interpreting dialed digits
- telephone exchange for the building housing the switching equipment
- telephone switch for the switching equipment
- concentrator for a device that concentrates traffic, be it remote or co-located with the switch
- off-hook On an ordinary two-wire telephone line, off-hook status is communicated to the telephone exchange by a resistance short across the pair. When an off-hook condition persists without dialing, for example because the handset has fallen off or the cable has been flooded, it is treated as a permanent loop or permanent signal for a tip condition or to describe a circuit that is in use (i.e., when a phone call is in progress)
- on-hook This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C" for an idle circuit (i.e., no phone call is in progress)
- wire center for the area served by a particular switch or central office
Many of the terms in this article have conflicting UK and US usages.
- central office originally referred to switching equipment and its operators. Now it is used generally for the building housing switching and related inside plant Around the turn of the century, DSLAMs became an important part of telephone company inside plant. Inside plant will also have distribution frames and other equipment including passive optical network equipment.
- telephone exchange means an exchange building in the UK, and is also the UK name for a telephone switch, and also has a legal meaning in U.S. telecoms.
- telephone switch is the U.S. term, but is in increasing use in technical UK telecoms usage, to make the CO/switch/concentrator distinction clear.
Manual service exchanges
1924 PBX switchboardWith manual service, the customer lifts the receiver off-hook On an ordinary two-wire telephone line, off-hook status is communicated to the telephone exchange by a resistance short across the pair. When an off-hook condition persists without dialing, for example because the handset has fallen off or the cable has been flooded, it is treated as a permanent loop or permanent signal and asks the operator With the development of computerized telephone dialing systems, many telephone calls which previously required a live operator can be placed automatically by the calling party without additional human intervention. Before the advent of automatic exchanges, an operator's assistance was required for anything other than calling telephones across a to connect the call to a requested number. Provided that the number is in the same central office, the operator connects the call by plugging into the jack on the switchboard A switchboard was a device used to connect a group of telephones manually to one another or to an outside connection, within and between telephone exchanges or private branch exchanges (PBXs). The user was typically known as an operator. Public manual exchanges disappeared during the last half of the 20th century, leaving a few PBXs working in corresponding to the called customer's line. If the call is to another central office, the operator plugs into the trunk for the other office and asks the operator answering (known as the "inward" operator) to connect the call.
Most urban exchanges were common-battery, meaning that the central office provided power for the telephone circuits, as is the case today. In common-battery systems, the pair of wires from a subscriber's telephone to the switch (or manual exchange) carry -48VDC (nominal) from the telephone company end, across the conductors. The telephone presents an open circuit when it is on-hook This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C" or idle. When the subscriber goes off-hook, the telephone puts a DC resistance short across the line. In manual service, this current flowing through the off-hook telephone flows through a relay coil actuating a buzzer and lamp on the operator's switchboard. The buzzer and lamp would tell an operator the subscriber was off-hook (requesting service).[9]
In the largest U.S. cities, it took many years to convert every office to automatic equipment, such as panel switches The panel switching system was an early type of automatic telephone exchange, first put into urban service by the Bell System in the 1920s and removed during the 1970s. The Panel and Rotary systems were developed in parallel by Bell Labs before World War I , and had many features in common, though the Rotary system was used in Europe. During this transition period, it was possible to dial a manual number and be connected without requesting an operator's assistance. This was because the policy of the Bell System was that customers should not need to know if they were calling a manual or automated office. If a subscriber dialed a manual number, an inward operator would answer the call, see the called number on a display device, and manually connect the call. For instance, if a customer calling from TAylor 4725 dialed a manual number, ADams 1233, the call would go through, from the subscriber's perspective, exactly as a call to LEnnox 5813, in an automated exchange.
In contrast to the common-battery system, smaller towns with manual service often had magneto A magneto is an electrical generator that uses permanent magnets to produce alternating current. Hand-cranked magneto generators were used to provide ringing current in early telephone systems. Magnetos adapted to produce pulses of high voltage are used in the ignition systems of some gasoline-powered internal combustion engines to provide power, or crank, phones. Using a magneto set, the subscriber turned a crank to generate ringing current, to gain the operator's attention. The switchboard would respond by dropping a metal tab above the subscriber's line jack and sounding a buzzer. Dry cell An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta, batteries have become a common power source for many household and industrial applications. According to a 2005 estimate, the worldwide battery industry batteries (normally two large "No 6" cells) in the subscriber's telephone provided the DC power for conversation. Magneto systems were in use in one American small town, Bryant Pond, Woodstock, Maine as late as 1983. In general, this type of system had a poorer call quality compared to common-battery systems.
Many small town magneto systems featured party lines In twentieth century telephone systems, a party line is an arrangement in which two or more customers are connected directly to the same local loop. Prior to World War II in the United States, party lines were the primary way residential subscribers acquired local phone service. British users similarly benefited from the party line discount, anywhere from two to ten or more subscribers sharing a single line. When calling a party, the operator would use a distinctive ringing signal A ringtone or ring tone is the sound made by a telephone to indicate an incoming call or text message. Not literally a tone, the term is most often used today to refer to customizable sounds used on mobile phones sequence, such as two long rings followed by one short. Everyone on the line could hear the rings, and of course could pick up and listen in if they wanted. On rural lines which were not connected to a central office (thus not connected to the outside world), subscribers would crank the correct sequence of rings to reach their party.
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