109-505: Centrex is a portmanteau of centr al ex change, a kind of telephone exchange . It provides functions similar to a PBX , but is provisioned with equipment owned by, and located at, the telephone company premises. Centrex service was first installed in the early 1960s in New York's financial district by New York Telephone. As of 2003, it was estimated that there were 20 million Centrex lines installed worldwide by 20 telephone companies, with
218-540: A CCITT standard. Similar schemes were used in the Americas and in some European countries including Spain. Digit strings between switches were often abbreviated to further improve utilization. For example, one switch might send only the last four or five digits of a telephone number . In one case, seven digit numbers were preceded by a digit 1 or 2 to differentiate between two area codes or office codes, (a two-digit-per-call savings). This improved revenue per trunk and reduced
327-446: A panel switch and a manual switchboard. Probably the most common form of communicating dialed digits between electromechanical switches was sending dial pulses , equivalent to a rotary dial 's pulsing, but sent over trunk circuits between switches. In Bell System trunks, it was common to use 20 pulse-per-second between crossbar switches and crossbar tandems. This was twice the rate of Western Electric/Bell System telephone dials. Using
436-523: A patent caveat at the US Patent Office. His caveat describes his invention, but does not mention a diaphragm, electromagnet, conversion of sound into electrical waves, conversion of electrical waves into sound, or other essential features of an electromagnetic telephone. The first American demonstration of Meucci's invention took place in Staten Island , New York in 1854. In 1861, a description of it
545-476: A 'multiplex' or many-ply telegraph, conveying several messages through the same wire at the same time. Each message can either be read by an operator by the sound, or from different tones read by different operators, or a permanent record can be made by the marks drawn on a ribbon of traveling paper by a Morse recorder. On July 27, 1875, Gray was granted U.S. patent 166,096 for "Electric Telegraph for Transmitting Musical Tones" (the harmonic). On February 14, 1876, at
654-456: A central office (C.O.) is a common carrier switching center Class 5 telephone switch in which trunks and local loops are terminated and switched. In the UK, a telephone exchange means an exchange building, and is also the name for a telephone switch. With manual service , the customer lifts the receiver off-hook and asks the operator to connect the call to a requested number. Provided that
763-590: A chronology of his invention of the telephone and tracing the history of the two legal trials involving Meucci and Alexander Graham Bell. They claim that Meucci was the actual inventor of the telephone, and base their argument on reconstructed evidence. What follows, if not otherwise stated, is a summary of their historic reconstruction. The above information was published in the Scientific American Supplement No. 520 of December 19, 1885, based on reconstructions produced in 1885, for which there
872-484: A circuit connecting a dialed call through an electromechanical switch had DC continuity within the local exchange area via metallic conductors. The design and maintenance procedures of all systems involved methods to avoid that subscribers experienced undue changes in the quality of the service or that they noticed failures. A variety of tools referred to as make-busy s were plugged into electromechanical switch elements upon failure and during repairs. A make-busy identified
981-523: A cornet solo played in Somerville was very distinctly heard. Still later, a three-part song came over the wire from Somerville, and Mr. Bell told his audience "I will switch off the song from one part of the room to another so that all can hear." At a subsequent lecture in Salem, Massachusetts , communication was established with Boston, eighteen miles distant, and Mr. Watson at the latter place sang "Auld Lang Syne",
1090-412: A digit receiver (part of an element called an Originating Register ) would be connected to a call just long enough to collect the subscriber's dialed digits. Crossbar architecture was more flexible than step offices. Later crossbar systems had punch-card-based trouble reporting systems. By the 1970s, automatic number identification had been retrofitted to nearly all step-by-step and crossbar switches in
1199-428: A double electromagnet, in front of which a membrane, stretched on a ring, carried an oblong piece of soft iron cemented to its middle. A funnel-shaped mouthpiece directed the voice sounds upon the membrane, and as it vibrated, the soft iron "armature" induced corresponding currents in the coils of the electromagnet. These currents, after traversing the wire, passed through the receiver which consisted of an electromagnet in
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#17328550610121308-517: A failed switch element. A trouble reporting card system was connected to switch common control elements. These trouble reporting systems punctured cardboard cards with a code that logged the nature of a failure. Electromechanical switching systems required sources of electricity in form of direct current (DC), as well as alternating ring current (AC), which were generated on-site with mechanical generators. In addition, telephone switches required adjustment of many mechanical parts. Unlike modern switches,
1417-427: A harmonic telegraph, following the examples of Bourseul, Reis, and Gray. Bell's designs employed various on-off-on-off make-break current-interrupters driven by vibrating steel reeds which sent interrupted current to a distant receiver electro-magnet that caused a second steel reed or tuning fork to vibrate. During a June 2, 1875, experiment by Bell and his assistant Thomas Watson , a receiver reed failed to respond to
1526-404: A horizontal panel containing two rows of patch cords, each pair connected to a cord circuit . When a calling party lifted the receiver, the local loop current lit a signal lamp near the jack. The operator responded by inserting the rear cord ( answering cord ) into the subscriber's jack and switched their headset into the circuit to ask, "Number, please?" For a local call, the operator inserted
1635-411: A hundred pair cable between switches, for example. Conductors in one common circuit configuration were named tip, ring, ear (E) and mouth (M). Tip and ring were the voice-carrying pair, and named after the tip and ring on the three conductor cords on the manual operator's console. In two-way trunks with E and M signaling , a handshake took place to prevent both switches from colliding by dialing calls on
1744-764: A junction point on the telegraph line to the neighbouring community of Mount Pleasant, which joined it to the Dominion Telegraph office in Brantford, Ontario. The third and most important test was the world's first true long-distance telephone call, placed between Brantford and Paris, Ontario on August 10, 1876. For that long-distance call Alexander Graham Bell set up a telephone using telegraph lines at Robert White's Boot and Shoe Store at 90 Grand River Street North in Paris via its Dominion Telegraph Co. office on Colborne Street. The normal telegraph line between Paris and Brantford
1853-485: A lamp on the operator's switchboard, signaling the operator to perform service. In the largest cities, it took many years to convert every office to automatic equipment, such as a panel switch . During this transition period, once numbers were standardized to the 2L-4N or 2L-5N format (two-letter exchange name and either four or five digits), it was possible to dial a number located in a manual exchange and be connected without requesting operator assistance. The policy of
1962-413: A large dinner party exchanged "....speech, recitations, songs and instrumental music". To bring telephone signals to Melville House, Alexander Graham audaciously "bought up" and "cleaned up" the complete supply of stovepipe wire in Brantford. With the help of two of his parents' neighbours, he tacked the stovepipe wire some 400 metres (a quarter mile) along the top of fence posts from his parents' home to
2071-399: A manual office, having listings such as Hillside 834 or East 23, was recognizable by the format in which the second letter was not capitalized. Rural areas, as well as the smallest towns, had manual service and signaling was accomplished with magneto telephones, which had a crank for the signaling generator. To alert the operator, or another subscriber on the same line, the subscriber turned
2180-407: A private telephone exchange is termed a private branch exchange (PBX), which connects to the public switched telephone network. A PBX serves an organization's telephones and any private leased line circuits, typically situated in large office spaces or organizational campuses. Smaller setups might use a PBX or key telephone system managed by a receptionist, catering to the telecommunication needs of
2289-403: A receiver consisting of a stretched diaphragm or drum of goldbeater's skin with an armature of magnetized iron attached to its middle, and free to vibrate in front of the pole of an electromagnet in circuit with the line. A second membrane-device was built for use as a transmitter. This was the "gallows" phone. A few days later they were tried together, one at each end of the line, which ran from
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#17328550610122398-455: A room in the inventor's house, located at 5 Exeter Place in Boston, to the cellar underneath. Bell, in the work room, held one instrument in his hands, while Watson in the cellar listened at the other. Bell spoke into his instrument, "Do you understand what I say?" and Watson answered "Yes". However, the voice sounds were not distinct and the armature tended to stick to the electromagnet pole and tear
2507-436: A single line. When calling a party, the operator used code ringing, a distinctive ringing signal sequence, such as two long rings followed by one short ring. Everyone on the line could hear the signals, and could pick up and monitor other people's conversations. Automatic exchanges , which provided dial service , were invented by Almon Strowger in 1888. First used commercially in 1892, they did not gain widespread use until
2616-464: A system called visible speech, developed by his father, to teach deaf children. In 1872 Bell founded a school in Boston , Massachusetts , to train teachers of the deaf. The school subsequently became part of Boston University, where Bell was appointed professor of vocal physiology in 1873. As Professor of Vocal Physiology at Boston University , Bell was engaged in training teachers in the art of instructing
2725-422: A telephone was Phillip Reis of Germany only musical not articulating. The first person to publicly exhibit a telephone for transmission of articulate speech was A. G. Bell. The first practical commercial telephone for transmission of articulate speech was invented by myself. Telephones used throughout the world are mine and Bell's. Mine is used for transmitting. Bell's is used for receiving. Cyrille Duquet invents
2834-513: A telephone with a dial tone . Telecommunication carriers also define rate centers for business and billing purposes, which in large cities, might encompass clusters of central offices to specify geographic locations for distance measurement calculations. In the 1940s, the Bell System in the United States and Canada introduced a nationwide numbering system that identified central offices with
2943-412: A thin disc of iron was fixed in a circular mouthpiece. The disc served as a combined diaphragm and armature. On speaking into the mouthpiece, the iron diaphragm vibrated with the voice in the magnetic field of the bar-magnet pole, and thereby caused undulatory currents in the coil. These currents, after traveling through the wire to the distant receiver, were received in an identical apparatus. This design
3052-463: A trunk as idle. Trunk circuitry hearing a 2,600 Hz tone for a certain duration would go idle. (The duration requirement reduced falsing .) Some systems used tone frequencies over 3,000 Hz, particularly on SSB frequency-division multiplex microwave radio relays . On T-carrier binary digital transmission systems, bits within the T-1 data stream were used to transmit supervision. By careful design,
3161-442: A tubular metal can having one end partially closed by a thin circular disc of soft iron. When the undulatory current passed through the coil of this electromagnet, the disc vibrated, thereby creating sound waves in the air. This primitive telephone was rapidly improved. The double electromagnet was replaced by a single permanently magnetized bar magnet having a small coil or bobbin of fine wire surrounding one pole, in front of which
3270-476: A unique three-digit code, along with a three-digit numbering plan area code (NPA code or area code), making central office codes distinctive within each numbering plan area. These codes served as prefixes in subscriber telephone numbers. The mid-20th century saw similar organizational efforts in telephone networks globally, propelled by the advent of international and transoceanic telephone trunks and direct customer dialing. For corporate or enterprise applications,
3379-677: A variant of a string telephone that used wire. Meucci has been further credited with the invention of an anti- sidetone circuit. However, examination showed that his solution to sidetone was to maintain two separate telephone circuits and thus use twice as many transmission wires. The anti-sidetone circuit later introduced by Bell Telephone instead canceled sidetone through a feedback process. An American District Telegraph (ADT) laboratory reportedly lost some of Meucci's working models, his wife reportedly disposed of others and Meucci, who sometimes lived on public assistance, chose not to renew his 1871 teletrofono patent caveat after 1874. A resolution
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3488-504: A wide range of advanced services. Local versions were called ARE11 while tandem versions were known as ARE13. They were used in Scandinavia, Australia, Ireland and many other countries in the late 1970s and into the 1980s when they were replaced with digital technology. Invention of the telephone The invention of the telephone was the culmination of work done by more than one individual, and led to an array of lawsuits relating to
3597-402: A year later. In 1887 Puskás introduced the multiplex switchboard . . Later exchanges consisted of one to several hundred plug boards staffed by switchboard operators . Each operator sat in front of a vertical panel containing banks of ¼-inch tip-ring-sleeve (3-conductor) jacks, each of which was the local termination of a subscriber 's telephone line . In front of the jack panel lay
3706-462: The Bell System stated that customers in large cities should not need to be concerned with the type of office, whether they were calling a manual or an automatic office. When a subscriber dialed the number of a manual station, an operator at the destination office answered the call after seeing the number on an indicator , and connected the call by plugging a cord into the outgoing circuit and ringing
3815-658: The Bell Telephone Company in Boston in 1877. The world's first state-administered telephone exchange opened on November 12, 1877 in Friedrichsberg close to Berlin under the direction of Heinrich von Stephan . George W. Coy designed and built the first commercial US telephone exchange which opened in New Haven, Connecticut in January, 1878, and the first telephone booth was built in nearby Bridgeport . The switchboard
3924-462: The Western Electric 1ESS switch , Northern Telecom SP1 , Ericsson AXE, Automatic Electric EAX-1 & EAX-2, Philips PRX /A, ITT Metaconta, British GPO/BT TXE series and several other designs were similar. Ericsson also developed a fully computerized version of their ARF crossbar exchange called ARE. These used a crossbar switching matrix with a fully computerized control system and provided
4033-546: The crossbar switch . Circuits interconnecting switches are called trunks . Before Signalling System 7 , Bell System electromechanical switches in the United States originally communicated with one another over trunks using a variety of DC voltages and signaling tones. Today, those simple digital signals have been replaced by more modern coded digital signals (typically using binary code). Some signaling communicated dialed digits. An early form called Panel Call Indicator Pulsing used quaternary pulses to set up calls between
4142-421: The patent claims of several individuals and numerous companies. Notable people included in this were Antonio Meucci , Philipp Reis , Elisha Gray and Alexander Graham Bell . The concept of the telephone dates back to the string telephone or lover's telephone that has been known for centuries, comprising two diaphragms connected by a taut string or wire. Sound waves are carried as mechanical vibrations along
4251-415: The telephone when the user removes the handset from the switchhook or cradle. The exchange provides dial tone at that time to indicate to the user that the exchange is ready to receive dialed digits. The pulses or DTMF tones generated by the telephone are processed and a connection is established to the destination telephone within the same exchange or to another distant exchange. The exchange maintains
4360-923: The 1st Baron Kelvin). In August 1876 at a meeting of the British Association for the Advancement of Science , Thomson revealed the telephone to the European public. In describing his visit to the Philadelphia Exhibition, Thomson said, "I heard [through the telephone] passages taken at random from the New York newspapers: 'S.S. Cox Has Arrived' (I failed to make out the S.S. Cox); 'The City of New York', 'Senator Morton', 'The Senate Has Resolved To Print A Thousand Extra Copies', 'The Americans In London Have Resolved To Celebrate The Coming Fourth Of July!' All this my own ears heard spoken to me with unmistakable distinctness by
4469-443: The A. Wallis Ellis store in the neighboring community of Mount Pleasant , received and may possibly have transferred his uncle's voice onto a phonautogram , a drawing made on a pen-like recording device that could produce the shapes of sound waves as waveforms onto smoked glass or other media by tracing their vibrations. The next day on August 4 another call was made between Brantford's telegraph office and Melville House, where
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4578-409: The Bell System required continuous maintenance, such as cleaning. Indicator lights on equipment bays alerted staff to conditions such as blown fuses (usually white lamps) or a permanent signal (stuck off-hook condition, usually green indicators). Step offices were more susceptible to single-point failures than newer technologies. Crossbar offices used more shared, common control circuits. For example,
4687-414: The Bell System. Electronic switching systems gradually evolved in stages from electromechanical hybrids with stored program control to the fully digital systems. Early systems used reed relay -switched metallic paths under digital control. Equipment testing, phone numbers reassignments, circuit lockouts and similar tasks were accomplished by data entry on a terminal. Examples of these systems included
4796-560: The National Anthem, and "Hail Columbia", while the audience at Salem joined in the chorus. On January 14, 1878, at Osborne House , on the Isle of Wight , Bell demonstrated the device to Queen Victoria , placing calls to Cowes, Southampton and London. These were the first publicly witnessed long-distance telephone calls in the UK . The queen considered the process to be "quite extraordinary" although
4905-463: The Reis equipment and found that "single words, uttered as in reading, speaking and the like, were perceptible indistinctly, notwithstanding here also the inflections of the voice, the modulations of interrogation, wonder, command, etc., attained distinct expression." He used Reis's work for the successful development of the carbon microphone . Edison acknowledged his debt to Reis thus: The first inventor of
5014-469: The Strowger's typical 10 pps—typically about 20 pps. At a later date many also accepted DTMF "touch tones" or other tone signaling systems. A transitional technology (from pulse to DTMF) had converters to convert DTMF to pulse, to feed to older Strowger, panel, or crossbar switches. This technology was used as late as mid-2002. Many terms used in telecommunication technology differ in meaning and usage among
5123-674: The US Patent Office, Gray's lawyer filed a patent caveat for a telephone on the very same day that Bell's lawyer filed Bell's patent application for a telephone. The water transmitter described in Gray's caveat was strikingly similar to the experimental telephone transmitter tested by Bell on March 10, 1876, a fact which raised questions about whether Bell (who knew of Gray) was inspired by Gray's design or vice versa. Although Bell did not use Gray's water transmitter in later telephones, evidence suggests that Bell's lawyers may have obtained an unfair advantage over Gray. Alexander Graham Bell had pioneered
5232-489: The affirmative, and soon was heard a voice singing "America". [...] Going to another instrument, connected by wire with Providence, forty-three miles distant, Mr. Bell listened a moment, and said, "Signor Brignolli, who is assisting at a concert in Providence Music Hall, will now sing for us." In a moment the cadence of the tenor's voice rose and fell, the sound being faint, sometimes lost, and then again audible. Later,
5341-471: The appropriated bits did not change voice quality appreciably. Robbed bits were translated to changes in contact states (opens and closures) by electronics in the channel bank hardware. This allowed direct current E and M signaling, or dial pulses, to be sent between electromechanical switches over a pure digital carrier which did not have DC continuity. Bell System installations typically had alarm bells, gongs, or chimes to announce alarms calling attention to
5450-407: 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 , 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
5559-468: 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 , an undertaker in Kansas City, Missouri , patented the stepping switch , a device which led to
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#17328550610125668-437: The circuit, allowing them to handle another call, while the caller heard an audible ringback signal, so that that operator would not have to periodically report that they were continuing to ring the line. In the ringdown method, the originating operator called another intermediate operator who would call the called subscriber, or passed it on to another intermediate operator. This chain of intermediate operators could complete
5777-471: The complex timbre, amplitude, and frequencies of speech at a distance. After Bell and Watson discovered on June 2, 1875, that movements of the reed alone in a magnetic field could reproduce the frequencies and timbre of spoken sound waves, Bell reasoned by analogy with the mechanical phonautograph that a skin diaphragm would reproduce sounds like the human ear when connected to a steel or iron reed or hinged armature. On July 1, 1875, he instructed Watson to build
5886-419: The connection until one of the parties hangs up. This monitoring of connection status is called supervision. Additional features, such as billing equipment, may also be incorporated into the exchange. The Bell System dial service implemented a feature called automatic number identification (ANI) which facilitated services like automated billing, toll-free 800-numbers , and 9-1-1 service. In manual service,
5995-578: The crank to generate ringing current. The switchboard responded by interrupting the circuit, which dropped a metal tab above the subscriber's line jack and sounded a buzzer. Dry cell batteries, normally two large N°. 6 cells in the subscriber's telephone, provided the direct current for the transmitter. Such magneto systems were in use in the US as late as 1983, as in the small town, Bryant Pond, Woodstock, Maine . Many small town magneto systems featured party lines , anywhere from two to ten or more subscribers sharing
6104-506: The current, which at the other end of the line passed through electromagnets and vibrated matching tuned steel reeds near the electromagnet poles. Gray's "harmonic telegraph", with vibrating reeds, was used by the Western Union Telegraph Company. Since more than one set of vibration frequencies – that is to say, more than one musical tone – can be sent over the same wire simultaneously, the harmonic telegraph can be utilized as
6213-574: The deaf how to speak and experimented with the Leon Scott phonautograph in recording the vibrations of speech. This apparatus consists essentially of a thin membrane vibrated by the voice and carrying a light-weight stylus, which traces an undulatory line on a plate of smoked glass . The line is a graphic representation of the vibrations of the membrane and the waves of sound in the air. This background prepared Bell for work with spoken sound waves and electricity. He began his experiments in 1873–1874 with
6322-468: The destination station. For example, if a dial customer calling from TAylor 4725 dialed a number served by a manual exchange, e.g., ADams 1383-W, the call was completed, from the subscriber's perspective, exactly as a call to LEnnox 5813, in an automated exchange. The party line letters W, R, J, and M were only used in manual exchanges with jack-per-line party lines. In contrast to the listing format MAin 1234 for an automated office with two capital letters,
6431-473: The enterprise. In the era of the electrical telegraph, its principal users were post offices, railway stations, the more important governmental centers (ministries), stock exchanges, very few nationally distributed newspapers, the largest internationally important corporations, and wealthy individuals. Despite the fact that telephone devices existed before the invention of the telephone exchange, their success and economical operation would have been impossible on
6540-616: The equipment has already been paid for, though leasing Centrex lines may be more expensive. Telephone exchange 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. The terminology used in telecommunications has evolved over time, with telephone exchange and central office often used interchangeably,
6649-486: The faster pulsing rate made trunk utilization more efficient because the switch spent half as long listening to digits. DTMF was not used for trunk signaling. Multi-frequency (MF) was the last of the pre-computerized methods. It used a different set of tones sent in pairs like DTMF. Dialing was preceded by a special keypulse (KP) signal and followed by a start (ST). Variations of the Bell System MF tone scheme became
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#17328550610126758-492: The field of aviation. Bell himself claimed that the telephone was invented in Canada but made in the United States. The first successful bi-directional transmission of clear speech by Bell and Watson was made on March 10, 1876, when Bell spoke into the device, "Mr. Watson, come here, I want to see you." and Watson complied with the request. Bell tested Gray's liquid transmitter design in this experiment, but only after Bell's patent
6867-435: The first decade of the 20th century. They eliminated the need for human switchboard operators who completed the connections required for a telephone call . Automation replaced human operators with electromechanical systems, and telephones were equipped with a dial by which a caller transmitted the destination telephone number to the automatic switching system. A telephone exchange automatically senses an off-hook condition of
6976-503: The first design of a "make-and-break" telephone in 1854. That is about the same time that Meucci later claimed to have created his first attempt at the telephone in Italy. Bourseul explained: "Suppose that a man speaks near a movable disc sufficiently flexible to lose none of the vibrations of the voice; that this disc alternately makes and breaks the currents from a battery: you may have at a distance another disc which will simultaneously execute
7085-424: 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 were arranged in banks, the first stage of which was a linefinder . If one of up to a hundred subscriber lines (two hundred lines in later linefinders) had the receiver lifted "off hook", a linefinder connected the subscriber's line to a free first selector, which returned
7194-399: The front cord of the pair ( ringing cord ) into the called party's local jack and started the ringing cycle. For a long-distance call, the operator plugged into a trunk circuit to connect to another operator in another bank of boards or at a remote central office. In 1918, the average time to complete the connection for a long-distance call was 15 minutes. Early manual switchboards required
7303-652: The future impact of these communication firsts". A later telephone design was publicly exhibited on May 4, 1877, at a lecture given by Professor Bell in the Boston Music Hall . According to a report quoted by John Munro in Heroes of the Telegraph : Going to the small telephone box with its slender wire attachments, Mr. Bell coolly asked, as though addressing someone in an adjoining room, "Mr. Watson, are you ready!" Mr. Watson, five miles away in Somerville, promptly answered in
7412-503: The handset. Duquet obtained a patent on 1 Feb. 1878 for a number of modifications "giving more facility for the transmission of sound and adding to its acoustic properties," and in particular for the design of a new apparatus combining the speaker and receiver in a single unit. Elisha Gray , of Highland Park, Illinois , also devised a tone telegraph of this kind about the same time as La Cour. In Gray's tone telegraph, several vibrating steel reeds tuned to different frequencies interrupted
7521-404: The impetus for the creation of a new industrial sector. As with the invention of the telephone itself, the honour of "first telephone exchange" has several claimants. One of the first to propose a telephone exchange was Hungarian Tivadar Puskás in 1877 while he was working for Thomas Edison . The first experimental telephone exchange was based on the ideas of Puskás, and it was built by
7630-500: The intermittent current supplied by an electric battery. Bell told Watson, who was at the other end of the line, to pluck the reed, thinking it had stuck to the pole of the magnet. Watson complied, and to his astonishment Bell heard a reed at his end of the line vibrate and emit the same timbre of a plucked reed, although there were no interrupted on-off-on-off currents from a transmitter to make it vibrate. A few more experiments soon showed that his receiver reed had been set in vibration by
7739-598: The inventor of the telephone. Others in Canada disagreed with the Congressional resolution, some of whom provided criticisms of both its accuracy and intent. A retired director general of the Telecom Italia central telecommunications research institute ( CSELT ), Basilio Catania, and the Italian Society of Electrotechnics, " Federazione Italiana di Elettrotecnica ", have devoted a Museum to Antonio Meucci, constructing
7848-408: The latter term originating from the Bell System . A central office typically refers to a facility that houses the inside plant equipment for one or several telephone exchanges, each catering to a specific geographical region. This region is sometimes known as the exchange area. In North America, the term wire center may be used to denote a central office location, indicating a facility that provides
7957-505: The magneto-electric currents induced in the line by the motion of the distant receiver reed in the neighborhood of its magnet. The battery current was not causing the vibration but was needed only to supply the magnetic field in which the reeds vibrated. Moreover, when Bell heard the rich overtones of the plucked reed, it occurred to him that since the circuit was never broken, all the complex vibrations of speech might be converted into undulating (modulated) currents, which in turn would reproduce
8066-602: The membrane. On 10 March 1876, in a test, between two rooms in a single building, above Palace Theatre , at 109 Court Street , not far from Scollay Square in Boston showed that the telephone worked, but so far, only at a short range. In 1876, Bell became the first to obtain a patent for an "apparatus for transmitting vocal or other sounds telegraphically", after experimenting with many primitive sound transmitters and receivers. Because of illness and other commitments, Bell made little or no telephone improvements or experiments for eight months until after his U.S. patent 174,465
8175-605: The most installations in the United States (15 million), Canada (2 million), and the United Kingdom (1 million). This accounted for approximately 5% of all installed business telephone lines, worldwide. In terms of user-visible features, Centrex and PBX are similar. Features include: In the United States, the usage of Centrex lines has fallen from 16.5 million in 2002 to 10.7 million in 2008 as users transition to IP-PBX (through VoIP). Centrex continues to be used by large institutions, government agencies, and universities as most of
8284-399: The number is in the same central office, and located on the operator's switchboard, the operator connects the call by plugging the ringing cord into the jack corresponding to the called customer's line. If the called party's line is on a different switchboard in the same office, or in a different central office, the operator plugs into the trunk for the destination switchboard or office and asks
8393-476: The number of digit receivers needed in a switch. Every task in electromechanical switches was done in big metallic pieces of hardware. Every fractional second cut off of call set up time meant fewer racks of equipment to handle call traffic. Examples of signals communicating supervision or call progress include E and M signaling , SF signaling, and robbed-bit signaling. In physical (not carrier) E and M trunk circuits, trunks were four wire. Fifty trunks would require
8502-432: The operator answering (known as the "B" operator) to connect the call. Most urban exchanges provided common-battery service, meaning that the central office provided power to the subscriber telephone circuits for operation of the transmitter, as well as for automatic signaling with rotary dials . In common-battery systems, the pair of wires from a subscriber's telephone to the exchange carry 48V (nominal) DC potential from
8611-538: The operator knows where a call is originating by the light on the switchboard jack field. Before ANI, long-distance calls were placed into an operator queue and the operator asked the calling party's number and recorded it on a paper toll ticket. Early exchanges were electromechanical systems using motors, shaft drives, rotating switches and relays . Some types of automatic exchanges were the Strowger switch or step-by-step switch, All Relay, panel switch , Rotary system and
8720-408: The operator to operate listening keys and ringing keys, but by the late 1910s and 1920s, advances in switchboard technology led to features which allowed the call to be automatically answered immediately as the operator inserted the answering cord, and ringing would automatically begin as soon as the operator inserted the ringing cord into the called party's jack. The operator would be disconnected from
8829-427: The part being worked on as in-use, causing the switching logic to route around it. A similar tool was called a TD tool. Delinquent subscribers had their service temporarily denied (TDed). This was effected by plugging a tool into the subscriber's office equipment on Crossbar systems or line group in step-by-step switches. The subscriber could receive calls but could not dial out. Strowger-based, step-by-step offices in
8938-420: The poles of a horseshoe magnet. He observed that connecting and disconnecting the current caused a ringing sound in the magnet. He called this effect "galvanic music". Innocenzo Manzetti considered the idea of a telephone as early as 1844, and may have made one in 1864, as an enhancement to an automaton built by him in 1849. Charles Bourseul was a French telegraph engineer who proposed (but did not build)
9047-679: The same schema and structure of the contemporary telegraph, as prior to the invention of the telephone exchange switchboard, early telephones were hardwired to and communicated with only a single other telephone (such as from an individual's home to the person's business ). A telephone exchange is a telephone system for a small geographic area that provides the switching (interconnection) of subscriber lines for calls made between them. Telephone exchanges replaced small telephone systems that connected its users with direct lines between each and every subscriber station. Exchanges made telephony an available and comfortable technology for everyday use and it gave
9156-414: The same trunk at the same time. By changing the state of these leads from ground to −48 volts, the switches stepped through a handshake protocol. Using DC voltage changes, the local switch would send a signal to get ready for a call and the remote switch would reply with an acknowledgment (a wink) to go ahead with dial pulsing. This was done with relay logic and discrete electronics. These voltage changes on
9265-440: The same vibrations.... It is certain that, in a more or less distant future, a speech will be transmitted by electricity. I have made experiments in this direction; they are delicate and demand time and patience, but the approximations obtained promise a favorable result". An early communicating device was invented around 1854 by Antonio Meucci , who called it a telettrofono ( lit. "electrophone") . In 1871 Meucci filed
9374-714: The sound was "quite faint". She later asked to buy the equipment that was used, but Bell offered to make a model specifically for her. Bell did for the telephone what Henry Ford did for the automobile. Although not the first to experiment with telephonic devices, Bell and the companies founded in his name were the first to develop commercially practical telephones around which a successful business could be built and grow. Bell adopted carbon transmitters similar to Edison's transmitters and adapted telephone exchanges and switching plug boards developed for telegraphy. Watson and other Bell engineers invented numerous other improvements to telephony. Bell succeeded where others failed to assemble
9483-511: The string or wire from one diaphragm to the other. The classic example is the tin can telephone , a children's toy made by connecting the two ends of a string to the bottoms of two metal cans, paper cups or similar items. The essential idea of this toy was that a diaphragm can collect voice sounds for reproduction at a distance. One precursor to the development of the electromagnetic telephone originated in 1833 when Carl Friedrich Gauss and Wilhelm Eduard Weber invented an electromagnetic device for
9592-457: The subscriber a dial tone to show that it was ready to receive dialled 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 and later by crossbar technology. These exchange designs promised faster switching and would accept inter-switch pulses faster than
9701-400: The telephone company end across the conductors. The telephone presents an open circuit when it is on-hook or idle. When a subscriber's phone is off-hook, it presents an electrical resistance across the line which causes current to flow through the telephone and wires to the central office. In a manually operated switchboard, this current flowed through a relay coil, and actuated a buzzer or
9810-568: The then circular disc armature of just such another little electro-magnet as this I hold in my hand." Only a few months after receiving U.S. Patent No. 174465 at the beginning of March 1876, Bell conducted three important tests of his new invention and the telephone technology after returning to his parents' home at Melville House (now the Bell Homestead National Historic Site ) for the summer. On March 10, 1876, Bell had used "the instrument" in Boston to call Thomas Watson who
9919-517: The transmission of telegraphic signals at the University of Göttingen , in Lower Saxony, helping to create the fundamental basis for the technology that was later used in similar telecommunication devices. Gauss's and Weber's invention is purported to be the world's first electromagnetic telegraph. In 1840, American Charles Grafton Page passed an electric current through a coil of wire placed between
10028-610: The transmitter was difficult to operate, since the relative position of the needle and the contact were critical to the device's operation. Thus, it can be called a "telephone", since it did transmit voice sounds electrically over distance, but was hardly a commercially practical telephone in the modern sense. In 1874, the Reis device was tested by the British company Standard Telephones and Cables (STC). The results also confirmed it could transmit and receive speech with good quality (fidelity), but relatively low intensity. Reis' new invention
10137-434: The trunk circuit would cause pops or clicks that were audible to the subscriber as the electrical handshaking stepped through its protocol. Another handshake, to start timing for billing purposes, caused a second set of clunks when the called party answered. A second common form of signaling for supervision was called single-frequency or SF signaling . The most common form of this used a steady 2,600 Hz tone to identify
10246-451: The various English speaking regions. For the purpose of this article the following definitions are made: A central office originally was a primary exchange in a city with other exchanges service parts of the area. The term became to mean any switching system including its facilities and operators. It is also used generally for the building that houses switching and related inside plant equipment. In United States telecommunication jargon,
10355-519: Was articulated in a lecture before the Physical Society of Frankfurt on 26 October 1861, and a description, written by himself for Jahresbericht a month or two later. It created a good deal of scientific excitement in Germany; models of it were sent abroad, to London, Dublin, Tiflis, and other places. It became a subject for popular lectures, and an article for scientific cabinets. Thomas Edison tested
10464-477: Was at the offices of the Walworth Manufacturing Company. Scientific American described the three test calls in their September 9, 1876, article, "The Human Voice Transmitted by Telegraph". Historian Thomas Costain referred to the calls as "the three great tests of the telephone". One Bell Homestead reviewer wrote of them, "No one involved in these early calls could possibly have understood
10573-631: Was awarded the French Volta Prize for his invention and with the money, founded the Volta Laboratory in Washington, where he continued experiments in communication, in medical research, and in techniques for teaching speech to the deaf, working with Helen Keller among others. In 1885 he acquired land in Nova Scotia and established a summer home there where he continued experiments, particularly in
10682-580: Was built from "carriage bolts, handles from teapot lids and bustle wire" and could handle two simultaneous conversations. Charles Glidden is also credited with establishing an exchange in Lowell, MA. with 50 subscribers in 1878. In Europe other early telephone exchanges were based in London and Manchester , both of which opened under Bell patents in 1879. Belgium had its first International Bell exchange (in Antwerp )
10791-570: Was claimed by many sources as the world's first long-distance call. The final test certainly proved that the telephone could work over long distances. Bell exhibited a working telephone at the Centennial Exhibition in Philadelphia in June 1876, where it attracted the attention of Brazilian emperor Pedro II plus the physicist and engineer Sir William Thomson (who would later be ennobled as
10900-477: Was granted and only as a proof of concept scientific experiment to prove to his own satisfaction that intelligible "articulate speech" (Bell's words) could be electrically transmitted. Because a liquid transmitter was not practical for commercial products, Bell focused on improving the electromagnetic telephone after March 1876 and never used Gray's liquid transmitter in public demonstrations or commercial use. Bell's telephone transmitter (microphone) consisted of
11009-729: Was ill at the time. Some of Meucci's notes purportedly written in 1857 describe the basic principle of electromagnetic voice transmission — or in other words, the telephone. In the 1880s Meucci was credited with the early invention of inductive loading of telephone wires to increase long-distance signals. Serious burns from an accident, a lack of English, and poor business abilities resulted in Meucci's failing to develop his inventions commercially in America. Meucci demonstrated some sort of instrument in 1849 in Havana, Cuba , however, this may have been
11118-495: Was in another room but out of earshot. He said, "Mr. Watson, come here – I want to see you" and Watson soon appeared at his side. In the first test call at a longer distance in Southern Ontario, on August 3, 1876, Alexander Graham's uncle, Professor David Charles Bell, spoke to him from the Brantford telegraph office, reciting lines from Shakespeare 's Hamlet (" To be or not to be.... "). The young inventor, positioned at
11227-413: Was no contemporary pre-1875 evidence. Meucci's 1871 caveat did not mention any of the telephone features later credited to him by his lawyer, and which were published in that Scientific American Supplement, a major reason for the loss of the 'Bell v. Globe and Meucci' patent infringement court case, which was decided against Globe and Meucci. The Reis telephone was developed from 1857 onwards. Allegedly,
11336-431: Was not quite 13 km (8 miles) long, but the connection was extended a further 93 km (58 miles) to Toronto to allow the use of a battery in its telegraph office . Granted, this was a one-way long-distance call. The first two-way (reciprocal) conversation over a line occurred between Cambridge and Boston (roughly 2.5 miles) on October 9, 1876. During that conversation, Bell was on Kilby Street in Boston and Watson
11445-570: Was passed by the United States House of Representatives in 2002 that said Meucci did pioneering work on the development of the telephone. The resolution said that "if Meucci had been able to pay the $ 10 fee to maintain the caveat after 1874, no patent could have been issued to Bell". The Meucci resolution by the US Congress was promptly followed by a Canada legislative motion by Canada's 37th Parliament , declaring Alexander Graham Bell as
11554-500: Was patented by Bell on January 30, 1877. The sounds were weak and could only be heard when the ear was close to the earphone/mouthpiece, but they were distinct. In the third of his tests in Southern Ontario, on August 10, 1876, Bell made a call via the telegraph line from the family homestead in Brantford, Ontario , to his assistant located in Paris, Ontario , some 13 kilometers away. This test
11663-523: Was published., but within a year the first telephone exchange was built in Connecticut and the Bell Telephone Company was created in 1877, with Bell the owner of a third of the shares, quickly making him a wealthy man. Organ builder Ernest Skinner reported in his autobiography that Bell offered Boston-area organ builder Hutchings a 50% interest in the company but Hutchings declined. In 1880, Bell
11772-427: Was reportedly published in an Italian-language New York newspaper, although no known copy of that newspaper issue or article has survived to the present day. Meucci claimed to have invented a paired electromagnetic transmitter and receiver, where the motion of a diaphragm modulated a signal in a coil by moving an electromagnet, although this was not mentioned in his 1871 U.S. patent caveat . A further discrepancy observed
11881-440: Was that the device described in the 1871 caveat employed only a single conduction wire, with the telephone's transmitter-receivers being insulated from a 'ground return' path. Meucci studied the principles of electromagnetic voice transmission for many years and was able to realise his dream of transmitting his voice through wires in 1856. He installed a telephone-like device within his house in order to communicate with his wife who
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