"Phone" redirects here. For other uses see Telephone (disambiguation) and Phone (disambiguation). Telephone An Olivetti rotary dial telephone c.1940s

The telephone (from the Greek: tle "far" and phn "voice") often colloquially referred to as a phone is a telecommunications device that transmits and receives sound most commonly the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other. It is one of the most common appliances in the developed world and has long been considered indispensable to businesses households and governments. The word "telephone" has been adapted to many languages and is widely recognized around the world.

All telephones have a microphone to speak into an earphone which reproduces the voice of the other person a ringer which makes a sound to alert the owner when a call is coming in and a keypad (or in older phones a telephone dial or no manual device) to enter the telephone number of the telephone being called. The microphone and earphone are usually built into a handset which is held up to the face to talk. The keypad may be part of the handset or of a base unit to which the handset would be connected. A landline telephone is connected by a pair of wires to the telephone network while a mobile phone or cell phone is portable and communicates with the telephone network by radio. A cordless telephone has a portable handset which communicates by radio with a base station connected by wire to the telephone network and can only be used within a limited range of the base station.

The microphone converts the sound waves to electrical signals which are sent through the telephone network to the other phone where they are converted back to sound waves by the earphone in the other phone's handset. Telephones are a duplex communications medium meaning they allow the people on both ends to talk simultaneously. The telephone network consisting of a worldwide net of telephone lines fiberoptic cables microwave transmission cellular networks communications satellites and undersea telephone cables connected by switching centers allows any telephone in the world to communicate with any other. Each telephone line has an identifying number called its telephone number. To initiate a telephone call a conversation with another telephone the user enters the other telephone's number into a numeric keypad on his/her phone. Graphic symbols used to designate telephone service or phone-related information in print signage and other media include (U+2121) (U+260E) (U+260F) and (U+2706).

Although originally designed for voice communication the system has been adapted for data communication such as Telex Fax and dial-up Internet communication. Contents 1 History 2 Basic principles 3 Details of operation 3.1 Early development 3.2 Early commercial instruments 4 Digital telephony 5 IP telephony 6 Usage 7 Telephone operating companies 8 Patents 9 See also 10 Notes 11 References 12 Further reading 13 External links History Main articles: History of the telephone and Timeline of the telephone Further information: Invention of the telephone Elisha Gray and Alexander Bell telephone controversy and Canadian Parliamentary Motion on Alexander Graham Bell Alexander Graham Bell's telephone patent1 drawing 7 March 1876.

Credit for the invention of the electric telephone is frequently disputed and new controversies over the issue have arisen from time to time. As with other influential inventions such as radio television the light bulb and the computer there were several inventors who did pioneering experimental work on voice transmission over a wire and improved on each other's ideas. Innocenzo Manzetti Antonio Meucci Johann Philipp Reis Elisha Gray Alexander Graham Bell and Thomas Edison among others have all been credited with pioneering work on the telephone. An undisputed fact is that Alexander Graham Bell was the first to be awarded a patent for the electric telephone by the United States Patent and Trademark Office (USPTO) in March 1876.2 That first patent by Bell was the master patent of the telephone from which all other patents for electric telephone devices and features flowed.

The early history of the telephone became and still remains a confusing morass of claims and counterclaims which were not clarified by the large number of lawsuits that hoped to resolve the patent claims of many individuals and commercial competitors. The Bell and Edison patents however were forensically victorious and commercially decisive.

A Hungarian engineer Tivadar Pusks quickly invented the telephone switchboard in 1876 which allowed for the formation of telephone exchanges and eventually networks. 3 Basic principles Figure 1: Schematic of a landline telephone installation.

A traditional landline telephone system also known as "plain old telephone service" (POTS) commonly handles both control and audio signals on the same twisted pair (C) of insulated wires: the telephone line. The signaling equipment (see figure 1) consists of a bell beeper light or other device (A7) to alert the user to incoming calls and number buttons or a rotary dial (A4) to enter a telephone number for outgoing calls. Most of the expense of wire-lines are the wires so having both received and sent voices on one pair of wires reduces the expense of wire-line service. Also a twisted pair line rejects electromagnetic interference (EMI) and crosstalk better than a single wire or an untwisted pair. The strong microphone voice signal does not overpower the weaker incoming speaker signal with a sidetone because a hybrid coil (A3) subtracts the microphone's signal from the signal sent to the local speaker. The junction box (B) arrests lightning (B2) and adjusts the line's resistance (B1) to maximize the signal power for the line's length. Telephones have similar adjustments for inside line lengths (A8). The wire's voltages are negative compared to earth to reduce galvanic corrosion. Negative voltage attracts positive metal ions toward the wires. Details of operation

The landline telephone consists of a switchhook (A4) and an alerting device usually a ringer (A7) that remains connected to the phone line whenever the phone is "on hook" (i.e. the switch (A4) is open) and other components which are connected when the phone is "off hook". The off-hook components include a transmitter (microphone A2) a receiver (speaker A1) and other circuits for dialing filtering (A3) and amplification. A calling party wishing to speak to another party will pick up the telephone's handset operating a lever which closes the switchhook (A4) which powers the telephone by connecting the transmitter (microphone) receiver (speaker) and related audio components to the line. The off-hook circuitry has a low resistance (less than 300 ohms) which causes a direct current (DC) which comes down the line (C) from the telephone exchange. The exchange detects this current attaches a digit receiver circuit to the line and sends a dial tone to indicate readiness. On a modern push-button telephone the caller then presses the number keys to send the telephone number of the called party. The keys control a tone generator circuit (not shown) that makes DTMF tones that the exchange receives. A rotary-dial telephone uses pulse dialing sending electrical pulses that the exchange can count to get the telephone number (as of 2010 many exchanges were still equipped to handle pulse dialing). If the called party's line is available the exchange sends an intermittent ringing signal (about 90 volts alternating current (AC) in North America and UK and 60 volts in Germany) to alert the called party to an incoming call. If the called party's line is in use the exchange returns a busy signal to the calling party. However if the called party's line is in use but has call waiting installed the exchange sends an intermittent audible tone to the called party to indicate an incoming call. The phone's ringer (A7) is connected to the line through a capacitor (A6) a device which blocks direct current but passes alternating current. So the phone draws no current when it is on hook (a DC voltage is continually connected to the line) but exchange circuitry (D2) can send an AC voltage down the line to ring for an incoming call. (When there is no exchange telephones often have hand-cranked magnetos to make the ringing voltage.) When a landline phone is inactive or "on hook" the circuitry at the telephone exchange detects the absence of direct current and therefore "knows" that the phone is on hook (therefore only AC current will go through) with only the alerting device electrically connected to the line. When a party initiates a call to this line the exchange sends the ringing signal. When the called party picks up the handset they actuate a double-circuit switchhook (not shown) which simultaneously disconnects the alerting device and connects the audio circuitry to the line. This in turn draws direct current through the line confirming that the called phone is now active. The exchange circuitry turns off the ring signal and both phones are now active and connected through the exchange. The parties may now converse as long as both phones remain off hook. When a party "hangs up" placing the handset back on the cradle or hook direct current ceases in that line signaling the exchange to disconnect the call. Calls to parties beyond the local exchange are carried over "trunk" lines which establish connections between exchanges. In modern telephone networks fiber-optic cable and digital technology are often employed in such connections. Satellite technology may be used for communication over very long distances. Further information: Telephone call In most landline telephones the transmitter and receiver (microphone and speaker) are located in the handset although in a speakerphone these components may be located in the base or in a separate enclosure. Powered by the line the transmitter (A2) produces a modulated electrical current which varies its frequency and amplitude in response to the sound waves arriving at its diaphragm. The resulting current is transmitted along the telephone line to the local exchange then on to the other phone (via the local exchange or via a larger network) where it passes through the coil of the receiver (A3). The varying current in the coil produces a corresponding movement of the receiver's diaphragm reproducing the original sound waves present at the transmitter. Along with the microphone and speaker additional circuitry is incorporated to prevent the incoming speaker signal and the outgoing microphone signal from interfering with each other. This is accomplished through a hybrid coil (A3). The incoming audio signal passes through a resistor (A8) and the primary winding of the coil (A3) which passes it to the speaker (A1). Since the current path A8 - A3 has a far lower impedance than the microphone (A2) virtually all of the incoming signal passes through it and bypasses the microphone. At the same time the DC voltage across the line causes a DC current which is split between the resistor-coil (A8-A3) branch and the microphone-coil (A2-A3) branch. The DC current through the resistor-coil branch has no effect on the incoming audio signal and so is irrelevant. But the DC current passing through the microphone is turned into AC current which then passes through only the upper branch of the coil's (A3) primary winding which has far fewer turns than the lower primary winding. This causes a small portion of the microphone output to be fed back to the speaker while the rest of the AC current goes out through the phone line. A Lineman's handset is a telephone designed for testing the telephone network and may be attached directly to aerial lines and other infrastructure components. Early development Main article: Timeline of the telephone 1896 Telephone from Sweden Early telephone with hand-cranked generator Wooden hand-cranked wall telephone early 1900s Candlestick phone Modern emergency telephone powered by sound alone 1844 Innocenzo Manzetti first mooted the idea of a speaking telegraph (telephone). 26 August 1854 Charles Bourseul published an article in a magazine L'Illustration (Paris) : "Transmission lectrique de la parole" electric transmission of speech. 26 October 1861 Johann Philipp Reis (18341874) publicly demonstrated the Reis telephone before the Physical Society of Frankfurt. 22 August 1865 La Feuille d'Aoste reported It is rumored that English technicians to whom Mr. Manzetti illustrated his method for transmitting spoken words on the telegraph wire intend to apply said invention in England on several private telegraph lines" however telephones were not demonstrated there until after Alexander Graham Bell received his patent in the United States of America in 1876. 28 December 1871 Antonio Meucci files a patent caveat (No. 3335) in the U.S. Patent Office titled "Sound Telegraph" describing communication of voice between two people by wire. 1874 Meucci after having renewed the caveat for two years does not renew it again and the caveat lapses. 6 April 1875 Bell's U.S. Patent 161739 "Transmitters and Receivers for Electric Telegraphs" is granted. This uses multiple vibrating steel reeds in make-break circuits. 11 February 1876 Gray invents a liquid transmitter for use with a telephone but does not build one. 14 February 1876 Elisha Gray files a patent caveat for transmitting the human voice through a telegraphic circuit. 14 February 1876 Alexander Bell applies for the patent "Improvements in Telegraphy" for electromagnetic telephones using undulating currents. 19 February 1876 Gray is notified by the U.S. Patent Office of an interference between his caveat and Bell's patent application. Gray decides to abandon his caveat. 7 March 1876 Bell's U.S. patent 174465 "Improvement in Telegraphy" is granted covering "the method of and apparatus for transmitting vocal or other sounds telegraphically by causing electrical undulations similar in form to the vibrations of the air accompanying the said vocal or other sound." 10 March 1876 The first successful telephone transmission of clear speech using a liquid transmitter when Bell spoke into his device Mr. Watson come here I want to see you. and Watson heard each word distinctly. 30 January 1877 Bell's U.S. patent 186787 is granted for an electromagnetic telephone using permanent magnets iron diaphragms and a call bell. 27 April 1877 Edison files for a patent on a carbon (graphite) transmitter. The patent 474230 was granted 3 May 1892 after a 15 year delay because of litigation. Edison was granted patent 222390 for a carbon granules transmitter in 1879. Early commercial instruments Early telephones were technically diverse. Some used a liquid transmitter some had a metal diaphragm that induced current in an electromagnet wound around a permanent magnet and some were "dynamic" - their diaphragm vibrated a coil of wire in the field of a permanent magnet or the coil vibrated the diaphragm. The dynamic kind survived in small numbers through the 20th century in military and maritime applications where its ability to create its own electrical power was crucial. Most however used the Edison/Berliner carbon transmitter which was much louder than the other kinds even though it required an induction coil actually acting as an impedance matching transformer to make it compatible to the impedance of the line. The Edison patents kept the Bell monopoly viable into the 20th century by which time the network was more important than the instrument. Early telephones were locally powered using either a dynamic transmitter or by the powering of a transmitter with a local battery. One of the jobs of outside plant personnel was to visit each telephone periodically to inspect the battery. During the 20th century "common battery" operation came to dominate powered by "talk battery" from the telephone exchange over the same wires that carried the voice signals. Early telephones used a single wire for the subscriber's line with ground return used to complete the circuit (as used in telegraphs). The earliest dynamic telephones also had only one port opening for sound with the user alternately listening and speaking (or rather shouting) into the same hole. Sometimes the instruments were operated in pairs at each end making conversation more convenient but also more expensive. At first the benefits of a telephone exchange were not exploited. Instead telephones were leased in pairs to a subscriber who had to arrange for a telegraph contractor to construct a line between them for example between a home and a shop. Users who wanted the ability to speak to several different locations would need to obtain and set up three or four pairs of telephones. Western Union already using telegraph exchanges quickly extended the principle to its telephones in New York City and San Francisco and Bell was not slow in appreciating the potential. Signalling began in an appropriately primitive manner. The user alerted the other end or the exchange operator by whistling into the transmitter. Exchange operation soon resulted in telephones being equipped with a bell first operated over a second wire and later over the same wire but with a condenser (capacitor) in series with the bell coil to allow the AC ringer signal through while still blocking DC (keeping the phone "on hook"). Telephones connected to the earliest Strowger automatic exchanges had seven wires one for the knife switch one for each telegraph key one for the bell one for the push-button and two for speaking. Rural and other telephones that were not on a common battery exchange had a magneto or hand-cranked generator to produce a high voltage alternating signal to ring the bells of other telephones on the line and to alert the operator. In the 1890s a new smaller style of telephone was introduced packaged in three parts. The transmitter stood on a stand known as a "candlestick" for its shape. When not in use the receiver hung on a hook with a switch in it known as a "switchhook." Previous telephones required the user to operate a separate switch to connect either the voice or the bell. With the new kind the user was less likely to leave the phone "off the hook". In phones connected to magneto exchanges the bell induction coil battery and magneto were in a separate bell box called a "ringer box". 4 In phones connected to common battery exchanges the ringer box was installed under a desk or other out of the way place since it did not need a battery or magneto. A U.S. candlestick telephone in use circa 1915 Cradle designs were also used at this time having a handle with the receiver and transmitter attached separate from the cradle base that housed the magneto crank and other parts. They were larger than the "candlestick" and more popular. Disadvantages of single wire operation such as crosstalk and hum from nearby AC power wires had already led to the use of twisted pairs and for long distance telephones four-wire circuits. Users at the beginning of the 20th century did not place long distance calls from their own telephones but made an appointment to use a special sound proofed long distance telephone booth furnished with the latest technology. What turned out to be the most popular and longest lasting physical style of telephone was introduced in the early 20th century including Bell's Model 102. A carbon granule transmitter and electromagnetic receiver were united in a single molded plastic handle which when not in use sat in a cradle in the base unit. The circuit diagram of the Model 102 shows the direct connection of the receiver to the line while the transmitter was induction coupled with energy supplied by a local battery. The coupling transformer battery and ringer were in a separate enclosure. The dial switch in the base interrupted the line current by repeatedly but very briefly disconnecting the line 1-10 times for each digit and the hook switch (in the center of the circuit diagram) disconnected the line and the transmitter battery while the handset was on the cradle. After the 1930s the base also enclosed the bell and induction coil obviating the old separate ringer box. Power was supplied to each subscriber line by central office batteries instead of a local battery which required periodic service. For the next half century the network behind the telephone became progressively larger and much more efficient but after the dial was added the instrument itself changed little until American Telephone & Telegraph Company (AT&T) introduced touch-tone dialing in the 1960s. Digital telephony Main article: Digital Telephony The Public Switched Telephone Network (PSTN) has gradually evolved towards digital telephony which has improved the capacity and quality of the network. End-to-end analog telephone networks were first modified in the early 1960s by upgrading transmission networks with T1 carrier systems designed to support the basic 3 kHz voice channel by sampling the bandwidth-limited analog voice signal and encoding using PCM. While digitization allows wideband voice on the same channel the improved quality of a wider analog voice channel did not find a large market in the PSTN. Later transmission methods such as SONET and fiber optic transmission further advanced digital transmission. Although analog carrier systems existed that multiplexed multiple analog voice channels onto a single transmission medium digital transmission allowed lower cost and more channels multiplexed on the transmission medium. Today the end instrument often remains analog but the analog signals are typically converted to digital signals at the (Serving Area Interface (SAI) central office (CO) or other aggregation point. Digital loop carriers (DLC) place the digital network ever closer to the customer premises relegating the analog local loop to legacy status. IP telephony Main article: Voice over Internet Protocol Hardware-based IP phone Internet Protocol (IP) telephony (also known as Voice over Internet Protocol VoIP) is a disruptive technology that is rapidly gaining ground against traditional telephone network technologies. As of January 2005 up to 10% of telephone subscribers in Japan and South Korea have switched to this digital telephone service. A January 2005 Newsweek article suggested that Internet telephony may be "the next big thing."5 As of 2006 many VoIP companies offer service to consumers and businesses. IP telephony uses an Internet connection and hardware IP Phones or softphones installed on personal computers to transmit conversations encoded as data packets. In addition to replacing POTS (plain old telephone service) IP telephony services are also competing with mobile phone services by offering free or lower cost connections via WiFi hotspots. VoIP is also used on private networks which may or may not have a connection to the global telephone network. IP telephones have two notable disadvantages compared to traditional telephones. Unless the IP telephone's components are backed up with an uninterruptible power supply or other emergency power source the phone will cease to function during a power outage as can occur during an emergency or disaster exactly when the phone is most needed. Traditional phones connected to the older PSTN network do not experience that problem since they are powered by the telephone company's battery supply which will continue to function even if there's a prolonged power black-out. A second distinct problem for an IP phone is the lack of a 'fixed address' which can impact the provision of emergency services such as police fire or ambulance should someone call for them. Unless the registered user updates the IP phone's physical address location after moving to a new residence emergency services can be and have been dispatched to the wrong location. Fixed telephone lines per 100 inhabitants 1997-2007 Usage By the end of 2009 there were a total of nearly 6 billion mobile and fixed-line subscribers worldwide. This included 1.26 billion fixed-line subscribers and 4.6 billion mobile subscribers. 6 Telephone operating companies Main article: List of telephone operating companies In some countries many telephone operating companies (commonly abbreviated to telco in American English) are in competition to provide telephone services. The above Main article lists only facilities based providers and not companies which lease services from facilities based providers in order to serve their customers. Patents Look up cordless telephone in Wiktionary the free dictionary. US 174465 -- Telegraphy (Bell's first telephone patent) -- Alexander Graham Bell US 186787 -- Electric Telegraphy (permanent magnet receiver) -- Alexander Graham Bell US 474230 -- Speaking Telegraph (graphite transmitter) -- Thomas Edison US 203016 -- Speaking Telephone (carbon button transmitter) -- Thomas Edison US 222390 -- Carbon Telephone (carbon granules transmitter) -- Thomas Edison US 485311 -- Telephone (solid back carbon transmitter) -- Anthony C. White (Bell engineer) This design was used until 1925 and installed phones were used until the 1940s. US 3449750 -- Duplex Radio Communication and Signalling Appartus -- G. H. Sweigert US 3663762 -- Cellular Mobile Communication System -- Amos Edward Joel (Bell Labs) US 3906166 -- Radio Telephone System (DynaTAC cell phone) -- Martin Cooper et al. (Motorola) See also Bell System Cordless telephone Dual-tone multi-frequency signaling Harvard sentences Satellite phone Sidetone Telecommunications Telephone keypad Telephone plug Telephone related articles Telephone switchboard Telephone tapping Timeline of the telephone Tip and ring (Wiring terminology) Videophone Notes US 174465  Alexander Graham Bell: "Improvement in Telegraphy" filed on February 14 1876 granted on March 7 1876. Brown Travis (1994). Historical first patents: the first United States patent for many everyday things (illustrated ed.). University of Michigan: Scarecrow Press. p. 179. ISBN 9780810828988. http://books.google.ca/bookseiWlVTSuiCE4e-yQS--PDiAg&idV-NUAAAAMAAJ&dq.  "Pusks Tivadar". Omikk.bme.hu. http://www.omikk.bme.hu/archivum/angol/htm/puskast.htm. Retrieved 2010-05-23.  "Ringer Boxes". Telephonymuseum.com. http://www.telephonymuseum.com/ringerboxes.htm. Retrieved 2010-05-23.  Sheridan Barrett. "Newsweek - National News World News Health Technology Entertainment and more... - Newsweek.com". MSNBC. http://msnbc.msn.com/id/6831938/site/newsweek/. Retrieved 2010-05-23. dead link Next-Generation Networks Set to Transform Communications International Telecommunications Union website 4 September 2007. Retrieved 5 July 2009. References Coe Lewis (1995) The Telephone and Its Several Inventors: A History. Jefferson North Carolina: McFarland & Co. Inc. ISBN 0-7864-0138-9 Evenson A. Edward (2000) The Telephone Patent Conspiracy of 1876: The Elisha Gray - Alexander Bell Controversy. Jefferson North Carolina: McFarland & Co. Inc. ISBN 0-7864-0883-9 Baker Burton H. (2000) The Gray Matter: The Forgotten Story of the Telephone. St. Joseph Michigan: Telepress. ISBN 0-615-11329-X Huurdeman Anton A. (2003) The Worldwide History of Telecommunications. Hoboken: New Jersey: Wiley-IEEE Press. ISBN 978-0-471-20505-0 John Richard R. Network Nation: Inventing American Telecommunications (Harvard University Press; 2010) 520 pages; traces the evolution of the country's telegraph and telephone networks. Josephson Matthew (1992) Edison: A Biography. Hoboken New Jersey: John Wiley & Sons Inc. ISBN 0-471-54806-5 Bruce Robert V. (1990) Bell: Alexander Graham Bell and the Conquest of Solitude. Ithaca New York: Cornell University Press. ISBN 0-8014-9691-8. Further reading Sobel Robert (1974) The Entrepreneurs: Explorations Within the American Business Tradition. Weybright & Talley. ISBN 0-679-40064-8. Todd Kenneth P. (1998) A Capsule History of the Bell System. American Telephone & Telegraph Company (AT&T). External links Wikimedia Commons has media related to: Telephone Look up telephone in Wiktionary the free dictionary. Early U.S. Telephone Industry Data 1911 Britannica "Telephone" article Virtual museum of early telephones The Telephone 1877 Modelling Telephone hybrids as 2 x 2 matrices