Telephone

The telephone or phone (Greek: τῆλε [ti:le] tele 'far away' and φωνή [fɒni:] phone 'voice') is a telecommunications device which is used to transmit and receive sound (most commonly voice and speech) across distance. Most telephones operate through transmission of electric signals over the Public Switched Telephone Network (PSTN) which allows almost any phone user to communicate with almost any other.

The engineering discipline of designing and operating telephone networks is called telephony.

Introduction

An elementary telephone system would consist of three elements:

• the equipment located at each subscriber which converts sound to electrical signals and back, and which allows the subscriber to answer or initiate a call,
• a central switching facility which interconnects all the subscribers. Originally, this used circuit switching
• wiring or other means to connect the subscriber to the central switching facility.

There are three principal ways a subscriber may be connected to the telephone network:

• Historically, and still very commonly, by dedicated physical wire (or optical fiber) connections run in overhead or underground cables;
• By radio, as in a cordless, cellular telephony, satellite or radiotelephone and
• By voice over internet protocol (VoIP) telephones, which use carry packets of digitized voice information, encapsulated in the Internet Protocol connections. VoIP need not run over the public Internet; it merely needs to comply with Internet Protocol Suite technical specifications

History

The identity of the inventor of the electric telephone remains in dispute. Antonio Meucci, Johann Philipp Reis, Alexander Graham Bell and Elisha Gray, among others, have all been credited with the invention.

The very early history of the telephone is a confusing morass of claim and counterclaim, which was not clarified by the huge mass of lawsuits which hoped to resolve the patent claims of individuals. Much money was expended, particularly in the Bell Telephone companies, and the aggressive defence of the Bell patents resulted in much confusion. Additionally, the earliest investigators preferred publication in the popular press and demonstration to investors instead of scientific publication and demonstration to fellow scientists. It is important to note that there is probably no single "inventor of the telephone". The modern telephone is the result of work done by many hands, all worthy of recognition of their addition to the field. Only in the last ten years, however, has the British government announced that it now recognizes (primarily for educational purposes) Antonio Meucci (see below) as the 'first inventor' of the telephone.

Early development

The following is a brief summary of the history of the invention of the telephone:

• 1849 Antonio Meucci, an Italian living in Havana, demonstrates a device he later called a telephone. (The demonstration involves direct electrical connections to people.)
• 1854 Charles Bourseul publishes a description of a make-break telephone transmitter and receiver but does not construct a working instrument.
• 1854 Meucci demonstrates an electric telephone in New York. [1]
• 1860 Johann Philipp Reis demonstrates a "telephon" using a pressure contact transmitter after the make-break design of Bourseul and a knitting needle receiver. Witnesses said they heard human voices being transmitted.
• 1860 Meucci demonstrates his telephone on Staten Island.
• 1861 Reis manages to transfer voice electrically over a distance of 340 feet, see Reis' telephone.
• 1864 In an attempt to give his musical automaton a voice, Innocenzo Manzetti invents the 'Speaking telegraph'. He shows no interest in patenting his device, but it is reported in newspapers.
• 1865 Meucci reads of Manzetti's invention and writes to the editors of two newspapers claiming priority and quoting his first experiment in 1849. He writes "I do not wish to deny Mr. Manzetti his invention, I only wish to observe that two thoughts could be found to contain the same discovery, and that by uniting the two ideas one can more easily reach the certainty about a thing this important." If he reads Meucci's offer of collaboration, Manzetti does not respond.
• 1871 Meucci files a patent caveat (a statement of intention to patent).
• 1872 Elisha Gray founds Western Electric Manufacturing Company.
• 1872 Prof Vanderwyde demonstrated Reis's telephone in New York.
• July 1873 Thomas Edison notes variable resistance in carbon grains due to pressure and builds a rheostat based on the principle.
• May 1874 Gray invents electromagnet device for transmitting musical tones. Some of his receivers use steel diaphragms.
• December 29, 1874 Gray demonstrates his musical tones device and transmitted "familiar melodies through telegraph wire" at the Presbyterian Church in Highland Park, Illinois.
• 2 June 1875 Alexander Graham Bell transmits the sound of plucked steel reeds using electromagnet instruments.
• 1 July 1875 Bell uses a bi-directional "gallows" telephone that was able to transmit "indistinct but voicelike sounds" but not clear speech. Both the transmitter and the receiver were identical membrane electromagnet instruments.
• 1875 Thomas Edison experiments with acoustic telegraphy and in November builds an electro-dynamic receiver but does not exploit it.
• 11 February 1876 Elisha Gray invents a liquid transmitter for use with a telephone, but does not build one.
• 14 February 1876 (about 9:30 am) Gray or his lawyer brings to the Patent Office Gray's caveat for the telephone. (A caveat was a notice of intention to file a patent application)
• 14 February 1876 (about 11:30am) Bell's lawyer brings to the Patent Office Bell's patent application for the telephone. Bell's lawyer requested that it be registered immediately in the cash blotter.
  • About two hours later Elisha Gray's caveat was registered in the cash blotter. Although Gray could have converted his caveat into a patent application, he did not do so.
• 7 March 1876 Bell's US patent 174,465 for the telephone is granted.
• 10 March 1876 Bell transmits speech "Mr. Watson, come here, I want you." using a liquid transmitter and an electromagnetic receiver.
• 16 May 1876 Thomas Edison files first patent application for acoustic telegraphy.
• 20 January 1877 Edison "first succeeded in transmitting over wires many articulated sentences" using carbon granules as a pressure sensitive variable resistance under the pressure of a diaphragm (Josephson, p143).
• 30 January 1877 Bell's US patent 186,787 is granted for an electro-magnetic telephone using permanent magnets, iron diaphragms, and a call bell.
• 4 March 1877 Emile Berliner invents a microphone based on the "loose contact" between two metal electrodes, an improvement on the Reis telephone, and in April 1877 files a caveat of an invention in process.
• 27 April 1877 Edison files for a patent on a carbon (graphite) transmitter. The patent 474,230 was granted May 3, 1892 after a 15 year delay due to litigation. In 1892 a federal court ruled Edison and not Berliner was the inventor of the carbon transmitter. Edison was granted patent 222,390 for a carbon granules transmitter in 1879. Edison's carbon granules transmitter and Bell's electromagnetic receiver were used, with improvements, by the Bell system for many decades thereafter (Josephson, p 146).

Later history

The history of additional inventions and improvements of the electrical telephone includes the carbon microphone (later replaced by the electret microphone now used in almost all telephone transmitters), the manual switchboard, the rotary dial, the automatic telephone exchange, the computerized telephone switch, Touch Tone® dialing (DTMF), and the digitization of sound using different coding techniques including pulse code modulation or PCM (which is also used for .WAV, .AIF files and compact discs).

Newer systems include IP telephony, ISDN, DSL, mobile cellular phone systems, cordless telephones, and the third generation cell phone systems that promise to include high-speed packet data transfer.

The industry has divided into telephone equipment manufacturers and telephone network operators (telcos). Operating companies often hold a national monopoly. In the United States, the Bell System was vertically integrated. It fully or partially owned the telephone companies that provided service to about 80% of the telephones in the country and also owned Western Electric, which manufactured or purchased virtually all the equipment and supplies used by the local telephone companies. The Bell System divested itself of the local telephone companies in 1984 in order to settle an antitrust suit brought against it by the United States Department of Justice.

In 1926 Bell Labs and the British Post Office engineered the first two-way conversation across the Atlantic.

The first commercial transatlantic telephone call was between New York City and London, United Kingdom and occurred on January 7, 1927.

Analog carrier technology

The most capital- and labor-intensive part of a telephone system was installing the wire over which the calls were transmitted. While 4 KHz of bandwidth is adequate for an understandable communications, copper pair of reasonable quality can carry higher frequencies. In analog multiplexing, the voice information was modulated into part of a shared medium. For example, among the last short-haul carrier systems introduced before digital telephony was N carrier, which used frequency modulation to put a group (telephony) of 12 channels onto a pair.

For longer-distance transmission, other analog multiplexing systems, intended for longer range, could combine groups into wider-frequency signals that usually traveled over coaxial cable rather than twisted pair, or perhaps over a free-space microwave transmission system. Many carrier systems were built around single or multiple mastergroups of 600 voice channels.

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 1960s with the advent of digitized voice over copper wires, specifically the T1 carrier transmission system. Each voice call entering this system was converted, by a channel bank of coder-decoders (codecs) was converted into 64 Kbps channel in the DS0 format; the process reversed to convert DS0 to a nominal 4KHz analog channel at the destination. In North America, 24 DS0 channels were combined with 8 Kbps of system overhead to form a 1.544 Mbps DS1 format signal. A set of 24 channels was initially called a digroup, to use terminology understandable to people familiar with the analog "group" terminology. T1 was a specific transmission system for DS1 signals, which ran over copper pair, with repeaters every several thousand feet

Different DS0 codecs were used in North America and Japan, and the rest of the world, so international calls might need to use transcoding between the various standards. North America and the rest of the world also used different multiplexing standards. For example, where North America used 24-channel T1, the European equivalent was E1 carrier, with an aggregate 2.032 Mbps bit rate.

Higher-capacity multiplexing also was used in digital telephony. The North American hierarchy of speeds was called the plesisochronous digital hierarchy (PDH) and the international standard hierarchy was the synchronous digital hierarchy (SDH). Typically, there was a rate at which high-capacity digital and analog multiplex systems could interwork. For example, the DS3 rate, at 44.736 Mbps, could carry 672 DS1 signals, but, in practice, often carried only 600, so one analog mastergroup could run in one DS3 channel.

Optical transmission

In the 1970s, the previously analog backbone, which had been moving to digital multiplexing over microwave or coaxial cable, took a massive leap in capacity and quality by moving to digital transmission over optical communications, usually in optical fiber.

There was a higher-capacity hierarchy for multiplexing communications both optical and digital, the synchronous optical network (SONET) and a comparable SDH network in Europe and elsewhere.

While today the plain old telephone service (POTS) end instrument remains analog, the analog signals reaching the aggregation point (Serving Area Interface (SAI) or the central office (CO) ) are typically converted to digital signals. Digital loop carriers (DLC) are often used, placing the digital network ever closer to the customer premises, relegating the analog local loop to legacy status. With the advent of broadband digital links to the small office and home (SOHO), digitized voice, computer data, and television could run over a common physical medium. Cable television systems often terminated their cable into a set-top box, which had conventional POTS, 300 ohm analog television, and Ethernet interfaces.

Wireless phone systems

While the term "wireless" means radio and can refer to any telephone that uses radio waves (such telephones have existed since 1915: see "Hello, Hawaii, How Are You?"), it is primarily used for cell phones. In the United States wireless companies tend to use the term wireless to refer to a wide range of services while the cell phone itself is called a mobile phone, mobile, PCS phone, cell phone or simply cell with the trend now moving towards mobile.

The changes in terminology is partially due to providers using different terms in marketing to differentiate newer digital services from older analog systems and services of one company from another.

Cordless telephone

Cordless telephones, invented by Teri Pall in 1965, consist of a base unit that connects to the land-line system and also communicates with remote handsets by low power radio. This permits use of the handset from any location within range of the base. Because of the power required to transmit to the handset, the base station is powered with an electronic power supply. Thus, cordless phones typically do not function during power outages. Initially, cordless phones used the 1.7 MHz frequency range to communicate between base and handset. Because of quality and range problems, these units were soon superseded by systems that used frequency modulation (FM) at higher frequency ranges (49 MHz, 900 MHz, 2.4 GHz, and 5.8 GHz). The 2.4 GHz cordless phones can interfere with certain wireless LAN protocols (802.11b/g) due to the usage of the same frequencies. On the 2.4 GHz band, several "channels" are utilized in an attempt to guard against degradation in the quality of the voice signal due to crowding. The range of modern cordless phones is normally on the order of a few hundred meters.

Mobile phones

Most modern mobile phone systems are cell-structured. Radio is used to communicate between a handset and nearby cell sites.

When a handset gets too far from a cell site, a computer system commands the handset and a closer cell site to take up the communications on a different channel without interrupting the call. Nicole powns.

Radio frequencies are a limited, shared resource. The higher frequencies used by cell phones have advantages over short distances. Connection distance is somewhat predictable and can be controlled by adjusting the power level. By only using enough power to connect to the "nearest" cell site phones using one cell site will cause almost no interference with phones using the same frequencies on another cell site. The higher frequencies also work well with various forms of multiplexing which allows more than one phone to connect to the same tower with the same set of frequencies.

Satellite phones

Some mobile telephones, especially those used in remote locations, where constructing a cell network would be too unprofitable or difficult, instead communicate directly with an orbiting satellite. Such devices tend to be bulkier than cell-based mobile phones, as they require a large antenna or dish for communicating with the satellite, but do not require ground based transmitters, making them useful for communicating from remote areas and disaster zones.

Semi-Cordless Phone

There are phones that work as a cordless phone when near their corresponding base station (and sometimes other base stations) and work as a wireless phone when in other locations but for a variety of reasons did not become popular.

Some kinds of cordless phones work like cellular phones but only within a small private network covering a building or group of buildings. These kinds of systems using VoIP are popular in hospitals and factories where the same wireless network can be used for both data and voice.

IP Telephony

IP Telephony, also called Telephony Over IP (TOIP), is a service based on Voice Over IP (VOIP), a disruptive technology that is rapidly gaining ground against traditional telephone network technologies. "IP Telephony" is a term that is often used to describe telephony services within an internal network (for instance within a company, a hospital, a school) to allow colleagues to talk to each other for free. IP telephony uses a broadband connection to transmit conversations as data packets. In addition to replacing Plain Old Telephone Service (POTS), IP telephony is also competing with mobile phone networks by offering free or lower cost connections via WiFi hotspots.

Telephone operating companies

In some countries, many telephone operating companies (commonly abbreviated to telco in American English) are in competition to provide telephone services. Some of them are included in the following list. However, the list only includes facilities based providers and not companies which lease services from facilities based providers in order to serve their customers. See also: List of telephone operating companies

Trivia

• The modern handset came into existence when a Swedish lineman tied a microphone and earphone to a stick so he could keep a hand free.
• The folding portable phone was an intentional copy of the fictional futuristic communicators (which in use actually more closely resembled walkie-talkies, Nextel-style) used in the television show Star Trek, though similar devices were seen in other TV shows before that.
• In Unicode, telephones are depicted with the characters whose hexadecimal codes are 2121 (℡), 260E (☎), 260F (☏) and 2706 (✆), (but may not display properly in some browsers).

Patents

• US 174,465 -- Telegraphy (Bell's first telephone patent) -- Alexander Graham Bell
• US 186,787 -- Electric Telegraphy (permanent magnet receiver) -- Alexander Graham Bell
• US 474,230 -- Speaking Telegraph (graphite transmitter) -- Thomas Edison
• US 203,016 -- Speaking Telephone (carbon button transmitter) -- Thomas Edison
• US 222,390 -- Carbon Telephone (carbon granules transmitter) -- Thomas Edison
• US 485,311 -- Telephone (solid back carbon transmitter) -- Anthony C. White (Bell engineer) This design was used until 1925 and installed phones were used until the 1940's.
• US 3,449,750 -- Duplex Radio Communication and Signalling Appartus -- G. H. Sweigert
• US 3,663,762 -- Cellular Mobile Communication System -- Amos Edward Joel (Bell Labs)
• US 3,906,166 -- Radio Telephone System (DynaTAC cell phone) -- Martin Cooper et al. (Motorola)