Telephone

The telephone or phone is a telecommunications device that transmits speech by means of electric signals.

Table of contents
1 History
2 Land-line based phone systems and fixed telephony
3 Cordless telephones
4 Wireless phone systems
5 Telephone equipment manufacturers
6 Telephone equipment research labs
7 Telephone operating companies
8 Related articles

History

The telephone was invented around 1860 by Antonio Meucci who called it teletrophone. The first recorded public demonstration of Meucci's invention took place in 1860, and had a description of it published in New York's Italian language newspaper.

In 1861 Philipp Reis presented a machine for electronic voice transmission.

Elisha Gray independently invented it and demonstrated it in 1874, but two hours before he submitted his patent announcement, Alexander Graham Bell submitted a patent (although his proposed design did not work). As a result, Alexander Graham Bell was usually credited with the invention.

The very early constructions of the telephone was based on sound transportation through air rather than generated electric signals from speech. According to a letter in the Peking Gazette, in 968, the Chinese inventor Kung-Foo-Whing invented the thumtsein, which probably transported the speech through pipes. Even the early inventions made by Meucci et al transported the sound through pipes.

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 used in the television show Star Trek.

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), the digitization of sound using different coding techniques including pulse code modulation or PCM (which is also used for .WAV files and compact discs).

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

The industry 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.

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

Land-line based phone systems and fixed telephony

The network that connects most phones together is known as the PSTN (public switched telephone network).

Fixed phone lines are usually copper wirelines which form a circuit between the subscriber and a subscriber-line interface. The SLI is nondescript street furniture, usually a box on the ground, or a silver can on a telephone pole. The SLI provides dial-tone, and converts voice and dialed numbers to digital signals, which are sent on a few wires to the exchange. SLIs were invented so that central offices could be smaller, thus less expensive, while giving better service. Some recent installations may use optical fiber to connect an SLI to the exchange. Some old installations may connect subscribers directly to an exchange without using SLIs.

An analog phone's twisted pair is self-contained, self-testing and designed to fail safely. It typically modulates incoming and outgoing conversations on the same pair of wires, and biases the lines at 48 volts DC to power the telephone. The power is provided from multiply-redundant power systems at the exchange- most phones will continue to work in a pwoer-failure. Further, the dial-tone is presented only when the SLI's, and exchange's computer believe the network is up.

An analog line uses frequencies of 0-3.5 kHz, with frequencies higher than this filtered at the SLI before it is converted to digital samples. The analog speech signals are carried over the digital backbone network as a stream of digitally encoded samples at a sample rate of 8 kHz (8,000 numeric samples representing sound-pressure per second). The frequences on the copper above 4 kHz can be utilized for DSL connections.

A line is a single voice communications circuit between the subscriber and the central switching office. A trunk is a single circuit between an SLI or central offices and may be analog or digital and is transmitted via copper, microwave, or fiber optics. A trunk group is a grouping of identical trunk circuits between two specific central offices.

Automatic telephone systems generally use numeric addresses, more commonly known as telephone numbers. The addressing system often distinguishes local, long-distance and international calls. Local calls are initiated by dialling the local number. A long-distance number is indicated by a long-distance prefix (CCITT recommends "0") followed by area code and a number local to that area. International phone calls require an international prefix (CCITT recommends "00") followed by area code and local number. US and Canadian phone systems use "1" as the long distance prefix and "011" for international prefix. See country calling codes for access codes to international telephone services.

Larger companies and organizations often employ a PABX (Private Automatic Branch Exchange). This is a telephone switch that defines its own local phone number range, which is commonly embedded in a public local phone number range. Some of the largest companies now even have their own internal telephone networks across the country, or even throughout the world, with limited gateways into the PSTN.

Most PSTN systems use analog communication between individual phones and the local switch. If digital communication is used for an individual phone, the system used is usually ISDN (Integrated Services Digital Network).

Between switches in the PSTN, most signalling is now digital using Signalling System 7 ("SS7").

Cordless telephones

Cordless telephones 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. Initially, cordless phones used the 1.7 MHz range to communicate between between base and handset. Because of quality and range problems, these units were soon superseded by systems that used frequency modulation in higher frequency ranges (49 MHz, 900 MHz, 2.4 GHz, and 5.8 GHz). The range of modern cordless phones is normally on the order of a few hundred yards.

Wireless phone systems

On the opening of the telephone exchange in Budapest, 1881, Nikola Tesla became the chief electrician to the telephone company (engineer to the Yugoslavian government and the country's first telephone system). Tesla invented a prercursor to modern wireless telephone, known as a telephone repeater (or sometimes a amplifier). The device could act as a audio speaker (not a audio transducer). The device had it's resonance tuned to a particular frequency of other repeaters to communicate between each. In 1916, Tesla described the prior developed audio transducers. According to Tesla, it was the "... [S]implest ways [to detect the radiant energy ...] the low frequency gave audible notes. [... in a field, ther was] placed a conductor, a wire or a coil, and then [Tesla] would get a note [...] characteristics of the audible note". The audible sounds were of the quality of the telephones diaphragms of that period of time. The invention was never patented nor released publicly (till years later by Tesla himself). The device also contained the following characteristics:

Modern mobile phone systems are cell-structured. Radio is used to communicate between a handset and a cell-site. Communication between cell-sites and the public switched telephone network can be by digital microwave radio, digital optic fiber or digital copper land lines communicating with a telephone exchange.

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.

Modern mobile phones use cells because radio frequencies are a limited, shared resource. Cell-sites and handsets have low power transmitters so that a limited number of radio frequencies can be reused by many callers with less interference. An incidental benefit is that the batteries in the handsets need less power.

There are many standards for common carrier wireless telephony, often with incompatible standards used in the same nation:

Telephone equipment manufacturers

Several manufacturers build telephones of all kinds. Some of these are:

Telephone equipment research labs

Bell Labs is a noted telephone equipment research laboratory, amongst its other research fields.

Telephone operating companies

In some countries, many telephone operating companies (commonly abbreviated to telco) are in competition to provide telephony services. Some of them include (in alphabetic order): AT&T, BC TEL, Belgacom, Bell, Bell Canada, British Telecom, Cable and Wireless, Deutsche Telekom, GTE, IDT, ITT, MCI, NTL, NTT, OTE, SBC Communications, Telefonica, Teleglobe, Telewest, Telstra, Telia, TELUS, Verizon

Related articles

610 (telephone), 431A, ADSL, AIOD leads, Answering machine, ANAC, Area code, Assistive Technology, Automatic redial, Basic exchange telecommunications radio service, Bell System, Blue box, Bomb threat, Call center, Call forwarding, Call originator, Call waiting, Called party, Caller, Caller ID, Calling party, Camp-on busy signal, COCOT, Competitive local exchange company (CLEC), Computer telephony integration (CTI), Crank call, Customer premises equipment (CPE), Deaf, Demon dialing, Dial Tone, Digital subscriber line, Direct dial, Direct distance dialing, Dual tone multi frequency (DTMF), Emergency telephone number, End instrument, Fax, Foreign exchange service, Help desk, Hunt Group, Incumbent local exchange company (ILEC), Infrastructure, Interactive voice response (IVR), IP Telephony, Line, Local exchange company (LEC), Local loop, Long-distance operator, Operator assistance, Party line, Modem, Payphone, Pen Register, Person-to-person, Plain Old Telephone Service (POTS), Phone, Phone phreaking, Photophone, Phreaking, Post office, Prank call, Private line, Public Switched Telephone Network (PSTN), Red telephone box, Red Box, Regional Bell operating company (RBOC), Ringer equivalency number (REN), Ringing signal, Rural radio service, Smartphone, Station-to-station, TAPI, Telautograph, Telecommunications Device for the Deaf (TDD or TTY), Telemarketing, Telephone booth, Telephone call, Telephone card, Telephone directory, Telephone exchange, Telephone tapping, Telegraph, Telemarketing, Teletype, Telex, Trap and trace, TWX, Vertical service code, Videotex, Voice over Internet Protocol (VOIP), Voicemail, War dialing, Western Union, Wide Area Telephone Service (WATS), WATS line, Wireless network, Wi-Fi, Zenith number

US-specific

Federal Standard 1037C-Glossary of telephony terms, Federal Regulations - Part 68, Modification of Final Judgment, Local access and transport area (LATA), Local exchange carrier, Interexchange carrier, Regional Bell operating company, Competitive local exchange carrier




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