Telephone

The telephone or phone is a telecommunications device designed to transmit
speech by means of electric signals. It was invented around 1860 by Antonio
Meucci who called it teletrophone, as recently recognized by the US Congress
in the resolution 269 on June 15th, 2002. Before that resolution it was
generally attributed to Alexander Graham Bell. 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.

There is also indication that the phone was already invented in 968 by the
chinese inventor Kung-Foo-Whing, who called it Thumtsein. The Swedish
weekly-letter AlingsŒs Weckoblad no. 3, january 11th, 1879, writes (free
translation from old Swedish):

     The telephone shall accordning to a source, that a learned chinese
     in Peking made public in a newspaper in Peking, not be any new
     invention, but be said to have already been known at 962 (!) and
     invented by a man in Peking.

The history of additional inventions and improvements 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(R) dialing (DTMF), the digitization of sound using different coding
techniques including pulse code modulation or PCM (which is commonly used
for .WAV files and on compact disks).

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

The industry was early on divided into telephone equipment manufacturers and
telephone network operators (telcos), the latter often holding 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.

Bell Labs

Telephone operating companies

Some Telco names (in alphabetic order) include: AT&T, BC TEL, Bell, Bell
Canada, British Telecom, Cable and Wireless, Deutsche Telekom, GTE, ITT,
MCI, NTL, NTT, SBC Communications, Telefonica, Teleglobe, Telewest, Telstra,
Telia, TELUS, Verizon

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 the exchange, although some recent installations may use
optical fiber for part of the distance. An analog line typically uses
frequencies of 0-3.5 kHz, with frequencies higher than this filtered at the
exchange. 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.
The frequences 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 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

Most wireless phone systems are cell-structured. Wireless communication is
used between the handsets and the cell. Communication between cells can be
wireless, or over ground cables. When an active handset moves from one cell
to another, the call is automatically transferred to the next cell without
interrupting the call.

There are now multiple standards for common carrier wireless telephony,
often with multiple incompatable standards used in the same nation: