Telephone exchange

exchangescentral officeexchangetelephone switchtelephone exchangesswitching centerswitchingtelephone switchingautomatic telephone exchangecentral offices
A telephone exchange is a telecommunications system used in the public switched telephone network or in large enterprises.wikipedia
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Dial tone

dial-tonedialling tonestutter dial tone
Central office locations may also be identified in North America as wire centers, designating a facility from which a telephone obtains dial tone.
A dial tone is a telephony signal sent by a telephone exchange or private branch exchange (PBX) to a terminating device, such as a telephone, when an off-hook condition is detected.

Bell System

BellBell Operating CompaniesBell Telephone
In the United States and Canada, the Bell System established in the 1940s a uniform system of identifying central offices with a three-digit central office code, that was used as a prefix to subscriber telephone numbers.
Within a few years local exchange companies were established in every major city in the United States.

Public switched telephone network

PSTNtelephone networkpublic telephone network
A telephone exchange is a telecommunications system used in the public switched telephone network or in large enterprises.
The PSTN consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all interconnected by switching centers, thus allowing most telephones to communicate with each other.

Telephone numbering plan

Area codeCalling codearea codes
All central offices within a larger region, typically aggregated by state, were assigned a common numbering plan area code.
The first few digits of the subscriber number typically indicate smaller geographical areas or individual telephone exchanges.

Tivadar Puskás

Puskás, Tivadar
One of the first to propose a telephone exchange was Hungarian Tivadar Puskás in 1877 while he was working for Thomas Edison.
Tivadar Puskás de Ditró (English: Theodore Puskás b. 17 September 1844, Pest – d. 16 March 1893, Budapest) was a Hungarian inventor, telephone pioneer, and inventor of the telephone exchange.

Telephone switchboard

switchboardswitchboardscentral switchboard
In 1887 Puskás introduced the multiplex switchboard. Later exchanges consisted of one to several hundred plug boards staffed by switchboard operators.
The switchboard was an essential component of a manual telephone exchange, and was operated by switchboard operators who used electrical cords or switches to establish the connections.

Panel switch

panelother exchange typespanel dial systems
Exchanges based on the Strowger switch were eventually challenged by other exchange types and later by crossbar technology. Some types of automatic exchanges were the Strowger switch or step-by-step switch, All Relay, X-Y, panel switch, Rotary system and the crossbar switch.
The Panel Machine Switching System is an early type of automatic telephone exchange for urban service, introduced in the Bell System in the 1920s.

Telephone call

callphone callphone calls
An exchange consists of electronic components and in older systems also human operators that interconnect (switch) telephone subscriber lines or virtual circuits of digital systems to establish telephone calls between subscribers.
Most telephone calls through the PSTN are set up using ISUP signalling messages or one of its variants between telephone exchanges to establish the end to end connection.

New Haven, Connecticut

New HavenNew Haven, CTNew Haven, Conn.
George W. Coy designed and built the first commercial US telephone exchange which opened in New Haven, Connecticut in January, 1878.
1878–1880: The District Telephone Company of New Haven creates the world's first telephone exchange and the first telephone directory and installs the first public phone. The company expanded and became the Connecticut Telephone Company, then the Southern New England Telephone Company (now part of AT&T).

Almon Brown Strowger

Almon B. StrowgerStrowger
On March 10, 1891, Almon Brown Strowger, an undertaker in Kansas City, Missouri, patented the stepping switch, a device which led to the automation of telephone circuit switching.
Almon Brown Strowger (February 11, 1839 – May 26, 1902) was an American inventor who gave his name to the Strowger switch, an electromechanical telephone exchange technology that his invention and patent inspired.

Dual-tone multi-frequency signaling

DTMFtouch-tonetouch tone
At a later date many also accepted DTMF "touch tones" or other tone signaling systems.
Dual-tone multi-frequency signaling (DTMF) is a telecommunication signaling system using the voice-frequency band over telephone lines between telephone equipment and other communications devices and switching centers.

Stepping switch

uniselectoruniselectorsstepping relay
On March 10, 1891, Almon Brown Strowger, an undertaker in Kansas City, Missouri, patented the stepping switch, a device which led to the automation of telephone circuit switching.
The major use of stepping switches was in early automatic telephone exchanges to route telephone calls.

Concentrator

A concentrator is a device that concentrates traffic, be it remote or co-located with the switch.
During the first generations of digital networks, analog signals were digitized on line cards attached to the telephone exchange switches.

Telephone exchange names

central office nametelephone exchangetelephone exchange name
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.
A telephone exchange name or central office name was a distinguishing and memorable name assigned to a central office.

Switchboard operator

telephone operatoroperatoroperators
Later exchanges consisted of one to several hundred plug boards staffed by switchboard operators.
Before the advent of automatic exchanges, an operator's assistance was required for anything other than calling telephones across a shared party line.

Trunking

trunktrunk linetrunks
For a long distance call, she plugged into a trunk circuit to connect to another operator in another bank of boards or at a remote central office.
A trunk is a single communications channel between two points, each point being either the switching center or the node.

Inside plant

Often, a central office is defined as a building used to house the inside plant equipment of potentially several telephone exchanges, each serving a certain geographical area.
All the cabling and equipment installed in a telecommunications facility, including the main distribution frame (MDF) and all the equipment extending inward therefrom, such as PABX or central office equipment, MDF heat coil protectors, and grounding systems.

Rotary dial

dialrotary telephonerotary phone
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 the first digit and then to swing horizontally in a contact row with one small rotation for each pulse in the next digit.
It is used when initiating a telephone call to transmit the destination telephone number to a telephone exchange.

On- and Off-hook

off-hookon-hookon hook
An off-hook condition represents a circuit that is in use, e.g., when a phone call is in progress.
On an ordinary two-wire telephone line, off-hook status is communicated to the telephone exchange by a resistance short across the pair.

Ringdown

Private line automatic ringdownmagneto crank telephonessecure 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.
The term originated in magneto telephone signaling in which cranking the magneto generator, either integrated into the telephone set or housed in a connected ringer box, would not only ring its bell but also cause a drop to fall down at the telephone exchange switchboard, marked with the number of the line to which the magneto telephone instrument was connected.

Ringtone

ringtonesring tonePolyphonic
When calling a party, the operator used code ringing, a distinctive ringing signal sequence, such as two long rings followed by one short ring.
Landline telephones typically receive an electric alternating current signal, called power ringing or ringing signal, generated by the telephone exchange to which the telephone is connected.

Rotary system

RotaryRotary exchanges
Some types of automatic exchanges were the Strowger switch or step-by-step switch, All Relay, X-Y, panel switch, Rotary system and the crossbar switch.
The rotary machine switching system, or most commonly known as the rotary system, was a type of automatic telephone exchange manufactured and used primarily in Europe from the 1910s.

Telephone line

phone linelinetelephone lines
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 1878, the Bell Telephone Company began to use two-wire circuits (called the local loop) from each user's telephone to end offices which performed any necessary electrical switching to allow voice signals to be transmitted to more distant telephones.

Crossbar switch

crossbarcross-bar switchmatrix switch
Exchanges based on the Strowger switch were eventually challenged by other exchange types and later by crossbar technology. Some types of automatic exchanges were the Strowger switch or step-by-step switch, All Relay, X-Y, panel switch, Rotary system and the crossbar switch.
A telephony crossbar switch is an electromechanical device for switching telephone calls.

Strowger switch

Strowgerstep-by-stepstep by step
Some types of automatic exchanges were the Strowger switch or step-by-step switch, All Relay, X-Y, panel switch, Rotary system and the crossbar switch.
The Strowger switch is the first commercially successful electromechanical stepping switch telephone exchange system.