Telephone exchangewikipedia
telephone exchangeexchangescentral officeexchangetelephone switchtelephone exchangesswitching centerswitchingtelephone switchingautomatic telephone exchange

Business telephone system

PBXprivate branch exchangekey telephone system
For corporate or enterprise use, a private telephone exchange is often referred to as a private branch exchange (PBX), when it has connections to the public switched telephone network.
Before the advent of large-scale integrated circuits, key systems were typically composed of electromechanical components (relays) as were larger telephone switching systems.

Dial tone

dial tonedial-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

Bell SystemBellBell Operating Companies
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

public switched telephone networkPSTNtelephone network
For corporate or enterprise use, a private telephone exchange is often referred to as a private branch exchange (PBX), when it has connections to the public switched 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.

Panel switch

panel switchpanelPanel system
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 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.

Class-5 telephone switch

Class 5end officeClass 5 switch
In United States telecommunication jargon, a central office (C.O.) is a common carrier switching center Class 5 telephone switch in which trunks and local loops are terminated and switched.
A Class-5 telephone switch is a telephone switch or telephone exchange in the public switched telephone network located at the local telephone company's central office, directly serving subscribers.

Telephone exchange names

telephone exchange namescentral office nametelephone exchange
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.

Telephone switchboard

switchboardtelephone switchboardswitchboards
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.

Concentrator

concentrator
During the first generations of digital networks, analog signals were digitized on line cards attached to the telephone exchange switches.

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 an in-band telecommunication signaling system using the voice-frequency band over telephone lines between telephone equipment and other communications devices and switching centers.

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.

Rotary dial

rotary dialdialrotary telephone
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.

Stepping switch

stepping switchuniselectoruniselectors
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.

Rotary system

Rotaryrotary systemRotary 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.

Panel call indicator

panel call indicatorPCICoded Call Indicator
When a subscriber dialed the number of a manual station, an operator at the destination office answered the call after seeing the number on an indicator, and connected the call by plugging a cord into the outgoing circuit and ringing the destination station.
Panel Call Indicator, or PCI, is a form of signalling used between two telephone offices.

Ringtone

ringtoneringtonesring tone
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.

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.

On- and Off-hook

off-hookon-hookon hook
With manual service, the customer lifts the receiver off-hook and asks the operator to connect the call to a requested number.
On an ordinary two-wire telephone line, off-hook status is communicated to the telephone exchange by a resistance short across the pair.

Telephone number

telephone numberphone numbertelephone numbers
For example, one switch might send only the last four or five digits of a telephone number.
Telephone numbers are entered or dialed by a calling party on the originating telephone set, which transmits the sequence of digits in the process of signaling to a telephone exchange.

Trunking

trunktrunkingtrunk line
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.

Stored program control

stored program controlstored program control exchangeswitch
Reed relay technology in stored program control exchange finally quieted the environment.
Stored program control (SPC) was a telecommunications technology used for telephone exchanges controlled by a computer program stored in the memory of the switching system.

Switchboard operator

telephone operatorswitchboard operatoroperator
With manual service, the customer lifts the receiver off-hook and asks the operator to connect the call to a requested number. 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.

Telephone call

telephone callcallphone call
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.