In data

Data

The term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...

 communications

Telecommunication

Telecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...

, an automatic switching system is a switching system in which all the operations required to execute the three phases of Information transfer

Information transfer

In telecommunications, information transfer is the process of moving messages containing user information from a source to a sink.Note: The information transfer rate may or may not be equal to the transmission modulation rate.-See also:...

 transactions are automatically executed in response to signals from a user

User (telecommunications)

In telecommunications, a user is a person, organization, or other entity that employs the services provided by a telecommunication system, or by an information processing system, for transfer of information....

 end-instrument.

In an automatic switching system, the information-transfer transaction

Information-transfer transaction

In telecommunication, an information-transfer transaction is a coordinated sequence of user and telecommunications system actions that cause information present at a source user to become present at a destination user....

 is performed without human intervention, except for initiation of the access phase and the disengagement phase by a user.

In telephony

Telephony

In telecommunications, telephony encompasses the general use of equipment to provide communication over distances, specifically by connecting telephones to each other....

, it refers to a telephone exchange

Telephone exchange

In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls...

 in which all the operations required to set up, supervise

Line signaling

Line signaling is a class of telecommunications signaling protocols. Line signaling is responsible for off-hook, ringing signal, answer, ground start, on-hook unidirectional supervision messaging in each direction from calling party to called party and vice versa...

, and release connections required for telephone call

Telephone call

A telephone call is a connection over a telephone network between the calling party and the called party.-Information transmission:A telephone call may carry ordinary voice transmission using a telephone, data transmission when the calling party and called party are using modems, or facsimile...

s are automatically performed in response to signals from a calling device. This distinction lost importance as manual switching

Telephone switchboard

A switchboard was a device used to connect a group of telephones manually to one another or to an outside connection, within and between telephone exchanges or private branch exchanges . The user was typically known as an operator...

declined during the 20th century.