Data Transmission

Data transmission, digital transmission, or digital communications is the physical transfer of data (a digital bit stream) over a point-to-point or point-to-multipoint communication channel. Examples of such channels are copper wires, optical fibres, wireless communication channels, and storage media. The data are represented as an electromagnetic signal, such as an electrical voltage, radiowave, microwave, or infrared signal.

Data representation can be divided into two categories:

Digital representation: which means that the information is encoded as a set of binary values, in other words a sequence of 0s and 1s?
Analogue representation: which means that the data will be represented by the variation in a continuous physical quantity?

Types of communication channels

In telecommunication, data transmission circuit is the transmission media and the intervening equipment used for the data transfer between data terminal equipments
A data transmission circuit includes any required signal conversion equipment.
A data transmission circuit may transfer information in (a) one direction only, (b) either direction but one way at a time, or (c) both directions simultaneously.

Simplex communication refers to communication that occurs in one direction only. Two definitions have arisen over time: a common definition, which is used in ANSI standard and elsewhere, and an ITU-T definition. The ITU definition of simplex is termed "half duplex" in other contexts ---------------------------
According to the ANSI definition, a simplex circuit is one where all signals can flow in only one direction. These systems are often employed in broadcast networks, where the receivers do not need to send any data back to the transmitter/broadcaster
(Examples)
Commercial radio and television broadcast (not two-way radio such as walkie-talkies)
Garage door openers
Baby monitors
Wireless microphones
Radio controlled models
Public address systems
Surveillance cameras