Data communication refers to the sharing of data in various forms like text, images, sound, etc. It is the transmission of data or information between a source and a receiver. The source transmits the data and the receiver receives it. Electronic communications, like emails and instant messages, as well as digital phone calls are examples of data communications.

Thus, data communication is the transmission of electronic data and information between two points, either via an analog signal or digital signal.

There are four basic elements in any data communication system.

The person, computer, or device that is used for sending data is called sender, source, or transmitter. In a modern digital communication system, the source is usually a computer.

The means through which data flows from one location to another is called transmission medium. Wired or wireless mediums are used to connect the receiver and sender.

The device or computer that receives the data is called the receiver. The receiver can be a computer, printer, or fax machine.

There are sets, rules, and formats under which data transmission takes place between sender and receiver. The data communication software is used to transfer data from one computer to another. The software that follows the same communication protocols can communicate and exchange data.

Let us take the simple example “A conversation between two persons A and B”. Person A is the sender, the air is medium and person B is the receiver. The purpose of communication is to get the message across to others clearly and unambiguously. Doing this involves effort from both the sender of the message and the receiver.

The way in which data is transmitted from one location to another location is called data transmission mode. There are three ways or modes for transmitting data from one location to another. These are:

In simplex mode, data is transmitted in only one direction on the communication line (medium). A terminal can only send data and cannot receive it or can only receive data but cannot send. In the communication mode, the receiver is the passive receiver who can’t respond to the sender. Simplex mode is usually used for a remote device that is supposed only to receive data. There is no return signal. It is not possible to confirm the successful transmission of data in simplex mode. Examples of simplex transmission are Radio and Television broadcasts on which the signal is sent from the transmission to the TV antenna. It is the cheapest communication method.

The communication mode in which communication takes in both directions. In this mode receiver is not a passive receiver who can respond to the sender. A device can be the sender and receiver of the data signal at the same time.

In half-duplex mode, data can be transmitted in both directions but only in one direction at a time. During any transmission, one is the transmitter and the other is the receiver. So each time for sending or receiving data, the direction of data communication is reversed, thus slows down the data transmission rate. In half-duplex modes, the transmission of data can be confirmed. Walkie-Talkie, fax machines are examples of half-duplex. Conversation on walkie-talkie is a half-duplex data flow. Each person takes turns while talking. If both talk at once – nothing occurs!

In full-duplex mode, data can be transmitted in both directions simultaneously. It is a faster mode for transmitting data because there are no time wastes in switching directions. An example of a full-duplex is a telephone set in which both the users can talk and listen at the same time. In computer networking, modems are configured to flow data in both directions.