When we talk about transmission medium, then some devices can send data but can not receive data and some devices can only receive data but can not send it.
There are three types of modes
1. Simplex mode -
In these systems, data is communicated only in one direction and only on one side. Such as a keyboard.
The text you type through the keyboard goes only to the computer. Data can not be directed from the computer to the keyboard.
Note - We have previously seen in the communication, both devices should understand what the other said. But here keyboard is sending the data to the computer, but the keyboard will not accept data, then how the communication will occur?
Simple, when we power on the system, the keyboard sends a "Request to connect" message to the computer, and after that computer sends a "Reply" message to the keyboard, telling him whether he can receive the data or not. The keyboard can receive the Reply, but can not accept data. If the computer said "Yes", the keyboard sends the data as input.
Let me give you one more example. When we put an earphone in mobile, then the data or audio of earphone goes only in one direction. So, both the keyboards and the earphones are a simplex devices.
2. Half-Duplex Mode -
We have two devices that must communicate with one another. So, one device sends the message and the second device receives it at the same moment. As long as the first device is sending the message, the second device did not send the message.
Only the first device makes use of the channel's capacity or bandwidth. When the first computer sends the message, the second computer sends data, and the first one receives it.
A very good example of this is a walkie-talkie. In a walkie-talkie, the first device sends the message and the second device listens but could not send the message. When the second device sends the message, the first one listens.
3. Full-duplex Mode -
In full-duplex mode, data transmission can be done from both sides or devices. This is two-way traffic. Both devices can send the message at the same time. The mobile call is a very good example of this full-duplex mode. If you are talking to someone, you can speak and listen at the same time.
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