• The way in which data is transmitted from one device to another device is known as transmission mode.
• The transmission mode is also known as the communication mode.
• Each communication channel has a direction associated with it, and transmission media provide the direction. Therefore, the transmission mode is also known as a directional mode.
• The transmission mode is defined in the physical layer.

The Transmission mode is divided into three categories:

• Simplex mode
• Half-duplex mode
• Full-duplex mode

Simplex mode

• In Simplex mode, the communication is unidirectional, i.e., the data flow in one direction.
• A device can only send the data but cannot receive it or it can receive the data but cannot send the data.
• This transmission mode is not very popular as mainly communications require the two-way exchange of data. The simplex mode is used in the business field as in sales that do not require any corresponding reply.
• The radio station is a simplex channel as it transmits the signal to the listeners but never allows them to transmit back.
• Keyboard and Monitor are the examples of the simplex mode as a keyboard can only accept the data from the user and monitor can only be used to display the data on the screen.
• The main advantage of the simplex mode is that the full capacity of the communication channel can be utilized during transmission.

Advantage of Simplex mode:

• In simplex mode, the station can utilize the entire bandwidth of the communication channel, so that more data can be transmitted at a time.

Disadvantage of Simplex mode:

• Communication is unidirectional, so it has no inter-communication between devices.

Half-Duplex mode

• In a Half-duplex channel, direction can be reversed, i.e., the station can transmit and receive the data as well.
• Messages flow in both the directions, but not at the same time.
• The entire bandwidth of the communication channel is utilized in one direction at a time.
• In half-duplex mode, it is possible to perform the error detection, and if any error occurs, then the receiver requests the sender to retransmit the data.
• A Walkie-talkie is an example of the Half-duplex mode. In Walkie-talkie, one party speaks, and another party listens. After a pause, the other speaks and first party listens. Speaking simultaneously will create the distorted sound which cannot be understood.

Advantage of Half-duplex mode:

• In half-duplex mode, both the devices can send and receive the data and also can utilize the entire bandwidth of the communication channel during the transmission of data.

Disadvantage of Half-Duplex mode:

• In half-duplex mode, when one device is sending the data, then another has to wait, this causes the delay in sending the data at the right time.

Full-duplex mode

• In Full duplex mode, the communication is bi-directional, i.e., the data flow in both the directions.
• Both the stations can send and receive the message simultaneously.
• Full-duplex mode has two simplex channels. One channel has traffic moving in one direction, and another channel has traffic flowing in the opposite direction.
• The Full-duplex mode is the fastest mode of communication between devices.
• The most common example of the full-duplex mode is a telephone network. When two people are communicating with each other by a telephone line, both can talk and listen at the same time.

Advantage of Full-duplex mode:

• Both the stations can send and receive the data at the same time.

Disadvantage of Full-duplex mode:

• If there is no dedicated path exists between the devices, then the capacity of the communication channel is divided into two parts.

Differences b/w Simplex, Half-duplex and Full-duplex mode