Transmission Modes & Transmission Types

 

Transmission modes

·         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

1. 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.

Advantages 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.

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

Disadvantages of simplex mode

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

2. 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.

3. 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.

Types of Transmission

 

·         Synchronous Transmission

·         Asynchronous Transmission

 

Synchronous Transmission:

In synchronous transmission, when sender is sending the data, receiver is ready to receive the data at the same time. In Synchronous Transmission, data is sent in form of blocks or frames. This transmission is the full duplex type. Between sender and receiver the synchronization is compulsory. In Synchronous transmission, There is no gap present between data. It is more efficient and more reliable than asynchronous transmission to transfer the large amount of data.

Asynchronous Transmission:
In Asynchronous Transmission, data is sent in form of byte or character. This transmission is the half duplex type transmission. In this transmission start bits and stop bits are added with data. It does not require synchronization.

Now, let’s see the difference between Synchronous and Asynchronous Transmission:

S.NO	Synchronous Transmission	Asynchronous Transmission
1.	In Synchronous transmission, Data is sent in form of blocks or frames.	In asynchronous transmission, Data is sent in form of byte or character.
2.	Synchronous transmission is fast.	Asynchronous transmission is slow.
3.	Synchronous transmission is costly.	Asynchronous transmission is economical.
4.	In Synchronous transmission, time interval of transmission is constant.	In asynchronous transmission, time interval of transmission is not constant, it is random.
5.	In Synchronous transmission, There is no gap present between data.	In asynchronous transmission, There is present gap between data.
6.	Efficient use of transmission line is done in synchronous transmission.	While in asynchronous transmission, transmission line remains empty during gap in character transmission.
7.	Synchronous transmission needs precisely synchronized clocks for the information of new bytes.	Asynchronous transmission have no need of synchronized clocks as parity bit is used in this transmission for information of new bytes.