Difference between Synchronous and Asynchronous Transmission

Computer Engineering Computer Network MCA

Both Synchronous and Asynchronous Transmission are types of serial data transmission techniques in which data is transmitted between the sender and the receiver based on a clock pulse used for synchronization.

Read through this article to find out more about synchronous and asynchronous transmission and how they are different from each other.

What is Synchronous Transmission?

Synchronous transmission is a technique of data transmission in which a sender transmits a continuous stream of data along with periodic timing signals supplied by an external clocking system in order to ensure that the transmitter and the receiver are in sync.

In Synchronous transmission, data is transferred at predetermined intervals based on a predefined clocking signal. It is intended for the consistent and reliable transmission of time-sensitive data such as VoIP and audio/video streaming.

Because data is delivered in huge blocks rather than individual characters, this type of transmission method is employed when huge volumes of data need to be transferred quickly. It can provide real-time communication between a transmitter and a receiver.

The data blocks are separated and clustered at regular intervals, with synchronous characters preceding them that a remote device decodes and uses to synchronize the connection between the endpoints.

What is Asynchronous Transmission?

In Asynchronous transmission, each character is a self-contained unit with its start and stop bits and an unpredictable delay. Hence, this form of transmission is also known as "start/top transmission".

The beginning and ending bits of asynchronous transmission are represented by start and stop bits. At the beginning and end of a transmission, the extra 1 notifies the receiver of the first and last characters being sent.

In asynchronous transmission method, data is transferred as packets rather than a continuous stream. Since the start and stop bits are polarized in the opposite direction, the receiver can tell when the second packet of data has been sent.

The following are the two main characteristics of asynchronous communication −

A start bit precedes each character, and one or more stop bits follow it.
Spaces frequently separate characters.

Asynchronous transmission, in general, has slower transmission rate, however it is highly flexible because it does not require the transmitter and receiver to be synchronized.

Difference between Synchronous and Asynchronous Transmission

The following table highlights the major differences between Synchronous and Asynchronous Transmission −

Key	Synchronous Transmission	Asynchronous Transmission
Definition	Synchronous transmission is the type of transmission in which a common clock pulse is shared between the transmitter and the receiver in order to permit synchronized communication.	Asynchronous transmission is the type of transmission in which the sender and the receiver have their own internal clocks; thus they do not need an external common clock pulse.
Data Unit	In Synchronous transmission, data is sent in the form of frames or blocks so the data unit is Frame/block.	In Asynchronous transmission, data is transmitted in the form of bytes or characters, so the data unit is byte/character.
Time Intervals	The time interval between two consecutive transmissions is constant in synchronous transmission.	In asynchronous transmission, the time interval between two consecutive transmissions is random.
Performance and Cost efficiency	Synchronous transmission is a quick process. Due to the implementation of common clock pulse in Synchronous transmission, the transmission of data is faster as compared to that in Asynchronous transmission but it makes this form of transmission costlier.	It takes a long time for asynchronous transmission to complete. In Asynchronous transmission, each sender and receiver has their own input clocks, hence the transmission depends on its synchronization. So it is slower as compared to Synchronous transmission but at the same time, significantly inexpensive.
Complexity	It is easy to design Synchronous transmission.	Asynchronous transmission is complex in nature and design.
Data Gap	Due to the common clock pulse in Synchronous transmission, there is no gap present between data.	In Asynchronous transmission, there is gap present between the data bytes. It contains start bits and end bits in the middle of which actual data is present.

Conclusion

The most important point that you should note here is that, data is transmitted as a continuous stream in synchronous transmission, while in the asynchronous transmission method, data is transferred as discrete chunks of packets.

Synchronous transmission requires carefully synchronized clocks for the transmission of data, whereas asynchronous transmissions do not require synchronized clocks because the parity bits convey the information about data bytes.