Difference Between Synchronous and Asynchronous Transmission

Synchronous and Asynchronous transmission are the 2 types of serial data transmission technique. But the crucial difference between synchronous and asynchronous transmission is that in synchronous transmission a common clock pulse is shared between transmitter and receiver in order to permission synchronized communication.

As against in asynchronous transmission, the sender and receiver have their own internal clocks thus do not need an external common clock pulse.
Synchronous transmission permits a continuous flow of data between the sender and receiver. However, an asynchronous transmission technique does not allow continuous data flow.

We will discuss some other important factors that differentiate synchronous transmission from the asynchronous one. But before that see what are the contents that we will discuss under this article.

Comparison Chart

Basis for ComparisonSynchronous TransmissionAsynchronous Transmission
MeaningTransmission starts with the block header which holds a sequence of bits.It uses start bit and stop bit preceding and following a character respectively.
Transmission mannerSends data in the form of blocks or framesSends 1 byte or character at a time
SynchronizationPresent with the same clock pulse.Absent
Implemented byHardware and softwareHardware only
Transmission Speed

Gap between the dataDoes not existExist
Time IntervalConstantRandom
ExamplesChat Rooms, Video Conferencing, Telephonic Conversations, etcetera.Letters, emails, forums, etcetera.


Definition of Synchronous Transmission

In Synchronous Transmission, data flows in a fully-duplex mode in the form of the frame. Synchronization between the sender and receiver is important so that the sender knows where the new byte starts (since there is no gap between the data). Therefore, each block of characters is labeled with the synchronization characters and the receiving device acquires the data until a special ending character is identified.difference between synchronous and asynchronous transmission

Synchronous Transmission is proficient, reliable and is used for transferring a large amount of data. It provides real-time communication between connected devices. Chat Rooms, Video Conferencing, telephonic conversations, etc. as well as face to face interactions, There are some of the examples of Synchronous Transmission.

The voice-band and broad-band channels are usually used in the synchronous transmission modes as it provides a faster speed up to 1200 bps and serves the purpose of high data transfer speed.

Definition of Asynchronous Transmission

In Asynchronous Transmission data flows in a half-duplex mode, 1 byte at a time. It transmits the data in a continuous stream of bytes. In general, the size of a character sent is 8 bits to which an equality bit is added, i.e. a start and a stop bit that gives a total of 10 bits.

It doesn’t require a clock for synchronization rather it uses the parity bits to inform the receiver how to interpret the data. These parity bits are called start and stop bits which control the transfer of the data.difference between synchronous and asynchronous transmission

It uses character-based synchronization so that the receiving terminal could synchronize itself with the receipt of data/informing on a character. It is simple, fast, profitable and does not require a 2-way communication. Letters, emails, forums, televisions, and radios, etc are some of the examples of Asynchronous Transmission.

The voice-band channels that a narrow type and operates on a slower speed are utilized in the asynchronous transfer. Here, the transmitting device works manually.

Key Differences Between Synchronous and Asynchronous Transmission

  1. The synchronous transmission allows the transmission of data in frame or block formats. Whereas, in asynchronous transmission, a byte/character is transmitted at a time.
  2. Due to the transmission of data in the form of frames the rate of data transmission is quite fast in synchronous transmission. While in asynchronous transmission the rate of data transmission is comparatively slow.
  3. Synchronous communication needs synchronization between the sender and receiver thus the two shares a common clock pulse. On the contrary, Asynchronous communication does not permit synchronized communication and thus the sender and receiver have their own internal clock.
  4. Due to the existence of a clock pulse, data in the form of frames can be continuously transmitted between the sender and receiver. While the absence of a common clock pulse causes the existence of gaps between data bits.
  5. The synchronous transmission does not require start and stop bits. As against in order to have asynchronous transmission between sender and receiver, start and stop bits are necessarily needed before and after the message signal bits.
  6. The time interval of transmission remains constant between the data to be transmitted. However, in the case of asynchronous transmission variable time intervals between the data bits exist.
  7. A system supporting synchronous transmission is comparatively complex than the asynchronous transmission system.
  8. Due to synchronized communication, the synchronous transmission is more proficient compared to asynchronous transmission.
  9. The complexing of the system in synchronous transmission increases the cost of the system. Thus synchronous transmission is more expensive than asynchronous transmission.


Both Synchronous and Asynchronous Transmission have advantages and disadvantages. Asynchronous is simple, economical and used for transmitting a small amount of data.

Conversely, Synchronous Transmission is used for transferring the bulk of data as it is efficient and has less overhead. Hence, we finish that both Synchronous and Asynchronous Transmission are necessary for data transmission.




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