10 Difference Between Synchronous And Asynchronous Data Transmission (With Examples)

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When two devices linked together by a transmission medium wish to exchange data, the problem of synchronizing the receiving device with the transmitting device usually arises. In this regard, there are two method of data transmission, that is, synchronous and asynchronous.  This article provides a detailed overview of the differences that exist between the two methods.

Synchronous Transmission

Synchronous transmission is a data transfer method which is characterized by a continuous stream of data in the form of signals which are accompanied by regular timing signals which are generated by an electric clock meant to ensure that both the sender and receiver are synchronized with each other.

Synchronous transmission modes are employed when large volumes of data have to be transferred very timely from one location to another. To attain a reasonably good speed of transmission, data is transferred in large blocks instead of individual characters. Before a large file is transmitted, it is first dissected into blocks of sentences; the blocks are then transferred over communication link to the target location.

Data transfer rates in this mode of communication is very fast due to absence of no-start and stop bits. Sometimes errors can occur because in the process of faster data transmission, the clocks might get out of sync and the receiving device would have the wrong time that had been agreed in the protocol for sending/receiving data, therefore some bytes could become corrupted by losing some bits.

Synchronous transmission provides real-time communication between connected devices. Face-to-face interactions, telephonic conversations, video conferencing and chartrooms are perfect example of synchronous transmission.

Characteristics of Synchronous Transmission

  • The syn characters are used between blocks of data for timing purposes.
  • Timing is supplied by modems or other devices at each end of the connection.
  • There are no gaps between characters being transmitted.
  • Special syn characters precede the data being transmitted.

Asynchronous Transmission

Asynchronous transmission is the transmission of data in which each character is a self-contained unit with its own start and stop bits and uneven interval between them. Each character is framed as an independent unit of data that may be transmitted and received independent.  Asynchronous transmission also referred to as start-stop mode or character mode.

The asynchronous transmission method is used in cases where data has to be sent in packets and not in solid stream. The start and stop bits have opposite polarity, allowing the receiver to understand when the second packet of information has been dent.  Emails, forums, letter, radios & televisions are a good example of asynchronous transmission.

Asynchronous transmission works perfectly well in cases where the exchange of data occurs over a reliable physical medium such as fiber optic or coaxial cabling. This plays an important role of minimizing errors and therefore, the time saved by forgoing establishing parameters actually results in a faster transfer from the end user’s point of view.

Some of the main characteristics of asynchronous transmission include:

  • Every character is preceded by a start bit and followed by one or more stop bits.
  • There might be spaces or gaps in between characters.

Key Difference

  1. In synchronous transmission, data is sent in the form of blocks or frames (chunks of data) whereas in asynchronous transmission, data is sent in form of byte or character.
  2. In synchronous transmission, time interval of transmission is constant while in asynchronous transmission, time interval of transmission is constant, it is random.
  3. Transmission of data through synchronous means is systematic and thus costly while transmission of data via asynchronous method is comparatively economical.
  4. The time gaps in synchronous transmission serves to be a constant whereas the time gaps in asynchronous transmission are randomly selected and keep changing with time.
  5. Synchronous data transmission is fast whereas asynchronous data transmission is comparatively slow.
  6. Synchronous transmission requires needs a clock signal between the source and target to let the target know of the new byte. On the other hand, in asynchronous transmission, a clock signal is not needed because of the parity bit attached to the data sent which serves as a start indicator of new byte.
  7. In synchronous transmission, there are no gaps present within the different packets of data as they get transmitted from their origin to the destination. On the other hand, in asynchronous transmission, there are gaps present in between two data packets.
  8. The timelines pertaining to internal state changes are in the control of users in synchronous transmission whereas in asynchronous data transmission, the changes belonging to the internal state of asynchronous circuits fail to be within the control of users.
  9. Examples of synchronous data transmission include: video conferencing, chat rooms, telephonic conversation etc. On the other hand, examples of asynchronous transmission include: email, forums letters etc.
  10. Synchronous data transmission method is more reliable when compared to asynchronous data transmission method because in synchronous transmission, all changes in the internal state happen to be under strict control of the master clock source and therefore the chances of failure are very much less.

Also Read: Difference Between High Level Data Link Control And Point-to-Point Protocol

Synchronous Vs. Asynchronous Data Transmission In Tabular Form

BASIS OF COMPARISON   SYNCHRONOUS DATA TRANSMISSION ASYNCHRONOUS  DATA TRANSMISSION
Data Transmission In synchronous transmission, data is sent in the form of blocks or frames (chunks of data).   In asynchronous transmission, data is sent in form of byte or character.
Time Interval Of Transmission In synchronous transmission, time interval of transmission is constant. In asynchronous transmission, time interval of transmission is constant, it is random.  
Cost Of Data Transmission Transmission of data through synchronous means is systematic and thus costly.   Transmission of data via asynchronous method is comparatively economical.
Time Gaps The time gaps in synchronous transmission serves to be a constant. The time gaps in asynchronous transmission are randomly selected and keep changing with time.  
Speed Of Transmission The speed of transmission of data in synchronous transmission is fast.   The speed of data transmission in asynchronous transmission is comparatively slow.  
Clock Signal Synchronous transmission requires needs a clock signal between the source and target to let the target know of the new byte.   In asynchronous transmission, a clock signal is not needed because of the parity bit attached to the data sent which serves as a start indicator of new byte.
Presence of Gaps Between Data Packets In synchronous transmission, there are no gaps present within the different packets of data as they get transmitted from their origin to the destination. In asynchronous transmission, there are gaps present in between two data packets.  
Internal State Changes The timelines pertaining to internal state changes are in the control of users in synchronous transmission. In asynchronous data transmission, the changes belonging to the internal state of asynchronous circuits fail to be within the control of users.  
Examples Examples include: video conferencing, chat rooms, telephonic conversation etc.   Examples include: email, forums letters etc.                
Reliability Synchronous data transmission method is more reliable when compared to asynchronous data transmission method because in synchronous transmission, all changes in the internal state happen to be under strict control of the master clock source and therefore the chances of failure are very much less.   Asynchronous data transmission method is less reliable when compared to synchronous data transmission method.

Also Read: Difference Between Simplex, Half Duplex And Full Duplex

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