Data Transmission

Data transmission is the transfer of analog or digital data between two devices. Data transmission enables the two devices to communicate with each other. In this section, we focus on digital data transmission. Digital data transmission is the transmission of bits between the two I/O devices or the components of the computer.

To set up the communication between two devices we have to first establish the link between the devices or components. To establish a link between the two I/O devices or components there are two kinds of data transmission techniques that are parallel data transmission and serial data transmission.

Data Transmission Techniques

  1. Parallel Transmission
  2. Serial Transmission

Parallel Data Transmission

In parallel data transmission, multiple bits are sent in each clock cycle. As we know digital data is in the form of 0s and 1s. These binary bits are organized into a small group of n bits (usually 8 bits or byte/character) and the computer sends and receives data in a group of bits.

Parallel Data Transmission

Now as the data is sent and received into a group of n bits at a time, the link between the sender and receiver must have n channels so that the n bits can be sent and received at a time.


  • As n bits are sent parallelly the parallel transmission is faster.


  • Organizing a parallel transmission is costlier as we have to establish n channels so that the n bits can be transferred parallelly.
  • Parallel data transmission is possible over a short distance only.

Serial Data Transmission

In serial transmission, there is a single channel line between the sender and the receiver, and the bits are transferred in a bit-serial fashion. Only one bit is transmitted at a time which when transmitted successfully is then followed by the next bit to be transmitted.

Serial Data Transmission


  • Single-channel for transmission reduces the cost of transmission.


  • The speed of transmission is slower as compared to parallel transmission.

However, serial transmission can be further classified into three types asynchronous, synchronous, and isochronous serial transmission.

1. Asynchronous Transmission

In asynchronous transmission, the bitstream is grouped into bytes (8-bits). Here the clock of sender and receiver are not synchronized. The sender sends this group of bits over the channel whenever the group of bits is ready to be transmitted.

Asynchronous Serial Data Transmission

A start bit (0) and end bit (1) are attached to every sent byte so that the receiver gets alter of the arrival and end of every new byte. Transmission of each byte may be followed by a gap of varying time this can be filled by the stop bits.


  • The sender can send the data whenever it is ready no synchronization is required.
  • Convenient for transmitting a small amount of data.
  • Low-cost implementation.


  • The transmission speed is slow.
  • Less efficient.

2. Synchronous Transmission  

In synchronous transmission, the bitstream is grouped into longer ‘frames’, where each frame consists of multiple bytes. In a frame there is no gap between the bytes, the receiver has to recognize the separate bytes into the frame.

Synchronous Serial Data Transmission

The sending and receiving devices must be synchronized which makes the receiving device capable of synchronizing the bits. Though there is no gap between the bytes inside a frame there can be an uneven gap between the frames.


  • More efficient than asynchronous transmission.
  • Transmission speed is comparatively higher than asynchronous transmission.
  • Suitable for transmitting a large amount of data.


  • The rate of transmission is not fixed.

3. Isochronous Transmission

Isochronous transmission is similar to synchronous transmission but the difference is that there must be no delay between the frames. For example, the images for television are broadcasted at the rate of 30 images per second if there will be any delay in the transmission it will create disturbance in the vision. With the isochronous transmission, the data is transmitted at a fixed rate.


  • The transmission rate is fixed and transmission is speed is much higher than synchronous and asynchronous transmission.


  • Expensive

In this way, data transmission defines several techniques to transfer data between digital devices. We have seen the behavior and performance of each technique.

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