What is Asynchronous transmission? What are the advantages and disadvantages of asynchronous transmission?

Asynchronous transmission

Asynchronous data transmission is one of the three methods of data transmission. In asynchronous data transmission, sender or source system sends one character of whole data at once to the receiver or destination system.

Characteristics of Asynchronous Transmission

  1. Sender can send data at any time and receiver can receive it at any time
  2. The delay in sending each character can be same or different
  3. Each 8bit character is preceded by a start bit and followed by 1 or 2 stop bits. The start bit, 8bit character and stop bit(s) creates a packet
Signal for sending a character in Asynchronous Transmission

This type of transmission is also referred as start/stop bit transmission. An usage scenario is data transmission between CPU and connected devices, such as keyboard. Keyboard sends data to CPU in asynchronous transmission method.

Whenever an user presses a key in keyboard, the keyboard sends the character to CPU. An user generally presses keys in irregular delays. For each transmission, the keyboard generates a 7 bit character data. A parity bit is added with this 7bits, to create final 8bits character. Then this 8bits or 1byte data is preceded by a start bit and one or two stop bits. In final transmission, it becomes 10 or 11 bits in size.

Read more: How computer accepts input from keyboard?

Advantages of Asynchronous Transmission

  1. Sender can send data at any time and receiver can receive it at any time, requires no synchronization
  2. Receiver don’t have to wait for next packets, as each packet is a complete
  3. Sender requires no primary storage device to transmit data
  4. Asynchronous transmission seizes the opportunity of re-synchronization by using the start and stop bits
  5. Cost effective in nature

Disadvantages of Asynchronous Transmission

  1. Though the method is cost effective, it can become expensive in case of microwave or satellite, as the transmission medium remains idle when no data is transmitting.
  2. This is less efficient than synchronous transmission
  3. Slower data transmission speed

Usage of Asynchronous Transmission

Asynchronous transmission is used in transmitting data from computer to printer, punch-card reader to computer, computer to card puncher device, keyboard to computer etc.