Difference Between Synchronous and Asynchronous Transmission

Sr. No.	Synchronous Transmission	Asynchronous Transmission
1	Synchronous data transmission is a data transfer method in which a continuous stream of data signals is accompanied by timing signals (generated by an electronic clock) to ensure that the transmitter and the receiver are in step (synchronized) with one another. The data is sent in blocks (called frames or packets) spaced by fixed time intervals.	In contrast, asynchronous transmission works in spurts and must insert a start bit before each data character and a stop bit at its termination to inform the receiver where it begins and ends. The term asynchronous is used to describe the process where transmitted data is encoded with start and stop bits, specifying the beginning and end of each character.
2	It uses start and stop frames.	It uses start and stop bits.
3	Synchronous Transmission sends packets of characters at a time. Each packet is preceded by a Start Frame. This Start Frame is used to tell the receiving station that a new packet of characters is arriving, and it   synchronizes the receiving station’s internal clock. The packets also have End Frames to indicate the end of the packet.	Asynchronous Transmission sends only 1 character at a time. A character can be a letter of the alphabet, a  number or a control character. Preceding each character is a Start bit and ending each character is 1 or more Stop bits.
4	Synchronous transmission is more difficult and  expensive to implement than asynchronous.	Asynchronous transmission is simple and inexpensive to implement.
5	It is used with all higher-communication transfer rates (Ethernet, Token Ring, etc.).	It is used mainly with Serial Ports and dialup connections to the Internet or Bulletin boards.