Asynchronous communication is a communication where the sender is able to send the data at any time, and with any time gaps the sender desires. In other words, it can be said as a transmission of data without the use of an external clock signal. It is a mediated form of communication in which the sender and receiver are not concurrently engaged in communication. Asynchronous communication at the
. data link layer or higher protocol layers is called as statistical multiplexing or packet mode communication, example is asynchronous transfer mode (ATM). In contrast, synchronous transmission is a precisely timed stream of bits in which the start of a character is located by using a clocking mechanism. You can find more information here: http://en.wikipedia.org/wiki/Asynchronous_communication
