asynchronous transmission

Data transfer method in which signals are sent in spurts, spaced by varying time intervals. Each data character is preceded by a start-bit and is followed by an end-bit to inform the receiving equipment where the character begins and ends. This arrangement is in contrast to synchronous transmission where data is sent in continuous blocks of characters (called 'frames' or 'packets') spaced by fixed time intervals. Asynchronous transmission is used commonly for communications over telephone lines, whereas most network protocols (such as Ethernet, SONET, Token Ring) use synchronous transmission.