A protocol used extensively in mainframe computer networks. With bisynchronous communications, both the sending and receiving devices must be synchronized before data transmission begins.
Data is collected into a package known as a frame. Each frame contains leading and trailing characters that allow the computers to synchronize their clocks. The structure of a bisynchronous communications frame is shown in the accompanying illustration. The STX and ETX control characters mark the beginning and end of the message. BCC is a set of characters used to verify the accuracy of the transmission.
A more modern form of this kind of protocol is SDLC (Synchronous Data Link Control), which is used in IBM's proprietary networking scheme, SNA.
See also asynchronous transmission; Synchronous Data Link Control.