(Bisynch) An IBM link protocol, developed in the 1960 and popular in the 1970s and 1980s.

Binary Synchronous Transmission has been largely replaced in IBM environments with SDLC. Bisync was developed for batch communications between a System 360 computer and the IBM 2780 and 3780 Remote Job Entry (RJE) terminals. It supports RJE and on-line terminals in the CICS/VSE environment. It operates with EBCDIC or ASCII character sets. It requires that every message be acknowledged (ACK) or negatively acknowledged (NACK) so it has high transmission overhead. It is typically character oriented and half-duplex, although some of the bisync protocol flavours or dialects support binary transmission and full-duplex operation.