Source : Free On-Line Dictionary of Computing

Binary Synchronous Transmission
     
         (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.
     
        (1997-01-07)