Binary Synchronous Communication (BISYNC)

Binary Synchronous Communication (BISYNC) is a character-oriented communication protocol developed by IBM that uses synchronous transmission to transfer data between devices. In BISYNC, data is transmitted in structured blocks called frames, which include control characters for synchronization and error detection.

BISYNC was designed to provide reliable data communication by using a complex set of control characters to manage data flow and maintain synchronization between sender and receiver. The protocol uses either EBCDIC or ASCII encoding for character representation and was commonly used with 3270 terminals for mainframe communication.

Types of Frames

BISYNC uses several types of frames for different communication purposes:

• Data frames Contain the actual information being transmitted, including header and trailer sections with metadata such as length and destination.

• Control frames Manage data flow and synchronization using characters like ENQ (enquiry) and ACK (acknowledge).

• Error-checking frames Include integrity verification mechanisms such as Cyclic Redundancy Check (CRC) or checksums.

• Connection frames Establish and terminate connections between devices using control characters like SOH and EOT.

Control Characters for BISYNC

BISYNC relies on specific control characters to manage communication:

• ENQ (Enquiry) Requests acknowledgment from the receiver to confirm readiness for data reception.

• ACK (Acknowledge) Confirms successful data reception and readiness for more data.

• NAK (Negative Acknowledge) Indicates error detection and requests frame retransmission.

• SYN (Synchronous Idle) Maintains synchronization during idle periods.

• STX/ETX (Start/End of Text) Mark the beginning and end of data frames.

• SOH/EOT (Start of Heading/End of Transmission) Used for connection establishment and termination.

Multiple Block Data Transmission

BISYNC supports multiple block data frames to improve transmission efficiency by sending several data blocks in a single message. These frames include:

• Header section Contains block count, length information, and transmission metadata.

• Sequential data blocks Multiple fixed-length data segments transmitted consecutively.

• Trailer section Includes end-of-block indicators and error-checking information.

Advantages and Disadvantages

Conclusion

BISYNC was a pioneering synchronous communication protocol that provided reliable data transmission through structured frames and control characters. While largely replaced by modern protocols like TCP/IP, it laid important groundwork for character-oriented communication in mainframe environments.