ISO 1155:1978 Overview
ISO 1155:1978 is an international standard developed by the International Organization for Standardization (ISO) that defines the use of longitudinal parity for detecting errors in information messages during data communication and processing. This standard addresses the need for reliable error detection in systems transmitting data using the 7-bit coded character set (ISO 646) and provides a robust method to identify errors by attaching a block check character to information blocks or text.
The standard was published in 1978 and is positioned within the broader scope of data communication protocols and error detection mechanisms to enhance data integrity during transmission.
Key Concepts in ISO 1155:1978
Longitudinal Parity Method
The core of ISO 1155:1978 is the longitudinal parity method, a technique for error detection that involves appending a block check character to the data block, which acts as an additional parity check beyond character-level parity.
- The block check character consists of 7 bits plus a parity bit.
- Each of the first 7 bits of the block check character is computed as the modulo 2 binary sum of all bits in the corresponding bit position across the transmitted characters in the block.
- The overall parity, including the block check character, must be even to ensure error detection.
- The parity bit sense follows the communication mode-odd parity for synchronous transmission, even parity for asynchronous transmission.
Block Check Character Generation
ISO 1155:1978 stipulates precise rules to generate the block check character:
- Summation for the block check character begins after the Start of Heading (SOH) or Start of Text (STX) characters.
- The SOH or STX character starting the block is excluded or included as specified when summing bits.
- All characters in the block-except certain control characters like SYN (Synchronous Idle)-are included in the checksum calculation up to the End of Transmission/Block (ETB) or End of Text (ETX).
- No characters may be introduced between the ETB/ETX and the block check character to maintain parity integrity.
Practical Applications
ISO 1155:1978 is vital for various data communication systems, particularly those employing 7-bit ASCII encoding. Common practical use cases include:
- Error detection in serial data transmission: Minimizes corrupted data reception in computer networks and telecommunications by identifying transmission errors through parity checks.
- Data integrity in messaging protocols: Ensures that information messages between devices are correct, reducing retransmissions.
- Embedded systems and industrial communication: Used in systems where reliable data exchange is critical and retransmission overhead must be minimized.
- Legacy system interoperability: Facilitates communication between devices adhering to older 7-bit coding and parity protocols.
By standardizing the longitudinal parity check method, ISO 1155 helps systems maintain a high level of data quality and integrity, providing a simple yet effective error detection mechanism.
Related Standards
ISO 1155:1978 works in concert with the following standards for comprehensive data communication and error handling:
- ISO 646: Specifies the 7-bit coded character set used for information processing interchange.
- ISO 1177: Defines character structure and parity bit rules for start/stop and synchronous transmission.
- ISO 1745: Covers basic mode control procedures for data communication systems using the 7-bit basic coded character set.
- Other error detection codes: Like cyclic redundancy checks (CRC) and checksum standards, complement parity checks for more robust error handling.
Understanding and implementing ISO 1155 alongside these standards ensures effective data exchange protocols adhering to international best practices.
Keywords: ISO 1155, longitudinal parity, error detection, information processing, block check character, 7-bit coded character, parity check, data communication, error detection code, ISO standards.
Open preview (PDF)Information processing — Use of longitudinal parity to detect errors in information messages