BS 4505-3 specifies a method for detecting errors in information messages by attaching one block check character to the transmitted information block (or text) and checking this character when it is received. The method of correcting errors when they are detected is subject to the particular application and is performed at a higher level.
BS 4505-3 on longitudinal parity to detect errors in information messages is useful for:
In data communication systems the information formats and the redundancy in the data to be transmitted differ widely from one application to another. It is therefore clear that a number of classes of error protection systems may be required.
BS 4505-3 defines one method of error detection which satisfies a wide range of applications. This will help you to accompany the data block or text by one checking character (in addition to character parity) which is often referred to as the “Longitudinal Parity Method”.
Overall, BS 4505-3 specifies the systems which use the 7-bit coded character set which is the subject of ISO 646, the 7-bit coded character set for information processing interchange, and the basic mode of implementing this 7-bit code in data communication systems
ISO 1155:1978