I've been working for several years on an FAA document covering good practices for CRC and Checksum use. At long last this joint effort with Honeywell researchers has been issued by the FAA as an official report. Those of you who have seen my previous tutorial slides will recognize much of the material. But this is the official FAA-released version.
Selection of Cyclic Redundancy Code and Checksum Algorithms to Ensure Critical Data Integrity
Philip Koopman, Kevin Driscoll, Brendan Hall
This report explores the characteristics of checksums and cyclic redundancy codes (CRCs) in an aviation context. It includes a literature review, a discussion of error detection performance metrics, a comparison of various checksum and CRC approaches, and a proposed methodology for mapping CRC and checksum design parameters to aviation integrity requirements. Specific examples studied are Institute of Electrical and Electronics Engineers (IEEE) 802.3 CRC-32; Aeronautical Radio, Incorporated (ARINC)-629 error detection; ARINC-825 Controller Area Network (CAN) error detection; Fletcher checksum; and the Aeronautical Telecommunication Network (ATN)-32 checksum. Also considered are multiple error codes used together, specific effects relevant to communication networks, memory storage, and transferring data from nonvolatile to volatile memory.
Key findings include:
- (1) significant differences exist in effectiveness between error-code approaches, with CRCs being generally superior to checksums in a wide variety of contexts;
- (2) common practices and published standards may provide suboptimal (or sometimes even incorrect) information, requiring diligence in selecting practices to adopt in new standards and new systems;
- (3) error detection effectiveness depends on many factors, with the Hamming distance of the error code being of primary importance in many practical situations;
- (4) no one-size-fits-all error-coding approach exists, although this report does propose a procedure that can be followed to make a methodical decision as to which coding approach to adopt; and
- (5) a number of secondary considerations must be taken into account that can substantially influence the achieved error-detection effectiveness of a particular error-coding approach.
Official FAA site for the report is here: http://www.tc.faa.gov/its/worldpac/techrpt/tc14-49.pdf