Managing redundancy in CAN-based networks supporting N-Version Programming

Software is a major source of reliability degradation in dependable systems. One of the classical remedies is to provide software fault tolerance by using N-Version Programming (NVP). However, due to requirements on non-standard hardware and the need for changes and additions at all levels of the system, NVP solutions are costly, and have only been used in special cases.In a previous work, a low-cost architecture for NVP execution was developed. The key features of this architecture are the use of off-the-shelf components including communication standards and that the fault tolerance functionality, including voting, error detection, fault-masking, consistency management, and recovery, is moved into a separate redundancy management circuitry (one for each redundant computing node).In this article we present an improved design of that architecture, specifically resolving some potential inconsistencies that were not treated in detail in the original design. In particular, we present novel techniques for enforcing replica determinism.Our improved architecture is based on using the Controller Area Network (CAN). This choice goes beyond the obvious interest of using standards in order to reduce the cost, since all the rest of the architecture is designed to take full advantage of the CAN standard features, such as data consistency, in order to significantly reduce the complexity, the efficiency and the cost of the resultant system.Although initially developed for NVP, our redundancy management circuitry also supports other software replication techniques, such as active replication.