J. Xu, J
B. Randell
University of Newcastle upon Tyne. 1992
This paper describes a software fault tolerance scheme, called t/(n-1)-Variant Programming (or t/(n-1)-VP), which is based on a particular system diagnosis technique and thereby has some special advantages involving a simplified adjudication mechanism and enhanced capability of tolerating faults. A detailed dependability evaluation of the t/(n-1)-VP architecture is conducted, compared with existing software fault tolerance schemes. The results drawn from the comparison clearly show that t/(n-1)-VP is a viable addition or alternative to present techniques. Classical researches on the dependability analysis of software fault tolerance approaches have almost been based on the simplest examples of architectures which can only tolerate single software faults, without considering tolerance to multiple or related faults. The conclusions from some such analysis are thus restricted. The dependability evaluation carried out in this paper deals with more complicated and general software redundancy, i.e., architectures tolerating two or more faults. It is not a great surprise that we come to new conclusions:both t/(n-1)-VP and the n version programming approach (NVP) have the ability to tolerate some related faults between software variants; in general, t/(n-1)-VP would have the highest reliability, whereas NVP would be the best from the safety point of view.