Time-Varying Network Fault Model for the Design of Dependable Networked Embedded Systems

Dependability is becoming a key design aspect of today networked embedded systems (NES's) due to their increasing application to safety-critical tasks. Dependability evaluation must be based on modelling and simulation of faulty application behaviors, which must be related to faulty NES behaviors under actual defects. However, NES's behave differently from traditional embedded systems when testing activities are performed on them. In particular, issues arise on the definition of correct behavior, on the best point to observe it, and on the temporal properties of the faults to be injected. The paper describes these issues, discusses some possible solutions and presents a new time-varying network-based fault model to represent failures in a more abstract and efficient way. Finally, the fault model has been used to support the design of a network-based control application where packet losses, end-to-end delay and signal distortion must be carefully controlled.