Expected Time for Obtaining Dependable Data in Real-Time Environment

In real-time environment, data usually has a lifespan associated with it. The semantics and the importance of the data depend on the time when data is utilized. Hence, the process of getting a consensus data from a group of replicated units must not take longer time than the lifespan of the data. However, in real environments, every unit, faulty or non-faulty, may encounter delays when processing and sending their data which inevitably increases the time of acquiring a consensus. The latency for obtaining a valid data hence depends not only on the time when individual voters make their votes, but also on the accuracy and credibility of the votes. Thus, a new metric, i.e. credibility function, need be taken into account in evaluating expected time and deciding replications. This paper presents analytical solutions for expected time under different voting schemes when dependable data can be obtained. We also show that if not all voters are truthful, adding more replications does not improve much on the time of obtaining valid results.