Conservative reliability assessment of a 2-channel software system when one of the channels is probably perfect

In this paper we subject to scrutiny some recent advances in conservative reliability assessment of 2-channel fault-tolerant software, based on the probability of perfection of one of the channels. Our approach extends the previous works by looking in detail at the implications of the assumptions made in these previous works about the relationships between the probability of failure of the channels and of the system, which have not been explored before. We demonstrate that the assumptions made by others impose significant constraints on the epistemic uncertainty of the probability of system failure and explore the implications of these constraints to derive new conservative bounds. An important difference of this work from the prior works is that we use a white-box model of a 2-channel system, while in the previous works a black-box system model was used. We discuss the limitations of an assessment based on a black-box model and compare our conservative results with those, derived by others using a black-box system model