Quantitative Comparison of the Error-Containment Capabilities of a Bus and a Star Topology in CAN Networks

There has been an increasing interest in using star topologies in field-bus communications, e. g., in Time Triggered Protocol for SAE class C applications (TTP/C), FlexRay, or controller area network (CAN), due to increased fault resilience and potential error-containment advantages. In this context, an innovative CAN-compliant star topology, CANcentrate, has been developed, whose hub includes enhanced fault-treatment mechanisms. However, despite this interest toward stars, it is still necessary to quantify their real dependability benefits. For this purpose and for the particular case of CAN, this paper presents models for the dependability features of CAN and CANcentrate using Stochastic Activity Networks (SANs). It quantitatively compares their reliability and error-containment capabilities under permanent hardware faults. These models rely on assumptions that ensure that results are not biased toward CANcentrate, which, in some cases, is too detrimental for it. Thus, despite not reflecting the full CANcentrate potential, results quantitatively confirm the improvement of error-containment it achieves over CAN. Additionally, the way in which the nodes' ability to contain their own errors affects the relevance of using a star topology has been quantified. Although this paper refers to the case of CAN, conclusions regarding the justification of using a star topology depending on this ability can be extrapolated to other field-bus technologies.