Achieving round-robin access in controller area networks

Controller Area Network (CAN) is a real-time network that was initially conceived for automotive applications, but which is now becoming very popular as a fieldbus for automated factory environments because of its appealing features and low implementation costs. Controller Area Networks (CANs) are being used more and more today to support communications in real-time systems. However, under heavy traffic conditions the CAN access protocol may exhibit a quite unfair behavior, in particular, when the control applications require the same quality of service to be ensured to a number of different objects. In this paper, a new technique is proposed which is based on CAN and introduces few changes to the original protocol. Such a solution is able to ensure a very fair behavior, which resembles the one obtained in token based networks while maintaining, at the same time, the reduced access delays typical of CAN when operating in low traffic conditions. Furthermore, it preserves an optimum degree of compatibility with the existing devices and applications based on CAN.