MUST: a quasi-round robin access scheme for CAN networks

Because of their low implementation costs, optimum responsiveness and widespread availability, controller area networks (CANs) are being more and more used today for supporting communications in real-time systems. However, under heavy traffic conditions, the access protocol of a CAN may exhibit a quite unfair behaviour, in particular when the control applications require that the same quality of service be ensured to a number of different objects. In this paper, a new technique is proposed, called MUST (medium utilisation state tracking), which is based on CANs and introduces few changes to the original protocol. Such a solution is able to ensure a very fair behaviour $which resembles the one obtained in token-based networks - while maintaining, at the same time, the reduced access delays typical of CANs when operating in low traffic conditions.