Independent yet Tight WCRT Analysis for Individual Priority Classes in Ethernet AVB

In the high-tech and automotive industry, bandwidth considerations and widely accepted standardization are two important reasons why Ethernet is currently being considered as an alternative solution for real-time communication (compared to the traditional fieldbusses). Although Ethernet was originally not intended for this purpose, the development of the Ethernet AVB standard enables its use for transporting high-volume data (e.g. from cameras and entertainment applications) with latency guarantees. The traditional busy-period analysis that ensures these latency guarantees relies on knowledge of all data streams, including interference. However, for complex industrial systems, the assumption that characteristics of all interfering data streams are known, is not realistic. As the amount of components connected to an Ethernet network grows, it becomes less likely that one can know or enforce the traffic patterns generated by all these components. In this paper, we present an independent real-time analysis based on so-called eligible intervals, which does not rely on any assumptions on interfering priority classes other than those enforced in the Ethernet AVB standard. We prove our analysis is tight when no additional information on interference is known. Furthermore, we compare the results of our approach to the two most recent busy-period analyses, point out sources of pessimism in these earlier works, and discuss the advantages of using eligible-intervals over busy-period analysis when studying idling servers.