Busy period analysis is often used as a basis for worst-case response time analysis of priority based systems. However, when shaping strategies are used to prevent starvation of lower priorities, it becomes difficult to achieve tightness results using this method. The reason for this is that a busy period is defined as the longest interval in which there exists pending load. It is exclusively based on execution time, and does not take the amount of provided bandwidth into account. As a consequence, it is less suitable for the study of idling systems. In particular, we do not yet have tightness results regarding the analysis of the Ethernet AVB standard, in which credit-based shaping is applied. In this paper, we propose an alternative to the use of busy periods. We show that, by defining an eligible interval in such a way that provisioning is taken into account, tight worst-case response time bounds can more easily be obtained for Ethernet AVB, at least in the case of either lower-or higher-priority interference.
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