Cost of Robustness of Independent WCRT Analysis for CBS of Ethernet AVB Using Eligible Intervals

The existing worst-case response time (WCRT) analysis for individual priority classes under credit-based shaping (CBS) in Ethernet AVB based on so-called eligible intervals is both independent and tight. This WCRT analysis does not rely on any assumptions on interfering inter-priority streams other than those enforced by the Ethernet standard. A major advantage of this independent analysis is that CBS may be viewed as resource reservation, where allocated bandwidth is both guaranteed and enforced. Although independent analysis provides inter-priority class robustness, it comes at a cost of over-provisioning bandwidth. We illustrate this cost of inter-priority class robustness by means of an example that requires 7.8 times the amount of bandwidth reservation for a given set of streams compared to a different analysis that takes knowledge of inter-priority streams into account.