Analysing and Upper Bounding Pessimism of Network Calculus Approach in SPQ-Based Real-Time Ethernet

Quality-of-Service mechanisms are required for the transmission of flows with different criticality levels on a real-time Ethernet network. Static Priority Queueing (SPQ) is such a popular mechanism since it can bound the impact of lower-criticality flows on higher-criticality ones. To ensure deadlines for critical flows, several worst-case traversal time (WCTT) analysis methods have been proposed for SPQ. However, they compute pessimistic upper bounds on delays, causing unnecessary network over-dimensioning. This paper identifies and analyses the sources of pessimism in Network Calculus based WCTT analysis under SPQ. We also propose a method to construct near-worst-case delay scenarios within a tractable search space, enabling estimation of an upper bound on pessimism. Our results reveal a significant gap between computed upper bounds and attainable near-worst-case delays, paving the way for improvements in WCTT analysis in real-time Ethernet networks.