A Credit Rate Round-Robin (CRR) Scheduling to Avoid Priority Assignment for Real-Time Networks

Real-time networks employ traffic shaping and scheduling mechanisms to provide bounded and low-latency services for safety-critical traffic. However, strict priority (SP) scheduling, while commonly used to meet stringent timing requirements, can lead to a coupling between priority assignment and real-time assurance. This coupling means that the deadline requirements of different priority classes do not always align with the actual criticality of the traffic, potentially compromising the performance of lower-priority safety-critical applications. To address this issue, we explore the priority-coupling problem and propose a Credit Rate Round-robin (CRR) scheduling method that simultaneously guarantees real-time performance and reserves bandwidth for safety-critical traffic. CRR utilizes the logical bandwidth <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">idleSlope</i> as a weight factor for round-robin queues and is analyzed under two configurations: with and without an upper-bound credit limit. Evaluation experiments demonstrate that CRR effectively decouples priority from real-time performance. Specifically, compared to SP+CBS, CRR without an upper-bound credit reduces the average delay for medium- and low-priority traffic by 18% and 47%, respectively, with a corresponding 13% increase in the average delay for high-priority traffic. These results demonstrate that the proposed CRR scheduling effectively circumvents priority assignments and mitigates the priority-coupling issue, thereby ensuring reliable real-time transmission for safety-critical applications.