An (m,k)-firm Elevation Policy to Increase the Robustness of Time-Driven Schedules in 5G Time-Sensitive Networks

Abstract: Current standardization efforts are advancing the integration of 5G and Time-Sensitive Networking (TSN) to facilitate the deployment of safety-critical industrial applications that require real-time communication. However, there remains a fundamental disconnect between the probabilistic 5G delay characteristics and the often idealistic delay models used to synthesize 5G-TSN network configurations. For time-driven schedules in particular, any delay outlier unforeseen during schedule synthesis can jeopardize the robustness of their real-time guarantees. To address this challenge, we present the (m,k)-firm Elevation Policy to uphold a base level of weakly hard real-time guarantees during unstable network conditions that do not match the expected delay characteristics. It augments the primary time-driven schedule with a dynamic priority-driven scheme to elevate the priority of m out of k consecutive frames if they are delayed. Our evaluations demonstrate that weakly hard real-time guarantees are essential to uphold the quality of control within a networked control system. At the same time, only a small overhead is imposed when the primary schedule can provide stronger quality of service guarantees. Our (m,k)-firm Elevation Policy thereby yields a robust but light-weight fallback mechanism to serve applications with meaningful guarantees during unstable network conditions.