(m,k)-firm model has recently drawn many attentions for providing a flexible real-time system with graceful degradation of the QoS. DBP algorithm is an attractive one as it dynamically assigns the priorities according to the system's current state (QoS-aware scheduling). However DBP cannot readily be used for systems requiring deterministic (m,k)-firm guarantee since the schedulability analysis was not done in the original proposition. In this paper a sufficient schedulability condition is given to deterministically guarantee a set of periodic or sporadic activities (jobs) sharing a common non-preemptive server. This condition is used for bandwidth dimensioning of the communication system of the distributed control system showing its practical usefulness.