Traffic shaping in real-time distributed systems: a low-complexity approach

In real-time systems, one generally identifies two types of timing requirem ents, hard and soft constraints. In this study, it is assumed that the Hard Real-Time traffic (HRT) is periodic with deadlines that must be guaranteed , while the Soft Real-Time traffic (SRT) is aperiodic with timing constrain ts that could occasionally be missed without major consequences. In this pa per, the problem of scheduling these two types of traffic with different pe rformance objectives will be addressed: (1) ensure that the timing requirem ents of HRT traffic are met; (2) minimize as much as possible the response time of SRT traffic while satisfying (1). For this purpose, we propose an e asily implementable and low-complexity traffic shaping policy, which preser ves feasibility and improves response times for SRT traffic. The underlying idea is that it is possible to diminish the response time of SRT traffic i f the busy periods induced by the HRT traffic are "harmoniously" distribute d over time, creating time intervals during which the resource (i.e, the pr ocessor or the medium) can be used by SRT traffic with minimum delay. A com puter-implementable algorithm that has to be executed independently on each node of the bus is also provided, as well as several extensions of the ori ginal model. (C) 1999 Elsevier Science B.V. All rights reserved.