Response Time Guarantees for Atm-networked Control Systems

We present the Response-Time Analysis (RTA) method for providing real-time guarantees in Asynchronous Transfer Mode (ATM) communication networks, and evaluates its suitability for use in hard real-time factory-type environments. RTA provides an analysis of the network tra c which can be used by an admission control mechanism to determine if the timing requirements of a new connection can be guaranteed without violating the requirements of already admitted connections. This type of admission control is required by several multimedia and almost all real-time control applications. RTA is based on traditional xed-priority/rate-monotonic real-time CPU schedulability analysis. This makes it possible to combine communication analysis with CPU schedulability analysis, thus allowing system designers to use the same technique for assessing the timely behaviour of the entire system, including both CPU and network scheduling. The only assumption RTA makes about the ATM-network is that the switches should be equipped with prioritised output queues, something which is true for many commercial switches. The main focus of this paper is on evaluating RTA. In the evaluation we compare RTA with Weighted Fair Queueing (WFQ) and the Calculus of Network Delays (CND). WFQ is the currently most popular method for providing performance guarantees, and CND provides an alternative analysis for prioritised queueing. The comparison shows that RTA outperforms both WFQ and CND for a set of realistic tra c scenarios.