EVALUATING DYNAMIC FAILURE PROBABILITY FOR STREAMS WITH (M,K)-FIRM DEADLINES

A real-time stream is said to have (m, k)-firm deadlines if at least m out of any k consecutive customers from the stream must meet their re spective deadlines. Such a stream is said to have encountered a dynami c failure if fewer than m out of any k consecutive customers meet thei r deadlines. Hamdaoui and Ramanathan recently proposed a scheduling po licy called Distance Based Priority (DBP) in which customers are servi ced with a higher priority if their streams are closer to a dynamic fa ilure. In terms of reducing the probability of dynamic failure, Hamdao ui and Ramanathan also showed, using simulation, that the DBP policy i s better than a policy in which all customers are serviced at the same priority level. In this paper, an analytic model is developed for com puting the probability of dynamic failure of a real-time stream for th e DBP and the single priority schemes. This model is useful for provid ing statistical quality of service guarantees to real-time streams. Th e probability of dynamic failure computed using this model is compared to the results from a discrete-event simulator. The comparison shows that the model is accurate for low and moderate loads.