Comparison of Local Deadline Assignment Techniques with FP/EDF Scheduling in a Real Time Context: Probabilistic QoS Guarantees

In this paper, we are interested in comparing local deadline assignment techniques in a multi-hop network supporting real time traffic with end to end delay constraints, when the FP/EDF scheduling is used. In each node, packets are scheduled according to their fixed priorities (FP), and within the same priority, packets are scheduled according to the earliest deadline first (EDF) policy, using local deadlines, which correspond to the sojourn times not to be exceeded in that node. Consequently, an accurate choice of these local deadlines must be done in order to respect the end to end delay constraint. As we are interested in giving probabilistic QoS guarantees, we develop a mathematical model to compare the performances of five existing deadlines assignment techniques in terms of deadline miss probabilities. We show that these techniques give very close results when the packets that miss their local deadlines aren´t discarded.