Probabilistic QoS Guarantees with FP/EDF Scheduling and Packet Discard in a Real Time Context: A Comparative Study of Local Deadline Assignment Techniques

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, assuming that packets which don’t respect their local delay constraints are discarded. 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 flows’ end-to-end delay constraints and minimize the packet discard rate. As we are interested in giving probabilistic QoS guarantees, we develop a mathematical model to compare the performances of five existing deadline assignment techniques. We show that all these techniques give very high packet discard rates. So, we propose to use another packet discard policy and we show that it gives better results.