Achieving High Utilization in Guaranteed Services Networks Using Early-Deadline-First Scheduling

Among packet-scheduling disciplines for providing end-toend Quality-of-Service (QoS) guarantees to different applications, including real-time services, two classes of algorithms have received particular attention: those based on Generalized Processor Sharing (GPS) and those based on Earliest Deadline First (EDF). One reason for the popularity of GPS-based schemes is that their powerful properties can translate in simple Call Admission Control (CAC) procedures. The intense research on GPS has also resulted in very efficient implementation techniques, which have made the cost of these schedulers very affordable. The EDF discipline in conjunction with per-node traffic shaping (which we refer to as Rate-Controlled EDF (RC-EDF)) has also been recently proposed as a candidate for end-to-end QoS provisioning. However, an appropriate framework for CAC with RC-EDF has not been developed, nor the possible advantages of using RC-EDF in place of GPS have been properly characterized. Furthermore, the implementation complexity of an RCEDF server is potentially very high, and no technique to reduce cost has been proposed. In this paper, we first formulate an end-to-end CAC framework for RCEDF that can be implemented in practice. Then, using this framework, we numerically compare the schedulable regions of RC-EDF and GPS and show that, when the traffic mix in the network consists of connections with both stringent and loose delay requirements, RC-EDF can substantialy outperform GPS in the number of admitted connections, and thus achieve much higher network utilization. Finally, we propose a technique to substantially reduce the implementation complexity of a RC-EDF server.