Ethernet passive optical networks (EPONs) are being designed to deliver different quality of service (QoS) to carry heterogeneous traffic of end users. For this purpose, hierarchical scheduling is needed for upstream bandwidth allocation, with high-level scheduling for inter-optical network unit (ONU) allocation and low-level scheduling for intra-ONU distribution. In this paper, we propose new User-oriented Hierarchical bandwidth Scheduling Algorithms (UHSAs) that support differentiated services and guaranteed fairness among end users. For inter-ONU scheduling, we adopt an improved hybrid cycle approach that separates a frame into a static part for high priority traffic and an adaptive dynamic part for low priority traffic. For intra-ONU scheduling, we propose credit-based scheduling approach to guarantee fairness among end users. To improve scheduling efficiency and lower queue management complexity, we design a novel credit-based common queue (CCQ) for each traffic class to enhance scheduling architecture and minimize average number of queues in the ONU. On the other hand, we propose a transmission priority scheme for different queue groups, which together with CCQ mechanism serves the objective of improving delay and delay variation performance of high priority traffic, guaranteeing throughput for bandwidth sensitive medium priority traffic, as well as providing fairness and throughput protection among different users. The UHSAs exhibit a feature of multiple transmission opportunities (M-opportunities) per-cycle for high priority traffic that is significant in improving delay and delay variation performance for high priority traffic as compared with previous solutions of single transmission opportunity (S-opportunity) per-cycle. Detailed simulation experiments are conducted to study the performance and validate the effectiveness of the proposed protocols. (C) 2010 Elsevier B.V. All rights reserved.
