Hierarchical scheduling to support differentiated services in Ethernet passive optical networks

The Ethernet passive optical network (EPON) has recently attracted more and more research attentions since it can be a perfect candidate for next generation access networks. Supporting differentiated services (DiffServ) is an important issue for service providers to design an EPON system. In this paper, we deploy the hierarchical scheduling for the medium access control (MAC) layer in EPONs, which consists of the inter-ONU scheduling and intra-ONU scheduling, to provide DiffServ as well as share the upstream bandwidth efficiently among multiple users. The inter-ONU scheduling among the ONUs uses the efficient MAC scheme that we have proposed before. It provides services to different ONUs based on the service level agreement (SLA). The intra-ONU scheduling within the ONU adopts the two-stage queuing (TSQ) mechanism to provide DiffServ to different traffics in the same ONU. It can provide better services to the lower-priority traffics to achieve better fairness than the strict priority queuing (SPQ) mechanism. The combined scheme greatly mitigates the light-load penalty that is obvious in other schemes. The simulation results show that our scheme for the hierarchical scheduling can effectively provide differentiated services for different types of traffics, and also achieve the fairness to some extent.