Downstream-Based Scheduling for Energy Conservation in Green EPONs
Maximizing the Optical Network Unit's (ONU) sleep time is an effective approach for achieving maximum energy conservation in green Ethernet Passive Optical Networks (EPONs). While overlapping downstream and upstream ONU transmissions can maximize the ONU sleep time, it jeopardizes the Quality of Service (QoS) performance of the network, especially for downstream traffic in case the overlapping is based on the upstream time slot. In this paper, the authors study the downstream traffic performance in green EPONs under the limited service discipline and the upstream-based overlapped time window. Specifically, they first derive the expected mean packet delay, and then present a closed-form expression of the ONU sleep time, setting identical upstream/downstream transmission cycle times based on a maximum downstream traffic delay requirement.