A method sets certain downstream traffic scheduling rules at an optical line terminal OLT and certain sleep control rules at optical network units ONUs. Both downstream traffic scheduling rules and sleep control rules are common information owned by both the OLT and ONUs. The method sets the traffic scheduling rules that each ONU is allocated with some time slots every cycle if the ONU has downstream traffic. Rather than using a control message to notify ONUs with their queue status, the method lets ONUs infer whether its downstream queue is empty or not based on downstream traffic scheduling and lets the OLT infer the status of an ONU based on sleep control rules.