Formal Methods for Energy-Efficient EPONs

Energy-efficient passive optical networks (PONs) have gained significant interest since they are estimated to be the largest energy consumers among the wired access networks for the next ten years. In Ethernet PONs (EPONs), the equipment placed at the customer premises, i.e., the optical network units (ONUs), has been shown to be responsible for almost 65% of the total EPON power consumption. Sleep mechanisms, implemented at ONUs' side, can contribute to the EPONs' energy-efficiency. However, the tradeoff between energy saving and quality of service (QoS) requirements should be carefully tuned, especially when the downstream transmission is considered, to achieve the desirable results. In this paper, we propose a general framework that exploits formal methods as an approach for EPONs' energy-efficiency. The idea is to build a holistic model representing both the state machine of the ONU in its details as well as the ONU's communication with the optical line terminal under EPONs' specifications. Verification results reveal that, guided by the QoS constraints and considering the transitions' cost, an “aggressive” policy defining long sleep periods of the 100 ms order can be up to 24.9% beneficial for energy-efficiency compared to a “conservative” policy with sleep periods of the 10 ms order.