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Recent IEEE and ITU-T standards for time division multiplexing-passive optical networks (TDM-PONs) with sleep mode recommend that the optical line terminal (OLT) in a TDM-PON should be in charge of invoking the optical network units (ONUs) to move into the sleep state in the absence of frames. It is considered that, upon upstream frame arrival, a sleeping ONU can leave the sleep state, in which an ONU turns off its transmitter or both its transmitter and receiver, immediately, prior to its assigned sleep interval length. In this paper, we refer to this approach as immediate early wake-up (IMEW). According to the standards, the OLT may or may not allow an ONU to trigger an early wake-up function (EWF) upon the upstream frames' arrival. If the OLT does not allow the EWF [we refer to this as not support early wake-up (NSEW)], an ONU should stay in the sleep state during its assigned sleep duration and buffer all the upstream frames while it is in this state. In IMEW, the upstream frames experience a small delay, but the ONU's energy consumption increases remarkably. Conversely, in NSEW, an ONU consumes less energy compared to IMEW at the price of increasing the upstream frame delay and the possibility of having its buffer overflow. In this paper, the limitations of IMEW and NSEW have motivated us to propose a novel early wake-up decision (EWuD) algorithm that aims at meeting the upstream frame delay requirement while reducing the ONUs' energy consumption as much as possible. The role of the EWuD algorithm is to select an appropriate time for triggering EWF, taking into consideration two factors: 1) buffer overflow probability and 2) delay requirement violation of upstream frames. We evaluate EWuD performances using our TDM-PON OPNET modular-based simulation model under a wide range of scenarios. The findings demonstrate that our proposed EWuD can successfully meet the delay requirements of all upstream frames while reducing the ONUs' energy consumption significantly.

Early wake-up decision algorithm for ONUs in TDM-PONs with sleep mode