the amount of energy saved at the ONTs with respect to the case that no sleep mode policies are implemented depends strongly on how much the ONT is consuming during the standby state. We evaluated that the energy saved ranges from the 65% in the best case(the ONT in sleep mode consumes a negligible amount of power) to about 30% when a more conservative case is selected (the ONT in sleep mode consumes 50% of the power consumption in working mode.) Aggregated traffic in metro and core networks varies relatively smoothly over time the day-night traffic variation offers the possibility to reduce power consumption of the network during low demand hours by deactivation(either switch off or power saving mode) of idle network devices The method usually consists of rerouting traffic over a smaller number of devices in order to reduce the overall power consumption of the network