several heuristics for the IP and optical layers have been proposed within trend in general, simple mechanisms provide lower power savings than the sophisticated ones, but require low computation times. Moreover,our studies showed that the algorithms addressing the IP layer achieve remarkable results (up to 81% of energy savings in the investigated realistic scenarios), and should be considered (subject for further improvements ) by the standardization bodies. Finally, the number of changes dynamically performed in the network needs to be considered since it may impact the Quality of Service(QoS). However, we have proven in that sleep modes are effective even when only 2 to 3 network (re) configurations are allowed per day