With the steady growth of traffic volume in core networks, it is predicted that future optical network communication will be constrained mainly by cost and power consumption. Thus, for Internet sustainability, it will be necessary to ensure cost and power efficiency in optical networks. The aims of this study are (i) to identify the main sources of cost and power consumption in fixed-grid (SLR and MLR) and flexi-grid (OFDM) optical networks, and (ii) to compare techniques for improving cost and
