The continuous growth of the Internet in the last decade has contributed to an unprecedented increase of the total amount of energy consumed by telecommunication networks worldwide. In this context, Wavelengths Division Multiplexed networks, besides providing benefits in terms of high transport capacity, have been recognized as an effective solution to achieve substantial power savings in core transport networks, which are the focus of our work. One critical issue for telecom operators is network resilience to failures. When provisioning network capacity, operators need to reserve additional (backup) resources, to be used in case of failures of currently used (i.e., working) resources. However, backup network resources do not need necessarily to be powered-on when not used. In fact some network services may have looser requirements in terms of connection recovery time, and they can be put into a low-power sleep (i.e., idle) state in order to save energy. Furthermore, according to the specific Quality of Service (QoS) to be guaranteed to the users, a different level of protection (i.e., dedicated/shared) or even no protection can be implemented for different demands, so energy consumption can be further reduced. In this paper, we provide an Integer Linear Program formulation for the power-minimized design of resilient optical core networks to investigate on the power saving obtained by enabling three power-reduction strategies: i) setting protection devices into low-power sleep state, ii) differentiating the level of protection provided to traffic demands according to their required QoS, and iii) adapting the devices (i.e. transmitting/receiving equipment) usage to a realistic hourly traffic variation profile. We find that up to 25% of power savings can be obtained in case of peak-hour traffic, while this advantage increases up to 63% during off-peak hours. Considering the energy consumption over a whole day, up to 44% of energy savings can be achieved.
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