Green routing and wavelength assignment in optical networks

As networks continue to expand, energy consumption is increasingly becoming a major issue, affecting not only the operational costs, but also the associated emission of greenhouse gasses (GHG). Thus, reducing power consumption, as well as GHGs (primarily CO2) to reduce the carbon footprint of the network, has started to play a significant role in network planning. In networks with both renewable and non-renewable power sources, minimizing only the overall power consumption without considering the associated CO2 levels emitted by individual nodes can lead to unnecessarily high levels of GHG emissions. Conversely, strictly minimizing GHG emission by avoiding non-renewable power sources may lead to longer routes with significantly increased overall power consumption (higher operational costs) which is not very attractive to operators. In this paper, we present a hybrid approach for green routing and wavelength assignment (RWA) in backbone optical networks which reduces both criteria, searching for an advantageous trade-off between costs and environmental-friendliness. An integer linear programming (ILP) formulation for the problem is proposed which minimizes the overall energy consumption as well as the total GHGs emitted, scaled by a tunable penalty factor. GHG emissions are calculated according to GHG-conversion factors of individual nodes representing the amount of CO2 emitted per kWh of energy consumed. Results indicate that advantageous trade-offs can be achieved by selecting appropriate penalty factor values which yield RWA solutions with low power consumption, GHG emissions, and, additionally, lower costs of the associated electric bill.