To reduce the energy consumption of the Internet, much research effort has been dedicated to the design of energy-minimized IP over WDM networks. In this study, we design energy-minimized IP over WDM networks based on modular router cards and by jointly applying the lightpath bypass and router-card sleeping strategies. As a key advantage, the design does not require rerouting of IP flows or optical channels in either the IP or optical layer. Rather, to save energy, we only need to sleep or wake up the router cards according to user traffic demands when applying the sleeping strategy, which significantly simplifies the network control and management. To minimize the total energy consumption of the IP over WDM network in a time period (e.g., 1 day), we develop a mixed integer linear programming (MILP) optimization model. Moreover, to alleviate the computational complexity of the MILP model, we divide the minimization problem into two subproblems, namely, 1) establishing a virtual topology and 2) allocating router ports on router cards to the optical channels on different virtual links. For each of the subproblems, we develop a separate MILP optimization model. Further, for large-network design, we also propose two efficient heuristics to optimize energy consumption. Simulation studies indicate that the joint MILP model with the lightpath bypass and router-card sleeping strategies can maximally reduce energy consumption, up to 40% compared to the nonsleeping case. In addition, under the router-card sleeping strategy, the approach of allocating the router ports on different router cards to the optical channels plays an important role in the design of an energy-minimized IP over WDM network. A mixed mode that jointly performs interleaving and sequential router-port allocations can achieve the highest energy savings.
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