Core network physical topology design for energy efficiency and resilience

In previous work, we investigated the optimization of physical topology design so that the total operational and embodied energy is minimized under normal operation. However, the loss of any link, through for example a fiber cut or the loss of a node, may result in a higher energy consumption as the traffic will be re-routed over the remaining links of the network. In this paper we identify the impact of traffic re-routing in case of link failure on the network energy consumption by defining a parameter called Network Energy Resilience (NER). Calculating the NER of different topologies under the non-bypass approach shows an increase in the energy consumption, in case of a single link failure, up to 19%, associated with topologies of higher average hop count as the power consumption of a connection is more effected by its hop count than its length. In order to design energy resilient physical topologies, we develop a mixed integer linear programming (MILP) model that considers in addition to minimizing the operational and embodied energy, minimizing the average hop count to ensures that when a link fails and a connection is rerouted the new route is not much longer in terms of hop count than the original route. The model results show a reduced NER while the total energy consumption of the network has hardly increased.