Several studies exhibit that the traffic load of routers only has a small influence on their energy consumption. Hence, the power consumption in networks is strongly related to the number of active network elements, such as interfaces, line cards, base chassis, etc. The goal is to find a routing that minimizes the (weighted) number of active network elements used when routing. In this chapter, the authors consider a simplified architecture where a connection between two routers is represented as a link joining two network interfaces. When a connection is not used, both network interfaces can be turned off. Therefore, in order to reduce power consumption, the goal is to find the routing that minimizes the number of used links while satisfying all the demands. The authors first define formally the problem and model it as an integer linear program. Then, they prove that this problem is not in APX, that is there is no polynomial-time constant-factor approximation algorithm. They propose a heuristic algorithm for this problem and also prove some negative results about basic greedy and probabilistic algorithms. Thus, the authors present a study on specific topologies, such as trees, grids, and complete graphs, that provides bounds and results useful for real topologies. They then exhibit the gain in terms of number of network interfaces (leading to a global reduction of approximately 33 MWh for a medium-sized backbone network) for a set of existing network topologies: the authors see that for almost all topologies more than one third of the network interfaces can be spared for usual ranges of operation. Finally, the authors discuss the impact of energy efficient routing on the stretch factor and on fault tolerance.
Energy Efficient Routing by Switching-Off Network Interfaces