Energy proportional solutions are provided for computer networks such as datacenters. Congestion sensing heuristics are used to adaptively route traffic across links. Traffic intensity is sensed and links are dynamically activated as they are needed. As the offered load is decreased, the lower channel utilization is sensed and the link speed is reduced to save power. Flattened butterfly topologies can be used in a further power saving approach. Switch mechanisms are exploit the topology's capabilities by reconfiguring link speeds on-the-fly to match bandwidth and power with the traffic demand. For instance, the system may estimate the future bandwidth needs of each link and reconfigure its data rate to meet those requirements while consuming less power. In one configuration, a mechanism is provided where the switch tracks the utilization of each of its links over an epoch, and then makes an adjustment at the end of the epoch.