Does Rate Adaptation at Daily Timescales Make Sense?

Today, networking hardware is not fast enough to save energy with rate adaptation. Or is it? While we are not (yet) able to turn on and off line cards in milliseconds, we can do so a couple of times per day. The question is, does it make sense to save energy? It may: We estimate we could potentially save in the order of MWh per year with link sleeping and down-rating in a cloud provider network. Importantly, these are "easy" gains: They would come without modifying the routing state nor impacting the quality of service of the traffic; it only leverages the typically low utilization of the links. This study provides only a rough approximation of the potential savings of rate adaptation and leaves several practical questions open. More than anything else, it motivates further investigation of the approach.