  The energy demands of Ethernet links have been an active focus of research in
the recent years. This work has enabled a new generation of Energy Efficient
Ethernet (EEE) interfaces able to adapt their power consumption to the actual
traffic demands, thus yielding significant energy savings. With the energy
consumption of single network connections being a solved problem, in this paper
we focus on the energy demands of link aggregates that are commonly used to
increase the capacity of a network connection. We build on known energy models
of single EEE links to derive the energy demands of the whole aggregate as a
function on how the traffic load is spread among its powered links. We then
provide a practical method to share the load that minimizes overall energy
consumption with controlled packet delay, and prove that it is valid for a wide
range of EEE links. Finally, we validate our method with both synthetic and
real traffic traces captured in Internet backbones.
