Energy-aware Routing with Rate-adaptive Network Elements

In this paper we investigate the opportunity for network energy savings via rate adaptation and routing optimization. We are motivated by the fact that current networks are over-provisioned, underutilized, and their energy consumption is insensitive to traffic load. Of particular interest to us is whether energy-aware routing has the potential to offer significant benefits (compared to, say, traditional min-hop routing) even when network elements are rate-adaptive. In our model of rate-adaptive network elements, energy consumption is a linear (or alternatively convex) function of traffic that exhibits a discontinuity at zero. The latter represents the energy expenditure for maintaining the element active instead of turning it off completely, and is referred to as startup cost. Under this model, we simulate energy-aware routing on synthetic instances based on real network topologies obtained from the Rocketfuel project. It is observed that as the startup cost decreases, energy consumption is also reduced significantly, as anticipated. At the same time, the impact of energy-aware routing ­ which is quite substantial in all test instances when the startup cost is high ­ diminishes, but remains significant especially when traffic load is relatively low. Obviously, if energy were perfectly proportional to traffic, implying zero startup cost, energy-aware routing would offer no benefit compared to min-hop routing. Nevertheless, this extreme case seems impossible to achieve, and hence energyaware routing should be a viable approach, together with rate adaptation, towards network energy savings.