Dynamic routing at different layers in IP-over-WDM networks — Maximizing energy savings

We estimate potential energy savings in IP-over-WDM networks achieved by switching off router line cards in low-demand hours. We compare three approaches to react on dynamics in the IP traffic over time, Fufl, Dufl and Dudl. They provide different levels of freedom in adjusting the routing of lightpaths in the WDM layer and the routing of demands in the IP layer. Using MILP models based on three realistic network topologies as well as realistic demands, power, and cost values, we show that already a simple monitoring of the lightpath utilization in order to deactivate empty line cards (Fufl) may bring substantial benefits. The most significant savings, however, are achieved by rerouting traffic in the IP layer (Dufl). A sophisticated reoptimization of the virtual topology and the routing in the optical and electrical domains for every demand scenario (Dudl) yields nearly no additional profits in the considered networks. These results are independent of the ratio between the traffic demands and capacity granularity, the time scale, distribution of demands, and the network topology for Dufl and Dudl. The success of Fufl, however, depends on the spatial distribution of the traffic as well as on the ratio of traffic demands and lightpath capacity.