On the energy efficiency of IP-over-WDM networks

In the next 10 to 15 years the Internet will undergo a substantial increase especially with respect to the bandwidth required by end-users. Since the current Internet already consumes a not-negligible percentage of the total world electricity, reducing the energy consumption of telecom networks is expected to become an increasingly-important challenge, being unacceptable that the Internet energy consumption grows proportionally to the served bandwidth. In this paper we focus on backbone transport networks, that serve large aggregated amount of traffic. We compare three different network architectures which implement the Wavelength Division Multiplexing (WDM)-based transport of IP packets over optical fiber links (IP-over-WDM networks). The differences between these three architectures, which we identify as IP with no Bypass (IP-NB), IP with Bypass (IP-B) and IP with Bypass and Grooming (IP-BG), concern the capabilities of performing aggregation of traffic (grooming) and optical switching. IP-NB architecture performs grooming in every network node, where the traffic is electronically processed and forwarded by the IP routers. IP-B enables switching of wavelength channels directly in the optical domain, thus bypassing the processing of IP packets in the intermediate IP routers. This architecture does not provide grooming capabilities, but it just allows aggregation of different traffic demands to be established between the same source/destination pairs. IP-BG architecture represents an intermediate solution between the previous, since it provides both grooming capabilities (as for IP-NB) in order to efficiently exploit network capacity, and optical switching (as for IP-B) to reduce expensive electronic processing operations. We perform a comparative study between these three architectures showing the trade-off between the reduction of the power consumption or the cost of the networks, and we analyze how minimizing one of these two factors can influence the other.