Amongst data center structures, flattened butterfly (FBFly) networks have been shown to outperform their common counterparts such as fat-trees in terms of energy proportionality and cost efficiency. This efficiency is achieved by using less networking equipment (switches, ports, cables) at the expense of increased control plane complexity. In this paper we show that cabling complexity can be further reduced by an order of magnitude, by reconfiguring the optical fully meshed components into optical “pseudo”-fully meshed components. Following established methods, optical star networks are obtained by exchanging the FBFly's regular (grey) optical transceivers for dense wavelength division multiplexing (DWDM or colored) optical transceivers and placing an arrayed waveguide grating router (AWGR) in the center. Depending on the data center configuration and equipment prices, our colored FBFly (C-FBFly) proposal yields lower capital expenditure than the original FBFly. The key advantage of our structural modification of FBFly, however, is that in large FBFly networks (e.g., > 50K nodes) it reduces the number of inter-rack cables by a factor as large as 48.

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Optical systems and technologies have been radically changing the telecommunication networks for past 15 years; today wavelength division multiplexing (WDM) technology, optical amplifiers, and simple optical switching elements like optical add-drop multiplexers (OADMs) are used in the backbone networks of all operators worldwide. Optical systems nowadays provide the basis for cost-effective transmission of large amounts of bandwidth over the Internet, and will enable its future growth and the spreading of new applications and services. This paper summarizes the main trends in optical networking and investigates potential future application areas. Optical system technology has become so pervasive in network design that it needs to be considered in the context of provisioning new applications and services. Therefore, the analysis is not limited to the aspects of physical transmission, but also takes into account recent developments in integrated network design as well as network control and management. The following sections describe the key functionalities of future optical network architectures, and the key findings of the theoretical analysis are supported by the results of a field trial of advanced transmission technology