Hybrid fat-tree: extending fat-tree to exploit optical switch transparency with WDM

Data center networks are the underlying infrastructure supporting the exponential growth of cloud services. Several data center network architectures based on electronic switches or on a combination of electronic and optical switches have been suggested in order to cope with ever-increasing demands. However, a common analytic model describing the network architectures in terms of servers, switches, transceivers, and fibers is lacking. Hence, a true comparison of the scaling in power consumption and cost between different topologies is difficult. This work presents a mathematical framework defining electronic and hybrid topologies under the same model parameters. It explores how the introduction of wavelength-division multiplexing (WDM) and optical switches in Fat-Tree like topologies impact their scaling. We find that these technologies reduce the required number of switches by 45%, transceivers by 60%, and fibers by 50% in the minimum hybrid networks. In such networks, our real case scenario study based on 25G technologies available at present predicts power savings of at least 55% and cost savings of at least 48%. On top of that, larger savings are foreseen when increased port-density transceivers become available.