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

•Novel analytic model to describe different types of hybrid network architectures.•Set of equations to derive the number of servers, switches, transceivers, and fibers.•Investigation of the impact of deployment of optical switching and WDM technologies.•Comparison of topologies in terms of power consumption and cost with actual data.•Up to 45% reduction in the number of switches with only 4 WDM channels per fiber.