Providing line-of-sight in a free-space-optics based data center architecture

To overcome the shortcomings of traditional static (wired) data center architectures, we recently proposed FireFly, a fully-flexible and fully-wireless data center network fabric based on free space optical (FSO) links. To facilitate a clear line-of-sight between the FSO devices placed on racks, FireFly uses a full-ceiling mirror for beam redirection. Use of a full-ceiling mirror imposes significant operational and infrastructural challenge and expense. The focus of our paper is to propose and evaluate alternative schemes to provide line-of-sight for FSO links in FireFly. In particular, we propose two schemes: (i) strategically placed multiple but small overhead mirrors, and (2) towers on top of racks, on which FSOs can be placed at regular heights. We develop comprehensive techniques for the above suggested schemes, and demonstrate the viability of these schemes by evaluating their performance using simulations for various performance metrics of interest.