Abstract

The world's hunger for connectivity appears to be endlessly growing, yet the capacity of the networks that underpin that connectivity is anything but endless. This thesis explores both short and long term solutions for increasing the capacity of the largest and most capacious of these networks, the backbones upon which the Internet is built: optical transport networks. In the short term, Flexi-grid technology has emerged as the evolution of fixed-grid WDM optical networks, providing higher potential throughput but suffering from an aggravated form of the spectrum ragmentation problem that affects fixed-grid networks. A novel path-based metric to better evaluate the fragmentation of spectral resources in flexi-grid networks is presented, which considers both the fact that free spectrum slices may not be available on all the links of a path, and the likelihood that an end-to-end spectral void is usable to route incoming connections, and tested by means of simulations, finding that it outperforms existing ones from literature. For the longer term, Space Division Multiplexing (SDM) is a promising solution to overcome the looming fiber capacity crunch, and, perhaps more importantly, can offer a beneficial ratio between the expected capacity gains and the resulting increase in the cost of the network thanks to Joint and Fractional Joint Switching architectures and integrated transceivers and amplifiers. A model for such network is presented, and multiple heuristics for solving the Routing, Space and Spectrum Allocation problem are described, studied via simulations and iteratively improved, with the objective of quantifying the likely performance of several SDM architectures under multiple traffic scenarios. In addition, possible improvements to joint switching architectures, and an experimental SDN control plane for SDM networks, are presented and characterized, again by means of simulations. SDM is shown to be an attractive technology for increasing future transport networks capacity, at a reasonable cost.