Metropolitan optical networks: A survey on single-layer architectures

Metropolitan optical networks are undergoing significant transformations to continue being able to provide services that meet the requirements of the applications of the future. The current deployment of the 5G networks and the envisioned 6G cyber–physical systems would expand the possibilities for offering IoT applications, autonomous vehicles, and smart city services while imposing strong pressure on the physical infrastructure. In order to guarantee the strictest quality of service and quality of experience requirements for users, new architectures have been proposed in the literature for metropolitan optical networks, with a growing interest in the last five years. However, due to the proliferation of a dozen new architectures in the last years, many questions need to be investigated regarding the planning, implementation, and management of these architectures, before they could be considered for practical application. This work presents a comprehensive survey of the new proposed single-layer (purely optical) architectures for metropolitan optical networks. First, we discuss the structural organization of the new metro ecosystems. Second, the already established and novel architectures are presented, highlighting their characteristics and application. Third, we carry out a comparative analysis of these architectures to identify future technological trends. Finally, we have drawn outstanding research questions to help direct future research in the field.