Strategies for Upgrading Multi-Granularity ROADMs in an Optical Transport Network

Abstract

Multi-granularity reconfigurable optical add-drop multiplexers (MG-ROADMs) can enhance the flexibility and resource utilization of optical transport networks (OTNs) in a cost-efficient manner, as they eliminate the need of expensive flexible wavelength selective switches (WSSs). This cost advantage makes MG-ROADM upgrades an attractive option for improving network performance. This paper addresses the problem of MG-ROADM upgrades and proposes three efficient upgrade strategies: traffic demand-based (TD), node connectivity-based (NC), and node upgradation gain-based (NUG). To evaluate their performance, we develop an efficient routing, granularity, and spectrum assignment (RGSA) algorithm that supports scheduling traffic demands in the optical networks where single-granularity (SG-) and MG-ROADMs coexist. Simulation results show that the NUG strategy selects an upgraded node set closely aligned with our developed mixed integer linear programming (MILP) optimization model, achieving higher average bandwidth utilization than the TD and NC strategies. © 2025 IEEE.