Optimization problems in metro ring network design

Economic deployment of higher managed bit rates in SONET/SDH networks in the face of high demands for low-speed services requires efficient subwavelength traffic grooming. In order to achieve maximal cost savings, network design should incorporate significant traffic grooming in order to ensure better wavelength packing. However, the increasing traffic, especially in access and metro networks, indicates that service providers are likely to encounter fiber exhaust in the near future. In the face of increasing bandwidth requirements, hybrid SDH/WDM (or SONET/WDM) ring networks provide a graceful transition from purely SDH (or SONET) networks to WDM networks and thus enable service providers to retain much of their capital investment. This study investigates 3 major network optimization problems-demand grooming, demand routing and wavelength assignment, that are relevant to hybrid SDH/WDM network design. While the best overall solution for a hybrid SDH/WDM network is achieved by solving these three problems simultaneously, in practice, such monolithic formulations can become intractable and may lack robustness. Hence, it is worthwhile to solve these problems individually. We present formulations of specific variants of these problems and give solution details for some real networks.