Mathematical models for optimal usage of tributary cards in wavelength assignment for DWDM ring networks

We investigate the problem of optimal usage of tributary cards in wavelength assignment for DWDM ring networks. Previous work in the literature has mostly concentrated on the minimal wavelength assignment or the minimal add/drop wavelength assignment problem at the optical layer. When this problem is viewed at the service layer, a completely different picture emerges. Ring networks consist of physical nodes and fibers. In each node, physical or structural limitations may exist; for example, each node could only have a limited number of service cards, and each card could only have a limited number of ports. This imposes important practical constraints on the wavelength assignment problem. Without considering such constraints, the network designed may not be feasible to implement. In this paper, we propose a different approach to DWDM network design. In the new approach, the goal of the network design is to minimize the total number of tributary cards and the total number of ADMs, or to minimize the total number of tributary cards and the total number of wavelengths used in the system. A mathematical model is then developed for each case, followed by a heuristic algorithm for solving the problem as well as an illustrative example.