In this paper, a semi-dynamic protection path configuration method is proposed for WDM optical networks. In the method, the protection path is established by connecting several sub-lightpaths from the source node to the destination node of the original working lightpath, as opposed to conventional path restoration method where a single protection lightpath between the source-destination pair performs restoration. The proposed method provides enhanced flexibility in protection path configuration and relieves the cost of spare capacity reservation. This paper also studies the effects of wavelength conversion capability of intermediate optical cross-connect nodes on protection path routing and spare capacity utilization. In terms of spare capacity utilization, the proposed method shows substantial reduction of spare capacity overhead compared with dedicated path restoration in all optical networks without wavelength conversion, and shows similar capacity efficiency compared with shared path restoration in opaque networks with full wavelength conversion capability. In terms of robustness, the proposed method shows nearly the same restoration ratio for double-link failure as that of dynamic restoration method.

In this paper, we propose a heuristic multicast routing algorithm, which minimizes the cost while satisfying both the wavelength required and hop length selection. The algorithm consists of two subproblems: the wavelength assignment & the routing path selection. For solving the wavelength assignment subproblem, an auxiliary graph is created where by the nodes and the links in the original network are transformed to the edges and the vertices, respectively, and the same availability wavelength of each edge is taken into a multicast group. Furthermore, for solving the routing path selection subproblem, the shortest-path routing strategy is adopted to choose transmission path between two multicast groups. Simulation results show that our algorithm performs much better than previously proposed algorithms with increasing call-connection probability by 28% and reducing the blocking probability by 52%.