WDM Network Planning Research Articles

Two-level iterated local search for WDM network design problem with traffic grooming

Two important problems arise in WDM network planning: network design to minimize the operation cost and traffic grooming to maximize the usage of the high capacity channels. In practice, however, these two problems are usually simultaneously tackled, denoted as the network design problem with traffic grooming (NDG). In this paper, a mathematical formulation of the NDG problem is first presented. Then, this paper proposes a new metaheuristic algorithm based on two-level iterated local search (TL-ILS) to solve the NDG problem, where a novel tree search based neighborhood construction and a fast evaluation method are proposed, which not only enhance the algorithm's search efficiency but also provide a new perspective in designing neighborhoods for problems with graph structures. Our algorithm is tested on a set of benchmarks generated according to real application scenarios. We also propose a strengthening formulation of the original problem and a method to obtain the lower bound of the NDG problem. Computational results in comparison with the commercial software CPLEX and the lower bounds show the effectiveness of the proposed algorithm.

Resource Criticality Analysis of Static Resource Allocations and Its Applications in WDM Network Planning

Various static resource allocation algorithms have been used in WDM networks to allocate resources such as wavelength channels, transmitters, receivers, and wavelength converters to a given set of static lightpath demands. However, although optimized resource allocations can be obtained, it remains an open issue how to determine which resources are the bottlenecks in achieving better performance. Existing static resource allocation algorithms do not explicitly measure the impact of changes of network resources or lightpath demands on the design objective. We propose such a measurement based on the Lagrangian relaxation framework. We use the optimized values of Lagrange multipliers as a direct measurement of the criticality of resources. Such a quantitative measurement can be naturally acquired along with the optimization process to obtain the optimal solution (or a near-optimal solution) to the static routing and wavelength assignment problem. We investigate three practical applications of the resource criticality (RC) analysis in WDM network planning. In the first application, we use our proposed measurement to identify critical resources and thus to decide the best way to add or reallocate resources. In the second application, we estimate the impact of the addition or removal of lightpath demands on the design objective. This kind of estimation helps to set a proper price for lightpath demands. In the third application, the results of the RC analysis are used to speed up the convergence of the optimization process for different network scenarios.

Long-Term Planning of WDM Networks: A Comparison between Single-Period and Multi-Period Techniques

This paper studies the long-term planning (e.g. a planning horizon of 2 to 5 years) of survivable WDM networks. The problem is formulated as a multi-period model that combines network topology and capacity expansion. The ability to determine network expansion schedules of this type becomes increasingly important to the telecommunications industry and to its customers. Two inherently different solution methods are presented: a sequential single-period approach, which designs the networks for every time period separately in chronological order, and an integrated multi-period approach, which considers all time periods at once. For each of these approaches, different network design cost models can be applied. Extensive simulations on a wide range of problem instances are carried out, to measure the influence of the applied network design cost model and to assess the cost savings that can be expected by opting for a multi-period planning approach instead of a sequential network design method.