Wavelength division multiplexing (WDM) technology offers the capability of building wide-area networks with high speed. Reconfigurability is a key feature of a WDM network that enables the network logical topology to change dynamically in response to the changing traffic patterns. There are two important issues involved in the reconfiguration of a network logical topology. One is how to determine the new logical topology corresponding to the current topology. It needs to consider a trade-off between the performance of the new target topology and the cost of the topology transition from the current topology to the new one. The other is how to determine the transition sequence from the current topology to the new one. It needs to control the disruption to the network as less as possible during the reconfiguration process. In this paper, we focus on the latter problem and propose several heuristic algorithms that reconfigure logical topologies in wide-area wavelength-routed optical networks. Our reconfiguration algorithms attempt to control the disruption to the network as less as possible during the reconfiguration process. For this purpose, a lightpath is taken as the minimum reconfiguration unit. The proposed algorithms are evaluated by using an NFSNET-like network model with 16 nodes and 25 links. The results show that very simple algorithms provide very small computational complexity but poor performance, i.e., large network disruption, and that an efficient algorithm provides reasonable computational complexity and very good performance. More complex algorithms may improve performance somewhat further but have unrealistically large computational complexity.

The shuffle-like network (SL-Net) is known as a logical topology for WDM-based multihop packet-switched networks. Even if we fix the logical topology to an SL-Net, we can still reposition nodes in the SL-Net by re-tuning wavelengths of transmitters and/or receivers. In conventional node placement algorithms, routes between nodes are assumed to be given. In this paper, we propose two heuristic node placement algorithms for the SL-Net to decrease the average end-to-end packet transmission delay under a given traffic matrix in the case that routes are design variables. The principal idea is to prevent too many traffic flows from overlapping on any link. To attain the idea, in one of the algorithms, a node is selected one by one in a decreasing order of the sums of sending and receiving traffic requirements in nodes, and its placement and routes between the node and all the nodes already placed are simultaneously decided so that the maximum of the amounts of traffic on links at the moment is minimum. In the other algorithm, a node is selected in the same way, and first it is placed so that the average distance between the node and all the nodes already placed is as large as possible, and then routes between the node and all the nodes already placed are decided so that the maximum of the amounts of traffic on links at the moment is minimum. Numerical results for four typical traffic matrices show that either of the proposed algorithms has better performance than conventional algorithms for each matrix, and show that the proposed algorithms, which are based on a jointed optimization approach of node placement and routing, are superior to algorithms which execute node placement and routing as two isolated phases.

WDM optical networks represent the future direction of high capacity wide-area network applications. By creating optical paths between several nodes in the core networks, a logical topology can be created over the physical topology. By reconfiguring the logical topology, network resource utilization can be optimized corresponding to traffic pattern changes. From the viewpoint of network operation, the complexity of reconfiguration should be minimized as well. In this paper we consider the logical topology reconfiguration in arbitrary topology IP over WDM networks with balancing between network performance and operation complexity. The exact formulation of the logical topology reconfiguration problem is usually represented as Mixed Integer Linear Programming, but it grows intractable with increasing network size. Here we propose a simulated annealing approach in order to both determine the target topology with a smaller logical topology change and also satisfy the performance requirement. A threshold on the congestion performance requirement is used to balance the optimal congestion requirement and operation complexity. This is achieved by tuning this threshold to a feasible value. For effective solution discovery, a two-stage SA algorithm is developed for multiple objectives optimization.

In this paper we consider algorithms for the logical topology design and traffic grooming problem in WDM networks with router interface constraints as well as optical constraints. The optical constraints include restricted transmission range due to optical impairments as well as limits on the number of available wavelengths. We formulate this problem as an integer linear program which is NP-complete. We then introduce heuristic algorithms which use a graphical modeling tool called the Virtual Neighbor Graph and add lightpaths sequentially. The best performing heuristic uses a so-called Resource Efficiency Factor to determine the order in which paths are provisioned for the traffic demands. By giving priority to demands that can be routed over paths that make efficient use of network resources, it is able to achieve good performance both in terms of weighted hop count and network throughput. For finding optimal multi-hop paths sequentially, we introduce interface constraint shortest path problem and solve it using minimum weight perfect matching.

Several regular topologies have been proposed to be used as the logical topology for WDM networks. These topologies are usually evaluated and compared based on the metrics related to network performance. It can be simply shown that this is generally not sufficient since better network performance can be achieved by increasing more network facilities. However, doing this eventually increases the network cost. Thus, the comparison of topologies must be performed by using an evaluation function that includes both the network performance metric and the network cost. In this paper, we propose a model to find the optimum regular logical topology for wavelength routed WDM networks. ShuffleNet, de Bruijn graph, hypercube, Manhattan Street Network, and GEMNet are the five well-known and commonly used regular topologies compared in this paper. By solving the two subproblems on node placement optimization, and routing and wavelength assignment, we obtain the evaluation function used in the topology comparison. Numerical results show that GEMNet is the optimum logical topology for the wavelength routed WDM networks, where it can take one of the three forms of ShuffleNet, de Bruijn graph, and its own configurations.

In this paper, we address the survivable routing problem with and without wavelength-continuity constraints by proposing a new Integer Linear Programming (ILP) algorithm, which is based on a simplified necessary and sufficient condition. Numerical results are given and discussed to show the efficiency of our algorithm and the impact of wavelength-continuity constraints.

An IP (Internet Protocol) over WDM network is expected to be an infrastructure for the next-generation Internet by directly carrying IP packets on the WDM-based network. Among several architectures for IP over WDM networks, one promising way is to overlay a logical topology consisting of lightpaths over the physical WDM network so that IP packets are carried on the lightpaths. The conventional methods for designing the logical topology have been focusing on maximizing throughput of the traffic. However, when the WDM network is applied to IP, the end-to-end path provided by the logical topology of the WDM network is not suitable to IP since IP has its own metrics for route selection. In this paper, we propose a new heuristic algorithm to design a logical topology by considering the delay between nodes as an objective metric. This algorithm uses a non-bifurcated flow deviation to obtain a set of routes that IP packets are expected to traverse. Our proposal is then compared with conventional methods in terms of the average packet delays and throughput. It is shown that our method becomes effective when the number of wavelengths is a limited resource.