Wavelength routed optical networks have emerged as a technology that can effectively utilize the enormous bandwidth of the optical fiber. Wavelength converters play an important role in enhancing the fiber utilization and reducing the overall call blocking probability of the network. As the distortion of the optical signal increases with the increase in the range of wavelength conversion in optical wavelength converters, limited range wavelength conversion assumes importance. Placement of wavelength converters is a NP complete problem in an arbitrary mesh network. In this paper, we investigate heuristics for placing limited range wavelength converters in arbitrary mesh wavelength routed optical networks. The objective is to achieve near optimal placement of limited range wavelength converters resulting in reduced blocking probabilities and low distortion of the optical signal. The proposed heuristic is to place limited range wavelength converters at the most congested nodes, nodes which lie on the long lightpaths and nodes where conversion of the optical signals is significantly high. We observe that limited range converters at a few nodes can provide almost the entire improvement in the blocking probability as the full range wavelength converters placed at all the nodes. Congestion control in the network is brought about by dynamically adjusting the weights of the channels in the link thereby balancing the load and reducing the average delay of the traffic in the entire network. Simulations have been carried out on a 12-node ring network, 14-node NSFNET, 19-node European Optical Network (EON), 30-node INET network and the results agree with the analysis.

A heuristic for placement of limited range wavelength converters in all-optical networks

Optical wavelength converters are expensive, and their technology is still evolving Deploying full conversion capability in all nodes of a large optical network would be prohibitively costly We present a new algorithm for the sparse placement of full wavelength converters based on the concept of a k-minimum dominating set (k-MDS) of graphs The k-MDS algorithm is used to select the best set of nodes that will be equipped with full-conversion capability To allow placement of full wavelength conversion at any arbitrary number of nodes, we introduce a HYBRID algorithm and compare its performance with the simulation-based k-BLK approach We also extend the k-MDS algorithm to the case of limited conversion capability by using a scalable and cost-effective node-sharing switch design Compared with full search algorithms previously proposed in the literature our algorithm has better blocking performance, has better time complexity, and avoids the local minimum problem The performance benefit of our algorithms is demonstrated by simulation

Dominating set algorithms for sparse placement of full and limited wavelengthconverters in WDM optical networks

Impact of wavelength converters in wavelength routed all-optical networks

Optical burst switching (OBS) is a proposed new communications technology that seeks to expand the use of optical technology in switching systems. However, many challenging issues have to be solved in order to pave the way for an effective implementation of OBS. Contention, which may occur when two or more bursts compete for the same wavelength on the same link, is a critical issue. Many contention resolution methods have been proposed in the literature but many of them are very vulnerable to network load and may suffer severe loss in case of heavy traffic. Basically, this problem is due to the lack of information at the nodes and the absence of global coordination between the edge routers. In this work, we propose another approach to avoid contention and decrease the loss. In this scheme, the intermediate nodes report the loss observed to the edge nodes so that they can adjust the traffic at the sources to meet an optimal network load. Furthermore, we propose a combination of contention reduction through congestion control and bursts retransmission to eliminate completely bursts loss. This new approach achieves fairness among all the edge nodes and enhances the robustness of the network. We also show through simulation that the proposed protocol is a viable solution for effectively reducing the conflict and increasing the bandwidth utilization for optical burst switching.

Congestion Control and Contention Elimination in Optical Burst Switching

This paper attempts to study the impact of wavelength converters in WDM wavelength routed all-optical networks. A new heuristic approach for placement of wavelength converters to reduce blocking probabilities is explored. Multihop virtual topology is designed to minimize the number and overall cost of the converters. Blocking probabilities for static lightpath establishment (SLE) and dynamic lightpath establishment (DLE) are analyzed. In the case of SLE, arranging lightpaths in ascending order of their path length reduces blocking probability. Wavelength converters placed at nodes with high nodal degree further reduces the blocking probabilities. Simulation studies performed on a 28-node USA long haul network and a 20-node arbitrary mesh network, validate the above observations.

P.S. Kumar

Papers

Performance analysis of wavelength converters in WDM wavelength routed optical networks