In this paper, we investigate the wavelength assignment issue in wavelength-routed all-optical WDM networks with Sparse-Partial Wavelength Conversion. Traditionally, wavelength assignment is only designed for the purpose of decreasing the blocking probability. In Sparse-Partial Wavelength Conversion, wavelength assignment can be used to decrease the number of wavelength converters if keeping the same level of blocking probability. We propose three different wavelength assignment algorithms, namely Segment-First First Fit (SFFF), Path-First First-Fit (PFFF), and Minimum Converter Allocation (MCA). Our results show that MCA is the best one among the three, and it can achieve very close performance to Sparse Wavelength Conversion by using a very small number of wavelength converters. The performance of PFFF is very close to MCA, and it is very simple to be implemented.
Wavelength conversion has been shown as one of the key techniques that can improve the blocking performance in a wavelength-routed all-optical network. Given that wavelength converters nowadays are still very expensive, how to make effective use of the limited number of wavelength converters becomes an important issue. In this paper, we propose a novel sparse-partial wavelength conversion (SPWC) architecture with the inherent flexibility that can facilitate network carriers to migrate the optical backbone to support wavelength conversion. We demonstrate that this architecture can significantly save the number of wavelength converters while still achieving excellent blocking performance. We further investigate the wavelength converter placement problem. Simulation results indicate that, with appropriate wavelength assignment and wavelength converter placement scheme, the performance of the wavelength-routed all-optical network with only 1-5% of wavelength conversion capability is very close to that of the networks with full-complete wavelength conversion capability.
Blocking has been the key performance index in the design of an all-optical network. Existing research demonstrates that an effective routing and wavelength assignment (RWA) strategy and a proper wavelength converter placement algorithm are the two primary vehicles for improving the blocking performance. However, these two issues have largely been investigated separately in that the existing RWA algorithms have seldom considered the presence of wavelength conversion, while the wavelength converter placement algorithms have largely assumed that a static routing and random wavelength assignment algorithm is employed. In this paper we present some strong evidences that these two issues need to be considered jointly, and call for the re-examination of both RWA and wavelength converter placement.
This article is divided into two parts. First we demonstrate that the conventional RWA algorithms do not work well in the presence of wavelength conversion since they usually only take into consideration the distribution of available wavelengths, and do not explicitly consider the lengths of routes. Through extensive simulation over a variety of topologies, we demonstrate that a weighted least-congestion routing and first-fit wavelength assignment (WLCR-FF) RWA algorithm can achieve much better blocking performance than static routing, fixed-alternate routing, or least-loaded routing algorithms in the environment of sparse or full wavelength conversion.
Secondly, using simulation we show that a heuristic-based converter placement algorithm called Weighted Maximum Segment Length (WMSL) algorithm proposed for a simple dynamic RWA (i.e., the least-loaded routing algorithm) under sparse wavelength conversion, not only outperforms existing wavelength converter placement algorithms by a large margin, but also can achieve almost the same performance as that of full wavelength conversion using the same RWA algorithm.
Sparse wavelength conversion and appropriate routing and wavelength assignment (RWA) algorithms are the two key factors in improving the blocking performance in wavelength-routed all-optical networks. It has been shown that the optimal placement of a limited number of wavelength converters in an arbitrary mesh network is an NP complete problem. There have been various heuristic algorithms proposed in the literature, in which most of them assume that a static routing and random wavelength assignment RWA algorithm is employed. However, the existing work shows that fixed-alternate routing and dynamic routing RWA algorithms can achieve much better blocking performance. Our study in this paper further demonstrates that the wavelength converter placement and RWA algorithms are closely related in the sense that a well designed wavelength converter placement mechanism for a particular RWA algorithm might not work well with a different RWA algorithm. Therefore, the wavelength converter placement and the RWA have to be considered jointly. The objective of this paper is to investigate the wavelength converter placement problem under fixed-alternate routing algorithm and least-loaded routing algorithm. Under the fixed-alternate routing algorithm, we propose a heuristic algorithm called Minimum Blocking Probability First (MBPF) algorithm for wavelength converter placement. Under the least-loaded routing algorithm, we propose a heuristic converter placement algorithm called Weighted Maximum Segment Length (WMSL) algorithm. The objective of the converter placement algorithm is to minimize the overall blocking probability. Extensive simulation studies have been carried out over three typical mesh networks, including the 14-node NSFNET, 19-node EON and 38-node CTNET. We observe that the proposed algorithms not only outperform existing wavelength converter placement algorithms by a large margin, but they also can achieve almost the same performance comparing with full wavelength conversion under the same RWA algorithm.