Routing and wavelength assignment versus wavelength converters placement in all-optical networks

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.