Protection mechanisms for optical WDM networks based on wavelength converter multiplexing and backup path relocation techniques

In this paper, we consider the problem of routing connections in survivable wavelength-routed optical wavelength-division multiplexing (WDM) networks with wavelength conversion capabilities. A circuit-switched network architecture, using path-level protection to provide 100% protection guarantee to single link failures, is assumed. The blocking performance in such a network depends on the routing and wavelength assignment algorithm used and the amount of wavelength conversion available. Optical wavelength conversion, however is an expensive technology and may also cause signal degradation. Hence, it is important to effectively utilize the wavelength converters present in the network. With path protection, each connection is given a primary and a link-disjoint backup path. In this paper, we present four primary and backup route computation mechanisms that attempt to improve overall network performance compared to existing solutions. First, we present a routing algorithm, termed conversion free primary routing (CFPR) that tries to compute primary paths that do not require wavelength conversion. Next, we present a converter multiplexing technique that is used to share wavelength converters among multiple backup paths. We then propose a backup path relocation scheme that migrates existing backup paths, whenever needed, to accommodate more primary paths and also to obtain primary routes with fewer hops. Finally, we introduce modified CFPR (m-CFPR) that improves on CFPR by trying to find routes that will minimize relocations, while still maintaining the blocking performance. The proposed techniques are analyzed in detail using a discrete-event simulation model. The results show that significant reduction in blocking probability is possible with the proposed routing mechanisms. The converter multiplexing technique is seen to significantly reduce the number of connections blocked due to wavelength converter unavailability, and the number of wavelength converters required at each node, thus reducing system cost. The number of converters required at each node to achieve a given blocking probability is also seen to be four times lower, compared to existing architectures based on static shortest path routing. The proposed m-CFPR technique achieves the same blocking performance as that of CFPR, while requiring only one fourth the total number of relocations required with CFPR.