Wavelength conversion in WDM optical networks: Strategies and algorithms for limiting the number of converters in the optical cross-connects

This paper considers the problem of wavelength conversion in optical networks using wavelength division multiplexing technique. In the previous literature, two main wavelength routing and assignment strategies have been introduced: wavelength path (WP) and virtual wavelength path (VWP), depending on whether the signal stays on the same wavelength or is converted to another during its travel throughout the network. While the former method does not require any wavelength conversion, the latter needs wavelength conversion in each optical node and, in particular, a wavelength converter per each signal handled by the node itself. From the previous literature emerged that the VWP leads to optical cross-connect (OXC) with lower dimensions compared to the ones required by the WP scheme, and that the difference between the WP and VWP schemes increases as the number of wavelengths carried by each fiber increases. In this paper a new strategy is introduced, named partial virtual wavelength path (PVWP), with the related wavelength routing and assignment algorithm, which makes limited use of wavelength conversion compared to the VWP scheme, and allows the same advantages of VWP to be attained with lower OXC dimensions. The paper reports a comparative analysis among the different strategies, considering both the cases of a network without failures and a network with the possibility of failure restoration. The main result is that the proposed PVWP strategy allows the same advantages of the VWP scheme with a strongly reduced number of wavelength converters (around 5% of the number required by VWP scheme). This figure does not vary appreciably if failure restoration is considered. The new strategy can be adopted by using an opportune OXC architecture, as illustrated in the paper, which allow a limited number of converters to be shared among all the channels as a common pool.