Decoupling wavelength assignments in dedicated protection switching bidirectional lightpath

In a recent study about Wavelength Division Multiplexing (WDM) networks, the authors showed that by decoupling the wavelength assigned to the outward circuit from the wavelength assigned to the inward circuit of the same bidirectional unprotected lightpath, it is possible to reduce the total required number of Wavelength Converters (WCs) when compared to the conventional Wavelength Assignment (WA) solution, in which both outward and inward circuits are assigned the same wavelength [1]. The goal of this paper is to generalize the study in [1] to account for dedicated path protection switching mechanisms applied to bidirectional lightpaths. In doing so, a second factor must be accounted for in the study, i.e., the wavelength assigned to the working circuit may be decoupled from the wavelength assigned to the protection circuit. As a result, four design options are possible by either enforcing or relaxing each of the following two constraints: 1) lightpaths are (are not) required to be assigned the same wavelength for the inward and outward circuit; 2) lightpaths are (are not) required to be assigned the same wavelength for the working and protection circuit. The four design options are compared in terms of their required average number of WCs in the network, revealing that the WC usage may differ significantly depending on the design used.