| The introduction of end-to-end (multi hop) optical circuits (lightpaths) is often seen as the natural extension of a point-to-point (single hop) Wavelength Division Multiplexing (WDM) transmission system, spanning across optical cross-connect nodes. Conventionally, a bidirectional lightpath (whether single or multi hop) comprises two lambda channels in fibers with opposite directions of signal propagation, which are assigned the same wavelength. This constraint is referred to as Identical Wavelength in Bidirectional Lightpath (IWBL).;While IWBL is a natural and historical choice in point-to-point system, the authors are going to demonstrate that IWBL may unnecessarily increase the number of Wavelength Converters (WCs), which are required to establish lightpaths in the network when the wavelength continuity constraint cannot be met. In the study, the IWBL constraint is relaxed, thus allowing the assignment of two distinct wavelengths to the same lightpath, one for each direction. A wavelength assignment algorithm is designed to both take advantage of the IWBL constraint relaxation and minimize the required number of WCs to establish a given set of lightpaths. The algorithm is then applied to a number of network topologies. The outcome has been analyzed in regular topologies as well as randomly generated topologies.;A second factor also has been accounted for in the study in dedication protection lightpaths, i.e., the identical wavelength constraint for the working and protection path called the Identical Wavelength in Protected Lightpath (IWPL) constraint. 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.;Network element failure may occur due to natural disasters, malfunctioning components, or human errors. For this reason, robust protection mechanisms resort to standby network resources, which are readily available upon failure occurrence. Preemption-based restoration mechanisms applied to optical connections (lightpaths) in WDM networks has been explored. The rationale for preempting some of the still functioning lightpaths—while performing rerouting of the failing ones—is to avoid highly unfair scenarios in which some node pairs starve for lightpaths significantly more than other pairs do, as a consequence of a failing network element. |
