In distributed lightpath restoration in wavelength-routed networks, different restoration operations may compete for the same wavelength on the same link and get blocked though there are still plenty of idle capacities on the link. In this paper, we propose two different wavelength assignment methods within the same framework for lowering such type of blocking. Simulation results show that the proposed methods significantly outperform the existing ones. Theoretical analysis confirms the optimality of the proposed methods for a special case; while for a few most important more general cases, it is shown that the optimal performance cannot be guaranteed by any distributed wavelength assignment method with a predefined wavelength searching sequence. For different cases where the original lightpath establishment has adopted random and first-fit wavelength assignments respectively, we discuss the different concerns in developing efficient distributed restoration schemes.
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