We develop a framework that supports impairment-aware lightpath routing and wavelength assignments in optical transport networks. Different from most existing studies, we consider a more generic optical transport network with physical-layer heterogeneity, including different fiber types, variable amplification span distances and attenuation coefficients. In addition, rather than a single amplifier type as in most of the existing studies, we consider multiple amplifier types for different amplification situations. Owing to the high cost of OEO regeneration, the total number of required regenerators is considered as the major objective for optimization. A signal-quality-aware routing algorithm is developed to find routes that are expected to require the fewest regenerators. The first-fit wavelength assignment algorithm is extended to assign wavelength(s) for lightpaths after placement of some regenerators which can freely function as wavelength converters. Simulation studies indicate that the proposed algorithm can significantly reduce the required number of regenerators compared to the simple shortest-path routing algorithm. Moreover, it is found that the signal-quality-aware algorithm shows stronger benefits when a network demonstrates higher physical-layer heterogeneity such as different fiber types and non-uniform span losses. The signal-quality-aware algorithm also demonstrates better performance when a network has a higher average nodal degree. Finally, the results indicate that multiple amplifier options are important for cost-effective optical transport network design. For a network with high physical-layer heterogeneity, multiple amplifier options can significantly reduce the required number of regenerators (up to 50%) over a single amplifier option.
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