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We investigate connection provisioning in an all-optical wavelength-division multiplexing (WDM) network in the presence of physical-layer impairments. As the channel bit rate increases, impairments pose a more serious problem, and lightpaths need to be routed intelligently, so that the destination node receives the signal with adequate quality. We study the models of major physical impairments that affect optical signals. With reasonable assumptions, we model the major impairments as link-based metrics and we formulate schemes for routing, which consider the impairment constraints imposed by the underlying physical infrastructure. Prior work in this area has focused on enumerating a set of paths based on criteria such as minimum hops/distances, and then selecting a path from this set based on complex calculations of signal quality. Our approach integrates verification of impairment constraints while searching for paths. Routing with multiple additive constraints being NP-hard, we give an optimal heuristic algorithm with fast execution time for practical networks, as well as a dynamic programming pseudo-polynomial-time algorithm for the case when one impairment constraint dominates. We also examine the case of a practical ??all-optical?? network with signal regeneration facility at some nodes. We explore routing in such a translucent network and discover that finding a simple feasible path passing through a regenerator is NP-complete.