The wavelength-division multiplexing (WDM) technology has been extensively studied as a key technology to solve global information explosions. WDM multiplexes plural signal paths using different wavelengths into one optical fiber. Among WDM-based network architectures, this paper focuses on a double-ring network for a next-generation metropolitan area network (MAN). Each node is normally equipped with two pairs of fast-tunable transmitters and wavelength-fixed receivers (TT-FR) as interface to two fibers. To enhance the network performance, additional transmitters/receivers at nodes and receiver wavelengths should be assigned optimally depending on its design requirement, so that the bandwidth bottleneck can be resolved both on nodes and fibers. This paper formulates this node configuration problem as a combinatorial optimization problem and presents its two-phase heuristic algorithm using the greedy and variable depth search (VDS) methods. Our approach is evaluated through network simulations, where the results verify the effectiveness of this joint assignment approach.