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This paper studies multihop optical networks in which nodes employ wavelength routing switches that enable the establishment of wavelength division multiplexed (WDM) channels, called lightpaths, between node pairs. In fact, most optical networks are multifiber networks. The problem of dynamical routing and assignment of wavelength (RAW) in such networks is studied in this paper. Two resource assignment strategies, PACK and SPREAD, are proposed. By virtue of a layered-graph, routing and assignment of wavelength subproblems can be considered simultaneously. These two strategies can be used to solve the RAW problem in networks with even links as well as that in networks with uneven links. Simulation shows that layered-graph-based RAW algorithms perform better than the existing ones. It also shows that SPREAD with distributive use of network resources can achieve better performance than PACK with collective use of resources in multifiber networks. The layered-graph-based algorithms can effectively deal with the failure of the fiber/link and node. By making use of the special structure of the layered-graph, we propose a shortest path algorithm, whose complexity is lower than that of the standard shortest path algorithm.