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This work is focused on the routing and wavelength assignment (RWA) problem for bidirectional paths in all-optical WDM networks without wavelength conversion. For this end, we use an intelligent GMPLS-enabled control plane for bidirectional lightpath provisioning wherein the wavelength continuity constraint must be guaranteed on each direction (i.e. downstream and upstream). Whereas the existing GMPLS signalling protocol addresses an efficient solution for ensuring the wavelength restriction for downstream wavelength allocation, there is not a similar scheme for the upstream direction which results in high blocking of bidirectional paths. Thus, we propose a CSPF routing algorithm which is aware of the global wavelength usage, fostering the computation of routes which satisfy the wavelength constraint in both directions. The numerical results show the improvement (blocking probability) of the proposed CSPF algorithm compared with a classical bandwidth-based algorithm.