The paper introduces a new analytical approach for estimating blocking probabilities in all-optical networks. The assumptions of the classical Lee approximation are discussed and their effects are evaluated. The paper proposes a better substitute for the independent link assumption. The new assumption takes all active paths, as well as all free links, as independent objects on the network topology. The new model is shown to generate estimates that fit exactly the blocking probabilities obtained through simulations on linear topologies using Poissonian, spatially homogeneous traffic. A extension to regular meshes is presented that is asymptotically good for very small and very large nodal degrees. Finally, the independent wavelength assumption is also evaluated for two different wavelength assignment algorithms.5285 324335Lee, C.Y., Analysis of switching networks (1955) Bell Syst. Tech. J., 34, pp. 1287-1315. , NovBarry, R.A., Humblet, P.A., Models of blocking probability in all-optical networks with and without wavelength changers (1996) IEEE J. Select. Areas Comm., 14 (5), pp. 858-867. , JunHui, J.Y., (1990) Switching and Traffic Theory for Integrated Broadband Networks, , Kluwer Academic PublishersZang, H., Jue, J.P., Mukherjee, B., A review of routing and wavelength assignment approaches for wavelength-routed optical WDM networks (2000) Optical Networks Magazine, 1 (1), pp. 47-60. , JanWaldman, H., Campelo, D.R., Camelo, R., Dynamic priority strategies for wavelength assignment in WDM rings (2000) Proc. IEEE GLOBECOM'00, pp. 1288-1292. , San Francisco, CA, NovFrey, M., Ndousse, T., Wavelength conversion and call connection probability in WDM networks (2001) IEEE Trans. Comm., 49 (10), pp. 1780-1787. , OctBirman, A., Computing Approximate Blocking Probabilities for a Class of All-Optical Networks (1996) IEEE J. Select. Areas Comm., 14 (5), pp. 852-857. , Jun