In this paper, we solve the radiative transfer equation for slab geometry, taking into account rigourously the interfaces. We use the discrete ordinate method. We underline the
important role of interfaces in the ballistic regime and also the diffuse regime. The angular
distribution and amplitude of transmitted flux is sensitive to refractive index. We also solve the
RTE for a multilayered geometry slab and show the sensitivity of the angular distribution of
transmitted and reflected fluxes for thin layers.