Optical WDM networks based on multiple interconnected rings can be deployed to cover large geographical areas and still make use of the simple and fast ring protection mechanisms. However, WDM networks with a multi ring physical topology require a more complex routing and wavelength assignment methodology than single WDM rings. Furthermore, the ring interconnection architecture, used to support traversing inter ring lightpaths, influences the wavelength requirements as well as the network reliability. This paper considers three interconnection architectures for WDM shared protection rings and describes a novel routing and wavelength assignment methodology designed for these networks. The final purpose of the paper is to provide a comparison of the interconnection architectures, taking into account both the wavelength requirements and the expected reliability.