This paper addresses the issues of routing and wavelength allocation in multi-wavelength all-optical ring networks with and without wavelength conversion capabilities. A mathematical modeling based on integer linear programming and several heuristic approaches are investigated. It is shown that optimal routing and wavelength allocation in the systems with wavelength conversion can be achieved almost effortlessly for ring networks of up to 70 nodes using the mathematical modeling. However, if no wavelength conversion is permitted, the computational time of the mathematical modeling becomes excessive even with a network as small as 7-10 nodes.Accordingly, heuristic techniques are proposed and their performance is extensively evaluated on various traftic scenarios. In addition, this study includes an investigation of the use of wavelength conversion for improving network resource utilization in ring network structures.