For a source-destination pair to communicate in a connection-oriented wavelength-routed optical network, a connection in the optical layer between the two nodes must be established. This process, also known as Routing and Wavelength Assignment (RWS), is realized by selecting a path between the two end nodes and allocating a suitable wavelength. The aim of the RWA process is to find routes and assign wavelengths for connection requests in a way that minimizes the consumption of network resources, while at the same time ensuring that no two lightpaths are assigned the same wavelength on a shared fiber link. Routing and wavelength assignment in wavelength-routed WDM networks is a major design issue, especially when survivability is a requirement. To minimize resources in such networks operating under static traffic environment, the problems of routing and wavelength assignment must be solved jointly as a single problem. This study proposes a different approach to formulate the problems of routing and wavelength assignment as Integer Linear Programming (ILP) problem. Unlike other formulations, where the routing sub-problem and wavelength assignment sub-problem are considered separately, this approach addresses the RWA problem compounded. Although this approach increases the number of variables in the problem, it guarantees the optimal solution. Furthermore, the problem may in many cases be solved using simpler linear programming techniques.