In WDM networks, the end users exchange information with each other through all optical WDM channels, called light-paths. A light-path must occupy the same wavelength on all the fiber links through which it traverses. In a WDM optical network, with a given set of connections, the question of setting up light-paths by routing and allocating a wavelength to each connection is called Routing and Wavelength Assignment (RWA) problem. Integer Linear Programming (ILP) is a mathematical formulation helps in minimizing and maximizing an object function under multiple constraints. This can help in formulating a mathematical model for RWA. This paper studies a mathematical model for RWA in WDM Optical networks which can lead to a good network planning. This paper suggests an enhancement proposal for Syrian telecommunication optical networks using ILP formulation.