In all optical network contention is a major issue. Nonlinearity is an inherent feature of fibre optic communication systems, and these nonlinear effects frequently impair the signal's quality as it travels through the optical fibre. However few nonlinearities may be used for performance enhancement as well. Four wave mixing (FWM) is a third-order Kerr type nonlinearity of an optical fiber. FWM occurs when two or more different wavelengths launched into a fiber and because of electric susceptibility new wavelengths generate. FWM occurring within a semiconductor optical amplifier (SOA) has been one of the most favorable methods of contention resolution in wavelength domain. In this paper realization of wavelength conversion using FWM in SOA has been proposed for contention resolution in WDM network due to its high conversion efficiency and fast speed response in all optical transmission.