In all optical WDM network the signal remains in optical domain between source and destination without optical to electrical (O-E) conversion at intermediate nodes. As the signal propagates through the network the fiber nonlinearities like four wave mixing (FWM), and stimulated Raman scattering (SRS) degrades the signal quality. This paper investigates the combined effect of FWM and SRS on the performance of WDM all optical networks. Performance comparison in terms of signal to noise ratio of the worst affected channel has been carried out when (a) thermal, shot, FWM and (b) thermal, shot, FWM and SRS noise are present. Numerical results are presented in the graphical forms for the practical values of parameters.