Physical layer impairments are the major limitation for the high speed optical WDM/DWDM networks. They significantly affect the signal quality resulting poor quality of transmission which is normally expressed in terms of bit-error rate. To cope of with the future demand, increase in the no of channels and data speed further enhances these impairments. Hence new techniques are needed, which mitigate these impairments and ensure a better quality of transmission. Among the physical layer impairments we have studied the impact of in-band crosstalk on transmission performance of a transparent WDM/DWDM network. Error probabilities and power penalties produced by crosstalk are also investigated. As traditional RWA scheme pays a little regard to the physical layer impairments and cannot provide optimized network performance in practical networks, we have proposed a novel BER constrained, FWM aware RWA algorithm. The performance of the proposed algorithm is demonstrated through simulation and the results show that our algorithm not only gives a guaranteed quality of transmission but also improves the network performance in terms of blocking probability
