In transparent optical networks as the signal propagates through a transparent network it experiences the impact of a variety of quality degrading phenomena that are introduced by different types of signal distortions. In this chapter we present a new optical networking paradigm for mesh topology, in which the impact of physical layer impairments are considered in lightpath routing (routing and wavelength assignment) process and also is integrated in the control plane and network planning and operational tools. We also show that by taking into account both, the physical impairments characterized by the Q-factor, as we propose and the features of the electrical layer will have a strong impact onto the impairments constraints based routing The number of regenerator ports in optical nodes is another constraint which has a strong impact onto the routing. We show the impact of these ports to a routing that is based on impairment constraints where the electronic layer can support traffic gro...