GMPLS protocol suite is unaware of optical signal physical impairments and quality of transmission. However, optical path computation and signaling nowadays requires to verify its practical feasibility considering the optical impairments (e.g. attenuation, PMD, etc) such that the end-to-end physical signals has an acceptable quality. In fact, current deployments of Wavelength Switched Optical Networks (WSON) implementations are subject to either transponder upgrade in bit rate or switching capability in network element, such that many wavelength paths cannot be any more considered pre-validated from the original network design phase. In this paper, the general problem of impairment-aware path computation is presented and then solutions based on extensions of the GMPLS signaling protocol are considered. Specifically, an overview is presented where different approaches for implementing Quality of Transmission (QoT) estimation and QoT measurements in transparent networks are outlined. In addition, techniques for exploiting sparse regeneration in translucent networks are illustrated. Numerical results show that the proposed schemes are effective in finding or designating QoT-validated paths in only a few set-up attempts when a fully transparent path is available. If the transparent path becomes unfeasible, the translucent approach is adopted showing how to optimally designate intermediate regenerators to satisfy the end-to-end QoT constraints.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.