Standard GMPLS protocols used for dynamic establishment of lightpaths in transparent optical networks suffer from lack of physical layer impairments (PLIs) information, which makes it difficult to evaluate optical feasibility. In this paper, we compare two impairment aware (IA)-GMPLS architectures: signalling based-in which RSVP-TE is extended to carry PLIs and hybrid architecture-in which RSVP-TE and OSPF-TE are extended to carry PLIs and wavelength availability information, respectively. We show that it is sufficient to extend OSPF-TE to disseminate wavelength availability information, while RSVP-TE carries PLIs to validate the optical feasibility and to achieve trade-off between performance and control overhead.