An apparatus comprising: a path computation element, PCE (320, 420), comprising a processor configured to: receive a path computation element protocol, PCEP, path computation request from a path computation client, PCC (310, 410), wherein the path computation request comprises an impairment validation request that directs the PCE (320, 420) to perform an impairment validation of a network path; after receiving the path computation request, compute a network path; perform an impairment validation of the network path specified by the impairment validation request; characterized in that the impairment validation request comprises an indicator that indicates whether the impairment validation should be performed at a network path level or at a network path link level, wherein the PCE (320, 420) performs the impairment validation of the network path based on the indicator by performing a validation of each link in the network path; and send a path computation reply to the PCC (310, 410), wherein the path computation reply comprises route and wavelength assignment, RWA, data indicating the impairment validations performed, the result of the validation, and the estimated impairment data associated with the network path's links. a path computation element, PCE (320, 420), comprising a processor configured to: receive a path computation element protocol, PCEP, path computation request from a path computation client, PCC (310, 410), wherein the path computation request comprises an impairment validation request that directs the PCE (320, 420) to perform an impairment validation of a network path; after receiving the path computation request, compute a network path; perform an impairment validation of the network path specified by the impairment validation request; characterized in that the impairment validation request comprises an indicator that indicates whether the impairment validation should be performed at a network path level or at a network path link level, wherein the PCE (320, 420) performs the impairment validation of the network path based on the indicator by performing a validation of each link in the network path; and send a path computation reply to the PCC (310, 410), wherein the path computation reply comprises route and wavelength assignment, RWA, data indicating the impairment validations performed, the result of the validation, and the estimated impairment data associated with the network path's links. receive a path computation element protocol, PCEP, path computation request from a path computation client, PCC (310, 410), wherein the path computation request comprises an impairment validation request that directs the PCE (320, 420) to perform an impairment validation of a network path; after receiving the path computation request, compute a network path; perform an impairment validation of the network path specified by the impairment validation request; characterized in that the impairment validation request comprises an indicator that indicates whether the impairment validation should be performed at a network path level or at a network path link level, wherein the PCE (320, 420) performs the impairment validation of the network path based on the indicator by performing a validation of each link in the network path; and send a path computation reply to the PCC (310, 410), wherein the path computation reply comprises route and wavelength assignment, RWA, data indicating the impairment validations performed, the result of the validation, and the estimated impairment data associated with the network path's links.