A novel heuristic algorithm that considers transmission impairment (especially amplified spontaneous emission (ASE) noise) is developed for traffic grooming in wavelength division multiplexing (WDM) optical networks. Span constraints, which are determined by the impairment, are added to constrain the maximal transparent reach limit of a lightpath. Under span constraints, a series of short lightpaths will be built up explicitly to relay traffic when a single lightpath cannot meet the requirement
