Traffic grooming problem (TGP) deals with efficiently combining low-speed traffic streams into high-capacity wavelength channels in order to improve bandwidth utilization and minimize network cost. In this paper, we investigate TGP in WDM optical networks regardless of underlying physical topology. The problem is formulated as an integer linear program (ILP) and a Lagrangian-based heuristic is proposed. Numerical results for ring and mesh networks are presented and analyzed.