In this paper we investigate and evaluate the performance of multicast routing in
grooming capable multi-layer optical wavelength division multiplexing (WDM) networks.
New wavelength-graph models are proposed for network equipments capable of optical-layer
branching of light-paths. We evaluate the cost-effectiveness of electronic and optical-layer
multicast and unicast as well. The high scalability of optical multicast against unicast
is also showed. All routing and technical constraints are formulated in ILP and realized
in our versatile simulator.