Next-generation transport network nodes integrate optical switching of coarse-grained wavelength channels with electrical switching of fine-grained optical channel data units (ODUs). This node design aims at a compromise between improving the wavelength channel fill ratio and maximizing the optical bypass of full or near-full wavelength channels, thereby minimizing transponder requirements. Moreover, the utilization of a control plane aware of both layers provides the adequate means for the dynamic setup and tear-down of multi-granular services. This paper assesses the trade-off between the blocking performance perceived by the network operator and the size of the transponder pool available at each node for different network and traffic configurations.