A similar problem referred to is the logical (wave-length, virtual) topologydesign (LTD), which has been studied. The LTD problem tries to build a logicaltopology for a given traffic matrix over a WDM optical (fiber) network topology with the minimum possible congestion. In fact, the FTD problem is much more complex because it requires two routing treatments, i.e., routing the logical paths (lightpaths) over the fiber topology and routing the fiber links over the physical topology.