The FTD problem proposed in this paper seeks to optimize the length of lightpaths because long lightpaths (in terms of hop count) suffer from many disadvantages, so network topologies with relatively small and concentrated distributed lightpath lengths are preferred. Current design can take advantage of multi-granularity optical switching technology, which can be used to construct a reconfigurable fiber topology over a fixed physical topology by configuring the fiber crossconnects
(F-OXC) parts of the multi-granularity OXC nodes equipped in multi-granularity optical networks.