Patent ID: 7362974

Claim:
A method for allocating a working lightpath and a spare lightpath to a connection request between a source node and a destination node of an optical network, said network comprising a number of nodes interconnected with each other by optical links according to a predetermined network topology, each optical link comprising at least one optical path, said method comprising the steps of: representing said network with a layered graph comprising a plurality of layers, each layer corresponding to and being labeled by a respective pair optical path-wavelength available in at least a portion of the network, each layer comprising a respective image node for each node of said network and a respective horizontal arc for each link of said network, so as to replicate in each layer said network topology, the layered graph further possibly comprising vertical arcs connecting with each other corresponding image nodes; assigning a cost at least to each horizontal arc in the layered graph, so as to determine an original layered graph; determining a first shortest path between an image of said source node and an image of said destination node on the original layered graph, said first shortest path comprising at least horizontal arcs and connecting at least two image nodes; providing a modified layered graph having: a) inverted horizontal arcs in place of the horizontal arcs of the first shortest path and in place of possible corresponding horizontal arcs thereof, such corresponding horizontal arcs connecting, in the original layered graph, image nodes connected by vertical arcs to the image nodes crossed by the first shortest path, each of said inverted horizontal arcs having an orientation and a cost opposite with respect to the orientation and the cost of the respective corresponding horizontal arc of the first shortest path; and b) no horizontal arcs in place of possible horizontal arcs corresponding, in the original layered graph, to the horizontal arcs of the first shortest path, such possible horizontal arcs connecting, in the original layered graph, image nodes not connected by vertical arcs to the image nodes crossed by the first shortest path; determining a second shortest path between an image of said source node and an image of said destination node on the modified layered graph, said second shortest path comprising at least horizontal arcs; eliminating possible co-linked horizontal arcs of said first and said second shortest path; connecting the horizontal arcs of said first and said second shortest path remaining after said step of eliminating, so as to build a working path and a spare path between an image of said source node and an image of said destination node; and associating to said working and spare path respectively said working and spare lightpath on said optical network.