In a transparent optical network it is desirable to have design control over the length of normal working paths and over the end-to-end length of paths in any restored network state. An obvious approach with p-cycles is to limit the maximum allowable circumference of candidate cycles considered in the network design. But this is somewhat inefficient and does not directly control the end-to-end length of paths in a restored state; it only controls the maximum length of protection path-segments that might be substituted into a working path on failure. Another basic strategy is now considered. It consists of systematically matching shorter working paths with longer protection path-segments through p-cycles, and vice versa, with direct consideration of the end-to-end length of paths in the restored network state during the design. This complementary matching notion is studied through an integer linear programming (ILP) model to minimize cost while intelligently associating longer working paths with shorter protection path-segments and vice versa. The basic ILP is adapted in one case to minimize the average restored state path lengths; in another to achieve the least possible longest path length; and, finally, to also constrain all restored path lengths under a fixed limit. Each variation can also be subject to a requirement of using only the theoretically minimal spare capacity or, through bi-criteria methods, a minimal amount of additional spare capacity for the corresponding objective on path lengths. Taken overall the work provides the means to design an entire transparent survivable island that respects the transparent reach limits of a given ultra-long-haul technology. A heuristic combination of ILP and genetic algorithm methods is also developed to solve some of the larger problems and is shown to perform well.
© 2008 Optical Society of AmericaPDF Article