Optimal regenerator placement in survivable translucent networks

In optical networks, the optical reach is defined as the distance an optical signal can travel, before its quality degrades to a level that requires 3R-regeneration. In a translucent optical network, if an optical signal has to be communicated over a distance that exceeds the optical reach, the signal is regenerated at selected nodes of the network, so that the signal quality never degrades to an unacceptable level. Given a value of the optical reach, the goal of the Regenerator Placement Problem (RPP) in dynamic Physical Impairment aware Route and Wavelength Assignment (PI-RWA), for survivable translucent networks, is to identify the minimum number of nodes capable of 3R regeneration, so that every pair of nodes (u, v) can establish a lightpath (either transparent or translucent) from u to v. In a survivable network, even if any fault occurs, it must be guaranteed that every pair of surviving nodes (u, v) can still establish a lightpath (either transparent or translucent) from u to v, avoiding all faulty nodes/edges. In this paper we have presented a Integer Linear Program (ILP) formulation that can optimally solve the survivable RPP problem for practical-sized networks within a reasonable amount of time. We have used a branch-and-cut approach to implement our algorithm, where we have intercepted the optimization process with control callbacks from the CPLEX callable library to introduce new constraints, as needed.