Logical topology design for fault-tolerant WDM networks

All-optical networks (AON), using wavelength division multiplexing (WDM), have become attractive candidates for building wide area networks (WANs). Finding a logical topology and a routing scheme making optimum use of network resources is a challenging task. A complication is that the survivability of AON has become an important issue. In designing a fault tolerant WDM network, the primary lightpaths, the corresponding backup lightpaths, and the routing scheme have to be determined simultaneously in such a way that network resources are used in an optimum manner. In this paper we first develop an Integer Linear Formulation (ILP) for designing a fault-tolerant logical using shared path protection. The objective is to design a survivable logical topology and a routing over that topology in such a way that the overall congestion is minimized. This formulation can be solved to give us the optimum logical topology for small WDM networks. However, for larger networks, this approach becomes infeasible due the large number of constraints and integer variables. For such networks, we outline a simple heuristic algorithm to find a feasible logical topology.