Abstract
Double-link failure models, in which any two links in the network fail in an arbitrary order, are becoming critical in survivable optical network designs. Optical networks that are over-dimensioned and purposely preplanned for full protection against any single-link failure may not survive well in an event of a double-link failure. It is therefore important to understand how much impact a subsequent second link failure may have upon traffic recovery of both failed links. This paper primarily aims to investigate traffic recoverability when a double-link failure occurs. We propose several methods for improving traffic recovery without using additional backup capacities other than the existing backup resources available for single-link failure recovery. In each proposed method, integer linear programming formulation is derived to optimize the backup resource allocation. Numerical results on various network configurations have shed some light on how network operators can choose one of five alternative methods to better handle a double-link failure. From numerical results, Method 1 offers some improvement on the traffic recoverability of the second failed link without disturbing the recovered traffic of the first failed link. Method 2 reveals that the traffic recoverability of the first failed link can be improved if the backup routes of the unrecovered traffic of the first failed link can be reassigned. Method 3 is useful for maximizing the traffic recoverability of the first failed link. Method 4 further increases the recoverability of the second failed link while maintaining the same recoverability of the first failed link as Method 3. Finally, Method 5 accomplishes the maximum overall traffic recoverability.
Published Version
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