Two node-disjoint hop-constrained survivable network design and polyhedra

Given a weighted undirected graphGwith a set of pairs of terminals {si, ti}, i = 1, ..., d, and an integer L ≥ 2, the two node-disjoint hop-constrained survivable network design problem (TNHNDP) is to find a minimum weight subgraph of G such that between every si and ti there exist at least two node-disjoint paths of length at most L. This problem has applications to the design of survivable telecommunications networks with QoS-constraints. We discuss this problem from a polyhedral point of view. We present several classes of valid inequalities along with necessary and/or sufficient conditions for these inequalities to be facet defining. We also discuss separation routines for these classes of inequalities. Using this, we propose a Branch-and-Cut algorithm for the problem when L = 3, and present some computational results.