Approximation algorithms for network design with metric costs

• Authors: Joseph Cheriyan;Adrian Vetta
• Venue: Proceedings of the thirty-seventh annual ACM symposium on Theory of computing
• Year: 2005

We study undirected networks with edge costs that satisfy the triangle inequality. Let n denote the number of nodes. We present an O(1)-approximation algorithm for a generalization of the metric-cost subset k-node-connectivity problem. Our approximation guarantee is proved via lower bounds that apply to the simple edge-connectivity version of the problem, where the requirements are for edge-disjoint paths rather than for openly node-disjoint paths. A corollary is that, for metric costs and for each k=1,2,…,n-1, there exists a k-node connected graph whose cost is within a factor of 24 of the cost of any simple k-edge connected graph. This resolves an open question in the area. Based on our O(1)-approximation algorithm, we present an O(log rmax)-approximation algorithm for the node-connectivity survivable network design problem where rmax denotes the maximum requirement over all pairs of nodes. Our results contrast with the case of edge costs of zero or one, where Kortsarz et al. [20]recently proved, assuming NP⊈, quasi-P, a hardness-of-approximation lower bound of 2log 1-εn for the subset k-node-connectivity problem, where ε denotes a small positive number.