Approximation Algorithms for Nonuniform Buy-at-Bulk Network Design

  • Authors:
  • C. Chekuri;M. T. Hajiaghayi;G. Kortsarz;M. R. Salavatipour

  • Affiliations:
  • chekuri@cs.illinois.edu;hajiagha@research.att.com;guyk@crab.rutgers.edu;mreza@cs.ualberta.ca

  • Venue:
  • SIAM Journal on Computing
  • Year:
  • 2010

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Abstract

Buy-at-bulk network design problems arise in settings where the costs for purchasing or installing equipment exhibit economies of scale. The objective is to build a network of cheapest cost to support a given multicommodity flow demand between node pairs. We present approximation algorithms for buy-at-bulk network design problems with costs on both edges and nodes of an undirected graph. Our main result is the first poly-logarithmic approximation ratio for the non-uniform problem that allows different cost functions on each edge and node; the ratio we achieve is $O(\log^4 h)$, where $h$ is the number of demand pairs. In addition we present an $O(\log h)$ approximation for the single sink problem. Poly-logarithmic ratios for some related problems are also obtained. Our algorithm for the multicommodity problem is obtained via a reduction to the single source problem using the notion of junction trees. We believe that this presents a simple yet useful general technique for network design problems.