Mertzios, G.B. and Sau, I. and Shalom, M. and Zaks, S. (2010) 'Placing regenerators in optical networks to satisfy multiple sets of requests.', in *Automata, Languages and Programming : 37th International Colloquium, ICALP 2010, 6-10 July 2010, Bordeaux, France ; proceedings, Part II.* Berlin, Heidelberg: Springer, pp. 333-344. Lecture notes in computer science. (6199).

## Abstract

The placement of regenerators in optical networks has become an active area of research during the last years. Given a set of lightpaths in a network G and a positive integer d, regenerators must be placed in such a way that in any lightpath there are no more than d hops without meeting a regenerator. While most of the research has focused on heuristics and simulations, the first theoretical study of the problem has been recently provided in [10], where the considered cost function is the number of locations in the network hosting regenerators. Nevertheless, in many situations a more accurate estimation of the real cost of the network is given by the total number of regenerators placed at the nodes, and this is the cost function we consider. Furthermore, in our model we assume that we are given a finite set of p possible traffic patterns (each given by a set of lightpaths), and our objective is to place the minimum number of regenerators at the nodes so that each of the traffic patterns is satisfied. While this problem can be easily solved when d = 1 or p = 1, we prove that for any fixed d,p ≥ 2 it does not admit a PTASUnknown control sequence '\textsc', even if G has maximum degree at most 3 and the lightpaths have length O(d)(d). We complement this hardness result with a constant-factor approximation algorithm with ratio ln (d ·p). We then study the case where G is a path, proving that the problem is NP-hard for any d,p ≥ 2, even if there are two edges of the path such that any lightpath uses at least one of them. Interestingly, we show that the problem is polynomial-time solvable in paths when all the lightpaths share the first edge of the path, as well as when the number of lightpaths sharing an edge is bounded. Finally, we generalize our model in two natural directions, which allows us to capture the model of [10] as a particular case, and we settle some questions that were left open in [10].

Item Type: | Book chapter |
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Additional Information: | This research was supported by the Israel Science Foundation (grant No. 1249/08) and by the British Council (grant No. UKTELHAI09). Event URL: http://icalp10.inria.fr/ |

Keywords: | Optical networks, Regenerators, Overprovisioning, Approximation algorithms, Hardness of approximation. |

Full text: | PDF - Accepted Version (319Kb) |

Status: | Peer-reviewed |

Publisher Web site: | http://dx.doi.org/10.1007/978-3-642-14162-1_28 |

Publisher statement: | The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-642-14162-1_28. |

Record Created: | 21 Feb 2012 15:20 |

Last Modified: | 22 Jun 2015 10:36 |

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