SIGCOMM '93 Conference proceedings on Communications architectures, protocols and applications
Bicriteria network design problems
Journal of Algorithms
Improved Steiner tree approximation in graphs
SODA '00 Proceedings of the eleventh annual ACM-SIAM symposium on Discrete algorithms
A Distributed Algorithm for Minimum-Weight Spanning Trees
ACM Transactions on Programming Languages and Systems (TOPLAS)
Core selection methods for multicast routing
ICCCN '95 Proceedings of the 4th International Conference on Computer Communications and Networks
Operations Research Letters
Distributed center-location algorithms
IEEE Journal on Selected Areas in Communications
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The selection of a core node in a network is a crucial step in the set-up of several multimedia applications such as videoconferences or multi-player games. For a given group of application users, a poorly chosen location can lead to a waste of bandwidth or to long communication delays. Since this kind of application usually involves unicast and multicast communications at the same time, we are naturally interested in a core location such that both the sum of the unicast path lengths to the users and the cost of the multicast tree spanning the users and the core are simultaneously small. While optimizing the first criterion is equivalent to finding a 1-median of the users, the second criterion corresponds to the minimum cost Steiner tree problem.The goal of this paper is to show that there always exists a core location for which both criteria are close to their optimum. More precisely, we give a continuum of results which proves in particular that both criteria can simultaneously be within 1.37 times their optimum. Finally we apply our results to the problem of minimizing a weighted sum of the criteria and we give an easy and fast heuristic with a small approximation ratio.