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Page 2 Lecture Notes in Computer Science 2865 Edited by G. Goos ...

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Complexity of Connected Components<strong>in</strong> Evolv<strong>in</strong>g Graphs and the Computationof Multicast Trees <strong>in</strong> Dynamic Networks ⋆Sandeep Bhadra 1 and Afonso Ferreira 21 Dept. of Electrical Eng<strong>in</strong>eer<strong>in</strong>g, Indian Institute of Technology,Madras, Chennai, Indiasandy@ee.iitm.ernet.<strong>in</strong>2 CNRS, I3S & INRIA-Sophia Antipolis, Projet Mascotte,2004 Rt. des Lucioles, BP93, F-06902 Sophia Antipolis, France.Afonso.Ferreira@<strong>in</strong>ria.frAbstract. New technologies and the deployment of mobile and nomadicservices are driv<strong>in</strong>g the emergence of complex communicationsnetworks, that have a highly dynamic behavior. This naturally engendersnew route-discovery problems under chang<strong>in</strong>g conditions over thesenetworks. Unfortunately, the temporal variations <strong>in</strong> the topology of dynamicnetworks are hard to be effectively captured <strong>in</strong> a classical graphmodel. In this paper, we use evolv<strong>in</strong>g graphs, which helps capture thedynamic characteristics of such networks, <strong>in</strong> order to compute multicasttrees with m<strong>in</strong>imum overall transmission time for a class of wirelessmobile dynamic networks. We first show that comput<strong>in</strong>g different typesof strongly connected components <strong>in</strong> evolv<strong>in</strong>g digraphs is NP-Complete,and then propose an algorithm to build all rooted directed m<strong>in</strong>imumspann<strong>in</strong>g trees <strong>in</strong> strongly connected dynamic networks.1 IntroductionInfrastructure-less mobile communication environments, such as mobile ad-hocnetworks and low earth orbit<strong>in</strong>g (LEO) satellite systems, present a paradigmshift from back-boned networks, such as cellular telephony, <strong>in</strong> that data is transferedfrom node to node via peer-to-peer <strong>in</strong>teractions and not over an underly<strong>in</strong>gbackbone of routers. Naturally, this engenders new problems regard<strong>in</strong>g optimalrout<strong>in</strong>g of data under various conditions over these dynamic networks [15].In this sett<strong>in</strong>g, the generalized case of mobile network rout<strong>in</strong>g us<strong>in</strong>g shortestpaths or least cost methods are complicated <strong>by</strong> the arbitrary movement ofthe mobile agents there<strong>by</strong> lead<strong>in</strong>g to random variations <strong>in</strong> l<strong>in</strong>k costs and connectivity[15]. This variable nature of the topology can be aprehended only <strong>by</strong>network updates of the l<strong>in</strong>k state between mov<strong>in</strong>g nodes, thus creat<strong>in</strong>g substantialcommunication overhead along the l<strong>in</strong>k. This naturally motivates study<strong>in</strong>g⋆ This work was partially supported <strong>by</strong> the European RTN project ARACNE, theEuropean FET project CRESCCO, and the AS CNRS Dynamo. It was done whilethe first author was visit<strong>in</strong>g the project MASCOTTE, INRIA/CNRS/UNSA.S. Pierre, M. Barbeau, and E. Kranakis (Eds.): ADHOC-NOW 2003, LNCS <strong>2865</strong>, pp. 259–270, 2003.c○ Spr<strong>in</strong>ger-Verlag Berl<strong>in</strong> Heidelberg 2003

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