CONCURRENCY AND COMPUTATION: PRACTICE AND EXPERIENCE Concurrency Computat.: Pract. Exper. 2010; 00:1–19 Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/cpe AOI-Cast in Distributed Virtual Environments: an Approach Based on Delay Tolerant Reverse Compass Routing Laura Ricci 1,3∗ , Luca Genovali 2 , Emanuele Carlini 1,2 , Massimo Coppola 1 , 1 Istituto di Scienza e Tecnologie dell’Informazione “A. Faedo”, ISTI-CNR, Pisa 2 IMT, Institutions, Markets, Technology, Institute for Advanced Studies, Lucca 3 Department of Computer Science, University of Pisa SUMMARY This paper presents a novel AOI-cast algorithm for Distributed Virtual Environments targeted to Delaunay- based P2P overlays. The algorithm exploits the mathematical properties of the Delaunay Triangulations to build a spanning tree supporting the notification of the events generated by a peer to the other ones located in its Area of Interest (AOI). The spanning tree is computed by reversing compass routing, a routing algorithm proposed for geometric networks. Our approach presents a set of novel features. First of all, it requires only the knowledge of the neighbours of a peer, so that the amount of traffic load on the P2P overlay is minimized. Furthermore, we prove that, for circular shaped AOI, the algorithm builds a spanning tree covering all and only the peers of the AOI. Finally, our approach takes into account the possible inconsistencies among the local views of the peers due to the network latency by introducing a tolerance threshold in the reverse compass routing. We present a set of simulations considering both synthetic data and real data traces taken from the HoN multiplayer game which show the effectiveness of our proposal. Copyright c  2010 John Wiley & Sons, Ltd. Received . . . KEY WORDS: Peer to Peer, Overlays, Distributed Virtual Environments, Delaunay, Voronoi, Multiplayer, Consistency 1. INTRODUCTION Distributed Virtual Environments (DVE)[1] such as military distributed simulations and massively multiplayer online games (MMOG), for instance World of Warcraft or Second Life, are currently gaining increasingly attention in the software market. In a DVE, users located at geographically distributed hosts interact within a virtual world which is populated by user controlled avatars. Each avatar moves within the DVE and may interact with other avatars and with the passive objects of the virtual world. Current DVE are generally developed according to a client server architecture where a single server is responsible both of the notifications of the avatar positional updates and of the management of the state which is modified due to clients interactions. According to this model, each client notifies any event to the central server, which, in turn, updates the state of the DVE and notifies the event to the interested clients. Furthermore, the server computes a meaningful ordering of the events. The main disadvantage of this solution lies into the low level of robustness and of scalability due to the presence of a single point of aggregation, which may easily saturate the bandwidth of the server. * Correspondence to: Laura Ricci, Dept of Computer Science, University of Pisa, e-mail: ricci@di.unipi.it † Please ensure that you use the most up to date class file, available from the CPE Home Page at http://www3.interscience.wiley.com/journal/117946197/grouphome/home.html Copyright c  2010 John Wiley & Sons, Ltd. Prepared using cpeauth.cls [Version: 2010/05/13 v3.00]