Enhancement of Collaborative Interest Management Mechanism for P2P Networked Virtual Environment Cheng Liu, Wentong Cai Parallel and Distributed Computing Center School of Computer Engineering Nanyang Technological University Singapore 639798 {LIUC0012, aswtcai}@ntu.edu.sg Abstract—Interest Management (IM) aims at eliminating ir- relevant state updates transmitted in Networked Virtual Envi- ronment (NVE), such as online games. The existing IM mech- anisms include area-based, cell-based mechanisms and hybrid IM mechanism which reduces the communication overhead by utilizing the cell-based mechanism to reduce Area-Of-Interest (AOI) updates in the area-based mechanism. Comparing to the existing IM mechanisms, the recently proposed collaborative IM mechanism (CIM) successfully reduces the communication cost further. However, two problems exist in the current CIM mechanism: i) the protocol may fail under certain circumstances; and ii) the protocol requires dividing the virtual environment into ſxed grids. In this paper, we focus on the approaches that could enhance the current CIM mechanism and we will evaluate the performance using simulation of multiplayer game scenarios. Index Terms—Interest management, P2P online game, Parallel and distributed algorithm I. I NTRODUCTION A Networked Virtual Environment (NVE) is a network application that comprises a set of interconnected nodes that cooperatively simulate the behavior of various entities in a shared virtual environment [1]. It originated with military simulators in 80’s [2] and has evolved to popular networked computer games. In the past few years, Massively Multiplayer Online Games (MMOG) [3], [4], emerged and thousands of players can cooperate and compete with each other on a large scale game world. The subscriptions of massively multiplayer online games have been increasing over the years, bringing considerable revenues and making itself the largest category in the online entertainment markets [5]. The client-server architecture adopts centralized servers to manage the virtual environment such as player’s commands and entities’ status in the virtual world. It is widely used in the NVEs including most of today’s commercial MMOGs due to its easy deployment for NVEs. However, the client- server architecture lacks of efſciency and scalability because servers may easily become the computation and commu- nication bottlenecks. Peer-to-Peer (P2P) architecture, which emerged in the past few years [6], [7], aims at achieving scalability by removing the capacity limitation in servers. The peers in the P2P architecture are allowed to send messages directly to other peers and the resources distributed in the peers can be shared among all the participating peers. Many NVEs [8], [9], [10] which were built on P2P architecture appeared recently. In these P2P NVEs, the entities in the virtual environment are maintained by peers which are actually players’ local machines, and the entity status updates are disseminated among players in a P2P manner. Therefore, the computation and communication overhead is shared among joining players. In order to keep a consistent view of virtual environment among players participating in an NVE, frequent entity status update is required. However, due to the lack of IP multicast support in the Internet, the update messages in P2P NVEs have to be sent to other players using unicast. This may increase the communication requirement beyond a player’s capacity. Two common approaches to reduce the status up- dates between players are dead reckoning [11] and Interest Management (IM) [12]. IM techniques, which also have been widely adopted in many other research ſelds [13], [14] rather than NVE, utilizes ſltering mechanism to avoid broadcasting communication among processes or network nodes. When adopted in P2P NVEs, IM mechanism is realized by deſning an Area-Of-Interest (AOI) for each entity, which describes a region in the virtual environment that the entity is interested in. In this paper, we only focus on a certain kind of entities called avatars, which are the presence of players in the virtual environment. The AOI of player’s avatar represents the region which is surrounding avatar’s position. By using IM approach, a player only needs to receive the status update messages (e.g., position updates) of other players’ avatars which are inside the player’s AOI, so the number of status updates can be signiſcantly reduced. The traditional IM mechanisms can be classiſed into cell- based mechanisms [15] and area-based mechanisms [16]. The hybrid IM mechanism is proposed in [17] for P2P NVEs and it focuses on the communication cost in IM mechanism and successfully reduces the number of AOI update messages in the area-based mechanism by utilizing the cell-based mecha- nism. However, the hybrid IM mechanism still requires each peer to maintain the global information about all players. Liu et.al. noticed the signiſcant communication overhead in hybrid IM mechanism and proposed the collaborative IM mechanism (CIM) [18]. Like the existing cell-based and hybrid IM mechanism, the CIM mechanism works on the virtual envi- 2012 ACM/IEEE/SCS 26th Workshop on Principles of Advanced and Distributed Simulation 978-0-7695-4714-5/12 $26.00 © 2012 IEEE DOI 10.1109/PADS.2012.16 149 2012 ACM/IEEE/SCS 26th Workshop on Principles of Advanced and Distributed Simulation 978-0-7695-4714-5/12 $26.00 © 2012 IEEE DOI 10.1109/PADS.2012.16 145