Area of Interest Management in Massively Multiplayer Online Games

Users participating in a Massively Multiplayer Online Game (MMOG) share a synchronous and persistent virtual world with each other through Avatars, i.e., the players alter ego in the virtual world. In order to enable an engaging experience typical of MMOG, the state of entities in the virtual world, such as avatars and objects, has to be replicated in avatar nodes in a timely fashion. However, broadcasting all state changes to every node in a MMOG is not a practical solution. Naturally, each avatar is interested to be updated in only a subset of the whole virtual world, which is commonly referred to as Area of Interest (AOI). The AOI management (AOIM), often referred to also as Interest Management (2002), is a core activity in the operations of a MMOG, and can be informally defined as the following: given an avatar, identify its AOI and activate those operations that support its timely update. AOIM is also referred to as spatial publish subscribe (Hu and Chen 2011). In this model, publishers perform action and interact with the virtual world (e.g., perform some movements), whilst subscribers manifest their interest of receiving updates for a specific area of the virtual world. AOIM is a fundamental operation in both centralized and distributed MMOG architecture. In the centralized ones, it is principally a mean to reduce the volume of messages exchanged by the client and the server, as well as the amount of data stored and elaborated locally to the client. In distributed MMOG architectures instead, how AOIM is performed greatly impacts on the whole architecture. In fact, AOIM often drives the design of the whole decentralized architecture, forcing an organization of the connections between nodes so that they are only communicating with other nodes that have relevant entities. AOIM can be divided into two main categories (Carter et al. 2012): spatial and geographic.