This work presents the design and implementation of our Browser-based Massively Multiplayer Online Game, Living City, a simulation game fully developed at the University of Messina. Living City is a persistent and real-time digital world, running in the Web browser environment and accessible from users without any client-side installation. Today Massively Multiplayer Online Games attract the attention of Computer Scientists both for their architectural peculiarity and the close interconnection with the social network phenomenon. We will cover these two aspects paying particular attention to some aspects of the project: game balancing (e.g. algorithms behind time and money balancing); business logic (e.g., handling concurrency, cheating avoidance and availability) and, finally, social and psychological aspects involved in the collaboration of players, analyzing their activities and interconnections.
The fast growth and the attention MMOGs captured is witnessed by several valid works on the subject; they focus on architectural issues (e.g distribution techniques @cite_17 , load balancing @cite_13 , persistence @cite_4 , etc.) and Software Engineering, e.g. usability @cite_18 , performances measurement @cite_3 , services platform @cite_8 .
@cite_18 @cite_4 @cite_8 @cite_3 @cite_13 @cite_17
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This study examines the usability challenges faced by new players of massively multiplayer online role-playing games (MMORPGs), one of the fastest-growing segments of the video game industry. Played in completely online worlds, these games allow players to communicate with one another, form groups and communities, and compete in a variety of fantasy environments.Nineteen subjects participated in an exploratory usability study of four games, three MMORPGs and a similar single-player game used for comparison. Results reveal that many people not usually considered as potential players of these games may be interested in them, but a wide variety of usability issues present serious problems for players inexperienced with the genre. Based on an analysis of the usability data and player feedback, specific recommendations are made to improve the experience of these games for new players. These results further demonstrate the applicability and importance of usability testing to video games. The most important asset of a Massively Multiplayer Online Game is its world state, as it represents the combined efforts and progress of all its participants. Thus, it is extremely important that this state is not lost in case of server failures. Survival of the world state is typically achieved by making it persistent, e.g., by storing it in a relational database. The main challenge of this approach is to track the large volume of modifications applied to the world in real time. This paper compares a variety of strategies to persist changes of the game world. While critical events must be written synchronously to the persistent storage, a set of approximation strategies are discussed and compared that are suitable for events with low consistency requirements, such as player movements. An analysis to better understand the possible limitations and bottlenecks of these strategies is presented using experimental data from an MMOG research framework. Our analysis shows that a distance-based solution offers the scalability and efficiency required for large-scale games as well as offering error bounds and eliminating unnecessary updates associated with localized movement. Large-scale multiplayer online games require considerable investment in hosting infrastructures. However, the difficulty of predicting the success of a new title makes investing in dedicated server and network resources very risky. A shared infrastructure based on utility computing models to support multiple games offers an attractive option for game providers whose core competency is not in managing large server deployments.In this paper we describe a prototype implementation of a shared, on demand service platform for online games. The platform builds on open standards and off-the-shelf software developed to support utility computing offerings for Web-based business applications. We describe our early experience with identifying appropriate performance metrics for provisioning game servers and with implementing the platform components that we consider essential for its acceptance. This paper presents traffic measurement of a Massively Multiplayer On-line Role Playing Game (MMORPG). This analysis characterizes the MMORPG traffic and shows its implications for future research issues. The target game is 'Lineage II' developed by NCsoft, which is one of the world's largest MMORPGs in terms of the number of concurrent users. We collected about 1 tera bytes of packets for four consecutive days including a weekend. The MMORPG traffic consists of two kinds of packets: client-generated packets and server-generated packets. We observe that the client packet has an average of 19 bytes payload size, while the average payload size of server packets is about 318 bytes. This asymmetry is due to the fact that the server transmits all the information to construct the visual environment for the clients in the same region. Likewise, the bandwidth usage of the server traffic is about ten times larger than that of the client traffic. The analysis of RTT reveals that client packets and server packets are transmitted mostly at the interval of 200 milliseconds due to TCP's delayed ACK. We find that there is a linear relationship between the number of users and the bandwidth usage except when the number of users is around 5000. Supporting thousands, possibly hundreds of thousands, of players is a requirement that must be satisfied when delivering server based online gaming as a commercial concern. Such a requirement may be satisfied by utilising the cumulative processing resources afforded by a cluster of servers. Clustering of servers allow great flexibility, as the game provider may add servers to satisfy an increase in processing demands, more players, or remove servers for routine maintenance or upgrading. If care is not taken, the way processing demands are distributed across a cluster of servers may hinder such flexibility and also hinder player interaction within a game. In this paper we present an approach to load balancing that is simple and effective, yet maintains the flexibility of a cluster while promoting player interaction. In this paper, we propose a new distributed event delivery method for MMORPG (Massively Multiplayer Online Role Playing Games). In our method, the whole game space is divided into multiple sub spaces with the same size and some player nodes are selected as responsible nodes to deliver game events occurring in their responsible sub spaces. Our method includes (1) a load balancing mechanism which allows each responsible node for the crowded sub space to dynamically construct a tree of multiple nodes and deliver events along the tree to reduce event forwarding overhead per node, (2) a technique to reduce end-to-end event delivery delay by dynamically replacing nodes in the tree, and (3) a technique to efficiently and seamlessly switch sub spaces to be observed while each player's view moves around in the game space. Through experiments, we show that our method achieves practical performance for MMORPG.