The growth in the popularity of interactive network games has increased the importance of a better understanding of the effects of packet loss and latency on user performance. While previous work on network games has studied user tolerance for high latencies and has studied the effects of latency on user performance in real-time strategy games, to the best of our knowledge, there has been no systematic study of the effects of loss and latency on user performance. In this paper we study user performance for Unreal Tournament 2003 (UT2003), a popular first person shooter game, under varying amounts of packet loss and latency. First, we deduced typical real world values of packet loss and latency experienced on the Internet by monitoring numerous operational UT2003 game servers. We then used these deduced values of loss and latency in a controlled networked environment that emulated various conditions of loss and latency, allowing us to monitor UT2003 at the network, application and user levels. We designed maps that isolated the fundamental first person shooter interaction components of movement and shooting, and conducted numerous user studies under controlled network conditions. We find that typical ranges of packet loss have no impact on user performance or on the quality of game play. The levels of latency typical for most UT2003 Internet servers, while sometimes unpleasant, do not significantly affect the outcome of the game. Since most first person shooter games typically consist of generic player actions similar to those that we tested, we believe that these results have broader implications.

Abstract — Multiplayer games become increasingly popular, mostly because they involve interaction among humans. Typically, multiplayer games are organized based on a Client-Server (CS) or a Peer-to-Peer (PP) architecture. In CS, players exchange periodic updates through a central server that is also responsible for resolving any state inconsistencies. In PP, each player communicates with every other player while state inconsistencies are resolved through a distributed agreement protocol. In this paper, we first examine these architectures from two perspectives: bandwidth requirement at the server and players, and latency to resolve any player state inconsistencies. Our results are based on both analysis and experimentation with an open-source game called “BZFlag”. The CS architecture is not scalable with the number of players due to a large bandwidth requirement at the server. The PP architecture, on the other hand, introduces significant overhead for the players, as each player needs to check the consistency between its local state and the state of all other players. We then propose an architecture that combines the merits of CS and PP. In that architecture, called Peer-to-Peer with Central Arbiter (PP-CA), players exchange updates in a peer-topeer manner but without performing consistency checks. The consistency of the game is checked by a central arbiter that receives all updates, but contacts players only when an inconsistency is detected. As a result, the central arbiter has a lower bandwidth requirement than the server of a CS architecture. Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page.

Online amusement applications, as distributed multiplayer videogames and interactive storytelling, are gaining increasing attention both from entertainment industry and from scientific community. Providing a pleasant experience to players requires a rapid delivery of game actions among the various nodes in the network. A high playability degree should be guaranteed independently of user's location, utilized device (PC, PDA, cellphone), type of connection (wired, wireless), and number of contemporary players. To this aim, we have devised an innovative approach to design the event delivery service for networked multiplayer game applications. Exploiting the semantics of the game, our scheme relaxes the ordering and reliability properties, upholding the interactivity level while preserving the game state consistency. The main contribution of our work is to show the benefits in event delivery synchronization obtainable employing, in this context, RED techniques borrowed from networking queuing management.

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We are concerned with the fundamental problem of event ordering in multiplayer peer-to-peer games. Event ordering, even without faults, requires all-to-all message passing with at least two rounds of communication [12]. Multiplayer games add real-time constraints to this scenario. To meet this challenge, we develop an event scoping mechanism that uses N-Trees for event propagation. Unlike traditional application-layer multicast, N-Trees organize peers by their application-level scope of interest, instead of by their delay-based shortest-path tree. This organization allows peers which are close by in the virtual world to order events without needing to communicate with other peers that are farther away. We show the asymptotic analysis of N-Trees indicates that they will perform well for scalable peer-to-peer event ordering. We also provide an analysis of N-Trees in comparison to other distributed architectures for peer-to-peer games.

Massively Multiplayer Online Games and Virtual Worlds are among the most popular applications on the Internet. As player numbers increase, the limits of the currently dominant client/server architecture are becoming obvious. To overcome those limits, the research community has developed protocols for these applications based on peer-to-peer technologies. However, no consensus has been found yet on how the potential of peer-to-peer can be optimally used for these applications. In this paper, we compare and evaluate three classes of proposed architectures that within themselves share common design principles. One representative protocol of each class is examined in greater detail. The performance of these protocols is then evaluated in different scenarios in a series of simulations. We show, that the architecture with the best performance in message delay is the one relying on mutual notification for detecting new neighbors and on direct connections to all neighbors for exchanging event messages. Furthermore, this architecture is still competitive regarding the required bandwidth.

In recent years many popular interactive computer games have gained online remote multiplayer functionalities, supported by standard Internet communication protocols and architectures. Due to the heterogeneous communication infrastructures and network asymmetries, some users (i.e. clients) may be suffering slow, congested and unreliable Internet connections, while others may have access to fast and reliable links. A different rate and latency in the delivery of users' commands and event notifications may lead to unfairness issues during the game play. Specifically, this happens in the class of real time and interactive games, which require frequent and prompt event notifications and reactions among all the users competing in the gaming environment. A dynamic adaptation of the gaming architecture to the limitations of the communication infrastructure could be exploited to reduce these problems. The communication network topology and performance should be considered in the management of the client allocation to the set of multiple servers. In this paper we present a simple client migration algorithm which can be adopted on a generic multi-player, multi-server online gaming architecture. Client migration among the servers of the gaming infrastructure is exploited to adapt to the dynamic performances of the general communication network infrastructure. The proposed mechanism has been modeled and simulated for the class of distributed multi-player and multi-server interactive games, implemented over a general communication network infrastructure. Results show a significant fairness improvement, more homogeneous performances, and the absence of significant overheads.

We introduce a computer game platform, AIsHockey, which is based on the real-world game of ice hockey. The platform allows us to implement and study autonomous, real-time synthetic players (i.e., computer-controlled actors in a game). By applying the Model-View-Controller architectural pattern we define the role of a synthetic player and recognize its responsibilities and interfaces in the software. We describe the AIsHockey system and discuss our experiences and observations in educational and research perspectives.

Abstract. Computer games played over the Internet have recently become an important class of distributed applications. In this paper we present a novel proxy server-network topology aiming at improved scalability of multiplayer games and low latency in client-server data transmission. We present a mechanism to efficiently synchronize the distributed state of a game based on the concept of eventual consistency. We analyse the benefits of our approach compared to commonly used client-server and peer-to-peer topologies, and present first experimental results. 1

Abstract. In this paper, we present the design and techniques of GiPSiNet, an open