Em geral, jogos classificados como ‘jogos online maciçamente multijogador’, ou massively multiplayer online games (MMOGs) são simulações interativas, competitivas, em tempo real e em larga escala, de mundos virtuais gráficos. Atualmente, a maioria (se não todos) os MMOGs lançados comercialmente são implementados como serviços centralizados, onde centenas ou até milhares de máquinas servidoras, mantidas pelo provedor do serviço do jogo, são responsáveis por executar quase toda a simulação do mundo virtual. Isto implica em gastos significativos em equipamentos e comunicação por parte dos provedores do jogo. Vários trabalhos tentam reduzir o custo de hospedar um MMOG propondo modelos de distribuição da simulação mais descentralizados (peer-to-peer), onde a simulação é movida parcialmente ou totalmente dos servidores (máquinas dos provedores do jogo) para os nós clientes, tipicamente PCs de jogadores conectados por banda larga residencial. Porém, a tentativa de descentralizar um MMOG cria problemas de segurança, na medida em que a simulação passa a ser delegada a nós clientes, que são nós intrinsecamente não-confiáveis que ganham a oportunidade de trapacear no jogo, burlando as regras, visto que as regras da simulação serão executadas por estes. Existem vários tipos de trapaças, mas nós mostramos nesta tese que é possível argumentar que a trapaça de estado (state cheating) e ataques de negação de serviço são as ameaças mais significativas para MMOGs peer-to-peer. Como consequência, nós propomos o FreeMMG 2, um novo modelo de descentralização de MMOGs baseado na divisão do mundo virtual em células que são mantidas individualmente por grupos separados de peers voluntários que executam um processo daemon, não-interativo de simulação. Cada peer de uma célula contém uma réplica completa do estado da célula e se sincroniza de forma tanto conservadora quanto otimista com cada outro peer (réplica) da célula, enquanto ao mesmo tempo recebe comandos de jogo e dissemina atualizações de jogo para as máquinas ‘cliente’ dos jogadores do jogo. Devido à replicação e à seleção aleatória de peers para as células, nós mostramos que o FreeMMG 2 é resistente a trapaça de estado. E, devido ao uso de um peer back-up secreto para cada peer réplica primária da célula, nós mostramos que ataques de negação de serviço contra os peers não irão aumentar de forma significativa a probabilidade de ocorrência de trapaça de estado ou de perda total do estado da célula atacada. Através de simulação de rede, nós mostramos que o FreeMMG 2 é escalável e que utiliza a largura de banda dos clientes de forma eficiente. Assim, mostramos que uma abordagem baseada em replicação de suporte a MMOGs, considerando clientes com conectividade à Internet realística (sem IP multicast e com banda larga doméstica), é viável. / Typically, games classified as ‘massively multiplayer online games’ (MMOGs) are competitive, real-time, large-scale interactive simulations of graphical virtual worlds. Currently, most (if not all) commercial MMOGs are implemented as centralized services, where hundreds or even thousands of ‘server’ machines, maintained by the game service provider, are responsible for running almost all of the virtual world simulation. This incurs a significant equipment and communication cost for the game providers. Several works attempt to reduce the cost of hosting a MMOG by proposing more decentralized, peer-to-peer models for distributing the simulation among client (player-owned PCs with consumer-grade broadband) and server (provider-owned) machines, with some going as far as eliminating the need for provider-owned machines altogether. Decentralizing a MMOG, however, creates security issues, as the simulation is now delegated to untrusted client nodes which gain opportunities to cheat the game rules, as the rules are now executed by them. There are several types of cheats, but we show in this thesis that a case can be made for considering state cheating and denial-of-service attacks as the most significant threats for peer-to-peer MMOGs. In light of this, we propose FreeMMG 2, a new MMOG decentralization model based on the division of the virtual world into cells that are maintained individually by separate groups of volunteer peers that are running a non-interactive, daemon simulation process. Each peer of a cell contains a full replica of the cell state and synchronizes both conservatively and optimistically with every other peers (replicas) of the cell, while at the same time receiving game commands and disseminating game updates to actual player machines. Due to its cell replication and random peer selection, we show that FreeMMG 2 is resistant to state cheating. And, due to the use of one secret back-up peer for every primary replica peer of the cell, we show that denial-of-service attacks don’t significantly increase the odds of either state cheating or cell state loss happening. Through network simulation we verify that FreeMMG 2 is scalable and bandwidth-efficient, showing that a replication-based approach to peer-to-peer MMOG support, considering peers with realistic Internet connectivity (no IP multicast and consumer-grade broadband), is a viable one.

Tradicionalmente, utiliza-se um servidor central para prover suporte a MMOGs (massively multiplayer online games, ou jogos online maciçamente multijogador), nos quais o número de participantes é da ordem de dezenas de milhares. Muitos trabalhos foram realizados com o intuito de criar um modelo de suporte completamente descentralizado, par-a-par, para este tipo de aplicação, minimizando o custo de manutenção da sua infraestrutura, mas algumas questões críticas persistem. Exemplos de problemas do modelo de suporte par-a-par são: vulnerabilidade a trapaça, sobrecarga da banda de envio dos pares e dificuldade para manter a consistência da simulação entre os diferentes participantes. Neste trabalho, é proposta a utilização de nodos de baixo custo geograficamente distribuídos, operando como um servidor distribuído de jogo. O modelo de distribuição proposto e alguns trabalhos relacionados também são apresentados. Para tratar o custo de comunicação imposto aos servidores, foi projetado aqui um novo refinamento para a técnica de gerenciamento de interesse, reduzindo significativamente a largura de banda necessária ao jogo. Foram realizadas simulações utilizando o simulador ns-2, comparando diferentes algoritmos de área de interesse. Os resultados demonstram que a nossa proposta é a que tem a menor utilização de largura de banda, com uma redução em 33,10% do tráfego máximo, e em 33,58% do tráfego médio, quando comparada com outros algoritmos de gerenciamento de interesse. Além disso, em uma arquitetura de servidor distribuído para MMOGs, com recursos heterogêneos, os nodos servidores podem ser facilmente sobrecarregados pela alta demanda dos jogadores por atualizações de estado. Neste trabalho, é proposto também um esquema de balanceamento de carga que utiliza o tráfego de rede como a carga a balancear entre os servidores e tem como objetivos principais: alocar a carga nos servidores proporcionalmente à capacidade de cada um e reduzir tanto quanto possível o overhead introduzido pela própria distribuição. O esquema de balanceamento é dividido em três fases: seleção local de servidores para participarem, o balanceamento em si e o posterior refinamento da divisão de carga. Quatro algoritmos foram propostos: ProGReGA, ProGReGA-KH, ProGReGA-KF e BFBCT. Destes, o ProGReGA foi o que introduziu o menor overhead de todos e o ProGReGA-KF foi o que se mostrou mais eficiente para reduzir o número de migrações de jogadores entre servidores. / Traditionally, a central server is used to provide support to MMOGs (massively multiplayer online games), where the number of participants is in the order of tens of thousands. Much work has been done trying to create a fully peer-to-peer model to support this kind of application, in order to minimize the maintenance cost of its infra-structure, but critical questions remain. Examples of the problems relative to peer-to-peer MMOG support systems are: vulnerability to cheating, overload of the upload links of the peers and difficulty to maintain consistency of the simulation among the participants. In this work, it is proposed the utilization of geographically distributed lower-cost nodes, working as a distributed server to the game. The distribution model and some related works are also presented. To address the communication cost imposed to the servers, we specify a novel refinement to the area of interest technique, significantly reducing the necessary bandwidth. Simulations have been made with ns-2, comparing different area of interest algorithms. The results show that our approach achieves the least bandwidth utilization, with a 33.10% maximum traffic reduction and 33.58% average traffic reduction, when compared to other area of interest algorithms. Besides, in a distributed MMOG server architecture, with heterogeneous resources, the server nodes may become easily overloaded by the high demand from the players for state updates. In this work, we also propose a load balancing scheme, which considers the network traffic as the load to balance between the servers, and it has the following main objectives: allocate load on the servers proportionally to the power of each one of them and reduce as much as possible the overhead introduced by the distribution itself. It is is divided in three phases: local selection of servers, balancing and refinement. Four algorithms were proposed: ProGReGA, ProGReGA-KH, ProGReGA-KF and BFBCT. From these, ProGReGA has proved to be the best for overhead reduction and ProGReGA-KF is the most suited for reducing player migrations between servers.

Context. In multiplayer games, player information takes time to reach other players because of network latency. This can cause inconsistencies because the actions from the other players are delayed. To increase consistency, movement prediction can be used to display other players closer to their actual position. Objectives. The goal was to compare different prediction methods and see how well they do in a 2D racing game. Methods. A testing framework was made to easily implement new methods and to get test results. Experiments were conducted to gather racing data from participants and was then used to analyze the performance of the methods offline. The distance error between the predicted position and the real position was used to measure the performance. Results. Out of the implemented algorithms, Input Prediction had the lowest average distance error at all latency. All methods tested did better than Dead Reckoning when above 600ms. Stored data algorithms did not do worse when predicting on a curvy part of the track unlike the other algorithms tested. Conclusions. Different methods are supported by different games and applications. Movement prediction should be tailored to its environment for best accuracy. Due to Input Predictions simple nature and its results here, it is a worthy contender as the go-to algorithm for games.

This thesis explores the problems and possibilities concerning the interaction between players physically located in different cars during temporary meetings in a gaming situation. The thesis is part of a study set out to investigate how traffic encounters can be used as a resource in a mobile, multiplayer game intended as entertainment for children travelling in the backseat of cars. The multiplayer capabilities are realised by using wireless networks in ad hoc peer- to-peer mode, GPS positioning and a digital compass. Designing the interaction for an ad hoc, mobile multiplayer experience introduces several design challenges, such as how to adapt to the temporality of traffic encounters and how to establish a connection between the digital game and the physical context. The nature of traffic encounters inspired us to take a newapproach to the interaction. The interaction is accomplished using a device, which enables direct interaction between players physically located in different cars. A prototype game was constructed within the frames of the project, which this thesis was part of, to test the functionality of the game concept. The prototype has been tested in its real setting, i.e. inside a car. The study and the work on this thesis was initialised and supervised by Liselott Brunnberg and the work was carried out at the Mobility Studio at the Interactive Institute in Stockholm during late spring and summer 2003.

In this study we examine how much latency is required in an RTS-game (Real-Time Strategy) before the player quits the game. In the study latency is simulated in the games Age of Mythology and Starcraft: Brood War with the program WANem, and then the testplayers are asked “Do you want to quit because of latency?”. This data is then gathered and compiled into graphs to show the results. These results show that the limit for when players want to quit differs between the two games and that there are two factors that play into this. These factors are mainly the games mechanic, how the game is played, and how the game itself handles the latency. The results show that the limit for when players want to quit in Age of Mythology lies around 1000 ms, while in Starcraft: Brood War the limit is around 600 ms. / I denna studie undersöks det hur hög latency som krävs i ett RTS-spel (RealtidsStrategi) innan spelaren avslutar spelet. I studien simuleras latency i spelen Age of Mythology och Starcraft: Brood War med hjälp av programmet WANem, därefter får testpersonerna följande fråga ställda till sig: “Vill du sluta spela på grund av latency?”, denna data samlas sedan in och kompileras till grafer för att kunna visa resultaten. Resultaten som studien får fram är att gränsen skiljer sig mellan spelen och att det finns två faktorer som bidrar till detta, faktorerna är Spelets mekanik och Hur spelet hanterar latency. De siffror som studien har fått fram är att gränsen i Age of Mythology ligger på cirka 1000 ms medan gränsen i Starcraft: Brood War ligger på cirka 600 ms.

The focus of this dissertation is on large-scale and long-running networked real-time multiplayer games. In this type of games, each player controls one or many entities, which interact in a shared virtual environment. Three attributes - scalability, security, and fault tolerance - are considered essential for this type of games. The normal approaches for building this type of games, using a client/server or peer-to-peer architecture, fail in achieving all three attributes. We propose a server-network architecture that supports these attributes. In this architecture, a cluster of servers collectively manage the game state and each server manages a separate region of the virtual environment. We discuss how the architecture can be extended using proxies, and we compare it to other similar architectures. Further, we investigate how a distributed database management system can support the proposed architecture. Since efficiency is very important in this type of games, some properties of traditional database systems must be relaxed. We also show how methods for increasing scalability, such as interest management and dead reckoning, can be implemented in a database system. Finally, we suggest how the proposed architecture can be validated using a simulation of a large-scale game.

This master’s thesis discusses game development on the computer tablet, with Apple’s iPadas the target platform. Its main focus is development of non-trivial components such asonline multiplayer and touch(screen) controls for a real-time action game, using frameworksand APIs that are mainly free and open source. For each non-trivial component problems arepointed out and possible solutions are presented, the resulting game, Battle Angels, isevaluated along with the game design and development. Battle Angels is a 2D real-timemultiplayer action game, the development of it lead to the conclusions and results in thisthesis.The abstract nature of the subject of this thesis makes it impossible to present a set of numerical values that can be compared to existing research. The result is therefore presented byshowing images from the actual game with a discussion. It could be concluded that designing and implementing a fast paced multiplayer game on a computer tablet system is a majorchallenge. It typically requires developers to incorporate a variety of different technologiesinto their implementation in order to succeed. It could also be concluded that each technology in its isolation were not a major issue, however combining them and allowing them toco-exist were.

Denna uppsats behandlar frågeställningen “Hur underlättar man en parallell utveckling av en- samt flerspelar-funktionalitet i ett spel?”. Anledningen till frågeställningen är att en separation mellan de två lägena, tror vi, får en positiv inverkan på agilitet i mjukvaruutvecklingsprojekt inriktat mot spel, något som spelutvecklingsföretagen och utvecklare historiskt sett haft problem med. Samtidigt som en separation av funktionaliteten delar de olika kunskapsområden (spellogik och nätverk) så att rätt person kan arbeta med rätt sak. Målet med denna uppsats är att försöka bana väg för vidare forskning snarare än att helt lösa problemet. Problemet har studerats genom att applicera aktionsforskning vilket praktiskt har lett till en iterativ process som resulterat i en potentiell lösning vilket på veckovis basis reflekterats över samt förbättrats. I rapporten beskriver vi en lösning i form av en mjukvarudesign och regler att förhålla sig till, samt erfarenheter vi har erhållit under arbetets gång. / This paper addresses the question formulation “How does one aid a parallel development of singleplayer and multiplayer in game development?” The reasoning behind is that we believe a separation between the two achieves a greater agility in software development minded towards games. Something that the industry and developers alike historically have struggled and had problems with. At the same time a separation of functionality divides the different areas of expertise (game logic and network) so that the right person can focus on the right thing in a development cycle. The contribution to the scarce research in the general area computer science more narrowly and specific, game development research is mainly to pave the way for further research. The problem has been tackled through Action Research, meaning the use of practical development iterated towards a potential solution, and on a weekly basis considered the solution and made improvements and adjustments on it. This paper describes a solution in form of a software design and a couple of rules to relate to as well as the experience we obtained throughout this project.

The goal of this Thesis is not only a plain description of common characteristics of Massive Multiplayer Online Games (their sorting and conditions on where they run are included), but also their integration to the wider phenomenon -- to cyberspace. Cyberspace reference is present in all recommendations and game specifics. Cyberspace is it`s base ingredient, the authority, to which all those parts are revoking to. And here it comes our second and main goal. The need of integration of players to that virtual world. To seek her desires, her true nature. That maybe done by describing various game devices and methods of connecting users of those devices to the cyberspace, let alone by expanding reader`s horizons to places, not known to her. All that is lead by one effort -- that the person, who will read that Thesis carefully, will be able to answer the question, if players get exactly what they need. And she`ll be able to do that before reading to the end.

Virtual Reality provides the ability to immerse users in realistic environments, which makes it possible to utilize the technology as an educational tool. The EIT Raw Materials Project MireBooks intend to teach mining students by simulating a VR mine and recreating learning experiences in it. With this comes challenges with regards to the networking performance and user experience. / MiReBooks