Architectural Challenges and Solutions for Peer-to-Peer Massively Multiplayer Online Games
Supervisor(s) and Committee member(s): Supervisor: Shervin Shirmohammadi
Massively Multiplayer Online Games (MMOG), now supporting millions of simultaneous participants on a regular basis, have become a significant contributor in human-to-human communications. While originally designed for games, they have now moved into serious realms of socialization, business, commerce, scientific experimentation, and others. As more and more people participate in these massive environments, the underlying infrastructure is starting to exhibit shortcomings that limit the progress, practicality, and applicability of MMOGs. This thesis explores various architectural challenges inherent in MMOGs and offers effective solutions in the context of a hybrid model. The key objective of this hybrid model, realized in a Massively Multiuser VIrtual Simulation Architecture (MM-VISA), is to form a stable and scalable collaboration platform that economically combines the resources of both servers and player peers, incorporating the advantages of a centralized architecture and a scalable Peer-to-Peer distributed system, which in turn leads to improved support for the participating masses.
Synchronous communication among massive number of users in an MMOG is a prime concern, and difficult and/or expensive to support. This massiveness causes challenges that cannot be solved with conventional techniques used in traditional collaborative environments. Massive number of players’ frequent and random movements in the virtual environment and zone-switching can break synchronous communication and cause strain on the underlying system, networking, and service infrastructure. To alleviate such problems, this thesis proposes a model consisting of interest-driven zone crossing, dynamic shared regions, clustering of players based on their attributes, multilevel multiphase load-balancing with several plug-able solutions, hybrid routing based on a combination of centralized and Peer-to-Peer (P2P) networking, and interest-management techniques considering dynamics of the area of interest. The model is shown to significantly improves overall system performance and enhances infrastructure stability in terms of load, network overlay, and other performance characteristics.
In MM-VISA, a set of master nodes regulate the operation of the MMOG, while each individual master also provides overlay services with the active participation of the players in its zone. In that sense, the system is hybrid as it combines the benefits of both centralized and distributed systems. In this model, most of the visibility issues and game functionalities are solved by the local ALM structure and through the master, who is also a member of the ALM tree. In addition, the master can learn the state of other zones through the exchange of explicit messages with other masters when needed. The thesis also makes the following contributions in the context of its proposed hybrid architecture:
Clustering of Players: within the same zone, players of different type are grouped together in order to stabilize the P2P trees inside that zone.
Message Overhead Reduction: bandwidth and processing is reduced by eliminating message delivery between players who, even though they are in the same group, are not within each other’s visibility radius.
Zone Crossing: connection/disconnection rate between a player and multiple masters is stabilized when the player crosses a given zone boundary back and forth repeatedly, which can happen during a battle in repeated shoot-and-run, return and shoot-and-run, …
Visibility: a player to see inside another zone when the player’s visibility crosses into that zone.
Seamless Player Handoff: how two masters should hand of a player from one master to the other without the player noticing any discontinuity or losing any updates.
Expedited State Sharing: to allow for faster message propagation in the system.
Load Balancing: three load-balancing techniques are presented – two for uniform and one for non-uniform zonal MMOGs.
Distributed and Collaborative Virtual Environment Research Lab (DISCOVER Lab), University of Ottawa, Canada
Research at the DISCOVER Lab is directed towards the enhancement of next generation human-human communication through advanced multimedia technology and virtual environments. Through our many projects, we are developing new ideas and technology that will make easy-to-use virtual environments a reality. Research projects at the DISOVER lab typically fall into the following categories:
- Networked Games and Collaborative Virtual Environments
- Multimedia Systems and Applications
- 3D Physical Modelling and Animation
- Intelligent Sensor Networks and Ubiquitous Computing
- Haptics and Teleoperation
- Multimedia-Assisted Rehabilitation Engineering