Bandwidth requirement and state consistency in three multiplayer game architectures

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-to-peer 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.

REFERENCES

• 1: J. Smed and T. Kaukoranta and H. Hakonen "Aspects of Networking in Multiplayer Computer Games". In Proceedings of International Conference on Applications and Development of Computer Games in the 21st Century, November 2001.
• 2: Lothar Pantel , Lars C. Wolf, On the impact of delay on real-time multiplayer games, Proceedings of the 12th international workshop on Network and operating systems support for digital audio and video, May 12-14, 2002, Miami, Florida, USA [doi>10.1145/507670.507674]
• 3: George Coulouris , Jean Dollimore , Tim Kindberg, Distributed systems (3rd ed.): concepts and design, Addison-Wesley Longman Publishing Co., Inc., Boston, MA, 2000
• 4: E. Cronin, B. Filstrup, and A. Kurc. "A Distributed Multi-Player Game Server System". EECS589, Course Project Report, University of Michigan, May 2001.
• 5: ID Software. "Quake". Available at http://www.quake.com, 2002.
• 6: L. Gautier and C. Diot and J. Kurose. "End-to-End Transmission Control Mechanisms for Multiparty Interactive Applications on the Internet". In Proceedings of IEEE INFOCOM, April 1999.
• 7: C. Diot and L. Gautier. "A Distributed Architecture for MultiPlayer Interactive Applications on the Internet". In IEEE Network magazine, 13(4), August 1999.
• 8: N. Baughman and B. Levine. "Cheat-Proof Playout for Centralized and Distributed Online Games". In Proceedings of IEEE INFOCOM, April 2001.
• 9: Li Zou , Mostafa H. Ammar , Christophe Diot, An Evaluation of Grouping Techniques for State Dissemination in Networked Multi-User Games, Proceedings of the Ninth International Symposium in Modeling, Analysis and Simulation of Computer and Telecommunication Systems (MASCOTS'01), p.33, August 15-18, 2001
• 10: T. Riker. "BZFlag". Available at http://www.bzflag.org, 2002.
• 11: P. Bettner and M. Terrano. "1500 Archers on a 28.8 Programming in Ages of Empires and Beyond". Technical report, Ensemble Studios, 2001.
• 12: Martin Mauve, How to Keep a Dead Man from Shooting, Proceedings of the 7th International Workshop on Interactive Distributed Multimedia Systems and Telecommunication Services, p.199-204, October 17-20, 2000
• 13: Eric Cronin , Burton Filstrup , Anthony R. Kurc , Sugih Jamin, An efficient synchronization mechanism for mirrored game architectures, Proceedings of the 1st workshop on Network and system support for games, p.67-73, April 16-17, 2002, Bruanschweig, Germany [doi>10.1145/566500.566510]