Server-Oriented Multiplayer Games

1. Server-Oriented Multiplayer Games Presented by: Eric Fesenmaier ecf1@cec.wustl.edu

2. Outline • A Short History of Multiplayer Games • Architectures for Multiplayer Games • Advantages/Disadvantages of Client-Server • Client-Server Design • Client-Server Design Issues

3. Multiplayer Game HistoryThey Had Computers Then? • 1958 – William Higinbotham designs two-player pong like game on analog computer and oscilloscope.

4. Multiplayer Game HistorySounds like something I played … • 1979 – First Multiplayer User Dimension (MUD) is created – a text based RPG. It can handle up to 250 players.

5. Multiplayer Game HistoryWow! • Coming soon – The makers of Everquest debut Planetside, a Multiplayer First Person Shooter (FPS) capable of handling 3500+ users per server.

6. Multiplayer Game ArchitecturesHow should I connect? • Client-Client (Peer-to-Peer) • Client-Server • Server Network (Server Pool)

7. Multiplayer Game ArchitecturesDo I want this model? • Client-Client (Peer-to-Peer) • Client-Server • Server Network (Server Pool)

8. Multiplayer Game ArchitecturesDo I want this model? • Client-Client (Peer-to-Peer) • Client-Server • Server Network (Server Pool)

9. Multiplayer Game ArchitecturesDo I want this model? • Client-Client (Peer-to-Peer) • Client-Server • Server Network (Server Pool)

10. AdvantagesWhy choose Client-Server? • Easier to connect • Simplicity • Consistency by default • Client and Server separate out functionality • Easier to develop • Security/Administration

11. DisadvantagesReasons to try something else • Server requirements – high bandwidth, high performance • Reliability – single point failure

12. DesignGeneric Multiplayer Game Player Threads Game State Connect Socket Clients

13. DesignGeneric Multiplayer Game Player Threads Game State Connect Socket events Clients

14. DesignGeneric Multiplayer Game Player Threads Game State changes Connect Socket events Clients

15. DesignGeneric Multiplayer Game Player Threads Game State update changes Connect Socket update events update update Clients

16. DesignThe Actors: Server vs. Client • Server • sets up connections • updates state based off current state and events. sn = f(sn-1, event) • sends out updates (when appropriate) • Client • sends events (when input changes) • renders updates

17. DesignTurn-Based vs. Real Time • Turn-Based – Clients only send a message when it is their turn (i.e. card games, board games). • Real Time – Clients continuously send messages. Latency and bandwidth becomes a problem.

18. Design IssuesBandwidth & Latency • Consider the bandwidth of a 28.8Kb/s modem (28.8Kb = 3.6KB): 3.6 KB/s = 120 bytes/frame 30 frame/s • Limits the number/size of messages • Average latency nation-wide is 50 – 200 ms • An estimation method can resolve these problems

19. Design IssuesDead Reckoning with Point-to-Point • Motivation: Clients can only receive 5 – 10 updates/s due to bandwidth, while fluid motion requires 30 updates/s. Also, the updates will be old due to latency. • Solution: Server only send updates when necessary. All clients use an agreed upon estimation method to render the scene until an update is received. This achieves a consistent view.

20. Design IssuesDead Reckoning with Linear Convergence • Point-to-Point method in example results in jerkiness • Clients don’t receive update until later • Solution: After receiving new point, create a smooth path

21. Design IssuesDead Reckoning with Cubic Splines • Linear convergence looks unnatural. You’d like a smooth path that takes initial and final velocities into account. • “Cubic Splines” are an easy way to fit a curve to some set of points • Whenever you receive an update: • Take current point, and the next estimated point • Take the updated point, and estimate two points in the near future • Use “Cubic Splines” to fit a smooth curves to the points • Equations in reference

22. Design IssuesDead Reckoning with Cubic Splines • Linear convergence looks unnatural. You’d like a smooth path that takes initial and final velocities into account. • “Cubic Splines” are an easy way to fit a curve to some set of points • Whenever you receive an update: • Take current point, and the next estimated point • Take the updated point, and estimate two points in the near future • Use “Cubic Splines” to fit a smooth curves to the points • Equations in reference

23. Design IssuesDead Reckoning with Cubic Splines • Linear convergence looks unnatural. You’d like a smooth path that takes initial and final velocities into account. • “Cubic Splines” are an easy way to fit a curve to some set of points • Whenever you receive an update: • Take current point, and the next estimated point • Take the updated point, and estimate two points in the near future • Use “Cubic Splines” to fit a smooth curves to the points • Equations in reference

24. Design IssuesDead Reckoning with Cubic Splines • Linear convergence looks unnatural. You’d like a smooth path that takes initial and final velocities into account. • “Cubic Splines” are an easy way to fit a curve to some set of points • Whenever you receive an update: • Take current point, and the next estimated point • Take the updated point, and estimate two points in the near future • Use “Cubic Splines” to fit a smooth curves to the points • Equations in reference

25. Design IssuesDead Reckoning with Cubic Splines • Linear convergence looks unnatural. You’d like a smooth path that takes initial and final velocities into account. • “Cubic Splines” are an easy way to fit a curve to some set of points • Whenever you receive an update: • Take current point, and the next estimated point • Take the updated point, and estimate two points in the near future • Use “Cubic Splines” to fit a smooth curves to the points • Equations in reference

26. Design IssuesDead Reckoning Example • Two cars in the X-Y plane with constant speed • Game State: • X, Y Position • X, Y Velocity • Orientation

27. Why use Client-Server? • Scalable • Easier to implement • Less synchronization issues

28. Conclusion • Architectures for Multiplayer Games • Advantages/Disadvantages of Client-Server • Client-Server Design • Client-Server Design Issues

29. Questions???

30. References • www.gamedev.net/reference/articles/article722.asp - the essentials of multiplayer games • staff.cs.utu.fi/~jounsmed/papers/AspectsOfMCGs.pdf – theory of multiplayer games • staff.cs.utu.fi/~jounsmed/papers/TR454.pdf – theory of multiplayer games • www.gamasutra.com/features/19970919/aronson_01.htm – articles and forums on designing multiplayer games • warriors.eecs.umich.edu/games/papers/quakefinal.pdf – honors thesis on multiplayer game architecture • www.gamedev.net/reference/articles/article914.asp– cubic splines in multiplayer games (with equations) • online.redwoods.cc.ca.us/instruct/darnold/laproj/Fall98/SkyMeg/splinepres/sld025.htm -- cubic splines made easy • www.internetgames.com – articles on new games • www.gamespy.com – articles on the history of multiplayer games • cec.wustl.edu/~cs333/calendar/Multi-threadServerTutorial.ppt -- multithreaded server diagram