Multiplayer games on networks

1. Multiplayer games on networks potential and tradeoffs

2. Brief history of real-time networking approximately... 1980’s (US) military simulations 1990’s distributive / collaborative virtual environments 2000’s multiplayer games but Ultima OnlineBattle.net Amaze Doom MUD 1980 2000 1990 COSC 4126 network games

3. Analyzing constraints on network games* • design constraints at three levels • physical: cabling and hardware - bandwidth, latency, processing • logical: architectures for communication (e.g., peer-to-peer, client/server), data and control (e.g., centralized, distributed, replicated) • application: interpretation (data meaning), integrity control (legal state), transferring (computation shared among nodes) COSC 4126 network games *Smed, Kaukoranta & Hakonen, 2003

4. Resource management – physical and logical influence on experience • resource requirements in distributed application: f(info sent, info received, processing rate) • IPE Information Principle Equation: Singal &Zyda, 1999 M: number of messages H: average number of destination nodes B: bandwidth required for message to one destination T: delay P: number of processor cycles to receive, process a message COSC 4126 network games

5. IPE • product is a measure of “quality of experience” • reducing a factor reduces resource requirements but also reduces experience • factors can be traded off against each other COSC 4126 network games

6. IPE example M: number of messages H: average number of destination nodes B: bandwidth required for message to one destination T: delay P: number of processor cycles to receive, process a message • packet aggregation • M decreased • B increased • P increased • T increased design question – is tradeoff valuable? COSC 4126 network games

7. Quality of experiencein networked game • consistency: similarity of view to actual data in the nodes of the network – “absolute consistency” is perfect data view match among nodes • responsiveness: – delay for an update event to be applied to game data • in database applications – consistency takes precedence over responsiveness • in game applications – responsiveness is more important and consistency may be compromised COSC 4126 network games

8. Data and control architectures centralized distributed replicated process data store network relay COSC 4126 network games

9. Consistency, responsivenessand architecture • high consistency  processes on remote nodes tightly coupled • high responsiveness  processes loosely coupled COSC 4126 network games

10. local input global output node network local output global input Relay • 2 – way relay assures consistency in combination with distributed or centralized architecture BUT responsiveness is vulnerable to network COSC 4126 network games

11. Relay • short-circuit relay assures high responsiveness but local data can become inconsistent with other nodes local input global output node network local output global input COSC 4126 network games

12. Resolving inconsistencies • games require responsiveness • inconsistencies will occur • mechanism for resolving inconsistencies must be provided COSC 4126 network games

13. Application level influence on experience • scalability – adapting to resource changes • persistence – effect of players leaving and entering • collaboration – consistency and sharing COSC 4126 network games

14. Scalability • game server issues • allocation of non-player computation among nodes • parallelism & concurrent computation model • each node burdens network but increases computation power ( H up, P down) COSC 4126 network games

15. Persistence • relationship of node to application • initializing state of node when player joins • on-going consistency • maintaining state when node leaves game • abrupt disruption – reallocation of responsibilities COSC 4126 network games

16. Collaboration • teams acting together • communication among team members • prioritized messages / dedicated channel • ‘interest management’ based on application-based closeness or ‘collaboration distance’ COSC 4126 network games

17. Reducing resource requirements • Architecture level • packet compression • internal – data compression within packet • suits UDP • external – data compression bsed on assumed receiver state • packet aggregation • merging removes some headers but adds delay to data waiting for packetizing • timeout or quorum-based aggregation tradeoffs COSC 4126 network games

18. Reducing resource requirements • Application level • interest management • premise – most packets only of interest to minority of nodes • transmit only to those, not all nodes • nodes ‘express interest’ in subset of information • M down, B down, P up COSC 4126 network games

19. Interest management • area of interest – ‘aura’ • application based – correlates to sensory capabilities of node system (typically character) • aura = focus(perception) + nimbus(perceptibility) • when focus intersects nimbus, nodes communicate COSC 4126 network games

20. Nimbus and Focus • Smed et al, 2003 COSC 4126 network games

21. Interest management • area of interest – ‘aura’ • ‘subscription manager’ server manages state, interest info for each node • subscription manager receives messages about state and retransmits to interested nodes • nodes submit changes of state and interest to the subscription manager COSC 4126 network games

22. Improving responsiveness • e.g., with less frequent packets due to aggregation • game state extrapolation techniques to continue response without input • ‘dead reckoning’ based on predicting state changes and correcting when info arrives COSC 4126 network games

23. dead reckoning example • Smed et al, 2003 based on recent positions, compute velocity, maybe acceleration and extrapolate when update arrives, plot ‘smooth’ convergence COSC 4126 network games