Multiplayer games on networks potential and tradeoffs

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

COSC 4126 network games 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) *Smed, Kaukoranta & Hakonen, 2003

COSC 4126 network games 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 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 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 Quality of experience in 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 Data and control architectures centralizeddistributedreplicated process relay data storenetwork

COSC 4126 network games Consistency, responsiveness and architecture  high consistency  processes on remote nodes tightly coupled  high responsiveness  processes loosely coupled

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

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

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

COSC 4126 network games 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 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 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 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 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 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 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 Nimbus and Focus  Smed et al, 2003

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