MCCA : A Communication Architecture for Online Multiplayer Games

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MCCA A Communication Architecture for Online
Multiplayer Games

• Armin Bahramshahry

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Outline

• Background
• Problem
• Solution
• Evaluation
• Summary

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Video Games

• Simulate a virtual world, and represent players
  as avatars with cool guns and swords ?

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Online Multiplayer Games

• Run multiple game instances and desire to
  converge to the same game state

Type Communicated Data Allow Discrepancy
Deterministic Player action ?
Non-deterministic Changes in game object properties ?
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Problem

• Traditional Challenges gt game traffic
• Limited upload capacity communication delay
• New Challenges gt heterogeneous traffic

Feature Latency Sensitive Require Reliability Require Order
VoIP ?
File transfer ?
Text chat ? ?
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Background
Area-of-Interest (AOI)
Predictive Contract Mechanism (PCM)
Network Quality of Service (e.g., OverQoS)
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Approach
Game
VoIP
File
Game
Optimizations
?
Requirements

MCCA
Services Information
Services
Network Services

• Simplify development
• Key Idea 1 Divide and Conquer
• Efficient use of network resources
• Key Idea 2 Cooperate with the Game
• Support for new game level optimizations
• Enable game adaptation to network conditions

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Key Ideas

• KEY 1 Divide and Conquer
• Differentiated Services
• Class Definition
• Priority
• Order reliability
• Loss rate
• Latency requirements
• Bit-rate throttling

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Key Ideas (cont.)

• KEY 2 Cooperate with the Game
• Network Condition Reports (local)
• Observed network conditions Loss, latency,
  jitter
• Group Communication Policy
• Quality Estimation
• Distributed Quality Aggregation(global)

Game
VoIP
File
Game
Optimizations
Requirements
Requirements Quality
?

Reports
MCCA
Differentiated Services
Message Forwarding
Network Services
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Quality Estimation

• Perceived QoS is Class Dependent
• Game
• Estimate game update quality
• Based on observed loss and delay
• VoIP
• Based on télécommunication standard (E-model)
• File Transfer
• Transfer rate

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Optimizations

• Optimistic Game
• Uses negative acknowledgments (i.e.,
  N-consecutive message losses)
• Avoids large updates and wasteful acknowledgments
• Adaptive Game Update Interval
• Dynamically sets the game update interval (based
  on the estimated observed quality)
• Reduces network traffic due to game updates
• VoIP Optimization
• Disables VoIP at low qualities
• Avoids useless VoIP traffic

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Evaluation Methodology
Game
VoIP
File
Game
Optimizations
Quality Estimation
Requirements Quality

Quality
Reports
MCCA
Differentiated Services
Message Forwarding
Network Services
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Workload Generators

• Game Update Generator
• First person shooting game, Quake III (based on
  the model by Bharambe et al., SIGCOMM08)
• Two-frame delta encoding
• 20 game updates per second
• VoIP Traffic
• On/Off Markov process(based on the model by
  Padungkrit et al.)
• 50 VoIP messages per second
• File Transfer
• At uniformly distributed intervals

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Network Simulator

• Operates at the message level
• Provides point-to-point communication
• Does not simulate cross network traffic
• Upload capacity ltlt Network core (Bharambe et al.)
• Network Simulator Validation
• Compare to a packet-level network emulator

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Evaluation

• Workload Combinations
• Game Level Optimizations
• Class Definitions
• Window-size
• Redundancy level and redundancy interval
• Forwarding policy
• Workload Definitions
• Real-Time Changes in
• Number of players
• Upload capacity
• Deployment Environment

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Comparing Effectiveness of Optimizations
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Effectiveness of Classification Optimizations
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Adaptiveness to Changing Conditions
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Summary of Evaluation Results

• Better gaming experience using
• Prioritization
• Classification
• Targeted QoS
• Efficient group communication
• Distributed quality aggregation enables game
  adaptation to network conditions
• Lower quality variability among players

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Contributions

• Demonstrated the benefits of
• Differentiated services
• Cooperation with the game
• Prototyped a generic communication layer for
  online games (MCCA)
• Experimental evaluation of MCCA

at the communication layer to improve players
experience.
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Summary

• Outcome
• Paper submission to NetGames 2009
• Network Engineer _at_ United Front Games
• Other Publications
• vanDisk An Exploration in Peer-To-Peer
  Collaborative Back-up Storage, Amir Javidan,
  Tony Angerilli, Armin Bahramshahry, Guy Lemieux,
  Roman Lisagor, Matei Ripeanu, 20th IEEE Canadian
  Conference on Electrical and Computer
  Engineering, Vancouver, BC, April 2007.
• A High-Performance GridFTP Server at Desktop
  Cost, Samer Al-Kiswany, Armin Bahramshahry,
  Hesam Ghasemi, Matei Ripeanu, Sudharshan S.
  Vazhkudai, poster, SC2007, Reno, NV, November
  2007.

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