Enabling PlayerCreated Online Worlds with Grid Computing and Streaming

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Enabling Player-Created Online Worlds with Grid
Computing and Streaming

• Gamasutra, September 18, 2003

Presented by Daniel Ferstay
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Overview

• Massively Multiplayer Online Games (MMOG)
• And the people who play them
• Content Distribution problem for MMOG
• Second Life
• The Grid
• Streaming
• Conclusions and Discussion

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Massively Multiplayer Online Games (MMOG)

• The hours and intensity with which players
  engage in games makes for very fast consumption
  of content

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How many hours and with how much intensity?

• Google search for everquest addiction gives
  interesting results
• EverQuest the Latest Addiction, Wired.com,
  July 29, 1999
• 150000 players total
• 34000 players online for 3-4 hours each during
  peak night hours
• EverQuest Widows
• Yahoo! group that offers a space for people to
  vent and support each other through relationship
  crises.
• Missed anniversaries, threatened divorce,
  breakups, etc.

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Good News, Bad News

• Game players who enjoy the content of a game play
  it a lot.
• The more players play, the more content they
  consume

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Question

• How can game designers provide enough content to
  keep players engaged?
• Previous approaches
• Provide large amounts of content in game (Final
  Fantasy)
• Make content reusable replay value (GranTurismo)
• Make experience dependent on interaction with
  other human players (Quake)

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Problem

• Persistent-world online games
• Players pay a monthly subscription fee to play
  the game
• Designers keep players engaged by frequently
  updating interactive content
• Exploration of 100 hours of content can take only
  a few weeks of game play.
• This approach is costly
• Balancing act between time/cost to develop
  content, time to play content and monthly
  subscription fee.

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Solution

• Allow players to modify and customize game
  content and features
• Works well for single player games and FPS where
  customization amounts to modifying local
  configuration files
• This approach raises technical problems for MMOG

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Second Life

• Persistent-World MMOG
• Online society shaped entirely by its residents
• Players create/modify their avatars to look and
  sound like anything
• World landscape is provided but players create
  the objects which populate the world
• Houses, boats, furniture, art, etc.
• See The Metaverse in Neal Stephensons Snow
  Crash

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Second Life
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Content Distribution Problem

• How do we distribute player-customized content
  (graphics, sound, geometry, animation, behaviour)
  to other players in real-time?
• The online world is one big contiguous space
  populated by players who can
• Create, edit, and move objects
• The world contains hundreds of thousands of
  objects that have unique
• Textures, physical properties, shapes,
  permissions, etc.

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Content Distribution Problem cont.

• Shipping the games current contents to users in a
  box requires gt 100 CDs
• Patching users with new in-world content when
  they logged in would require downloads of 10s of
  megabytes per day
• Storing and manipulating all of the game content
  on a centralized database would yield a
  transaction rate of gt 10000 read/writes per
  second during peak hours
• These numbers grow linearly with the number of
  players

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Content Distribution Solution The Grid

• Distribute the objects across a tiled grid.
• Each tile in the grid represents one machine
  running a sim
• Simulates physics, manages objects/behaviours/terr
  ain for a fixed square region of space (16
  acres)

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The Grid cont.

• Simulator machines talk to their four nearest
  neighbours in the grid
• Solves scaling problem as world becomes large
• As objects move around the world, their
  representations are transferred from simulator to
  simulator
• Using higher order prediction, players and
  objects transition across simulation borders
  seamlessly.

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The Grid cont.

• As players move around the grid, they maintain
  streaming connections only to the simulator
  machines they are near.
• Simulators compute the information and objects
  that can be seen
• Transmits only information that is new to the
  player (or has changed)
• Players need only a thin client (a world viewer)
  to play the game
• To grow the world, add simulator machines to the
  grid.

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Streaming

• Game requires a broadband connection.
• Average bandwidth to a client 100Kbps
• Compression is needed
• Each sim supports 10000 objects players can see
  a large percentage of these.
• Graphical representations of objects are built
  out of simple geometric shapes.
• Generalized meshes are too complex and dont
  compress as efficiently

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Streaming cont.

• Texture and audio data are compressed
• Allows players to put thousands of large textures
  and a large number of audio sources into a scene.

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Streaming is expensive

• Clients receive information related to
• Frustum culling, change detection, motion
  interpolation/extrapolation, compression, and
  packet construction and management.
• Multiple servers stream data to different ports
  on the client machine via UDP
• UDP allows for a more responsive/controllable
  stream then TCP.
• Avoids TCPs slow start congestion controls.
• Reliability built around loss detection and data
  correction
• Not retransmission

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Conclusions

• A Grid of simulators solves the problem of scale
  when users are allowed to create and modify
  objects in a large online world
• Streaming data to players in real time allows
  users to modify the online world in a
  collaborative and interactive manner.

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Thank You

• Any Questions?

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Discussion

• In what ways could this game be improved?
• Graphics are simple, low polygon count
• Multiple UDP streams get blocked by Firewalls
• Adaptive congestion control vs. 100Kbps magic
  number for client bandwidth
• Is it reasonable to expect players to create all
  of the content in the game?