Virtual World Architecture II

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Virtual World Architecture II

• Network Architecture

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Styles of Networking Architecture

• Peer to Peer Client - Server

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Broadcast

• Peer to Peer Client - Server

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Broadcast

• Peer to Peer Client - Server

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Direct Message

• Peer to Peer Client - Server

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Direct Message

• Peer to Peer Client - Server

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Peer to Peer Pros/Cons

• Good when
• 2 x latency btw client and server too high for
  interactivity
• No one trusted to be central relay
• Bad when
• Server has far more bandwidth than others
• peer-peer links cannot be established everywhere
• one slow peer-peer link slows down progression of
  simulation

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Client/Server Pros/Cons

• Good when
• Server faster or better distributed than clients
• Clients behind firewalls
• Insulation
• Bad when
• Many peer to peer messages must be relayed
• Untrusted server
• Round trip time too high for application

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Examples

• Peer to Peer
• Starcraft other RTSs
• Croquet virtual world
• Gnutella
• Client/Server
• Xwing vs Tie fighter
• Doom and Quake
• Unreal Tournament
• Half Life / Garrys Mod
• World of Warcraft MMORPGs

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Another way to slice the cake

• Full Disclosure
• All input events relayed to all clients
• Each client simulates the world using inputs from
  all players
• Need-to-know
• All input events sent to server
• Server updates each client with only information
  relevant to that client

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In practice who uses what
Full Disclosure Need-to-know
Peer to Peer Star Craft, Croquet Gnutella
Client/Server X-wing vs Tie Fighter Doom, Quake, Unreal,Half life, World of Warcraft
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In practice who uses what
Full Disclosure Need-to-know
Peer to Peer Star Craft, Croquet Gnutella
Client/Server X-wing vs Tie Fighter Doom, Quake, Unreal,Half life, World of Warcraft
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Star Craft
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How Star Craft works

• Full Disclosure
• Each clients sends mouse clicks and timestamp to
  all other clients
• If everyone acknowledges receipt in sufficient
  time, action performed
• Otherwise game halted until all can perform
  action
• AI players are deterministic and react to world
  state
• Peer to Peer (8 players)
• Once Star Craft game started, all clients are
  equal
• If someone is cheating, they only cheat themselves

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In practice who uses what
Full Disclosure Need-to-know
Peer to Peer Star Craft, Croquet Gnutella
Client/Server X-wing vs Tie Fighter Doom, Quake, Unreal,Half life, World of Warcraft
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Croquet
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How Croquet works

• Full disclosure
• Clients only send input events to each other
• Complex worlds with few actors are simulated in
  full by each client
• Peer to peer (8-16 peers per room)
• Save round trip time by sending data directly to
  each other

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In practice who uses what
Full Disclosure Need-to-know
Peer to Peer Star Craft, Croquet Gnutella
Client/Server X-wing vs Tie Fighter Doom, Quake, Unreal,Half life, World of Warcraft
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X-wing vs Tie Fighter
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How X-wing vs Tie Fighter works

• Full disclosure
• Clients only send input events to each other
• Most (95) of the craft are AI
• simulated on each client
• Client/Server (8 players)
• If one player acts as host
• Can reduce burden of other players
• Slightly increase burden of host
• Broadband server can host 7 modem players

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Full Disclosure Pros/Cons

• Good when
• objects predictable w/ full game state gt
  unpredictable objects
• No one is trusted with game state
• Total transparency/information awareness
• Bad when
• num unpredictable objects large
• one slow link slows down updates for everyone
• Full world state can lead to cheating
• Star Craft map hack

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In practice who uses what
Full Disclosure Need-to-know
Peer to Peer Star Craft, Croquet Gnutella
Client/Server X-wing vs Tie Fighter Doom, Quake, Unreal,Half life, World of Warcraft
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Gnutella
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How Gnutella Works

• Need To Know
• Only file requests are relayed around
• Full sharing data of network is not available
• Peer to Peer (30,000 peers)
• No central server to demand file list from (like
  napster had)
• If a host is inaccessible a pull command can be
  sent
• Malicious (RIAA) hosts can disrupt network
  effectiveness by relaying false world state

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In practice who uses what
Full Disclosure Need-to-know
Peer to Peer Star Craft, Croquet Gnutella
Client/Server X-wing vs Tie Fighter Doom, Quake, Unreal,Half life, World of Warcraft
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Doom First Person Shooters
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How First Person Shooters Work

• Need-to-Know
• Portal/Room based maps
• Only people in your or adjacent rooms relevant
• Server only updates relevant clients
• Event timestamps still important
• Keep dead folks from shooting
• Client/Server (32 players)
• Host has high bandwidth, can make relevancy
  decisions easier
• Central connecting point for late-joiners

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In practice who uses what
Full Disclosure Need-to-know
Peer to Peer Star Craft, Croquet Gnutella
Client/Server X-wing vs Tie Fighter Doom, Quake, Unreal,Half life, World of Warcraft
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World of Warcraft
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How MMORPGs work

• Need-to-know
• Impossible to update everyone about goings on in
  a large world
• Designers wish to keep some information secret
• Treasure locations
• Monster health
• Locations of players
• Client/Server (300 players)
• Trusted server(s) with high bandwidth
• Everyone connects to a server, some anonymity
  provided

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Need-to-know Pros/Cons

• Good when
• unpredictable objects too large for all clients
  to keep up with changes
• Server faster or better distributed than clients
• clients behind firewalls
• Bad when
• Untrusted server/relay
• Round trip time too high for application

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Analogy to government types

• Full Disclosure Democracy
• Pure democracy -- town hall style
• Everyone talks to everyone else
• Education critical
• Everyone should be informed of all actions
• Otherwise can be duped by clients
• Check balance system possible, but not easy
• Need-To-Know Dictatorship
• ministry of information
• Keeps true world state
• Broadcasts only needed info
• Clients trust the server for world state

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Managing large commercial systems

• Divide servers into shards

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US West
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Managing large commercial systems

• Divide shards into instances

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Managing large commercial systems

• Many-to-many serverclient relationships

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Massive Virtual WorldsCurrent Efforts

• Shards
• World of Warcraft
• Instances as well
• Everquest
• Unified World
• MUDs
• EVE
• Second life

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Dead Reckoning
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Where Dead Reckoning fails
Path
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How to patch dead reckoning
path
Rewind Simulation To 25
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Conclusion

• Many solution exist to put folks together in a
  virtual world
• Usually tailored to the specification of the
  world
• No one size fits all solution
• Networking architectures are only going to get
  more complex in the future