1. Virtual World Architecture II
Network Architecture

2. Styles of Networking Architecture
Peer to Peer Client - Server
client
client
client
client
server
client
client
client
client
client
client

3. Broadcast Peer to Peer Client - Server client client client client

4. Broadcast Peer to Peer Client - Server client client client client

5. Direct Message Peer to Peer Client - Server client client client

6. Direct Message Peer to Peer Client - Server client client client

7. Peer to Peer Pros/Cons Good when Bad 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

8. 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

9. Examples Peer to Peer Client/Server Starcraft + other RTS’s
Croquet virtual world
Gnutella
Client/Server
Xwing vs Tie fighter
Doom and Quake
Unreal Tournament
Half Life / Garry’s Mod
World of Warcraft + MMORPGs

10. 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

11. 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

12. 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

13. Star Craft

14. How Star Craft works Full Disclosure Peer to Peer (8 players)
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

15. 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

16. Croquet

17. How Croquet works Full disclosure Peer to peer (8-16 peers per room)
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

18. 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

19. X-wing vs Tie Fighter

20. 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

21. Full Disclosure Pros/Cons
Good when
# objects predictable w/ full game state > # 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

22. 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

23. Gnutella

24. How Gnutella Works Need To Know Peer to Peer (30,000+ peers)
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

25. 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

26. Doom + First Person Shooters

27. 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

28. 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

29. World of Warcraft

30. How MMORPG’s work Need-to-know Client/Server (300 players)
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

31. 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

32. 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

33. Managing large commercial systems
Divide servers into “shards”
client
client
client
client
US West
US East
client
client
client
client
client
client

34. Managing large commercial systems
Divide shards into “instances”
client
client
US West
client
client
Instance
server
client

35. Managing large commercial systems
Many-to-many server:client relationships
client
client
client
client
server
server
server
client
client
server
server
client

36. Massive Virtual Worlds:Current Efforts
Shards
World of Warcraft
Instances as well
Everquest
Unified World
MUDs
EVE
Second life

37. Dead Reckoning Final Location 4 seconds Sent 00:28 Received 00:04 Lag
00:24

38. Where Dead Reckoning fails
4 seconds
Path
Final
Location
4 seconds
00:25
Sent
00:29
Received
00:04
Lag
Sent
00:28
Received
00:04
Lag
00:24

39. How to patch dead reckoning
4 seconds
Final
Location
4 seconds
path
Rewind
Simulation
To 25
00:25
Sent
00:29
Received
00:04
Lag
Sent
00:28
Received
00:04
Lag
00:24

40. 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