1. Scalable Peer-to-Peer Networked Virtual Environment
Shun-Yun Hu* & Guan-Ming Liao+
* Dept. of CSIE, Tamkang Univ.
+ Institute of Physics, Academia Sinica
Taiwan
2004/08/30
2004/08/30

2. The BIG Question
How do we create a true cyberspace (Networked Virtual Environment)?
“True” means:
3D-based, interactive and persistent
Feels realistic and immersive
REALLY BIG 
Scalability Problem
2004/08/30

3. Issues for Creating NVE
Consistency
Performance (Responsiveness) multiplayer
Security
Scalability
Persistency massively multiplayer
Reliability (Fault-tolerance)
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4. The Scalability Problem
Many nodes on a 2D plane ( > 1,000,000)
Need to interact with those within Area of Interest (AOI)
How does each node receive only the necessary messages?
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5. Scalability Solutions
Strategies
Increase resource  More servers
Decrease consumption  Interest management (message filtering)
Architectures:
Point-to-point (LAN) tens 10^1
Client-server hundreds 10^2
Server-cluster thousands 10^3
? millions ^6 …
Peer-to-Peer
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6. Promise & Challenge of P2P
Promises
Growing resource, decentralized  Scalable
Commodity hardware  Affordable
Nobody has done it yet!  Cool 
Challenges
Topology maintenance  dynamic join/leave
Efficient content retrieval  no global knowledge
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7. Design Goals
Observation: desired content is specifically defined (messages from neighbors within AOI)
 locality of interest to be exploited
Solve the Neighbor Discovery Problem in a fully-distributed, message-efficient manner.
Specific goals:
Scalability  Limit & minimize message traffics
Performance  Direct connection with AOI neighbors
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8. Voronoi Diagram
Plane partitioned into regions by sites, each region contains all the points closest to its site
Can be used to find k-nearest neighbor easily
Neighbors
Region
Site
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9. Design Concepts Use Voronoi to solve Neighbor Discovery Problem
Identify enclosing and boundary neighbors
Each node constructs a Voronoi of its neighbors
Enclosing neighbors are maintain as the minimal set
Mutual collaboration in neighbor discovery
Circle
Area of Interest (AOI)
White
self
Yellow
enclosing neighbor
L. Blue
boundary neighbor
Pink
enclosing & boundary
Green
other neighbor
D. Blue
unknown neighbor
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10. Procedure (JOIN) Send join request to any existing node
Join request forwarded to acceptor region
Acceptor region’s node sends back its neighbor list
Joining host contacts those neighbors one-by-one
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11. Procedure (MOVE)
Send movement to all neighbors, mark boundary neighbors
B. Neighbors check for AOI & enclosing neighbors overlap
Connect to new neighbor upon notification (update Voronoi)
Disconnect any non-overlapped neighbor
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12. Procedure (LEAVE, etc.) Leave Other actions (chat, jump, trade)
Simply disconnect
Others update Voronoi (query new boundary)
Other actions (chat, jump, trade)
Exchange message with individual or all neighbors
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13. Problems of Voronoi Approach
Performance
Circular round-up of nodes
Redundant message sending
Incomplete neighbor discovery
Inconsistent / incorrect neighbor list
Fast moving node
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14. Related Works P2P support for MMP Games (Univ. of Pennsylvania)
DHT-based, Pastry + Scribe
[Knutsson et al. INFOCOM 2004]
P2P Message Exchange Scheme for LS-NVE (Univ. of Tokyo)
Constant exchange of neighbor list
[Kawahara et al. Telecommunication System 2004]
Solipsis (France Telecomm R&D)
Mutual collaboration between nodes, maintain within convex hull
[Keller and Simon. PDPTA 2003]
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15. Summary Scalability in P2P is a neighbor discovery problem
Desirable properties for Voronoi P2P NVE
Efficient message transmission due to direct connection
Low overhead P2P topology maintenance
Problems with current approach
Moving speed limit
Lack of recovery mechanism from inconsistency
Interesting and promising direction
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16. Future Works Recovery mechanism from inconsistency Variable-radius AOI
Game states persistency (OceanStore)
3D content distribution (3D streaming on P2P)
Towards a true cyberspace 
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17. Acknowledgement WISE Lab, Tamkang Univ.
Joaquin Keller (France Telecomm R&D)
Laboratory of Statistical & Computational Physics, Academia Sinica
Anonymous reviewers
Dr. Chin-Kun Hu
Prof. Wen-Bing Horng
Prof. Jiung-Yao Huang
2004/08/30

18. Q & A
Thank You!
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