Scalable PeertoPeer Networked Virtual Environment

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Scalable Peer-to-Peer Networked Virtual
Environment

• Master Thesis Oral Examination
• Dept. of CSIE, Tamkang Univ.
• Advisor Dr. Chen Jui-Fa
• Shun-Yun Hu
• 2005/01/07

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Outline

• Introduction
• Voronoi-based Overlay Network (VON)
• Simulation Results
• Analysis
• Conclusion

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What is Networked Virtual Environment (NVE)?

• Virtual Reality Internet
• 3D environment with people (avatar), objects,
  terrain, agents
• Military simulations (80) ?
• Massively Multiplayer Online Games (mid-90)
• Trends larger scale, more realistic simulation

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(No Transcript)
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NVE A Shared Space
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Issues for Creating NVE

• Consistency (events/states)
• Responsiveness multiplayer
• Security
• Scalability
• Persistency massively multiplayer
• Reliability (Fault-tolerance)

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The Scalability Problem

• Many nodes on a 2D plane ( gt 1,000)
• Message exchange with those within Area of
  Interest (AOI)
• How does each node receive the relevant messages?

Area of Interest
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A simple solution (point-to-point)
Source Funkhouser95

• N (N-1) connections O(N2) ? Not scalable!

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A better solution (client-server)
Source Funkhouser95

• Message filtering at server to reduce traffic
• N connections O(N) ? server is bottleneck

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Current solution (server-cluster)
Source Funkhouser95

• Still limited by servers. Expansive to deploy
  maintain.

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Scalability Analysis

• Scalability constrains
• Computing resource (CPU)
• Network resource (Bandwidth)
• Non-scalable system vs. Scalable system

Resource limit
x number of entities y resource consumption at
the limiting system component
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What Next?

• Strategies
• Increase resource ? More servers
• Decrease consumption ? Message filtering
• Architectures Scale
• Point-to-point (LAN) tens 101
• Client-server hundreds 102
• Server-cluster thousands 103
• ? millions 106
• Peer-to-Peer

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What is Peer-to-Peer (P2P)?

• Stoica et al. 2003
• Distributed systems without any centralized
  control or hierarchical organization
• Runs software with equivalent functionality
• Examples
• File-sharing Napster, Gnutella, eDonkey
• Distributed computing SETI_at_Home (UC Berkeley)
• VoIP Skype

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Peer-to-Peer Overlay

• A P2P overlay network source Keller Simon
  2003

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Promise Challenge of P2P

• Promises
• Growing resource, decentralized ? Scalable
• Commodity hardware ? Affordable
• Challenges
• Topology maintenance ? dynamic join/leave
• Efficient content retrieval ? no global knowledge

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Issues for Creating P2P NVE

• Consistency (events/states)
• Responsiveness multiplayer
• Security
• Scalability
• Persistency massively multiplayer
• Reliability (Fault-tolerance)
• Consistency (topology) ? P2P NVE

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Related Works (1) SimMUD

• Knutsson et al. 2004 (Univ. of Pennsylvania)
• Pastry Scribe
• Regions
• Coordinators
• (super-nodes)
• Fixed-size region
• Relay overhead

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Related Works (2)

• Kawahara et al. 2004 (Univ. of Tokyo)
• Fully-distributed
• Nearest-neighbors
• List exchange
• High transmission
• Overlay partition

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Related Works (3) Solipsis

• Keller Simon 2003 (France Telecomm RD)
• Links with AOI neighbor
• Mutual cooperation
• Inside convex hull
• Potentially slow discovery
• Inconsistent topology

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Outline

• Introduction
• Voronoi-based Overlay Network (VON)
• Simulation Results
• Analysis
• Conclusion

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Design Goals

• Observation
• for virtual environment applications, the
  contents we want are messages from AOI neighbors
• Content discovery is a neighbor discovery problem
• Solve the Neighbor Discovery Problem in a
  fully-distributed, message-efficient manner.
• Specific goals
• Scalable ? Limit minimize message traffics
• Responsive ? Direct connection with AOI neighbors

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Voronoi Diagram

• 2D 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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Design Concepts
Use Voronoi to solve the neighbor discovery
problem

• Identify enclosing and boundary neighbors
• Each node constructs a Voronoi of its neighbors
• Enclosing neighbors are minimally maintained
• Mutual collaboration in neighbor discovery

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Procedure (JOIN)

• 1) Joining node sends coordinates to any existing
  node
• Join request is forwarded to acceptor
• 2) Acceptor sends back its own neighbor list
• joining node connects with other nodes on the
  list

Joining node
Acceptors region
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Procedure (MOVE)

• 1) Positions sent to all neighbors, mark messages
  to B.N.
• B.N. checks for overlaps between movers AOI and
  its E.N.
• 2) Connect to new nodes upon notification by B.N.
  
• Disconnect any non-overlapped neighbor

Boundary neighbors
Non-overlapped neighbors
New neighbors
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Procedure (LEAVE)

• 1) Simply disconnect
• 2) Others then update their Voronoi
• new B.N. is discovered via existing B.N.

New boundary neighbor
Leaving node (also a B.N.)
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Dynamic AOI

• Crowding within AOI can overload a particular
  node
• Its better if AOI-radius can be adjusted in real
  time

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Adjustment Conditions

• AOI-radius decrease
• Number of connections gt maximum allowable
  connections
• AOI-radius increase
• Maximum connections not exceeded
• Current AOI-radius lt preferred AOI-radius
• Delay counter
• To avoid fluctuations

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Demonstration

• Simulation video
• General movements (20 nodes, 800x600 world)
• Local vs. global view
• Dynamic AOI adjustment

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(No Transcript)
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Outline

• Introduction
• Voronoi-based Overlay Network (VON)
• Simulation Results
• Analysis
• Conclusion

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Simulation Method

• C implementation of Voronoi-based algorithm
• World size 1000 x 1000, AOI 150
• Trials from 10 250 nodes
• Connection limit per node 10
• 1000 time-steps
• ( 100 simulated seconds, assuming 10
  updates/seconds)
• Behavior model
• Random movement random direction
• Constant velocity 5 units/step
• Movement duration random (1 25 steps)

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Consistency Metrics

• Topology Consistency Kawahara, 2004
• Number of observed AOI neighbors
• Number of actual AOI neighbors
• Drift Distance Diot, 1999
• Distance between observed position and actual
  position
• (average over all nodes)

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Basic ModelTopology Consistency
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Basic ModelScalability (1)
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Basic ModelScalability (2)
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Dynamic AOI Model
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Dynamic AOIScalability (1)
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Dynamic AOIScalability (2)
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Dynamic AOIScalability (3)
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Dynamic AOITopology Consistency (1)
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Dynamic AOITopology Consistency (2)
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Dynamic AOIReliability (1)
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Dynamic AOIReliability (2)
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Outline

• Introduction
• Voronoi-based Overlay Network (VON)
• Simulation Results
• Analysis
• Conclusion

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Analysis of Design

• Consistency (Topology)
• Topology is fully connected consistent ?
  enclosing neighbors
• Responsiveness
• Lowest latency ? direct connection, no relay
• Scalability
• Resource-growing decentralized resource
  consumption
• Reliability
• Self-organizing for small number of node failures

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P2P NVE Comparisons
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Problems of Voronoi Approach

• Message traffic
• Circular round-up of nodes
• Redundant message sending
• (inherent to fully-distributed design)
• Incomplete neighbor discovery
• Can happen with inconsistent / incorrect neighbor
  list
• Fast moving node

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Outline

• Introduction
• Voronoi-based Overlay Network (VON)
• Simulation Results
• Analysis
• Conclusion

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Conclusion

• NVE scalability is achievable with P2P
  architecture and is a neighbor discovery problem
• A promising solution Voronoi-based P2P Overlay
• Leverage knowledge of each peer to maintain
  topology
• Properties
• Scalable fully-distributed, dynamic AOI
• Efficient low irrelevant messages, zero relay
• Robust consistent and self-organizing
  topology

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Potential Applications

• Online games
• Relieve server from position updates in current
  MMOGs
• Military
• Enable large-scale, affordable military training
  simulation
• 3D Web
• Provide multi-user interactivity to static 3D
  world
• Scientific simulations
• Distribute spatial simulation requiring frequent
  synchronization

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Future Works

• Short-term
• Reliability measurements ? latency, packet loss,
  node fail
• Distributed event/state consistency
• Recovery from overlay partition
• Long-term
• Persistency issue (P2P-based database)
• Security issue (protection from malicious
  nodes)
• 3D content distribution (3D streaming on P2P)
• Massive, persistent 3D environment sharable by
  all!

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Acknowledgements

• Dr. Jui-Fa Chen (?????)
• Dr. Wei-Chuan Lin (?????)
• Members of the Alpha Lab, TKU CS
• Guan-Ming Liao (???)
• Dr. Chin-Kun Hu (?????)
• LSCP, Institute of Physics, Academia Sinica
• Joaquin Keller (France Telecomm RD, Solipsis)
• Bart Whitebook (butterfly.net)
• Jon Watte (there.com)
• Dr. Wen-Bing Horng (?????)
• Dr. Jiung-yao Huang (?????)

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Inconsistency caused by dAOI
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Reliability (0-500 steps)
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Reliability (501-1000 steps)