Unreliable Transport Protocol for CommodityBased OpenGL Distributed Visualization

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Unreliable Transport Protocol for Commodity-Based
OpenGL Distributed Visualization

• Samuel Thibault ENS Lyon
• Xavier Cavin SCI Institute/Inria Lorraine
• Olivier Festor Inria Lorraine
• Eric Fleury - Inria Rhônes-Alpes

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Outline

• Motivation
• Network interconnect
• Distributed OpenGL
• Experimentations with Chromium
• Conclusion and future works

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Outline

• Motivation
• Network interconnect
• Distributed OpenGL
• Experimentations with Chromium
• Conclusion and future works

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Motivation

• Clusters of commodity computers
• Dedicated, expensive network interconnect
• Both transfer time and packets loss are very low
• Reliable transport protocol (TCP)
• Cheaper network interconnects ( wireless
  cluster)
• Unreliable transport protocol (UDP)
• Degradation of rendering quality

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Outline

• Motivation
• Network interconnect
• Distributed OpenGL
• Experimentations with Chromium
• Conclusion and future works

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Network interconnect

• Transfer Control Protocol (TCP)
• Guaranteed delivery
• Acknowledgment mechanism
• User Datagram Protocol (UDP)
• Unreliable transport protocol
• Fast but no delivery or order guarantee
• Maximum Transmission Unit (MTU)
• Biggest packet size (no fragmentation)
• TCP automatically adapts to the MTU
• UDP does not

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Outline

• Motivation
• Network interconnect
• Distributed OpenGL
• Experimentations with Chromium
• Conclusion and future works

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Distributed OpenGL

• Basic brick

OpenGL decoder
OpenGL application
OpenGL calls
OpenGL calls
Network
OpenGL library
OpenGL encoder
Display
TCP
UDP
Rendering client
Rendering server
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Distributed OpenGL

• TCP only

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Distributed OpenGL

• UDP versus TCP
• Remove the acknowledgment mechanism
• Some data may not be received
• Or not in the order they were sent
• UDP only
• Almost always fatal crash
• Some OpenGL calls shall not be lost use TCP
• Some can glBegin/glEnd contents (i.e. glVertex)

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Distributed OpenGL

• Interleaved UDP/TCP
• Synchronization

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UDP
TCP
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Distributed OpenGL

• Interleaved UDP/TCP
• Result

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Distributed OpenGL

• Fixing interleaved UDP/TCP
• MTU consideration no loss example

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1
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Sent
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Distributed OpenGL

• Fixing interleaved UDP/TCP
• MTU consideration single vertex loss example

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1
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Received
Rendered
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Distributed OpenGL

• Fixing interleaved UDP/TCP
• MTU consideration triplet of vertices loss
  example

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Received
Rendered
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Distributed OpenGL

• Fixed interleaved UDP/TCP
• Result

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Experimentations

• Implementation in Chromium
• Framework for OpenGL rendering on clusters of
  workstations
• http//chromium.sourceforge.net
• Added features (patches-1-branch of CVS
  repository)
• IPv6 support
• Interleaved UDP/TCP support

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Experimentations

• Test applications
• Crocodile OpenGL viewer
• Rings Chromiums test program
• Chromium B.S.U. OpenGL game

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Experimentations
100 Mbps
2.2 fps
110 fps
playable
2.7 fps
110 fps
playable
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Experimentations
10 Mbps
0.28 fps
34 fps
playable
0.36 fps
39 fps
playable
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Experimentations
Wireless
0. 066 fps
5.5 fps
quite playable
0.37 fps
8 fps
non playable
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Conclusion

• Interleaved UDP/TCP is adapted
• If geometry represents most of the traffic
• When rendering quality is not the first interest
• When it is animated
• If the network is the bottleneck or has huge loss
• It is not
• When the application parts are closely
  synchronized
• On local high bandwidth networks

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Future works

• Multiple rendering
• UDP IPv6 multicast
• What about TCP packets?
• UDP buffering sendmsg/recvmsg
• MTU constraints
• UDP 1.5 KB
• TCP 16 KB gt less system calls
• UDP traffic control
• When sender is too fast for network or receiver
• Big losses

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Acknowledgments

• Support
• VTHD Very High Broadband (French ministry of
  industry)
• AVTC (DOE VIEWS)
• People
• Chromium community
• Alain Filbois
• Bruno Levy (Graphite software)