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Unreliable Transport Protocol for Commodity-Based OpenGL Distributed Visualization: 

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

Outline: 

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

Outline: 

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

Motivation: 

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

Outline: 

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

Network interconnect: 

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

Outline: 

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

Distributed OpenGL: 

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

Distributed OpenGL: 

Distributed OpenGL TCP only

Distributed OpenGL: 

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)

Distributed OpenGL: 

Distributed OpenGL Interleaved UDP/TCP Synchronization 4 5 5 6 6 6 7 UDP TCP

Distributed OpenGL: 

Distributed OpenGL Interleaved UDP/TCP Result

Distributed OpenGL: 

Distributed OpenGL Fixing interleaved UDP/TCP MTU consideration: no loss example 1 2 3 4 5 6 7 8 9 Sent

Distributed OpenGL: 

Distributed OpenGL Fixing interleaved UDP/TCP MTU consideration: single vertex loss example 1 2 4 5 6 7 8 9 Received 1 2 4 5 6 7 8 9 Rendered

Distributed OpenGL: 

Distributed OpenGL Fixing interleaved UDP/TCP MTU consideration: triplet of vertices loss example 4 5 6 7 8 9 Received 4 5 6 7 8 9 Rendered

Distributed OpenGL: 

Distributed OpenGL Fixed interleaved UDP/TCP Result

Experimentations: 

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

Experimentations: 

Experimentations Test applications Crocodile: OpenGL viewer Rings: Chromium’s test program Chromium B.S.U.: OpenGL game

Experimentations: 

Experimentations 100 Mbps 2.2 fps 2.7 fps 110 fps 110 fps playable playable

Experimentations: 

Experimentations 10 Mbps 0.28 fps 0.36 fps 34 fps 39 fps playable playable

Experimentations: 

Experimentations Wireless 0. 066 fps 0.37 fps 5.5 fps 8 fps quite playable non playable

Conclusion: 

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

Future works: 

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

Acknowledgments: 

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

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