1. Workshop on Commodity-Based Visualization Clusters 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

2. Workshop on Commodity-Based Visualization Clusters 2 Outline Motivation Network interconnect Distributed OpenGL Experimentations with Chromium Conclusion and future works

3. Workshop on Commodity-Based Visualization Clusters 3 Outline Motivation Network interconnect Distributed OpenGL Experimentations with Chromium Conclusion and future works

4. Workshop on Commodity-Based Visualization Clusters 4 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

5. Workshop on Commodity-Based Visualization Clusters 5 Outline Motivation Network interconnect Distributed OpenGL Experimentations with Chromium Conclusion and future works

6. Workshop on Commodity-Based Visualization Clusters 6 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

7. Workshop on Commodity-Based Visualization Clusters 7 Outline Motivation Network interconnect Distributed OpenGL Experimentations with Chromium Conclusion and future works

8. Workshop on Commodity-Based Visualization Clusters 8 Distributed OpenGL Basic brick Rendering client OpenGL decoder OpenGL library OpenGL encoder OpenGL calls OpenGL application Rendering server Display Network TCP UDP

9. Workshop on Commodity-Based Visualization Clusters 9 Distributed OpenGL TCP only

10. Workshop on Commodity-Based Visualization Clusters 10 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)

11. Workshop on Commodity-Based Visualization Clusters 11 Distributed OpenGL Interleaved UDP/TCP –Synchronization 4556667 UDP TCP

12. Workshop on Commodity-Based Visualization Clusters 12 Distributed OpenGL Interleaved UDP/TCP –Result

13. Workshop on Commodity-Based Visualization Clusters 13 Distributed OpenGL Fixing interleaved UDP/TCP –MTU consideration: no loss example Expected 1 2 3 4 5 6 7 8 9 Sent 1 2 3 4 5 6 7 8 9 Rendered

14. Workshop on Commodity-Based Visualization Clusters 14 Distributed OpenGL Fixing interleaved UDP/TCP –MTU consideration: single vertex loss example Expected 1 2 4 5 6 7 8 9 Received 1 2 4 5 6 7 8 9 Rendered

15. Workshop on Commodity-Based Visualization Clusters 15 Distributed OpenGL Fixing interleaved UDP/TCP –MTU consideration: triplet of vertices loss example Expected 4 5 6 7 8 9 Received 4 5 6 7 8 9 Rendered

16. Workshop on Commodity-Based Visualization Clusters 16 Distributed OpenGL Fixed interleaved UDP/TCP –Result

17. Workshop on Commodity-Based Visualization Clusters 17 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

18. Workshop on Commodity-Based Visualization Clusters 18 Experimentations Test applications –Crocodile: OpenGL viewer –Rings: Chromium’s test program –Chromium B.S.U.: OpenGL game

19. Workshop on Commodity-Based Visualization Clusters 19 Experimentations TCP UDP CrocodileRingsChromium B.S.U. 100 Mbps 2.2 fps 2.7 fps 110 fps playable

20. Workshop on Commodity-Based Visualization Clusters 20 Experimentations TCP UDP CrocodileRingsChromium B.S.U. 10 Mbps 0.28 fps 0.36 fps 34 fps 39 fps playable

21. Workshop on Commodity-Based Visualization Clusters 21 Experimentations TCP UDP CrocodileRingsChromium B.S.U. Wireless 0. 066 fps 0.37 fps 5.5 fps 8 fps quite playable non playable

22. Workshop on Commodity-Based Visualization Clusters 22 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

23. Workshop on Commodity-Based Visualization Clusters 23 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

24. Workshop on Commodity-Based Visualization Clusters 24 Acknowledgments Support –VTHD: Very High Broadband (French ministry of industry) –AVTC (DOE VIEWS) People –Chromium community –Alain Filbois –Bruno Levy (Graphite software)