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Challenges In Mesh Networking

Challenges In Mesh Networking. S. Keshav School of Computer Science University of Waterloo. Outline. Why Mesh? WLAN challenges Mesh challenges Perspective. Why Mesh?. Eliminate cost of wired backhaul Support a mobile workforce Increase coverage at little additional cost

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Challenges In Mesh Networking

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  1. Challenges In Mesh Networking S. Keshav School of Computer Science University of Waterloo

  2. Outline • Why Mesh? • WLAN challenges • Mesh challenges • Perspective

  3. Why Mesh? • Eliminate cost of wired backhaul • Support a mobile workforce • Increase coverage at little additional cost …if WiFi is good, then mesh must be better…

  4. Unfortunately… • WiFi is hard, and mesh is harder! • We scarcely understand howto do WiFi well…

  5. Interference Irregular coverage Dynamic coverage Hidden terminals Exposed terminals Parameter hell RF environment Interference verses transmission range Legacy clients Time synchronization Top10 WLAN problems

  6. 1. Interference • Wired  wireless • Due to simultaneous reception of two transmissions at the same receiver • 4 types • AP::AP • AP + AP :: client • AP + client :: client • Client :: client

  7. 2. Irregular Coverage Source: J. Yeo, M. Youssef, A. Agrawala, Characterizing the 802.11 Traffic: The Wireless Side, UMD Tec. Report (CS-TR-4570)

  8. 3. Dynamic coverage Source: J. Yeo, M. Youssef, A. Agrawala, Characterizing the 802.11 Traffic: The Wireless Side, UMD Tec. Report (CS-TR-4570)

  9. 4. Hidden terminal

  10. 5. Exposed Terminal

  11. 6. Parameter Hell • For each AP, need to select • Technology: a, b, g (or n?) • Channel: 1 of 3 or 12 • Power level: 1 of about 50 • Sensitivity: a number from 1 to 90 • Security type: WEP, WPA, 802.1x, … • Vendor-specific extensions • …

  12. 7. RF environment Source: V. Bahl, Openness and the Public Airwaves, Presentation at MobiHoc 2005

  13. 8. Interference Verses Transmission Range Transmission range Interference range

  14. 9. Legacy Clients • Can’t assume that you can change all client software • even in corporate environments!

  15. 10. Time Synchronization • Any kind of coordination betweenAPs requires microsecond-level synchronization • Not easy to achieve

  16. If You Think WLAN Is Bad…

  17. Mesh Is Worse! • All the problems of WLAN, and also • Congestion near gateways • Backhaul consumes a channel • Hard to give QoS bounds • Control and data share channel • Delays in control loop • Fault diagnosis is hard

  18. Perspective • Our understanding of WLANs and meshes is inadequate • Are we biting off more than we can chew by rushing to deployment?

  19. Perspective • After all, there is an alternative!

  20. Thanks! & Questions?

  21. © 2006 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries. The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

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