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Scaling Mesh for Real

Scaling Mesh for Real. Ed Knightly ECE Department Rice University http://www.ece.rice.edu/~knightly. Scalable Mesh. High bandwidth 400 Mb/sec to residences and small businesses High availability Nomadicity Large-scale deployment High reliability and resilience Economic viability

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Scaling Mesh for Real

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  1. Scaling Mesh for Real Ed Knightly ECE Department Rice University http://www.ece.rice.edu/~knightly

  2. Scalable Mesh • High bandwidth • 400 Mb/sec to residences and small businesses • High availability • Nomadicity • Large-scale deployment • High reliability and resilience • Economic viability • $$/square mile

  3. Research Challenges • Physical layer • 400 Mb/s • Media access • Target multi-hop and exploit PHY capabilities • Fairness and traffic control • Prevent starvation, remove spatial bias • Prototypes, Testbeds, and Measurement Studies • Platforms for experimentation and proof-of-concept • Architecture • Node placement, security, economics, etc.

  4. Rice Transit Access Point (TAP) Platform • 400 Mb/sec via 4x4 MIMO custom design • Single 20 MHz WiFi channel at 2.4 GHz and 20 bits/sec/Hz efficiency • Feedback-based algorithms for beam-forming MIMO • Custom MAC design and FPGA implementation

  5. Rice Transit Access Point (TAP) Platform • 400 Mb/sec via 4x4 MIMO custom design • Single 20 MHz WiFi channel at 2.4 GHz and 20 bits/sec/Hz efficiency • Feedback-based algorithms for beam-forming MIMO • Custom MAC design and FPGA implementation

  6. Technology For All – Houston, Texas (non-profit) Empower low income communities through technology Neighborhood: income 1/3rd national average, 37% of children below poverty Applications Education and work-at-home Technology For All Deployment

  7. Multi-hop IEEE 802.11 wireless network covering 40,000 residents Single wireline Internet backhaul Long-haul directional links OTS programmable platform $25k/square mile Technology For All Mesh Deployment

  8. TFA Research Issues • Architecture • Node/wire placement • Sustainable non-profit business model • Protocol deployment • traffic management • Security • Measurement studies

  9. Two Tier Architecture • Access: connects homes to mesh nodes • Backhaul: connects mesh nodes to wires

  10. Parking Lot Scenario • One branch of the access tree is shown • Parking lot is dominant traffic matrix

  11. Parking Lot Measurements (FTP/TCP upload) • Single flow scenario widely studied • Concurrent flows • Without RTS/CTS, hidden terminals  starvation • With RTS/CTS, multi-hop flows achieve 20% of 1-hop flows

  12. Parking Lot Measurements (FTP/TCP bi-directional) • Near starvation with 3 or more hops • TCP unable to throttle short flows to leave capacity for long flows • MAC hidden terminals and Information Asymmetry [GSK05] • Ongoing work: • congestion control over an imperfect MAC • MAC redesign

  13. collision no collision Internet TAP3 TAP2 TAP4 TAP1 Hidden Terminals in Access Networks

  14. RTS RTS TAP2 sets its NAV No CTS Internet TAP3 TAP2 TAP4 TAP1 Information Asymmetry • Asymmetric view of channel state • Node with more information knows when to contend; other attempts randomly

  15. Result on Information Asymmetry [GSK05] • Analytical model to predict throughput • If randomly place nodes: • IA scenario is the most probable resulting in severe throughput imbalance • Previous studies in mobile settings missed by focusing on average throughput • Information Asymmetry is a fundamental property of wireless: state cannot be perfectly shared

  16. Conclusions • Communications advances enabling 400 Mb/s links • At 3-4 hops, TCP/WiFi utilizes 1% of this • We can do better! • Challenges • MAC – multi-hop protocols • Fairness – distributed fairness algorithms • Prototypes – testbeds and proof-of-concept • Architecture – placement, economics, security, …

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