scaling mesh for real
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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 - PowerPoint PPT PresentationTRANSCRIPT
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Scaling Mesh for Real
Ed Knightly
ECE Department
Rice University
http://www.ece.rice.edu/~knightly
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Ed 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– $$/square mile
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Ed Knightly
Research Challenges
1. Physical layer– 400 Mb/s
2. Media access– Target multi-hop and exploit PHY capabilities
3. Fairness and traffic control– Prevent starvation, remove spatial bias
4. Prototypes, Testbeds, and Measurement Studies– Platforms for experimentation and proof-of-concept
5. Architecture– Node placement, security, economics, etc.
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Ed Knightly
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
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Ed Knightly
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
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Ed Knightly
Technology For All Deployment
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
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Ed Knightly
Technology For All Mesh Deployment
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
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Ed Knightly
TFA Research Issues
Architecture– Node/wire placement
Sustainable non-profit business model
Protocol deployment– traffic management
Security
Measurement studies
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Ed Knightly
Two Tier Architecture
Access: connects homes to mesh nodes Backhaul: connects mesh nodes to wires
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Ed Knightly
Parking Lot Scenario
One branch of the access tree is shown
Parking lot is dominant traffic matrix
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Ed Knightly
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
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Ed Knightly
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
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Ed Knightly
Hidden Terminals in Access Networks
Ethernet
Ethernet
Ethernet
Ethernet
Internet
TAP1 TAP2 TAP3 TAP4
collision no collision
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Ed Knightly
Information Asymmetry
Ethernet
Ethernet
Ethernet
Ethernet
Internet
TAP1 TAP2 TAP3 TAP4
RTS
TAP2 sets its NAVNo CTS
RTS
• Asymmetric view of channel state
• Node with more information knows when to contend; other attempts randomly
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Ed Knightly
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
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Ed Knightly
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, …