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Managing Chaotic Wireless Networks

Managing Chaotic Wireless Networks. David Wetherall University of Washington. Credits. UW/CSE wireless group John Zahorjan, Maya Rodrig, Charlie Reis, Ratul Mahajan, Ed Lazowska Intel Research Seattle Yatin Chawathe, Mike Chen, Brian Noble, Anthony Nicholson CMU

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Managing Chaotic Wireless Networks

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  1. Managing Chaotic Wireless Networks David Wetherall University of Washington

  2. Credits • UW/CSE wireless group • John Zahorjan, Maya Rodrig, Charlie Reis, Ratul Mahajan, Ed Lazowska • Intel Research Seattle • Yatin Chawathe, Mike Chen, Brian Noble, Anthony Nicholson • CMU • Srini Seshan et. al. for “Chaotic” wireless

  3. Context: WiFi boom deployments • Advantages: minimal infrastructure, mobility • Technologies: 802.11 a/b/g/n, and more • Deployments: hotspots, home networks measure cost-performance time

  4. Chaotic Wireless Networks Two consequences of growth: • Overlapping (dense) deployments • Compete for spectrum • Seen in urban areas today • That are independently managed • Limited visibility into the operation of others • Focus on their own goals; no central planning Chaotic = overlapping + independent Claim for chaotic environments: • Today’s 802.11 designs won’t fare well • There’s an opportunity to do much better

  5. CSE Allen Center, 3rd floor 10 802.11b/g APs per floor, managed as a whole: Channels 1, 6, 11 20/30 mW power Omni-directional antennas Site surveys, sparse deployments, and decoupling are the basis for good coverage and performance. A single 802.11 network architecture

  6. Adverse interactions across networks • 802.11 won’t degrade gracefully in chaotic environments • Ideally CSMA/CA would provide reasonable sharing … • Default channel assignments • Crowding, non-orthogonal effects • Static power management • Wastefully high, leads to interference • Rate diversity • High rate transmissions beat out by low rates • Hidden terminals and capture • Poor access from some locations • Other unlicensed band transmissions • Don’t argue with a phone/microwave … • Problems increase with density, load and heterogeneity

  7. A Band-aid: Dynamic tuning • One possible fix: dynamic parameter tuning • Each network measures environment and chooses the channel/power/routes that works best for it • Claim: dynamic tuning isn’t enough • Adaptation is necessary but not sufficient • There are opportunities to do much better

  8. Top: AP conflict on channel 1 (middle two blue nodes) can’t be resolved by individual tuning Bottom: but a solution needs only a simple switch between two adjacent nodes Pitfalls (1) – you can get stuck 1 5 4 3 2 6 1 5 4 3 2 6

  9. Pitfalls (2) – lack of stability • To avoid getting stuck, need to perturb the system, changing channels even without immediate gain • Q: What happens to in the configuration below? • A: Four APs dance around three channels • Tradeoff between stability and convergence 4 1 3 2

  10. Pitfalls (3) – power escalation • Suppose APs adjust their transmit power (between min and max) based on delivery to their clients • What will the APs on channel 1 do? • Higher power increases delivery/rate and interference • Potential tragedy of the commons (lose/lose) 4 1 3 2

  11. Opportunities for Coordination • Suppose we go beyond dynamic tuning … • Coordination = actively exchange information and make joint decisions (for selfish gain), rather than merely try to avoid each other • Claim: coordination beats tuning • Improves outcome for pitfalls • Enables new beneficial scenarios

  12. Relaying for coverage/performance • Relaying can leave both networks better off • Use of better links allows higher rates, • i.e., one transmission per packet at 1 Mbps vs. two transmissions per packet, each at 55Mbps 1 AP1 C1 55 55 55 55 1 AP2 C2

  13. Backup for reliability/performance • Use neighbor AP for backup Internet access • Or always use neighbor’s surplus for performance • Need to consider AUP issues Internet Internet X AP1 AP2 C1 C2

  14. Goal: Wireless internetworking • Wireless Internet = architecture that coordinates multiple individual wireless networks for better coverage, performance and reliability • Predictably allocate wireless and access bandwidths • Leave individual networks better off than before • Architectural roles: • Effectively allocate underlying resource • Allow new applications to flourish • IP does both; 802.11 does neither …

  15. Research agenda • How does wireless work in practice? • Predict what will happen for a given choice of channel/power/routes and protocols • What information is exchanged where? • Need to find small regions with tight coupling • How do we make this win-win? • Choices that benefit all players • How do we foster a grassroots effort? • Deployment incentives

  16. Questions?

  17. Aside: WiFi vs Cellular data • WiFi • Local = high bandwidth, inexpensive • Many islands of coverage • Cellular data • Wide-area = low bandwidth, expensive • Build-out for good coverage “away from home” • So concentrate on WiFi here • Potential for combining the best of both worlds

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