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Robert Morris Daniel Aguayo, John Bicket, Sanjit Biswas, Douglas De Couto, Glenn Judd

MIT Roofnet Performance MSR Mesh Summit, June 2004. Robert Morris Daniel Aguayo, John Bicket, Sanjit Biswas, Douglas De Couto, Glenn Judd http://pdos.lcs.mit.edu/roofnet. Roofnet node map. 1 kilometer. Typical rooftop view. Roofnet radio links. 1 kilometer.

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Robert Morris Daniel Aguayo, John Bicket, Sanjit Biswas, Douglas De Couto, Glenn Judd

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  1. MIT Roofnet Performance MSR Mesh Summit, June 2004 Robert Morris Daniel Aguayo, John Bicket, Sanjit Biswas, Douglas De Couto, Glenn Judd http://pdos.lcs.mit.edu/roofnet

  2. Roofnet node map 1 kilometer

  3. Typical rooftop view

  4. Roofnet radio links 1 kilometer

  5. A Roofnet Self-Installation Kit 50 ft. Cable ($40) Low loss (3dB/100ft) Antenna ($65) 8dBi, 20 degree vertical Miscellaneous ($75) Chimney Mount, Lightning Arrestor, etc. Computer ($340) 533 MHz PC, hard disk, CDROM Software (“free”) Our networking software based on Click 802.11b card ($155) Engenius Prism 2.5, 200mW Total:$685 Takes a user about 45 minutes to install on a flat roof

  6. Roofnet Node Software sshd apache dhcpd User-space Linux Kernel Linux TCP/IP ETX NAT antenna srcrr Click 802.11b eth Living-room ethernet

  7. Basic Roofnet performance • High TCP throughput even w/ many hops • Why is 2-hop b/w less than half 1-hop b/w?

  8. Multi-hop collisions cut b/w by about 2x • x-axis: expected multi-hop b/w based on single-hop b/w • y-axis: actual Roofnet b/w is often much lower

  9. Roofnet link quality distribution 1 megabit/second Packet Delivery Probability 11 mbits/sec Node Pair • Why do most links have intermediate loss rates?

  10. S/N vs loss w/ cable + attenuator • In principle, the intermediate-loss S/N region is narrow

  11. S/N vs loss for Roofnet links • Roofnet loss rates cannot be explained by S/N

  12. Effect of transmit power level on Roofnet • Higher tx power increases radio “range” • Increase in # of links between 1/r2 and 1/r3

  13. What is a typical radio range? Delivery probability Distance (Meters)

  14. Would a less-dense mesh work? • Roofnet is about twice as dense as it needs to be • Higher densities provide higher throughput

  15. Mesh versus access points • 5 APs are required for full connectivity • N mesh gateways give higher throughput than N APs

  16. Conclusions • Roofnet provides Internet access to 40+ users • Even 9-hop routes average 150 kilobits/second • Radio range up to 2km • Hard to beat mesh performance w/ access points • Multi-hop packet loss costs about a factor of two

  17. Transmit bit-rate choice 11 megabits/second 5.5 Packets/second received 2 1 Node Pair

  18. How reliant on the “best” nodes? Average Throughput (KB/s) Number of Best Nodes Eliminated

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