Robert Morris Daniel Aguayo, John Bicket, Sanjit Biswas, Douglas De Couto MIT Roofnet Performance

2 Roofnet node map 1 kilometer

3 Typical rooftop view

4 Roofnet radio links 1 kilometer

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

6 Roofnet Node Software eth Linux TCP/IP Click Linux Kernel User-space sshdapache dhcpd antenna Living-room ethernet NAT srcrr ETX

7 Roofnet link quality distribution Node Pair Packet Delivery Probability 1 megabit/second 11 mbits/sec

8 S/N vs loss w/ cable + attenuator

9 S/N vs loss for Roofnet links

10 Transmit bit-rate choice Node Pair Packets/second received 11 megabits/second

11 Basic Roofnet performance HopsNode Pairs Throughput Kilobits/sec Latency ms

12 Multi-hop packet loss?

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

14 Effect of transmit power level

15 Would a less-dense mesh work? NodesConnectivityThroughput Kilobits/sec Hop Count 417% % % % % % % Roofnet is about twice as dense as it needs to be Higher densities provide higher throughput

16 Mesh versus access points APs or gateways AP throughput AP connections Mesh throughput APs are required for full connectivity N mesh gateways give higher throughput than N APs

17 Conclusions Roofnet provides Internet access to 40+ users Easy for users to install, self-configuring Throughput > 200 kilobits/second for most users Even 9-hop routes average 150 kilobits/second Radio range up to 2km, density 10 nodes/km 2 Hard to beat mesh performance w/ access points Multi-hop packet loss costs about a factor of two

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