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Routing in Multi-Radio, Multi-Hop Wireless Mesh Networks

Routing in Multi-Radio, Multi-Hop Wireless Mesh Networks. Richard Draves, Jitu Padhye, Brian Zill Microsoft Research. Self-Organizing Neighborhood Networks. Key Properties No network engineer Very little mobility Energy not a concern One challenge: network capacity

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Routing in Multi-Radio, Multi-Hop Wireless Mesh Networks

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  1. Routing in Multi-Radio, Multi-Hop Wireless Mesh Networks Richard Draves, Jitu Padhye, Brian Zill Microsoft Research

  2. Self-Organizing Neighborhood Networks • Key Properties • No network engineer • Very little mobility • Energy not a concern • One challenge:network capacity • Our approach: multiple radios

  3. Results • Ad-hoc routing at layer 2.5 works well • Link quality is important, but not all metrics are created equal • Multiple radios provide significant capacity improvement if the routing utilizes channel-diversity, data rate, loss rate (Please see our SIGCOMM & Mobicom papers for more details.)

  4. Layer 2 vs Layer 3 • Layer 2 (link layer): like ethernet switches − Limited to single link technology + Supports multiple protocols (IPv4, IPv6, IPX) + Preserves link abstraction • Layer 3 (network layer) + Supports multiple link technologies − Limited to single network protocol − Link-local mechanisms don’t work • DHCP, RA/RS

  5. Our Approach: Routing at Layer 2.5 • A virtual link-layer + Supports multiple link technologies + Supports IPv4, IPv6 etc unmodified + Preserves the link abstraction + Agnostic to choice of ad-hoc routing algorithm IPv4 IPv6 IPX Mesh Connectivity Layer (with LQSR) Ethernet 802.11 802.16

  6. Mesh Connectivity Layer (MCL) Packet Format • Virtual ethernet adapter • Virtual ethernet addresses • Multiplexes heterogeneous physical links • Physical links need not be ethernet Ethernet MCL Payload: TCP/IP, ARP, IPv6…

  7. Link-Quality Source Routing (LQSR) • Source-routed link-state routing protocol • Derived from DSR • Part of Mesh Connectivity Layer (layer 2.5) • Supports link-quality modules • Both on-demand/proactive mechanisms • Route Discovery • Route Maintenance • Metric Maintenance

  8. LQSR Metric Support • HOP: shortest-path routing • closest to DSR • RTT: round-trip time latency • PktPair: packet-pair latency • ETX: expected transmission count • WCETT: designed for multiple radios

  9. Multi-Radio Routing • Previous metrics (HOP, ETX) not suitable for multiple radios per node • Do not leverage channel, range, data rate diversity • Weighted Cumulative Expected Transmission Time • Weight links according Expected Transmission Time (ETT) • Takes link bandwidth and loss rate into account • Combine link ETTs into Weighted Cumulative ETTs (WCETT) • Takes channel diversity into account • Incorporated into source routing

  10. All hops on a path on the same channel interfere Add ETTs of hops that are on the same channel Path throughput is dominated by the maximum of these sums Need to avoid unnecessarily long paths - bad for TCP performance - bad for global resources Given a n hop path, where each hop can be on any one of k channels, and tuning parameter β: WCETT: Combining link ETTs Select the path with min WCETT

  11. Testbed • 23 nodes in building 113 • Cheap desktop machines • HP d530 SF • Two radios in each node • NetGear WAG or WAB • Proxim OriNOCO • Cards can operatein a, b or g mode.

  12. TCP Throughput Test • Select 100 sender-receiver pairs at random (out of 23x22 = 506) • 2-minute TCP transfer • Two scenarios: • Baseline (Single radio): • NetGear cards in 802.11a mode • Proxim OFF • Two radios • NetGear cards in 802.11a mode • Proxim cards in 802.11g mode • Repeat for shortest-path, ETX, WCETT

  13. Results WCETT uses 2nd radio better than ETX or shortest path.

  14. Two-Radio Throughput CDF

  15. Two-Radio Path Length vs Throughput

  16. WCETT Improvement by Path Length

  17. Conclusions • Ad-hoc routing at layer 2.5 works well • Link quality is important for performance • Previous routing metrics do not work well in heterogeneous multi-radio scenarios • WCETT improves performance by making judicious use of additional capacity and channel diversity provided by the 2nd radio

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