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 Our approach: multiple radios

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.)

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

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 Ethernet Mesh Connectivity Layer (with LQSR) IPv4IPv6IPX

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

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

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

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

WCETT: Combining link ETTs 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: Select the path with min WCETT

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 operate in a, b or g mode.

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 a mode Proxim OFF –Two radios NetGear cards in a mode Proxim cards in g mode Repeat for shortest-path, ETX, WCETT

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

Two-Radio Throughput CDF

Two-Radio Path Length vs Throughput

WCETT Improvement by Path Length

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 2 nd radio