Architecture and Algorithms for an IEEE 802 Architecture and Algorithms for an IEEE 802.11-based Multi-channel Wireless Mesh Network Ashish Raniwala Tzi-cker Chiueh Experimental Computer Systems Lab Stony Brook University

Motivation Characteristics- Characteristics - Applications - Goal - 802.11 Deployment Characteristics- Wireless last-hop (AP-to-Mobile) Wired backbone Wireless Mesh Network Characteristics - Wireless backbone Single channel Low capacity Applications - Last-mile ISP connectivity Wireless campus backbone Hyacinth Architecture Goal - High-capacity wireless mesh network Using Multiple channels No MAC modifications (off-the-shelf hardware) Wires

Hyacinth Architecture Research Issues Outline Motivation Hyacinth Architecture Research Issues Load-balancing Routing Traffic-aware Channel Assignment Throughput and Latency Gains Hyacinth Prototype Conclusions

Interconnection Network ? Network Model Internet NFS ERP Enterprise Resources Gateways Interconnection Network ? Access Net

Hyacinth Architecture Internet NFS ERP Enterprise Resources Gateways Access Net

Hyacinth Architecture Wired Network 4 3 3 5 4 2 1 3 2 1 5 4 2 1 3 2 Virtual link operating on Channel 2 Mesh router operating on Channel 2 and Channel 3

Connectivity Optimal Capacity Research Issues Interface Channel Assignment Channel assignment => Bandwidth of virtual links Connectivity vs. radio spectrum utilization efficiency Workload awareness Connectivity Optimal Capacity Packet Routing Routing => Traffic load on virtual links and gateways Network-wide load balance Interaction between routing and channel assignment Goal: Maximize network cross-section goodput

Load-Balancing Routing: Problem 30 20 40 10 30 10 40 50 20

Load-Balancing Routing: Solution 802.1D-like Gateway Discovery Protocol Each node joins one (or more) gateways Messages: ADVERTISE/JOIN/ACCEPT/LEAVE Structure: Forest of trees rooted at gateway nodes. Cache extra advertisements for failure recovery Metrics Hop-count + stable because mostly static - load-imbalance Gateway residual capacity + load balanced, adapts to traffic - route flaps because dynamic Path residual capacity + handles non-gateway bottlenecks (1) (2) (3)

Traffic-Aware Channel Assignment: Problem 70 110 60 30 40 40 30 40 30 20

Traffic-Aware Channel Assignment Workload-Awareness Why ? Need to distribute load uniformly across channels. How ? 1. Periodically construct a neighborhood channel-usage map 2. Re-assign channels to balance traffic load across channels 3. Coordinate with direct neighbors 10 40 30 Channel load imbalance 10 40 30 10 40 30 Channel load balanced

Traffic-Aware Channel Assignment Channel Dependency Issue Each node has a limited number of interfaces. Hence each interface is used to communicate with multiple neighbors. Control Channel - Physical: Extra NIC on dedicated channel - Virtual: Multi-hop connectivity to neighbors C E SOLUTION D B A Channel Load Metrics - Contention group size Aggregated channel usage Weighted sum of the two

Performance Evaluation: Throughput Gains Simulation Setup 60 nodes with 4 gateway nodes 2 or 3 NICs/node, 12 channels 30 random flows to wired net Cross-section goodput X Results Baseline: Single-channel net Identical CA: 2x improvement Centralized CA: 6-7x gains Distributed CA: 6-7x gains Single-NIC Multi-channel: only marginal improvement

Performance Evaluation: Latency Reductions Simulation Setup 64 nodes with 4 gateway nodes 2 NICs/node, 12 channels HTTP traffic requests/response Traffic intensity:0, X, 2X, 3X, 4X Results Reduced average delay Saturation point: 4x users with multi-channel networking

Hyacinth Channel/Route Allocation Daemon Prototype Implementation Hyacinth Channel/Route Allocation Daemon User Channels Routes Statistics NDIS Miniport Driver Kernel Routing Tables Windows Performance Counters Kernel Optional Wired Interface Hardware Wireless Network Interfaces

Prototype Evaluation Configuration – 9 Win XP desktops, 2 gateway nodes Two 802.11a NICs / node FTP Throughput – 5-times improvement Should be higher for larger testbed Fail-over – Node 6 fails; Node 3 switches to Node 2 < 700 msec to recover ~450 msec for changing route tables

IEEE 802.11 beyond AP—mobile communication Conclusions.. IEEE 802.11 beyond AP—mobile communication Multi-channel wireless mesh backbone Multiple commodity cards per node Workload-aware channel assignment Load-balancing routing Many-fold improvement with small increase in price Applicable to IEEE 802.16a Ongoing Mesh Networking Research:- Link-aware transport layer Station-transparent mobility management Secure routing protocol Self-diagnosing and self-healing network management Directional antenna: Spatial Diversity Project site: http://www.ecsl.cs.sunysb.edu/multichannel