Architecture and Algorithms for an IEEE 802.11-based Multi-channel Wireless Mesh Network

Ashish Raniwala, Tzi-cker ChiuehStony Brook University

Infocom2005

OutlineOutline

IntroductionIntroduction Hyacinth ArchitectureHyacinth Architecture ApproachApproach

Load-balancing RoutingLoad-balancing Routing Traffic-aware Channel AssignmentTraffic-aware Channel Assignment

SimulationSimulation ConclusionsConclusions

IntroductionIntroduction

Wireless Mesh Network (WMN)Wireless Mesh Network (WMN) Definition:Definition: A network of static routers inter- A network of static routers inter-

connected by wireless links.connected by wireless links. Examples:Examples: Enterprise backbone network, campus Enterprise backbone network, campus

network, ISP last-mile networknetwork, ISP last-mile network

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

IntroductionIntroduction

Capacity IssuesCapacity Issues 802.11: MAC contention, PLCP header, ACK, bit 802.11: MAC contention, PLCP header, ACK, bit

errorserrors Ad-hoc: Single-channel across the networkAd-hoc: Single-channel across the network

=> Inter-path and Intra-path interference=> Inter-path and Intra-path interference

Increasing CapacityIncreasing Capacity Frequency: Multiple channelsFrequency: Multiple channels Spatial: Directional antennas, Transmit power Spatial: Directional antennas, Transmit power

controlcontrol

IntroductionIntroduction

Channel AssignmentChannel Assignment Channel assignment => Bandwidth of Channel assignment => Bandwidth of

virtual linksvirtual links Connectivity vs. radio spectrum utilization Connectivity vs. radio spectrum utilization

efficiencyefficiency Workload awarenessWorkload awareness

Connectivity Optimal Capacity Routing

Routing => Traffic load on virtual links and gateways Network-wide load balance Interaction between routing and channel assignment

Hyacinth ArchitectureHyacinth Architecture

Internet NFSERP

Standard 802.11Access Network

Multi-channel Wireless Mesh Backbone (2 NICs/node)

Enterprise Resources

=>5-channel network

Load-balancing RoutingLoad-balancing Routing

4030

50

2030

10

20

40

10

Load-balancing RoutingLoad-balancing Routing• 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

• Metrics1. Hop-count

+ stable because mostly static

- load-imbalance

2. Gateway residual capacity

+ load balanced, adapts to traffic

- route flaps because dynamic

3. Path residual capacity

+ handles non-gateway bottlenecks

(1)

(2)

(3)

Traffic-aware Channel AssignmentTraffic-aware Channel Assignment

110

4030

30

20

60 70

4040 30

Traffic-aware Channel AssignmentTraffic-aware Channel Assignment Workload-AwarenessWorkload-Awareness

Why ?Why ? Need to distribute load uniformly across channels.Need to distribute load uniformly across channels.

How ? How ? 1. Periodically construct a neighborhood channel-1. Periodically construct a neighborhood channel-

usage mapusage map 2. Re-assign channels to balance traffic load across 2. Re-assign channels to balance traffic load across

channelschannels 3. Coordinate with3. Coordinate with directdirect neighborsneighbors

10 40 30

10 40 30 Channel loadimbalance

10 40 30Channel loadbalanced

Traffic-aware Channel AssignmentTraffic-aware Channel Assignment Channel Dependency IssueChannel Dependency Issue

Each node has a limited number of Each node has a limited number of interfaces. Hence each interface is interfaces. Hence each interface is used to communicate with multiple used to communicate with multiple neighbors.neighbors.

SOLUTION

A

B

CD

E

SimulationSimulation

60 nodes with 4 gateway nodes 2 or 3 NICs/node, 12 channels 30 random flows to wired network

SimulationSimulation

SimulationSimulation

ConclusionsConclusions IEEE 802.11 beyond AP—mobile communicationIEEE 802.11 beyond AP—mobile communication Multi-channel wireless mesh backboneMulti-channel wireless mesh backbone

Multiple commodity cards per nodeMultiple commodity cards per node Workload-aware channel assignmentWorkload-aware channel assignment Load-balancing routingLoad-balancing routing

Applicable to IEEE 802.16aApplicable to IEEE 802.16a Ongoing Mesh Networking Research:-Ongoing Mesh Networking Research:-

Station-transparent mobility managementStation-transparent mobility management Secure routing protocol Secure routing protocol Self-diagnosing and self-healing network managementSelf-diagnosing and self-healing network management Directional antenna: Spatial DiversityDirectional antenna: Spatial Diversity