CSE 6590Fall 2010

Routing Metrics for Wireless Mesh Networks

1 22 April 2023

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Wireless Mesh NetworksMostly static nodesLimited bandwidthAmple energy supplyPossibly multi-radio/multi-channel/multi-

rate

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New Routing Metrics for WMNs

MotivationLimited bandwidth require efficient routing

GoalsHigh throughputLow end-to-end delay

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Intra Flow Interference Nodes on the path of the same flow compete with

each other for channel bandwidth Causes throughput to decrease sharply Increases delay at each hop Increases bandwidth consumption

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Inter Flow InterferenceA node which transmits also contends for

bandwidth with the nodes in the neighbouring area of its path.Leads to bandwidth starvation Some nodes may never get to transmit

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Routing Protocols for Mesh Networks

RoutingProtocols

On DemandRouting

ProactiveRouting

SourceRouting

Hop-by-HopRouting

Routing Protocols for Mesh Networks

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On Demand RoutingOriginally designed for mobile ad hoc

networkse.g., DSR, AODV

Flood-based route discovery when source needs to communicate with destinationGood for maintaining network connectivity

under frequent changes in topologyHigh overhead is unnecessary in networks with

static nodes

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Table-Driven (Proactive) RoutingProactively maintain and update routing tablesBroadcast route update messages

PeriodicallyTopology changes

Lower overhead than on-demand routing in static networks

Cannot cope with frequent metrics changesRoute flappingHigh message overhead

Two approaches:Source routingHop-by-hop routing

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Source RoutingExample protocol: LQSRSource nodes put entire path in packet headerLarge packet headers waste network

bandwidthDoes not scale

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Hop-by Hop RoutingDistance-vector routing (slow convergence )Link-state routing (fast convergence)Packet only carries destination addressSmall overheadScalablePreferable, especially link-state routing

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Least Cost Path RoutingRouting protocols route packets along minimum weight

pathsPerformance of minimum weight paths impact the performance

of routing protocols

Characteristics of pathPath lengthLink packet loss ratioLink capacityIntra-flow interferenceInter-flow interference

Capture as many characteristics as possibleNote: In multi-channel multi-radio networks, channel

assignment and routing must work together for optimal performance.

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Routing Metrics for WMNsHop CountExpected Transmission Count (ETX)Expected Transmission Time (ETT)Weighted Cumulative ETT (WCETT)Metric of Interference and Channel

Switching (MIC)The metrics evolved, each incorporating

features of the previous ones

ETX

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Expected number of transmissions required for successfully receiving a packet over that link.

ETX = 1 / (Pf . Pr)

Pf : packet delivery ratio in forward direction

Pr : packet delivery ratio in backward direction

To get Pf and Pr : sending one probe packet per second.

ETX is an additive metricPath cost = sum of link costs on that path

ETT

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Expected transmission timeETT = ETX x (S / B)

S: average packet sizeB: data rate

WCETT

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Weighted cumulative expected transmission time

Addresses the issue of channel reuse along a path

WCETT (2)

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WCETT Example

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Loop Free Routing - IsotonicityDefinition

The order of the weights of two paths must be preserved when we append or prefix a common third path on the two paths

MIC

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Metric of Interface and Channel switchingImproves upon WCETT

MIC (2)

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MIC (3)IRU (Interference-aware Resource Usage)

The aggregated channel time of all the neighbouring nodes (include end points of link l) consumed by the transmission on link l

Captures path length, link capacity, loss ratio and inter-flow interference

CSC (Channel Switching Cost)Captures intra-flow interference

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Routing Metrics for WMNs

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Performance Evaluation Single ChannelCompare MIC, ETT and hop countSimulation parameters

One radio per nodeAll radios configured to the same channel1000m x 1000m, 100 nodes, 20 flows

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Single Channel ─ Results

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Performance EvaluationMultiple ChannelsCompare MIC, ETT, WCETT and hop countSimulation parameters

2 radios per nodeEach can be configured to 1 of 3 channels1000m x 1000m, 100 nodes, 20 flows

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Multiple Channels ─ Results

References

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“Wireless Mesh Networking” book, section 1.8.