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CSE 6590Fall 2009
Routing Metrics for Wireless Mesh Networks
1 20 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 BW Causes throughput to decrease sharply Increases delay at each hop Increases BW consumption
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Inter Flow InterferenceA node which transmits also contends for BW
with the nodes in the neighboring area of its path.Leads to BW 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 ad hoc networks
e.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 protocolsCharacteristics of path
Path lengthLink packet loss ratioLink capacity Intra-flow interference Inter-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 transmission attemptsETX = 1 / (Pf . Pr)
Pf : loss probability in forward direction
Pr : loss probability in backward direction
To get Pf and Pr : sending one probe packet per second.
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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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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Routing Metrics for WMNs
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Routing Metrics for WMNs
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Routing Metrics for WMNs
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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, chapter 2.