Routing Metrics for Wireless Mesh
Networks
CSE 6590
Fall 2010
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13 April, 2015
Wireless Mesh Networks
 Mostly static nodes
 Limited bandwidth
 Ample energy supply
 Possibly multi-radio/multi-channel/multi-rate
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New Routing Metrics for WMNs
Motivation
 Limited bandwidth require efficient routing
Goals
 High throughput
 Low end-to-end delay
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Intra Flow Interference
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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
Inter Flow Interference
 A 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
Routing Protocols for Mesh Networks
Routing
Protocols
On Demand
Routing
Proactive
Routing
Source
Routing
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Hop-by-Hop
Routing
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On Demand Routing
 Originally designed for mobile ad hoc networks
 e.g., DSR, AODV
 Flood-based route discovery when source needs to communicate
with destination
 Good for maintaining network connectivity under frequent changes
in topology
 High overhead is unnecessary in networks with static nodes
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Table-Driven (Proactive) Routing
 Proactively maintain and update routing tables
 Broadcast route update messages
 Periodically
 Topology changes
 Lower overhead than on-demand routing in static networks
 Cannot cope with frequent metrics changes
 Route flapping
 High message overhead
 Two approaches:
 Source routing
 Hop-by-hop routing
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Source Routing
 Example protocol: LQSR
 Source nodes put entire path in packet header
 Large packet headers waste network bandwidth
 Does not scale
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Hop-by Hop Routing
 Distance-vector routing (slow convergence )
 Link-state routing (fast convergence)
 Packet only carries destination address
 Small overhead
 Scalable
 Preferable, especially link-state routing
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Least Cost Path Routing
 Routing protocols route packets along minimum weight paths
 Performance of minimum weight paths impact the performance of routing protocols
 Characteristics of path
 Path length
 Link packet loss ratio
 Link capacity
 Intra-flow interference
 Inter-flow interference
 Capture as many characteristics as possible
 Note: In multi-channel multi-radio networks, channel assignment and routing
must work together for optimal performance.
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Routing Metrics for WMNs
 Hop Count
 Expected 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
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ETX
 Expected number of transmissions required for successfully
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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 metric
 Path cost = sum of link costs on that path
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ETT
 Expected transmission time
 ETT = ETX x (S / B)
 S: average packet size
 B: data rate
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WCETT
 Weighted cumulative expected transmission time
 Addresses the issue of channel reuse along a path
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WCETT (2)
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Loop Free Routing - Isotonicity
 Definition
 The order of the weights of two paths must be preserved when we
append or prefix a common third path on the two paths
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MIC
 Metric of Interface and Channel switching
 Improves upon WCETT
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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 Channel
 Compare MIC, ETT and hop count
 Simulation parameters
 One radio per node
 All radios configured to the same channel
 1000m x 1000m, 100 nodes, 20 flows
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Single Channel ─ Results
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Performance Evaluation
Multiple Channels
 Compare MIC, ETT, WCETT and hop count
 Simulation parameters
 2 radios per node
 Each can be configured to 1 of 3 channels
 1000m x 1000m, 100 nodes, 20 flows
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Multiple Channels ─ Results
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References
“Wireless Mesh Networking” book, section 1.8.
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