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CSE 6590

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Title: Routing Metrics for Wireless Mesh Networks Author: Uyen Trang Last modified by: Uyen Trang Created Date: 10/4/2007 4:40:02 PM Document presentation format – PowerPoint PPT presentation

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Learn more at: http://www.eecs.yorku.ca
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Title: CSE 6590


1
Routing Metrics for Wireless Mesh Networks
  • CSE 6590
  • Fall 2009

2
Wireless Mesh Networks
  • Mostly static nodes
  • Limited bandwidth
  • Ample energy supply
  • Possibly multi-radio/multi-channel/multi-rate

3
New Routing Metrics for WMNs
  • Motivation
  • Limited bandwidth require efficient routing
  • Goals
  • High throughput
  • Low end-to-end delay

4
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

5
Inter Flow Interference
  • A 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

6
Routing Protocols for Mesh Networks
7
On Demand Routing
  • Originally designed for 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

8
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

9
Source Routing
  • Example protocol LQSR
  • Source nodes put entire path in packet header
  • Large packet headers waste network bandwidth
  • Does not scale

10
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

11
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.

12
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

13
ETX
  • Expected transmission attempts
  • ETX 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.

14
ETT
  • Expected transmission time
  • ETT ETX x (S / B)
  • S average packet size
  • B data rate

15
WCETT
  • Weighted cumulative expected transmission time
  • Addresses the issue of channel reuse along a path

16
WCETT (2)
17
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

18
MIC
  • Metric of Interface and Channel switching
  • Improves upon WCETT

19
MIC (2)
20
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

21
Routing Metrics for WMNs
22
Routing Metrics for WMNs
23
Routing Metrics for WMNs
24
Routing Metrics for WMNs
25
Routing Metrics for WMNs
26
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

27
Single Channel - Results
28
Performance EvaluationMultiple 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

29
Multiple Channels - Results
30
References
  • Wireless Mesh Networking book, chapter 2.
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