Design and Evaluation of iMesh: an Infrastructuremode Wireless Mesh Network

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Design and Evaluation of iMesh an
Infrastructure-modeWireless Mesh Network

• Vishnu Navda, Anand Kashyap and Samir R. Das
• Computer Science Department
• State University of New York at Stony Brook
• Stony Brook, NY 11794-4400, U.S.A.

2005 IEEE
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Outline

• Introduction
• Design and Implementation
• Link Layer Handoff
• Network Layer Handoff
• Testbed and Performance Evaluation
• Conclusion

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Introduction

• The access routers are rather interconnected via
  wireless links to form a backbone wireless
  network.
• The fundamental design goal that we pursue is
  client side transparency.
• The clients still associate with an AP using a
  traditional association mechanism in wireless
  LANs.

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Design and Implementation

• We refer to our architecture as iMesh.
• A mesh network could be built simply by using
  bridging.
• Bridges are unable to handle hierarchies in the
  network

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Design and Implementation (cont.)

• Link Layer Handoff

AP
Client (station)
Probe request (broadcast)
Probe response (at the same channel)
Collect all the probe response Select one AP with
best SINR on the probe response
authenticate
Re-association request
Re-association response
Layer-2 handoff completes!!
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Design and Implementation (cont.)

• Network Layer Handoff
• TMIP (Transparent Mobile IP)
• Mobile Location Register (MLR)
• a centralized server
• keeps the information about the home AP for
  every mobile station
• the foreign AP sends a query to the MLR to find
  out about its home AP.
• packets directed to the mobile are intercepted by
  the home AP and tunneled to the foreign AP.

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Design and Implementation (cont.)

• OLSR (Optimized Link State Routing)
• In the iMesh testbed we have chosen a link-state
  based routing protocol
• external route
• The OLSR protocol advertises such external routes
  via the so-called HNA messages(Host and Network
  Association) 5 designed specifically to inject
  external routes to the mesh network.

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Design and Implementation (cont.)
Mesh network
IP-to-MAC address mapping table
AP1
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Testbed and Performance Evaluation

• Our testbed uses 6 APs and 1 mobile station.
• 4-of APs and station run redhat 8 with
  Linux-2.4.22 kernel
• Each AP is equipped with a single Prism 2.5
  chipset based 802.11b PCMCIA card
• Mobile node 2 NICs, one for association, one for
  monitoring
• WDS etc. are logic interfaces

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Handoff latencies for iMesh using OLSR routing
with no background traffic for (a) without
probing and (b) with probing on a single channel.
The notation i-gtj indicates hand-off from Ni
directly to Nj.
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Handoff latencies for TMIP with no background
traffic for (a) without probing and (b) with
probing on a single channel.
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Handoff latencies for iMesh using OLSR routing
with background traffic of 2.5Mbps for (a)
without probing and (b) with probing on a single
channel.
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RTT Measurements for ping packets for iMesh
withOLSR and TMIP. Handoffs occur at intervals of
10 sec.
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Conclusion

• The goal of our design is client-side
  transparency, so that existing mobile clients can
  seamlessly use such a mesh network in lieu of a
  wireless LAN
• We presented detailed experimental results
  involving measurements of handoff latencies at
  both layer-2 and layer-3
• We consider this an excellent performance
  relative to recent studies on wireless LAN.