Routing and Interface Assignment in MultiChannel MultiInterface Wireless Networks

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Routing and Interface Assignment in Multi-Channel
Multi-Interface Wireless Networks

• Pradeep Kyasanur, Nitin H. Vaidya
• University of Illinois at Urbana-Champaign
• IEEE Communication Society / WCNC 2005
• Speaker Chi-Yu Li
• Date 10/11

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Outline

• Introduction
• Related work
• Motivation
• Interface assignment
• Routing strategy
• Discussion
• Conclusion

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Introduction

• Multiple channels can increase the available
  network capacity, but require new protocols to
  exploit the available capacity
• This paper studies the problem of improving the
  capacity of multi-channel wireless networks by
  using multiple interfaces
• Classify interface assignment strategies
• propose a new interface assignment strategy
• Identify routing heuristics that are suitable for
  the proposed interface assignment strategy

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Related Work

• Nasipuri et al.3,4, and Jain et al.5
  propose a class of protocols where all nodes have
  an interface on each channel
• Wu et al.6 and Hung et al.7 propose a MAC
  layer solution that requires two interfaces
• So et al.8 propose a MAC solution that uses a
  single interface

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Motivation

• Benefits of using multiple interfaces
• When a single interface is used, there is an
  increase in the end-to-end latency and less
  connectivity
• There is the ability to receive and transmit data
  in parallel
• Issues with interface switching
• The switching delay will reduce to a few tens of
  microseconds

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Motivation (Cont.)

• Need for specialized routing protocols
• Existing routing protocols for multi-hop networks
  such as DSR and AODV may not be suitable for
  multi-channel networks

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Interface Assignment Classification of interface
assignment strategies

• Static Assignment
• Static assignment strategies assign each
  interface to a channel either permanently or for
  long interval
• Common channel approach
• Varying channel approach
• Well-suited for use when the interface switching
  delay is large
• Nodes that share a channel on one of their
  interfaces can directly communicate with each
  other

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Interface Assignment (Cont.) Classification of
interface assignment strategies

• Dynamic Assignment
• Allow any interface to be assigned to any
  channel, and interfaces can frequently switch
  from one channel to another
• The coordination mechanism
• visit a common rendezvous channel periodically
• the use of pseudo-random sequences
• Hybrid Assignment
• Combine static and dynamic assignment strategies
• Allow simplified coordination algorithms
  supported by static assignment while retaining
  the flexibility of dynamic assignment

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Interface Assignment (Cont.) A Hybrid Interface
Assignment Strategy

• The interfaces at each node are classified to
  fixed interfaces and switchable interfaces
• Fixed interface stay on the specified channel
  for long durations of time
• Switchable interface frequently switch between
  any of the remaining channels, based on the data
  traffic
• A coordination protocol is required to decide
  what channel to assign to the fixed interface,
  and also for enabling neighbors to know about it
• Use some well-known function f of its node
  identifier
• Explicitly Hello packets

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Interface Assignment (Cont.) A Hybrid Interface
Assignment Strategy
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Interface Assignment (Cont.) Supporting
Broadcasts in Multi-Channel networks

• Nodes in a neighborhood may be listening to
  different channels
• The broadcast packet has to be separately
  transmitted on all channels when using multiple
  channels
• More expensive
• May be sent at slightly different times
• Solution
• At least three interfaces are available, and one
  channel can be set apart for broadcast purpose

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Routing Strategy

• The shortest path metric may not be suitable for
  multi-channel, multi-interface networks, because
  it doesnt consider the interface switching and
  the available channel diversity

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Routing StrategyCost of Interface Switching

• Switching delay impacts a node only if the number
  of distinct channels is more than that of
  available interfaces
• Nodes impacted by the switching delay as
  interface bottlenecked nodes
• The cost of interface switching is measured in
  terms of the number of interface bottlenecked
  nodes along the route

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Routing StrategyMeasuring Channel Diversity

• If a node X along a route has i other interfering
  nodes receiving on the same channel as X, then
  the diversity cost of X is defined to be i
• The diversity cost of the whole route is defined
  as the maximum diversity cost of any node along
  the route

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Routing StrategyRouting Protocol

• Enhanced shortest path metric
• The switching cost the number of interface
  bottlenecked links
• The diversity cost the max-interference method
• The global resource usage cost the total number
  of hops on the route
• Routing protocol (based on DSR)
• The destination node sends RREP back for every
  RREQ
• The source node selects the least cost route by
  RREP
• Two-phase route discovery process
• Forward the RREQ only on the channel with the
  least cost
• A full route discovery is invoked, if the RREP
  isnt received

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Discussion

• Impact of Mobility
• The neighbor set frequently changes
• The Hello packet mechanism
• Topology Control
• Distributing nodes across channels, thereby
  reducing contention
• Integrate with transmission power control
• Other issues
• Selecting the number of interfaces each node
  should have depends on the network density,
  topology, and the desired cost or performance
• Multiple channels may simplify the use of
  multi-path routing algorithm

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Conclusion

• Interface assignment and routing strategy
• Multi-channel Hidden Terminal Problem

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