Routing and Medium Access Control and in Wireless Mesh Networks by liaoqinmei


									Fault Tolerant Routing in
Tri-Sector Wireless Cellular
Mesh Networks
    Yasir Drabu and Hassan Peyravi
    Kent State University
    Kent, OH - 44240

    Introduction
          Wireless Network Overview
    Problem Definition
    Proposed Solutions
          Shortest Path Routing
          Fault Tolerant Routing
    Conclusion

Kent State University          PDCS - 06   2
Intro - Wireless Network Architectures
  Point to Point                      Point to Multipoint      Multipoint to Multipoint

 Dedicated links                 Currently Most Common              Our Focus

Topology                Reliability Adaptability Scalability Routing Complexity
P to P                  High       Low            None       None
P to M                  Low        Low            Moderate   Moderate
M to M                  High       High           High       High

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Wireless Mesh Networks (WMN)
                                              Structured, energy rich
                        INTERNET               wireless multi-hop
                                                  Wireless Client
                                                      Mobile, no routing,
                                                       limited power
                                                  Wireless Router
                                                      Low mobility, routing and
                                                       power rich
                                                  Wireless Gateway
                                                      Access to wired network.
                                              Solves – “Last Mile

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Problem Definition

    How do you route packets in a Wireless
     Mesh/Multi-Hop network?
    Given:
          Faulty wireless – multi path fading, selective
           fading, noise etc.
          Shortest path may not be the best alternative.
          Multiple hops/ multiple channel – radio limitations,
           channel allocation problem etc.

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   Many wireless routing algorithms:
          Pro-active (DBF) , reactive (DSR, TORA) and hybrid
        None are very fault tolerant and very focused on energy
         poor applications
   Few provide fault tolerance
        Agarwal 2004 (Stony Brook research lab) – build routing
         using spanning trees then re-associate to different root
         when link fails.
              Slow, high message complexity, order of seconds.

    However not much work done on using
     topological properties of wireless network

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Proposed Honey Comb WMN Model
                                   Modified to
                                   Honey Comb

        Typical Cellular Network                    Proposed Honeycomb Model

    No wired backbone for each node
    Place wireless elements on the edge instead
     of the center in a typical network
    Uses more nodes with lower power for better
     coverage and higher throughput
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Honey Comb Network Comparison
Cellular Network:                           Honeycomb Network:
          Central Base Station                      BS as the edge
          Omni-directional antenna                  Directional antennas

    Advantages                                  Advantages
     + Established Technologies                   +   Lower power per node
     + Fewer Base Stations                        +   Better coverage
                                                  +   Higher throughput
    Limitations                                  +   Fault tolerance
     – High power consumption                     +   Wireless interconnect, cheaper
     – Limited coverage                               to deploy when wired
     – Lower bandwidth                                infrastructure is factored in
     – No Fault tolerance
     – Expensive to deploy and                   Limitations
        maintain due to wired back                –   More complex hardware
        bone infrastructure.                      –   More nodes for same area

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Proposed Tri-Sector Node Model
                                                  Four Radios
                            Router                    Three directional antennas for
                                                       communication with other
                                                      One omni-directional for
                                                       wireless clients
                                                  The directional antenna
                                                   can be on the same
                                                   channel as they are
                                                   spatially multiplexed.
                                                      Using different channels on
                                                       different lobes will add to the
                                                       complexity of the problem.
                                                  Omni-directional antenna is
                                                   on a separate channel to
                                                   minimize interference.

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Earlier routing in Honeycomb Network

    Honeycomb routing
     was introduced in
    Issues:
          Uses (x, y, z) co-
           ordinates to route.
          No consideration for link
                                            Src: Stojmenovic:97

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Honeycomb Brick Representation

                              Isomorphic pruned 2D
                              square mesh


    Two dimensional representation of
    Each node can be represented by a
     co-ordinate (x,y)
    They have 25% smaller degree than
     regular grid meshes.

Kent State University                   PDCS - 06    11
Shortest Path Routing Algorithm

Kent State University   PDCS - 06   12
    Fault Tolerance In Brick Networks

    Link faults common in
     wireless networks
    How do we handle a fault
     in a mesh network?
          Localized Temporal Routing
    Temporal Routing Based
          Final direction of packet
          Position of fault
          Number of faults

    Kent State University              PDCS - 06   13
Fault Tolerant Routing Algorithm

                                   Fault detection:
                                    Physical layer or the
                                    Medium Access Layer
                                    detects the fault.
                                   Fault avoidance: Once
                                    a fault has been
                                    detected, the algorithm
                                    goes into recovery
                                    mode. Exploited
                                    topological properties to
                                    define alternate path.
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Fault Routing – Single and Multiple

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    Fault tolerance is a trade-off between delay
     and deliverability.
          More hops introduce delay.
    Model needs ground up deployment
    Topological Rigidity
          Cannot be deployed on all terrains

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    Contributions:
          Modeled fault tolerant network topology
          Efficient addressing scheme
          Shortest path routing algorithm
          Developed fault tolerant routing which can handle
           multiple faults.
    Future Work:
          Gateway Placement
          Resource allocation (channel assignment)

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Wireless Multi-hop Networks
    Type of multi-hop networks (Application Level
          Ad hoc
                Limited power, high mobility, relatively small.
                Primary application – file sharing and collaboration.
          Sensor Networks
                Very low power, low bandwidth, large networks.
                Primary application – Data accusation and sensing.
          Wireless Mesh Networks (WMN)
                Power rich, structured, high throughput
                Primary application – access network to end users.

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Routing Challenges in WMN
    Time varying link behavior
    Shortest Path not always the best route
    Using spanning trees do not exploit the natural
     robustness of a WMN.
    Exploit alternate routes to make WMN fault tolerant
    How to achieve load balancing.
      How to maintain alternate routes?

      How to choose one route over the other? On what


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