Fault Tolerant Routing in Tri-Sector Wireless Cellular Mesh Networks

1
Fault Tolerant Routing in Tri-Sector Wireless
Cellular Mesh Networks

• Yasir Drabu and Hassan Peyravi
• Kent State University
• Kent, OH - 44240

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Agenda

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

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Intro - Wireless Network Architectures
Point to Multipoint
Multipoint to Multipoint
Point to Point
Dedicated links
Our Focus
Currently Most Common
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 wireless multi-hop
  networks
• Wireless Client
• Mobile, no routing, limited power
• Wireless Router
• Low mobility, routing and power rich
• Wireless Gateway
• Access to wired network.
• Solves Last Mile Connectivity

INTERNET
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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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Background

• Many wireless routing algorithms
• Pro-active (DBF) , reactive (DSR, TORA) and
  hybrid (ZRP)
• 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
Proposed Honeycomb Model
Typical Cellular Network

• 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
• Central Base Station
• Omni-directional antenna
• Advantages
• Established Technologies
• Fewer Base Stations
• Limitations
• High power consumption
• Limited coverage
• Lower bandwidth
• No Fault tolerance
• Expensive to deploy and maintain due to wired
  back bone infrastructure.

• Honeycomb Network
• BS as the edge
• Directional antennas
• Advantages
• Lower power per node
• Better coverage
• Higher throughput
• Fault tolerance
• Wireless interconnect, cheaper to deploy when
  wired infrastructure is factored in
• Limitations
• More complex hardware
• More nodes for same area

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Proposed Tri-Sector Node Model

• Four Radios
• Three directional antennas for communication with
  other routers
• 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.

Wireless Router
N
1200
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Earlier routing in Honeycomb Network

• Honeycomb routing was introduced in
  Stojmenovic97
• Issues
• Uses (x, y, z) co-ordinates to route.
• No consideration for link failure.

Src Stojmenovic97
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Honeycomb Brick Representation
stretch
Isomorphic pruned 2Dsquare mesh
stretch

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

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Shortest Path Routing Algorithm
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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 on
• Final direction of packet
• Position of fault
• Number of faults

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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 failures
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Limitations

• 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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Conclusions

• 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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Questions?
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Wireless Multi-hop Networks

• Type of multi-hop networks (Application Level
  Classification)
• 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
  basis/metrics?