Xiaomei Liu

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Providing a Bi-Directional Abstraction for
Unidirectional Ad Hoc Networks

• Xiaomei Liu
• Instructor Dr. Sandeep Kulkarni

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Roadmap

• Introduction and Problem definition
• Solution- Sub Routing Layer
• Simulation
• Performance Analysis
• Case study AODV routing protocol based on SRL
  solution
• Conclusions
• Questions

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Introduction

• Ad Hoc network
• Network of mobile nodes using peer-to-peer
  communication.
• No fixed Infrastructure

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Ad-Hoc Network
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Unidirectional links

• Due to Diversity Transmission Powers
• RTS-CTS /ACK based scheme fails
• Link Detection and Neighbor Discovery Service Not
  Available

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Routing Protocol in Ad-Hoc Network

• Bidirectional Network
• Ad-hoc On-demand Distance Vector (AODV)
• Temporally Ordered Routing Algorithm (TORA)
• Unidirectional Network
• Dynamic Source Routing (DSR)
• Zone Routing Protocol (ZRP)
• Tunneling
• Internet MANET Encapsulation Protocol (IMEP)

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Ad-Hoc On-demand Distance Vector

• Broadcasts rout requests (RREQs)
• Use bidirectional links (reverse routes) to
  transmit route replies(RREPS)
• Fail in case of unidirectional link

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Ad-Hoc On-demond Distance Vector
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Temporally Ordered Routing Algorithm

• Utilize services provided by IMEP to route
  packets about bidirectional links
• Breaks in case of unidirectional

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Dynamic Source Routing (DSR)

• Routes discovery
• Broadcasting route reqs and route replies
• Source Routed Data Packets
• Not scalable
• Several modes respond to same route reqs
  resulting in high volume of route reply broadcasts

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Zone Routing Protocol (ZRP)

• Routing Zone
• Proactive InterZone Routing Protocol
• Continuously evaluate routes
• Route known and immediately available
• Reactive IntraZone Routing Protocol
• On-Demand
• Bordercasting

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Tunneling

• Control/Acknowledgement Packet tunneling back to
  Source
• May lead to inefficiencies
• Existence of unidirectional links may not be
  known at source

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Internet MANET Encapsulation Protocol

• Detect and monitor occurences of unidirctional
  links
• Not maintain reverse routes and facilitate use
  of unidirectional links for data traffic

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Sub Routing Layer

• Provide Reverse Route Information Abstraction for
  other Protocols
• Create reverse route via intermediate Node

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Sub Routing Layer (SRL)
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Nomenclature

• Out-neighbor/In-Neighbor
• if A B, B Out-Neighbor of A
• A In-Neighbor of B
• Reverse Route Shortest Route of B A
• Locality radius Size of Local Region
• Same order of of hops required to establish
  reverse routes

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Routing Algorithm of SRL

• Reverse Distributed Bellman-Ford

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Distributed Bellman-Ford Algorithm

• Neighbors update route information periodically
• Only next neighbor in the route table
• If Dx(Y,W)gtc(X,V)newVal, update route table as
  Dx(Y,V)
• Send all neighbors about update information

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Distributed Bellman-Ford Algorithm

• Find out minimum spanning tree
• Works Asynchronously
• Converge If Network Remains Stable For Sufficient
  Time
• Problem
• If B A but not B A ?

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Reverse Distributed Bellman-Ford Algorithm

• Each Node Aims At Finding Shortest
• Distance From Other Nodes To Itself Rather
  Than From Itself To Other Nodes

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Reverse Distributed Bellman-Ford Algorithm

• A B
• A periodically sends to B update message known
  shortest from other nodes within locality radius
  to A
• B extract reverse route A B, i.e. B A
• Update reverse route according to received update
  message
• Ignore Path Longer Than Locality Radius

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Reverse Distributed Bellman-Ford Algorithm

• Redundant NeighborCast Update Message
• Periodic update packet containing only route
  change information
• Infrequent complete updates information

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Interface of SRL

• Non-Transparent
• Need to know unidirectional and power varying
  nature of environment
• Provide Bi-directional Abstraction via Service of
  Reverse Routing/Sub-Routing
• Enable Reliable Service in MAC Layer In Case Of
  Unidirectional Link

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Simulation

• GloMoSim Global Mobile Information Systems
  Simulation Library. (UCLA)
• Parallel Processing Parsec
• Unidirectional Link Simulation
• Turn off RTS/CTS exchange
• Acknowledgement received by sender iff case of
  bi-directional link
• Accept different power levels

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Simulation

• Average Number of Neighbors
• Increase in average of neighborhood increases
  connectivity of network
• Average Reverse Route Length
• locality radius
• Affected by diversity of transmission power

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Performance of SRL
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of Local Nodes
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of Update Packets Sent
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Size of Periodic Packets Sent
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Application Case AODV Based on SRL

• AODV
• Route only along bidirectional links
• Black list of unidirectional links
• Reqs from neighbor in black list are ignored
• Black list may not be accurate reflection of
  unidirectional link
• Waste resource of unidirectional links

• AODVSRL
• Enable route along unidirectional links via
  bi-directional link abstraction
• Detect link breakages via checking reverse route
  of next hop

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Performance of AODV versus AODVSRL
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Packet Throughput
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Goodput Ratio

• Goodput

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Goodput Ratio
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Average Route Length
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Conclusions

• Advantage
• Provides bi-directional abstraction for existing
  routing protocols
• Enable MAC layer reliable transmission in case of
  unidirectional links
• Use both unidirectional and bi-directional links

• Disadvantage
• Not transparent
• Increased complexity
• Increase power consumption
• Increase traffic overhead

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? Questions

• How AODV Uses Black-list to Work on a
  Unidirectional Network

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• Thank you!