Geographic Routing without Location Information

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Geographic Routing without Location Information

• Ananth Rao et al
• University of California-Berkeley
• (Selected at MOBICOM03)
• Presented by
• Vinod Namboodiri

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Outline

• What is Routing in Networks (Not Channel Routing
  of VLSI!!)
• Geographic Routing
• Geographic Routing without Location Information

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Routing

• The routing problem is of finding a sequence of
  hops between the originator of a packet and the
  packets destination
• The problem is solved by modeling the network as
  a graph and computing all-pairs shortest paths on
  the edge weights of this graph
• Best route stored in routing tables at each node
  (node is device which is capable of sending and
  receiving packets)
• Wired network uses hierarchical routing so that
  state per node is minimized

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Routing in Wireless Networks

• However, no hierarchical routing possible in
  all-wireless networks
• Each node needs to keep routing state for every
  other node O(N) state per node
• Example Large-scale sensor network deployed in
  a forest for sensing wildlife patterns
• Sensor networks typically have multiple
  constraints in power, memory, computation and more

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Geographic Routing

• Make routing decisions based on geographic
  positions of nodes in the network
• Makes use of
• As density on a wireless network increases,
  shortest paths correspond increasingly closely to
  the Euclidean straight line between them
• Positions of geographically nearby nodes
  determine which links exist
• Routing by coordinates is a good way to avoid
  O(N) per node routing state

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Working
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Each node forwards packet to a node closer to
destination than itself
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Key Ideas of Geographic Routing

• Hence, improves scalability in 2 ways
• Reduces absolute volume of routing protocol
  message traffic
• Reduces size of state to be stored at routers
• Assumptions
• Each node knows about its location, and its
  neighbors location, using something like GPS
• A location service is available to map address to
  location.

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So why geographic routing without location
information?

• GPS takes power, doesnt work indoors, difficult
  to incorporate into small sensors
• Obstacles, non-ideal radios
• Coordinates computed will reflect true
  connectivity and not the geographic locations of
  nodes

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Example

• A is closer to D in virtual space than S
• So, S sends packet to A
• Using true co-ordinates, connectivity information
  is not captured

• Obstacles, non-ideal radios
• Coordinates computed will reflect true
  connectivity and not the geographic locations of
  nodes

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Geographic Routing Without Location Information

• Main Idea Assign all nodes virtual location
  coordinates based on the known locations of some
  perimeter nodes and knowledge of neighbors
• Geographic routing can use these virtual
  coordinates for its operation

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Related to Graph Embeddings
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Rubber Band Method

• Iterative process for picking coordinates for a
  node
• Some nodes along the periphery of the network
  know their correct (relative) locations and are
  fixed
• Other nodes compute coordinates by relaxation
• Assume that nodes are connected by rubber bands
  and slowly converge to the equilibrium

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Rubber Bands
Every nodes coordinate is the average of its
neighbors coordinates at each step in the
iteration
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Algorithm Working Example
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Initial Position
Iteration 1-Node 5
Iteration 1-Node 6
Iteration 1-Node 7
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Neighbors of 5 1,4,6 6 2,5 7 3,4
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Iteration 2-Node 5
Iteration 2-Node 6
Iteration 2-Node 7
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Perimeter nodes are known (10 iterations)
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Perimeter nodes are known (100 iterations)
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Perimeter nodes are known (1000 iterations)
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Success rate of greedy routing
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Obstacles
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Summary of results

• Geographic routing is useful even without
  location information
• Coordinates reflect the true underlying radio
  connectivity
• Wireless Ad-hoc routing can easily scale to tens
  of thousands of nodes with acceptable overhead

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• Thank You!!