GPSR: Greedy Perimeter Stateless Routing for Wireless Networks

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GPSR Greedy Perimeter Stateless Routing for
Wireless Networks
EECS 600 Advanced Network Research, Spring 2005
Shudong Jin February 14, 2005
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Recall Last Lecture

• Dynamic Source Routing
• Who gives the path?
• How to obtain a path?
• What is the routing metric?
• What information is maintained?
• Different from Internet routing, but are there
  any similarities?

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This Lecture Another Approach

• Geographical Routing
• Who gives the path?
• Routing is done locally by individual routers
  (hop-by-hop)
• How to obtain a path?
• Decided at the time of routing, no pre-computed
  full path
• What is the routing metric?
• Distance as the routing metric
• What information is maintained?
• A little local connectivity (and location)
  information is maintained by each router

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GPSR Greedy Perimeter Stateless Routing

• Novel routing protocol for wireless datagram
  networks that uses the positions of routers and
  the destination to make packet forwarding
  decisions.
• Greedy forwarding used wherever possible and
  decisions made using only information about the
  routers immediate neighbors.
• Perimeter forwarding used where Greedy forwarding
  not possible i.e. algorithm recovers by routing
  around the perimeter of the region.
• Stateless in that a router keeps state only about
  local topology, hence scales better as the number
  of destinations increases.

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Greedy Forwarding

• Assumed Packets are marked by the originator
  with their destinations location.
• A forwarding node can make a locally optimal,
  greedy choice in choosing a packets next hop.
• Most of the times the locally optimal choice is
  the neighbor closest to the packets destination.
  (how locally?)
• The ideal case The packet is successfully
  forwarded using closer geographic hops to reach
  the destination.

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Greedy forwarding example
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How to Know the Positions?

• Periodically each node transmits a beacon to the
  broadcast MAC address, containing its identifier
  (e.g. IP address ) and position.
• X and Y co-ordinates are encoded by two 4-byte
  quantities.
• Mean Beacon Transmission interval is uniformly
  distributed. 0.5B 1.5B
• Upon not receiving a beacon for longer than the
  time out interval 4.5B, a GPSR router assumes
  that either the neighbor has failed or has moved
  out the GPSR router deletes that entry from its
  table.

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More Optimizations on Beaconing

• Handling mobility
• Choice of beaconing interval to keep nodes
  neighbor tables current depend on the mobility in
  the network and range of nodes radios.
• Reducing overhead
• Beaconing generates proactive traffic. To avoid
  this additional cost, GPSR piggybacks the local
  sending node's position on all data packets it
  forwards. Thus all packets serve as beacons.
• Q How to enforce random beacon interval, then?

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Greedy Forwarding May Fail

• The Greedy forwarding algorithm might fail in
  circumstances where the only route to a
  destination requires a packet to move temporarily
  away from the destination.
• An example from the paper
• More knowledge on topology help?

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Perimeters

• When Greedy Forwarding fails, how can we get out
  of the situation?
• Right-hand rule to route around voids

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Perimeter Forwarding

• Perimeter forwarding makes use of Planarized
  graphs which are graphs in which there are no
  crossing edges.
• Why need the no-crossing heuristics? Give an
  example
• Two algorithms RNG (Relative Neighborhood Graph)
  and GG (Gabriel Graph)

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RNG (Relative Neighborhood Graph)
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GG (Gabriel Graph)
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Planarized Graphs Example
Full graph, the GG subset, the RNG subset.
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GPSR

• This algorithm combines greedy forwarding on the
  full network graph and perimeter forwarding on
  the planarized graph.
• State information All nodes maintain neighbor
  tables which store addresses of all radio-hop
  neighbors.
• Packet header fields
• GPSR packet headers include a field which
  indicates whether the packet is currently in
  greedy mode or perimeter mode.
• All data packets are marked originally as greedy
  mode.
• Only the packets source sets the destination
  field.

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GPSR Operations

• Upon receiving a greedy-mode packet
• the node forwards it to the geographically
  closest neighbor if there is one.
• When no neighbor is closer, the node marks the
  packet to the perimeter mode. GPSR also records
  in the packet, the location Lp, the site where
  greedy forwarding failed.
• These perimeter mode packets are forwarded using
  Planar Graphs.
• Upon receiving a perimeter mode packet.
• Forward the packet using a planar graph
  traversal. GPSR also compares the location Lp
  with the forwarding nodes location. It then
  returns the packet to greedy mode if the distance
  from the forwarding node to D is less than that
  from Lp to D.
• Perimeter forwarding is only intended to recover
  from local maximum.

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Simulation Results and Evaluation

• Packet delivery ratio
• Routing protocol overhead
• Path length
• Effect of network diameter (size)
• Number of states per router

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More discussions
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GPSR Example