1. GPSR Greedy Perimeter Stateless Routing
Jennifer Ogunlowo
Sarah El-Helw

2. Background and Motivation
Routing algorithms & Scalability are essential for a rapidly changing network topology.
Informing the entire network of current state is costly and isn’t efficient.
Nodes need a more efficient way to determine locations
Quick changes in topology for mobile networks.

3. Introduction Geography assures scalability via geographic routing.
Greedy Perimeter Stateless Routing (GPSR) is motivated by geography.
GPSR measures scalability by evaluating:
Cost to route of each message
Delivery success rate.
Per-node state.

4. GPSR Algorithms There are two GPSR Algorithms: Greedy Forwarding
Used when nodes are within radio range of one another.
Preferable method of forwarding
Shortcoming when there’s a void (an area with no nodes in radio range).
Perimeter Forwarding
Used when greedy forwarding fails (void case)
Returns to greedy forwarding once possible.

5. GPSR Algorithms Greedy Forwarding
Destination locations marked by originator.
Forwarding node greedily forwards packet to geographically closest neighbor.
Based on nodes’ knowledge of optimal next hop.
Process repeats until destination is reached.
Beaconing is used to realize neighbors positions.

6. Greedy Forwarding
Destination C B No A

7. Greedy Forwarding Shortcoming
Destination
Route to destination may not have any nodes in radio range close to destination
Perimeter forwarding solves this problem
VOID

8. Perimeter Forwarding Navigate around perimeter using Right-Hand Rule.
Destination
Navigate around perimeter using Right-Hand Rule.
Right-Hand Rule: Traverse edges in counter-clockwise order:
x-w-v-D-z-y-x
Returns to greedy mode when location is closer than where greedy failed. z v
VOID y w x

9. Simulations Compare GPSR with DSR performance:
Simulation in ns-2 environment.
Network of 50 nodes.
Nodes follow random waypoint model.
Pause times of 0, 30, 60, and 120 seconds.
Each source annotates packets it originates with destinations’ positions

10. Results: Packet Delivery Success Rate
At all pause times, GPSR delivers greater fraction of packets than DSR.
Increase in B, beaconing interval, results in slightly reduced delivery success rate.

11. Results: Routing Protocol Overhead
GPSR has constant overhead as mobility increases (pro-active).
GPSR offers greater savings in routing protocol overhead.

12. Results : Path Length
GPSR delivers 97% of its packets along optimal-length paths
vs.
84.9% for DSR.

13. Related Work Greedy forwarding + flooding search when greedy fails.
LAR (Location Aided Routing), an optimization to DSR.
GLS, a scalable and robust location database that store nodes’ locations.

14. Critique Approach used to evaluate path length (GPSR).
Solution: Simulate over much sparser networks to evaluate path lengths under perimeter forwarding.

15. Summary and Conclusions
GPSR achieves
Small per-node routing state.
Small routing protocol message complexity
Robust packet delivery on densely deployed mobile networks.
GPSR benefits from Geographic routing info for forwarding decisions.