GPSR: Greedy Perimeter Stateless Routing for Wireless Networks

1. GPSR: Greedy Perimeter Stateless Routing for Wireless Networks B. Karp, H. T. KungBorrowed slides from Richard Yang

2. Motivation • A sensor net consists of hundreds or thousands of nodes • Scalability is the issue • Existing ad hoc net protocols, e.g., DSR, AODV, ZRP, require nodes to cache e2e route information • Dynamic topology changes • Mobility • Reduce caching overhead • Hierarchical routing is usually based on well defined, rarely changing administrative boundaries • Geographic routing • Use location for routing

3. Scalability metrics • Routing protocol msg cost • How many control packets sent? • Per node state • How much storage per node is required? • E2E packet delivery success rate

4. Assumptions • Every node knows its location • Positioning devices like GPS • Localization • A source can get the location of the destination • 802.11 MAC • Link bidirectionality

5. Closest to D A Geographic Routing: Greedy Routing S D • Find neighbors who are the closer to the destination • Forward the packet to the neighbor closest to the destination

6. Benefits of GF • A node only needs to remember the location info of one-hop neighbors • Routing decisions can be dynamically made

7. Greedy Forwarding does NOT always work • If the network is dense enough that each interior node has a neighbor in every 2/3 angular sector, GF will always succeed GF fails

8. Dealing with Void: Right-Hand Rule • Apply the right-hand rule to traverse the edges of a void • Pick the next anticlockwise edge • Traditionally used to get out of a maze

9. Right Hand Rule on Convex Subdivision For convex subdivision, right hand rule is equivalent to traversing the face with the crossing edges removed.

10. Right-Hand Rule Does Not Work with Cross Edges z u D • x originates a packet to u • Right-hand rule results in the tour x-u-z-w-u-x w x

11. Remove Crossing Edge z u D • Make the graph planar • Remove(w,z)from the graph • Right-hand rule results in the tour x-u-z-v-x w x

12. Make a Graph Planar • Convert a connectivity graph to planar non-crossing graph by removing “bad” edges • Ensure the original graph will not be disconnected • Two types of planar graphs: • Relative Neighborhood Graph (RNG) • Gabriel Graph (GG)

13. Relative Neighborhood Graph • Connection uv can exist if w  u, v, d(u,v) < max[d(u,w),d(v,w)] not empty  remove uv

14. Gabriel Graph • An edge (u,v) exists between vertices u and v if no other vertex w is present within the circle whose diameter is uv. w  u, v, d2(u,v) < [d2(u,w) + d2(v,w)] Not empty  remove uv

15. Properties of GG and RNG RNG • RNG is a sub-graph of GG • Because RNG removes more edges • If the original graph isconnected, RNG is also connected GG

16. w Connectedness of RNG Graph • Key observation • Any edge on the minimumspanning tree of the originalgraph is not removed • Proof by contradiction: Assume (u,v) is such an edge but removed in RNG u v

17. Examples Full graph GG subset RNG subset • 200 nodes • randomly placed on a 2000 x 2000 meter region • radio range of 250 m • Bonus: remove redundant, competing path  less collision

18. Greedy Perimeter Stateless Routing (GPSR) • Maintenance • all nodes maintain a single-hop neighbor table • Use RNG or GG to make the graph planar • At source: • mode = greedy • Intermediate node: • if (mode == greedy) { greedy forwarding; if (fail) mode = perimeter; } if (mode == perimeter) { if (have left local maxima) mode = greedy; else (right-hand rule); }

19. greedy fails GPSR Greedy Forwarding Perimeter Forwarding have left local maxima greedy works greedy fails

20. Implementation Issues • Graph planarization • RNG & GG planarization depend on having the current location info of a node’s neighbors • Mobility may cause problems • Re-planarize when a node enters or leaves the radio range • What if a node only moves in the radio range? • To avoid this problem, the graph should be re-planarize for every beacon msg • Also, assumes a circular radio transmission model • In general, it could be harder & more expensive than it sounds

21. Performance evaluation • Simulation in ns-2 • Baseline: DSR (Dynamic Source Routing • Random waypoint model • A node chooses a destination uniformly at random • Choose velocity uniformly at random in the configurable range – simulated max velocity 20m/s • A node pauses after arriving at a waypoint – 300, 600 & 900 pause times

22. 50, 112 & 200 nodes • 22 sending nodes & 30 flows • About 20 neighbors for each node – very dense • CBR (2Kbps) • Nominal radio range: 250m (802.11 WaveLan radio) • Each simulation takes 900 seconds • Take an average of the six different randomly generated motion patterns

23. Packet Delivery Success Rate

24. Routing Protocol Overhead

25. Related Work • Geographic and Energy Aware Routing (GEAR), UCLA Tech Report, 2000 • Consider remaining energy in addition to geographic location to avoid quickly draining energy of the node closest to the destination • Geographic probabilistic routing, International workshop on wireless ad-hoc networks, 2005 • Determine the packet forwarding probability to each neighbor based on its location, residual energy, and link reliability

26. Beacon vector routing, NSDI 2005 • Beacons know their locations • Forward a packet towards the beacon • A Scalable Location Service for Geographic Ad Hoc Routing, MobiCom ’00 • Distributed location service • Landmark routing • Paul F. Tsuchiya. Landmark routing: Architecture, algorithms and issues. Technical Report MTR-87W00174, MITRE Corporation, September 1987. • Classic work with many follow-ups

27. Questions?