1. Di Wu 03/03/2011 Geographic Routing in Clustered Multi-layer Vehicular Ad Hoc Networks for Load Balancing Purposes

2. VANET: Vehicular Ad Hoc Networks Integrate ad hoc network, WLAN and cellular technology, etc. Achieve intelligent inter-vehicle communications and improve road traffic safety and efficiency. Three categories: pure cellular/WLAN, pure ad hoc, and hybrid.

3. WMN: Wireless Mesh Networks Self-organized and self-configured WMN Mesh routers: minimal mobility, backbone Mesh clients: stationary or mobile Integration with other networks: gateway and bridging in mesh routers. Three categories: Infrastructure/Backbone WMNs, Client WMNs, Hybrid WMNs. VANET differs from MANET High mobility, rapid topology change, various environments MANET Routing in VANET Break very frequently Overhead increases: route repairs Low delivery ratios High transmission delays.

4. GGLR: Geographic Greedy and Load-Balance Routing Regionalized and hierarchical VANET The AR (Area Role) node: the backbone A vehicle node can communicate with AR node and other vehicles. Enhances the stability of the network Facilitates network load balancing Forwarding set Two-hop neighbor information table Broadcast HELLO message:  source node's ID  forwarder node's ID  location of each node. Set TTL to be 2: number of HELLO messages transmitted  After sending a message, TTL minus 1.  When the TTL equals 0, stop forward The nearest node from the destination is chosen from the table, Hidden Problem After receiving a new packet, the node checks member IDs of the forwarder’s forwarding set. The same node is removed form the node’s forwarding set.

5. GGLR: Geographic Greedy and Load-Balance Routing Load balancing on AR BUSY: data cache reaches a threshold FREE: not under congestion Periodically broadcast FREE/BUSY to local vehicles. Bypassing mechanism on vehicle When the AR is busy, vehicle will bypass it and search for another suitable AR. In this way, the AR node which is busy will avoid to fall into a congestion state.

6. GGLR: Geographic Greedy and Load-Balance Routing Greedy scheme used in inter-vehicle routing When a Local Max happens, the data is sent to the destination in the help of local AR.  Local Max: if no neighbor is closer to the destination than the node itself. If the local AR is in congestion at the same time, store-carry- forward routing will be used. Store, Carry and Forward Buffer and carry the packet when no routes Forward the packet to the nodes moves into the vicinity which can help packet delivery GPS service could provide the location and velocity information on the road. Help to choose next-hop node.

7. Performance Evaluation Simulator: NCTUns 6.0: Supports VANET simulation Simulation Setting: Area Size600m*600 m Road StructureTwo Lanes MAC802.11 DCF Communication Range 100 m Packet TypeUDP Packet Size1400 Bytes Moving Speed10 m/s Simulation Time 150 s

8. End to end transmission delay Successful packet transmission ratio

9. Conclusion Clustered multi-layer VANET based on WMN infrastructure is an effective hybrid networking to provide quality of service in high dynamic VANET communication scenarios. The hierarchical structure not only enhances the stability of the network topology, reduces the amount of redundant data and increases the network scalability, but also expands a scope of network services. The GGLR protocol uses location information and forwarding set to better deal with data routing in highly dynamic topology. The algorithm provides better network load balancing solution by node congestion detection, AR-assisted forwarding, and vehicle bypassing mechanism. GGLR presents stable routing and load balancing in hybrid VANET. It could be used in reliability and real-time oriented services.

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