Connectivity-Aware Routing (CAR) in Vehicular Ad Hoc Networks Valery Naumov & Thomas R. Gross ETH Zurich, Switzerland IEEE INFOCOM 2007

Outline Introduction Related Works Connection-Aware Routing (CAR) Simulation Conclusion

Introduction Vehicular ad hoc networks (VANETs) using based WLAN technology have recently received considerable attention in many projects However, many geographic routing (GR) protocols are designed assuming a random and uniform distribution of nodes

Introduction For this study of VANETs, it use realistic mobility traces (from the simulator) Several GR protocols use an idealized mechanism such that for every originated data packet the true position of the destination is known – e.g. based on the simulator’s global view

Introduction Another problem is that, all of the GR protocols do not take into account if a path between source and destination is populated. This paper presents a novel position-based routing scheme called Connectivity-Aware Routing (CAR) to adress these problems

Outline Introduction Related Works Connection-Aware Routing (CAR) Simulation Conclusion

Related Works AODV (Ad-hoc On-demand Distance Vector) – A non-geographic routing protocol. – Broadcast path request on demand. GPSR (Greedy Perimeter Stateless Routing) – A geographic routing protocol – Packets are marked with their destinations’locations. – Relay nodes make a local greedy routing.

Related Works

Outline Introduction Related Works Connection-Aware Routing (CAR) Simulation Conclusion

Connection-Aware Routing (CAR) The CAR protocol consists of four main parts: – (1) destination location and path discovery – (2) data packet forwarding along the found path – (3) path maintenance with the help of guards – (4) error recovery

Connection-Aware Routing (CAR) The HELLO beacon includes location, velocity vector (moving direction and speed) Every node maintain a neighbor table – set expiration time separated by more than 80% of range after two HELLO intervals Drawbacks: waste bandwidth, delay data packet, increase network congestion

Connection-Aware Routing (CAR) Adaptive beaconing mechanism: – Beacon interval is changed according to the number of nearby neighbors. Beacons can be appended in the data packets.

Connection-Aware Routing (CAR) Guard ()

Connection-Aware Routing (CAR) Destination location discovery A source broadcast a path discovery (PD) Each node forwarding the PD updates some entries of PD If two velocity vectors’angle > 18°, anchor is set.

Connection-Aware Routing (CAR) If two velocity vectors’angle > 18°, anchor is set. – Anchor contains coordinates and velocity vector of current node and previous node.

Connection-Aware Routing (CAR) A route reply will send to the source with unicast Advantages – Finds the path that exist in reality – Takes connectivity into account – No try-and-error route test – Only source-destination pares keep anchor path to each other

Connection-Aware Routing (CAR) Greedy forwarding over the anchored path – A neighbor that is closer to the next anchor point is chosen, instead of destination. – Each forwarding node relays to anchor if the distance is less than half coverage

Connection-Aware Routing (CAR) Path maintenance If an end node (source or destination) changes position or direction, standing guard will be activated to maintain the path.

Connection-Aware Routing (CAR)

Path maintenance If end node changes direction against the direction of communication, traveling guard will be activated. – A traveling guard runs as end node’s old direction and speed, and reroute the packets to the destination. – End node will send a notification to source

Connection-Aware Routing (CAR)

Routing error recovery The reason for routing error – A temporary gap between vehicles – Long-term disconnection a suddenly closed road or big gap in traffic. – The destination could not activate a guard due to lack of neighbors. Timeout algorithm with active waiting cycle Walk-around error recovery

Connection-Aware Routing (CAR) Timeout algorithm When a node detects a gap – It tells other nodes and starts buffering packets. – It tries to detest a next hop node, sends requests. A node receives the request will reply with a HELLO beacon.

Connection-Aware Routing (CAR)

Walk-around error recovery When fail to find the destination at its estimate position – Start a location discovery limited half the number of anchors in the old path When Timeout algorithm fail – Limit to the number of anchors from the node to the destination plus 50%.

Connection-Aware Routing (CAR) If location discovery is unsuccessful – Start a new path discovery. If successful, the new path will send to source – Source analyzes the new path and current position, Start a new path discovery if the source is closer then the node to the destination.

Outline Introduction Related Works Connection-Aware Routing (CAR) Simulation Conclusion

Simulation Scenarios – City – Highway Traffic density – Low – less than 15 vehicles/km – Medium – vehicles/km – High – more then 50 vehicles/km

Simulation- Packet Delivery Ratio

Simulation- Average data packet delay

Simulation- Routing overhead

Outline Introduction Related Works Connection-Aware Routing (CAR) Simulation Conclusion

Adaptive beaconing PGB, AGF, and velocity vectors Anchor points Path maintenance with guards Error recovery Higher performance and lower routing overhead than GPSR

Conclusion Advantages – Don’t need a digital map. – No local maximum problem. – Take path situation into account. – Guard concept weakness – Selection some needless node as anchors