Connectivity-Aware Routing (CAR) in Vehicular Ad Hoc Networks

Valery Naumov & Thomas R. GrossETH Zurich, Switzerland

IEEE INFOCOM 2007

Outline

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

Introduction

• Vehicular ad hoc networks (VANETs) using 802.11-based WLAN technology have recently received considerable attention in many projects

• Several geographic routing (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 kind of problems

Outline

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

Related Works

• GPSR (Greedy Perimeter Stateless Routing)– A geographic routing protocol– Packets are marked with their destinations’locations.– Relay nodes make a local greedy routing.– Greedy mode & Perimeter mode

Related Works

Related Works

Outline

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

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)

• 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)

• 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 pairs 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.

Connection-Aware Routing (CAR)

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)

Connection-Aware Routing (CAR)

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)

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

• When Timeout algorithm fail

– Start a location discovery

Connection-Aware Routing (CAR)

• If location discovery is unsuccessful– Source starts 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 – 30-40 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

Conclusion

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

overhead than GPSR