connectivity-aware routing (car) in vehicular ad hoc networks valery naumov & thomas r. gross...

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

• 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

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)

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)

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)

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 – 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

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