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