Challenge: Peers on Wheels – A Road to New TrafficInformation Systems

Jedrzej Rybicki, Björn Scheuermann, Wolfgang KiessChristian Lochert, Pezhman Fallahi, Martin Mauve

Computer Networks Research GroupHeinrich Heine University

Düsseldorf, Germany

MobiCom 2007

presenter: James

Agenda• Introduction• P2P networks• A First System – Traffic Information Sharing

– Challenges• Conclusion

– Key points & contribution– Pros & Cons– Relevance to our research

Introduction• Vehicular ad-hoc networks (VANETs)

– Community: Public authorities, academia, car manufacturers – Applications: reduction of road casualties

• brake warning, intersection assistance, collision avoidance system• Parking lots, route plan, coordinating car flow

• Technology– Infrastructure-based: 3G, GPRS, WiMax, WiFi

• Internet connection• DHT (distributed Hash Table), P2P• Multiple hops vs. over long distances

P2P networks• Overlay virtual network

– Locate the resource? DHT: Chord, CAN, Tapestry• Resources mapped to peers by “Hash function”

– Peer knows a subset of the other peers– Lookup can be routed– Logarithmic complexity

Traffic Information Sharing

• Basic: road segment ID in DHT• System load and scalability issue

– Update/query rate? (think close-by segments)• Independent vs. adjacent support (shortcuts)• N-dimensional ID space (CAN), road ID vs. position

• Fairness and reliability issue– High update/query rate? (In a node responsible for

highway intersection)• Load balancing & redundancy group concept

Traffic Information Sharing• Bootstrapping (Join) issue

– DHT provides a well-known always on nodes• Non-cars peers on the internet

• In-network aggregation issue– Query for a whole possible route

• Query each segment separately (traffic) vs. one node responsible for aggregation (computation)

• Distributed caching, local storage space vs. reduced reoccurring queries traffic

• Trustworthiness & privacy issue– Abnormal data will be easy to notice.– Cryptography and decentralized approach protects user’s privacy

• Route plan, IDs?

Traffic Information Sharing• Connectivity issue

– Abrupt loss & disconnect voluntarily• The level of required redundancy in the overlay• Delay of restructuring

• Publish/Subscribe TIS issue– Query the system periodically? Ex. All possible route?

•Detection of changes•History of observations & bring it to respective peers.

•Manage subscriptions•Car’s route is stored and indexed!

•Dissemination service•Burden of sending msg to each subscriber multicast, redundancy•Acceptable delay for changing alternative route.

Traffic Information Sharing

• Further think into car-to-car info exchange– Processing specific requests

• Ex. Sunny road (sensors in car)?– Allows to query relevant sensor readings on demand.– System as a broker

– Traffic coordination & distributed computation• Ex. Rush hour. All has its good route by themselves.

– Cooperate for route planning and information sharing • Ex. Query optimal route may travel through the

network and get final answer.

Conclusion• Key points & contribution

– Present a traffic information system using an infrastructure-based p2p network made up of vehicles.

– Describe the technical challenges from this approach. • Pros

– Easy to understand. It Leverages DHT concept in VANET• Cons

– Not address current problems in VANET/C2C TIS• Relevance to our research

– P2P/Sensor network in VANET/C2C TIS