1. Challenge: Peers on Wheels – A Road to New Traffic Information Systems Jedrzej Rybicki, Björn Scheuermann, Wolfgang Kiess Christian Lochert, Pezhman Fallahi, Martin Mauve Computer Networks Research Group Heinrich Heine University Düsseldorf, Germany MobiCom 2007 presenter: James

2. Agenda Introduction P2P networks A First System – Traffic Information Sharing –Challenges Conclusion –Key points & contribution –Pros & Cons –Relevance to our research

3. 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

4. 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

5. 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

6. 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?

7. 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.

8. 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.

9. 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