1. Data Pouring and Buffering on the Road - A New Data Dissemination Paradigm for Vehicular Ad Hoc Networks Δημόκας Νικόλαος Data Engineering Laboratory, Aristotle University of Thessaloniki

2. VANETs New research challenges Due to fast vehicle movement, the link topology changes rapidly => well studied structures such as tree, clustering, grid are hard to set up and maintain. The conventional broadcast mechanism may lead to broadcast storm The vehicle mobility is partially predictable since it is limited by the traffic pattern and the road layout.

3. Push-based Data Dissemination in VANET Task Deliver the data to all the vehicles within a given area Applications Transportation control E-advertisement Emergency announcement Metrics Dissemination capacity The maximum number of data items can be disseminated by the system Delivery ratio The percentage of the data items can be received by the vehicles Network traffic

4. Opportunistic Dissemination (OD) Idea: opportunistic data exchange Vehicles store and carry the data Propagate data to the encountered vehicles and obtain new data in exchange Dissemination capacity is low. Performance suffers when vehicle density is high Excessive interference Hard to schedule the transmission Too many redundant exchanges

5. Data Pouring Scheme (DP) Basic idea: explore road layout and partially predictable vehicle moving pattern Pour the data along several selected Primary Road (P-Road) by periodic broadcasting All the roads intersected with the P-Roads are called Crossing Roads (C-Roads) Vehicles on the C-Road passively receive the data when moving through the intersections on the P-Roads. Primary Road P-Road Crossing Road C-Road Techniques to make it reliable Invalidation High overhead

6. Reliable DP RTS/CTS handshake to reduce collisions and hidden node problem Sender node rebroadcast the data if it does not hear the rebroadcast from the next forward node Advantage Improve data delivery ratio Disadvantage Complicates the transmission with more control messages A lot of bandwidth will be wasted

7. DP with Intersection Buffering (DP-IB) Basic idea of DP-IB Each intersection buffers the data, and rebroadcasts periodically Data center only broadcasts for data invalidation or refresh the lost data copies. Objective of DP-IB Reduce the amount of data poured from the source Increase the broadcast throughput Find the broadcast cycle time through analysis

8. DP with Intersection Buffering (DP-IB) Intersection data buffering and rebroadcasting In the first period the IBer broadcast its buffered data while the forwarding nodes hold their data (busy period) In the second period, the forwarding nodes forward pending packets (idle period) Intersection contention avoidance protocol All nodes switch between two modes: active and inactive forward mode A node switches to inactive after receiving a broadcast data packet from an IBer Node switches back to active if it does not receive broadcast packet from the IBer for a time period

9. DP with Intersection Buffering (DP-IB) n – number of data items D avg – average data items m – number of data centers which have stored data at the IBer I i – receives the data packet from the ith data center every I i time interval T – broadcast cycle of IBer