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Vehicular Networks - Content distribution and data retrieval

Vehicular Networks - Content distribution and data retrieval. Slides are integrated from researchers at UCLA. Outline. Urban Grid Car Torrent. Urban Grid “opportunistic” ad hoc networking. From Wireless to Wired network Via Multihop. Opportunistic piggy rides in the urban mesh.

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Vehicular Networks - Content distribution and data retrieval

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  1. Vehicular Networks -Content distribution and data retrieval Slides are integrated from researchers at UCLA

  2. Outline • Urban Grid • Car Torrent

  3. Urban Grid “opportunistic” ad hoc networking From Wireless to Wired network Via Multihop

  4. Opportunistic piggy rides in the urban mesh • Pedestrian transmits a large file in blocks to passing cars, busses • The carriers deliver the blocks to the hot spot

  5. Car to Car communications for Safe Driving Vehicle type: Cadillac XLRCurb weight: 3,547 lbsSpeed: 65 mphAcceleration: - 5m/sec^2Coefficient of friction: .65Driver Attention: YesEtc. Vehicle type: Cadillac XLRCurb weight: 3,547 lbsSpeed: 75 mphAcceleration: + 20m/sec^2Coefficient of friction: .65Driver Attention: YesEtc. Alert Status: None Alert Status: None Alert Status: Inattentive Driver on Right Alert Status: Slowing vehicle ahead Alert Status: Passing vehicle on left Vehicle type: Cadillac XLRCurb weight: 3,547 lbsSpeed: 45 mphAcceleration: - 20m/sec^2Coefficient of friction: .65Driver Attention: NoEtc. Vehicle type: Cadillac XLRCurb weight: 3,547 lbsSpeed: 75 mphAcceleration: + 10m/sec^2Coefficient of friction: .65Driver Attention: YesEtc. Alert Status: Passing Vehicle on left

  6. DSRC*/IEEE 802.11p : Enabler of Novel Applications • Car-Car communications at 5.9Ghz • Derived from 802.11a • three types of channels: Vehicle-Vehicle service, a Vehicle-Gateway service and a control broadcast channel . • Ad hoc mode; and infrastructure mode • 802.11p: IEEE Task Group that intends to standardize DSRC for Car-Car communications * DSRC: Dedicated Short Range Communications

  7. DSRC Channel Characteristics

  8. Hot Spot Hot Spot Vehicular Grid as Opportunistic Ad Hoc Net

  9. Power Blackout Power Blackout Hot Spot Hot Spot Vehicular Grid as Emergency Net

  10. Power Blackout Power Blackout Vehicular Grid as Emergency Net

  11. CarTorrent : Opportunistic Ad Hoc networking to download large multimedia files Published 2005

  12. You are driving to VegasYou hear of this new show on the radioVideo preview on the web (10MB)

  13. Highway Infostation download Internet file

  14. Incentive for “ad hoc networking” Problems: Stopping at gas station to download is a nuisance Downloading from GPRS/3G too slow and quite expensive Observation: many other drivers are interested in download sharing (like in the Internet) Solution: Co-operative P2P Downloading via Car-Torrent

  15. CarTorrent: Basic Idea Internet Download a piece Outside Range of Gateway Transferring Piece of File from Gateway

  16. Co-operative Download Internet Vehicle-Vehicle Communication Exchanging Pieces of File Later

  17. Bit Torrent review • Swarming: Parallel downloads among a mesh of cooperating peers • Scalable: System capacity increases with increase in number of peers • Tracker • Handles peer discovery • Centralized Tracker, single point of failure • Observation: Might not work for Wireless scenarios, because of intermittent connectivity • Issue: Mobility increases churn of nodes participating in a download

  18. BitTorrent…. A picture.. Uploader/downloader Uploader/downloader Uploader/downloader Tracker Uploader/downloader Uploader/downloader

  19. CarTorrent: Gossip protocol A Gossip message containing Torrent ID, Chunk list and Timestamp is “propagated” by each peer Problem: how to select the peer for downloading

  20. Peer Selection Strategies Possible selections: • 1) Rarest First:BitTorrent-like policy of searching for the rarest bitfield in your peerlist and downloading it • 2) Closest Rarest: download closest missing piece (break ties on rarity) • 3) Rarer vs Closer:weighs the rare pieces based on the distance to the closest peer who has that piece.

  21. Experimental Evaluation

  22. Impact of Selection Strategy

  23. n √n log n Analytical Model

  24. Why is the Car-Torrent solution attractive? • Bandwidth at the infostation is limited and “not convenient” • It can become congested if all vehicles stop • It is a nuisance as I must stop and waste time • GPRS and 3G bandwidth is also limited and expensive • The car to car bandwidth on the freeway is huge and practically unlimited! • Car to car radios already paid for by safe navigation requirement • CarTorrent transmissions are reliable - they involve only few hops (proximity routing)

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