vehicular networks - content distribution and data retrieval
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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Vehicular Networks - Content distribution and data retrieval
Slides are integrated from researchers at UCLA
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Outline
• Urban Grid • Car Torrent
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Urban Grid “opportunistic” ad hoc networking
From Wireless toWired networkVia Multihop
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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
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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: 45 mphAcceleration: - 20m/sec^2Coefficient of friction: .65Driver Attention: NoEtc.
Vehicle type: Cadillac XLRCurb weight: 3,547 lbsSpeed: 75 mphAcceleration: + 20m/sec^2Coefficient of friction: .65Driver Attention: YesEtc.
Vehicle type: Cadillac XLRCurb weight: 3,547 lbsSpeed: 75 mphAcceleration: + 10m/sec^2Coefficient of friction: .65Driver Attention: YesEtc.
Alert Status: None
Alert Status: Passing Vehicle on left
Alert Status: Inattentive Driver on Right
Alert Status: None
Alert Status: Slowing vehicle aheadAlert Status: Passing vehicle on left
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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
F o r w a r d r a d a r
C o m p u t i n g p l a t f o r m
E v e n t d a t a r e c o r d e r ( E D R )
P o s i t i o n i n g s y s t e m
R e a r r a d a r
C o m m u n i c a t i o n f a c i l i t y
D i s p l a y
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DSRC Channel Characteristics
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Hot Spot
Hot Spot
Vehicular Grid as Opportunistic Ad Hoc Net
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Hot Spot
Hot Spot
PowerBlackout
STOP
PowerBlackout
STOP
Vehicular Grid as Emergency Net
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PowerBlackout
STOP
PowerBlackout
STOP
Vehicular Grid as Emergency Net
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CarTorrent : Opportunistic Ad Hoc networking to download
large multimedia files
Published 2005
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You are driving to VegasYou hear of this new show on the radio
Video preview on the web (10MB)
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Highway Infostation download
Internet
file
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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
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CarTorrent: Basic Idea
Download a piece
Internet
Transferring Piece of File from Gateway
Outside Range of Gateway
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Co-operative Download
Vehicle-Vehicle Communication
Internet
Exchanging Pieces of File Later
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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
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BitTorrent…. A picture..
Uploader/downloader
Uploader/downloader
Uploader/downloader
Uploader/downloader
TrackerUploader/downloader
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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
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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.
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Experimental Evaluation
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Impact of Selection Strategy
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Analytical Model
n
√n
log n
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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)