1 Vehicular Networks - Content distribution and data retrieval Slides are integrated from researchers at UCLA
Transcript
Slide 1
1 Vehicular Networks - Content distribution and data retrieval
Slides are integrated from researchers at UCLA
Slide 2
Outline Urban Grid Car Torrent
Slide 3
Urban Grid opportunistic ad hoc networking From Wireless to
Wired network Via Multihop
Slide 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
Slide 5
Car to Car communications for Safe Driving Vehicle type:
Cadillac XLR Curb weight: 3,547 lbs Speed: 65 mph Acceleration: -
5m/sec^2 Coefficient of friction:.65 Driver Attention: Yes Etc.
Vehicle type: Cadillac XLR Curb weight: 3,547 lbs Speed: 45 mph
Acceleration: - 20m/sec^2 Coefficient of friction:.65 Driver
Attention: No Etc. Vehicle type: Cadillac XLR Curb weight: 3,547
lbs Speed: 75 mph Acceleration: + 20m/sec^2 Coefficient of
friction:.65 Driver Attention: Yes Etc. Vehicle type: Cadillac XLR
Curb weight: 3,547 lbs Speed: 75 mph Acceleration: + 10m/sec^2
Coefficient of friction:.65 Driver Attention: Yes Etc. Alert
Status: None Alert Status: Passing Vehicle on left Alert Status:
Inattentive Driver on Right Alert Status: None Alert Status:
Slowing vehicle ahead Alert Status: Passing vehicle on left
Slide 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
Slide 7
DSRC Channel Characteristics
Slide 8
Hot Spot Vehicular Grid as Opportunistic Ad Hoc Net
Slide 9
Hot Spot Power Blackout Power Blackout Vehicular Grid as
Emergency Net
Slide 10
Power Blackout Power Blackout Vehicular Grid as Emergency
Net
Slide 11
CarTorrent : Opportunistic Ad Hoc networking to download large
multimedia files Published 2005
Slide 12
You are driving to Vegas You hear of this new show on the radio
Video preview on the web (10MB)
Slide 13
Highway Infostation download Internet file
Slide 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
Slide 15
CarTorrent: Basic Idea Download a piece Internet Transferring
Piece of File from Gateway Outside Range of Gateway
Slide 16
Co-operative Download Vehicle-Vehicle Communication Internet
Exchanging Pieces of File Later
Slide 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
Slide 18
BitTorrent. A picture.. Uploader/downloader Tracker
Uploader/downloader
Slide 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
Slide 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.
Slide 21
Experimental Evaluation
Slide 22
Impact of Selection Strategy
Slide 23
Analytical Model n n log n
Slide 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)