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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 toWired networkVia Multihop

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

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

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

DSRC Channel Characteristics

Hot Spot

Hot Spot

Vehicular Grid as Opportunistic Ad Hoc Net

Hot Spot

Hot Spot

PowerBlackout

STOP

PowerBlackout

STOP

Vehicular Grid as Emergency Net

PowerBlackout

STOP

PowerBlackout

STOP

Vehicular Grid as Emergency Net

CarTorrent : Opportunistic Ad Hoc networking to download

large multimedia files

Published 2005

You are driving to VegasYou hear of this new show on the radio

Video preview on the web (10MB)

Highway Infostation download

Internet

file

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

CarTorrent: Basic Idea

Download a piece

Internet

Transferring Piece of File from Gateway

Outside Range of Gateway

Co-operative Download

Vehicle-Vehicle Communication

Internet

Exchanging Pieces of File Later

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

BitTorrent…. A picture..

Uploader/downloader

Uploader/downloader

Uploader/downloader

Uploader/downloader

TrackerUploader/downloader

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

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.

Experimental Evaluation

Impact of Selection Strategy

Analytical Model

n

√n

log n

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)