VTube: Towards the Media Rich City Life with Autonomous Vehicular Content Distribution

Tom H. Luan*, Lin X. Cai*, Jiming Chen§, Xuemin (Sherman) Shen*, and Fan Bai†

*University of Waterloo, ON, Canada§ Zhejiang University, China

†General Motors Corporation, MI, USA

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Roadmap: Motivation of the research Methodology – system model and algorithms Simulation Conclusion and Q&A

Goal and RoadmapGoal: To design a large-scale cost-

effective infrastructure-based content distribution network using

off-the-shelve technologies

VTube: Cost-effective Vehicular Content DistributionSECON’11

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The Dream: to download file contents for free at high speed Contents such as video clips (like using YouTube),

MP3s, HD images, flyers, magazines … The Reality, the bandwidth is

Expensive: Rogers: 50 CAD for 500MB; AT&T: 60 USD for 5GB

Unreliable: pure vehicle-to-vehicle (V2V) or ad hoc content distribution is unreliable and far to be practical

Can we achieve large-scale content distribution in the urban area with low-cost? Download everywhere in the city with no need to pay

VTube: Cost-effective Vehicular Content DistributionSECON’11

Motivation: Dream v.s. Reality

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Roadside Buffers (RSB) Low cost infrastructure

installed on the roadside: buffer storage (e.g., 20GB) + wireless interface

Store contents and distribute to subscribed users

Components of the System Vehicles

With caching storage and wireless interface

Download/upload contents from/to RSBs, and swap contents among each other

Transport contents cross the city

50 USD

30 USD

+

(e.g., flyers)(deployed by the store)

(deployed by the bus company to distribute bus schedules)

(interested in the contents)

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RSBs are bought and deployed by distributed entities like movie theatres, malls, hotels, schools, to distribute their

own information content, like movie trailers, room pictures in hotels

RSBs distributedly deployed cross the city forms VTube, an integrated infrastructure for content distribution

Why would stores like to buy RSBs? Because they are Cheap: Lump sum of 80 dollars on devises and no further fees

No extra charge on the bandwidth (not connected to Internet) No messy cabling works (simply mount RSBs high on a pole and configure

them using wireless communications) Profitable:

Upload contents, like advertisements, flyers, …, and distribute to users on the street for free

VTube: Cost-Effective ApproachShare costs to build

the content distribution

infrastructure

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Contents are published by distributed entities through the RSBs which

they have deployed transported by vehicles and spread in the city to vehicles

and RSBs at different locations A distributedly and additively built network

Entities deploy their own RSBs without any coordination with others

New RSBs work distributedly and can be additively incorporated into the existing system

Design Problem: How to enable RSBs to distributedly and selectively cache contents from vehicular networks to minimize the average download delay of contents?

VTube: Autonomous System

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Compared with femtocells and infostations [1, 2] no connections to the Internet focusing on content replications and buffer management with V2V

(vehicle-to-vehicle) and V2R (vehicle-to-RSB) communications built in a decentralized and additively manner by distributed

entities Compared with the V2V content distribution [3, 4]

RSB as the content injection points focusing on the design of RSBs and can be incorporated with the

V2V schemes proposed can also be used to distribute contents to PDAs, tablets, etc

Compared with the existing infrastructure-based vehicular content distribution network [5, 6] incorporate V2V communications in the content distribution propose a detailed and practical system architecture

Comparison with Related Works

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Design of VTube: Model RSBs: randomly deployed with

equal buffer to store L files at most : set of files published in the city : portion of vehicles that

subscribe to download file i : portion of vehicles have file i

stored in their buffer : probability that a RSU stores

file i in its buffer : average download delay of file

i is function of and

: buffer storage of RSB given

i

ixX

otherwise

cachedisifilexi ,0

,1

At any given time

Design at each RSB to minimize the overall delay of content dissemination

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Design of VTube: Assumptions A homogeneous network

Files have equal size RSBs are homogeneous with

equal buffer storage and follow the same policy to store files

Each RSB selects a file i to store with the probability

How to evaluate ? How to solve the optimization

problem How to design distributed

algorithm

Design at each RSB to minimize the overall delay of content dissemination

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Each file is of equal size and chopped into k pieces Randomly select a vehicle to examine the download

delay of file i (time to download all k pieces of file i) Model the file download of the vehicle by a 2D

Markov process with state (X(t), Y(t)) X(t): number of blocks downloaded Y(t): Y(t) = 1, if the vehicle is inside a RSB, and 0, otherwise

Model of Average Download Delay

Download rate of file i outside any RSBs

Download rate of file i inside a RSB

Rate to depart the coverage of an RSB

Rate to drive into the coverage of an RSB

AVERAGE DOWNLOAD

DELAY (MEAN FIRST PASSAGE

TIME)

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Using the Markov model, we can derive the expression of download delay represented by the file availability at vehicles and RSBs : portion of vehicles with file i stored in local

buffer : probability that a RSB store file i in its buffer

Apply this result, Chebyshev inequality and KKT to

we have an optimal solution of as

Centralized Content Distribution

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Select file i to store in RSBs with probability

Random walk based approach1) RSBs issue walkers to the vehicular networks2) Walkers are forwarded among files stored at

vehicles for TTL steps3) The files with stopped walkers are select to

be uploaded to RSBs

Decentralized Algorithm

( )

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Trace-driven Session level simulator coded in C++ 1000 vehicles randomly selected in the Shanghai taxi trace

within 24-hour period on Feb. 20th, 2010 200 RSBs are randomly deployed in a region of 50

30 km2

(download demand of file i) follows the Zipf-like distribution

Simulation Verification

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Average Download Delay

portion of vehicles subscribe to download file i

utilityaverage download delay of file i

• Global: store files based on b*

• Distributed algorithm: random walk based algorithm

• Local greedy: RSB always select the files with the largest di to download

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While wireless networking and various personal electronics (e.g., PDA, tablet, smartphones) have proliferated in the past decade, low-cost content distribution is still unavailable

A content distribution infrastructure is necessary Traditional cellular networks are expensive whereas the

pure ad hoc networks are unreliable and not practical so far

We propose to build distributed infrastructure with shared expenses

VTube: Roadside Buffers + vehicular networks Optimal content replication with central information Distributed content replication using the random walk

algorithm

Conclusions

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Q&A

VTube: Towards the Media Rich City Life with Autonomous Vehicular Content Distribution

Tom H. Luan*, Lin X. Cai*, Jimin Chen§, Xuemin (Sherman)

Shen*, and Fan Bai†*University of Waterloo, ON, Canada

§ Zhejiang University, China†General Motors Corporation, MI, USA