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CodeTorrent : Content Distribution using Network Coding in VANET. Uichin Lee, JoonSang Park, Joseph Yeh, Giovanni Pau, Mario Gerla Computer Science Dept, UCLA http://www.cs.ucla.edu/NRL. Content Distribution in VANET. Multimedia-based proximity marketing: Virtual tours of hotel rooms

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Codetorrent content distribution using network coding in vanet l.jpg

CodeTorrent: Content Distribution usingNetwork Coding in VANET

Uichin Lee, JoonSang Park, Joseph Yeh, Giovanni Pau, Mario Gerla

Computer Science Dept, UCLA

http://www.cs.ucla.edu/NRL


Content distribution in vanet l.jpg
Content Distribution in VANET

  • Multimedia-based proximity marketing:

    • Virtual tours of hotel rooms

    • Movie trailers in nearby theaters

  • Vehicular ad hoc networks (VANET):

    • Error-prone channel

    • Dense, but intermittent connectivity

    • High, but restricted mobility patterns

    • No guaranteed cooperativeness (only, users of the same interests will cooperate)

  • How do we efficiently distribute content in VANET?

    • Traditional approach: BitTorrent-like file swarming


Bittorrnet like file swarming l.jpg
BitTorrnet-like File Swarming

  • A file is divided into equal sized blocks

  • Cooperative (parallel) downloading among peers

From Wikipedia


Swarming limitation missing coupon l.jpg
Swarming Limitation: Missing Coupon!

C1 Sends Block 1

C2 Sends Block 2

C3 Sends Block 2

B2

B2

B2

B1

B1

B2

C1

C2

C3

B2

B2

B1

B2

B2

C4

C5

C6

C5 Sends Block 2

B1 is STILL missing!!


Network coding l.jpg

a1,1=1

E1

10

Coded Block

a2,1=1

E2

11

Coded Block

a1,2=0

Matrix Inversion

a2,2=1

10

B1

01

B2

Network Coding

  • Let a file has k blocks: [B1 B2 … Bk]

  • Encoded block Ei is generated by

    • Ei = ai,1*B1 + ai,2*B2 + … + ai,k*Bk

    • ai,x : randomly chosen over the finite field

  • Any “k” linearly independent coded blocks can recover [B1 B2 … Bk] by matrix inversion

  • Network coding maximizes throughput and minimizes delay

B1

B2

Network coding over the finite field GF(2)={0,1}


Network coding helps coupon collection l.jpg
Network Coding Helps Coupon Collection

C1 Sends Block 1

C2 Sends a Coded Block: B1+B2

C3 Sends Block 2

B1+B2

B1+B2

B2

B2

B1

B1+B2

B1

B1

B2

C1

C2

C3

B1+B2

B2

B1+B2

B1

B1

B1+B2

B2

C4

C5

C6

C4 and C6 successfully recovered both blocks

C5 Sends a Coded Block: B1+B2


Outline l.jpg
Outline

  • Previous Work: CarTorrent

  • Basic Idea

  • CodeTorrent

  • Simulation

  • Conclusion


Previous work cooperative downloading with cartorrent l.jpg

Y

R

R

R

R

Y

Y

Y

Y2

G

Previous Work: Cooperative Downloading with CarTorrent

Internet

Gossiping Availability of Blocks

Exchange Blocks via multi-hop pulling

Downloading Blocks from AP


Codetorrent basic idea l.jpg

Single-hop pulling (instead of CarTorrent multihop)

Buffer

Buffer

Buffer

B1

*a1

B2

*a2

*a3

File: k blocks

B3

+

“coded” block

*ak

Bk

Random Linear Combination

CodeTorrent: Basic Idea

Internet

Re-Encoding: Random Linear Comb.of Encoded Blocks in the Buffer

Outside Range of AP

Exchange Re-Encoded Blocks

Downloading Coded Blocks from AP

Meeting Other Vehicles with Coded Blocks


Design rationale l.jpg
Design Rationale

  • Single-hop better than multihop

    • Multi-hop data pulling does not perform well in VANET (routing O/H is high)

    • Users in multi-hop may not forward packets not useful to them (lack of incentive)!

  • Network coding

    • Mitigate a rare piece problem

    • Maximize the benefits of overhearing

  • Exploits mobility

    • Carry-and-forward coded blocks


Codetorrent beaconing l.jpg

+

+

+

CodeTorrent - Beaconing

  • Periodic broadcasting of peer ID and its code vector

  • Used for searching helpful nodes: those who have at least one linearly independent code block

Red is Helpful!


Codetorrent single hop pulling l.jpg

Random Linear combination

CodeTorrent - Single-hop pulling

  • A peer pulls coded blocks from the helpful peers

    1. G pulls a coded block from R

    2. G checks helpfulness and repeats

R

GetBlock

Y

G

G sends a GetBlock message to R

R prepares a re-encoded block

R broadcasts the re-encoded block

Check helpfulness: If helpful, store it!


Simulations setup l.jpg
Simulations - Setup

  • Qualnet 3.9

  • IEEE 802.11b / 2Mbps

  • Real-track mobility model (Westwood map)

    • 2.4x2.4 km2

  • Distributing 1MB file

    • 4KB/block * 250 blocks

    • 1KB per packet

  • # of APs: 3

    • Randomly located on the road sides

  • Comparing CarTorrent (w/ AODV) with CodeTorrent

    • AODV w/ net-diameter 3 hops

    • CodeTorrent with GF(256)

Near UCLA Campus


Simulation results l.jpg
Simulation Results

  • Avg. number of completion distribution

200 nodes40% popularity

Time (seconds)


Simulation results15 l.jpg
Simulation Results

  • Multi-hop pulling in CarTorrent

    • As content spreads, CarT shows locality

CarTorrent

Avg. hop count exceeding 1 hop

200 nodes40% popularity

Time (seconds)


Simulation results16 l.jpg
Simulation Results

  • Impact of mobility

    • Speed helps disseminate from AP’s and C2C

    • Speed hurts multihop routing (CarT)

    • Car density+multihop promotes congestion (CarT)

Avg. Download Time (s)

40% popularity


Conclusion l.jpg
Conclusion

  • Multihop-based CarTorrent:

    • Not scalable due to routing overhead

    • Cooperation may be a problem

    • Coupon problem

  • CodeTorrent:

    • Scales to mobility; favors cooperation; eliminates a coupon problem

  • Future work

    • Modeling the impact of mobility

    • CodeTorrent testbed


Simulation results18 l.jpg
Simulation Results

  • Novelty of coded blocks

    • As speed increases, novelty improves