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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

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
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
BitTorrnet-like File Swarming
  • A file is divided into equal sized blocks
  • Cooperative (parallel) downloading among peers

From Wikipedia

swarming limitation missing coupon
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

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
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
Outline
  • Previous Work: CarTorrent
  • Basic Idea
  • CodeTorrent
  • Simulation
  • Conclusion
previous work cooperative downloading with cartorrent

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
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
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

+

+

+

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

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
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
Simulation Results
  • Avg. number of completion distribution

200 nodes40% popularity

Time (seconds)

simulation results15
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
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
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
Simulation Results
  • Novelty of coded blocks
    • As speed increases, novelty improves
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