Placement of Continuous Media in Wireless Peer-to-Peer Network
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Placement of Continuous Media in Wireless Peer-to-Peer Network
Shahramram Ghandeharizadeh, Bhaskar Krishnamachari, and Shanshan SongIEEE Transactions on Multimedia, April 2004
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H2O Framework
Home-to-Home Online (H2O) devices collaborate to deliver continuous media
H2O may act as: A producer of data An active client A router
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Motivation
A new replication technique that Provide on-demand access to continuous
media Minimize the total storage space
required
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Assumptions
CBR continuous data Total size of available clips exceeds
the storage capacity of one device Bandwidth between two H2O devices
exceeds the bandwidth required to display a clip
One hop distance is a constant
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Hi: the Farthest Number of Hops a Block Can be Located
Cycle: period to display a block D=Sb/BDisplay
The farthest number of hops that the block i can be located: Hi=((i-1)D)/h
block size playback rate
time to retrieve a block from one hop away
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Data Placement and Replication For each video clip X:
Divide X into equal-sized blocks with size Sb Place first block, b1 on each node. For each block bi, 1<i<=z, compute delay toler
ance Hi Compute ri based on Hi Construct ri replicas of bi and place them
ri is a topology dependent computation
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Topology I: Worst Case Linear Topology
Block i should be replicated ri times: Hi=(i-1)D/h ri=N-Hi Reset ri to one if ri is zero or negative
Total storage space (SC,R) occupied by a clip with z blocks:
1 2 3 8 9…
z
i
z
i ibibRC rSrSS1 1, )(
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Percentage Saving Compared with Full Replication in Linear Topology
•N=1000, h=0.5,•BDisplay = 4Mbps•y: 100x(1-SC,R)/(SCxN)
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Topology II: Grid Topology
Organize N nodes in a square area At least one copy of bi must be placed
within Hi hops There are nodes within Hi
hops of every node
Total storage required:
122 2 ii HH
122 2
iii HH
Nr
z
iii
b
z
i biRC HH
NSSrS
1 21, 122
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Total Storage Space Required as a Function of Block Size (1/2)
•h=0.75s
•2 min clip (total 60MB)
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Total Storage Space Required as a Function of Block Size (2/2)
•h=0.75s
•2 hour clip (total 3600MB)
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Topology III: Average Case Topology (1/2)
Network connectivity depends on radio range R
N nodes are scattered in area A There are on average between and
nodes within Hi nodes.)/())(2( 2 ANRH i )/())(( 2 ANRH i
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Topology III: Average Case Topology (2/2)
Using the upper boundary, the H number of replicas ri required by bi is:
Total storage required for a clip:S
2)( RH
Ar
ii
z
i
z
i ibibRC rSrSS1 1, )(
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Percentage Saving Comparison
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Distributed Implementation H2Op: publish a clip X
Compute block size Sb, number of blocks z, and Hi for each block
Flood the network to query which H2O will host a copy of which block of X
H2Oj: each recipient of the message Compute a binary array Aj that consists of z e
lements whose values are 0 or 1 Two computation methods: TIMER or ZONE
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Technique I: TIMER
When H2Oj receives query message Perform z rounds of elections Pick a random timer value between 1
and M then count down The one first count down to zero stores a
copy and send suppress message within Hi hops
May generate more than one copies of a block within Hi hops
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Technique II: ZONE
Assume each node is aware of its (x, y) coordinate
Place each copy in a separate square zone whose size is such that all nodes can be reached within Hi hops
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Simulation: TIMER vs. ZONE
•N=300, R=100m, A=1km2, z=60
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Simulation: Comparison of Analytical Models for Graph Topology with 2 Implementations
SC=60MB R=100m A=1km2
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Simulation: How Many Blocks a H2O Device Have When Using TIMER
•N=300, R=100m, A=1km2
•Average # of blocks per node for a clip is marked as dashed line
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Conclusion
Provide a novel replication technique for on-demand clips Minimize startup delay Storage saving compared with full
replication Provide two distributed
implementations