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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
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
Motivation
A new replication technique that Provide on-demand access to continuous
media Minimize the total storage space
required
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
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
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
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, )(
Percentage Saving Compared with Full Replication in Linear Topology
•N=1000, h=0.5,•BDisplay = 4Mbps•y: 100x(1-SC,R)/(SCxN)
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
Total Storage Space Required as a Function of Block Size (1/2)
•h=0.75s
•2 min clip (total 60MB)
Total Storage Space Required as a Function of Block Size (2/2)
•h=0.75s
•2 hour clip (total 3600MB)
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
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, )(
Percentage Saving Comparison
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
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
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
Simulation: TIMER vs. ZONE
•N=300, R=100m, A=1km2, z=60
Simulation: Comparison of Analytical Models for Graph Topology with 2 Implementations
SC=60MB R=100m A=1km2
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
Conclusion
Provide a novel replication technique for on-demand clips Minimize startup delay Storage saving compared with full
replication Provide two distributed
implementations