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Climber extension with Multiple Description Coding (MDC)
Kunwoo ParkSeoul National University, Korea
Live Streaming Services• Cost
– Building a CDN costs too much– Encourage peers to contribute to the system
• Resilience– Live Earth concert in July 2007 rated 237,000
simultaneous viewers at the peak– A system should work in the presence of high
churn• Delay
– Live streaming is not like that of file downloading service
– Packets should be delivered in time
4/12
Climber
• An Incentive-based Resilient P2P System for Live Streaming Services
• A hybrid of a tree and a mesh– Tree - main structure, forward streaming– Mesh - enhance resilience by redundant
edges• Random Edge
• Design concepts– Incentive– Resilience
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Random Edge?
• A directed edge to a random peer– Only the sequence
number of the stream is sent along a random edge
• For each available outdegree, a node makes a random edge with low probability
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0
1
3
2
4
5Randomedge
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A node climbs a tree by a Random Edge
3
congested/failed node
random edge
Node 7 climbs the tree by being a child of node 2
• Climber greatly simplifies the recovery procedure caused by node failures
• Actually, Climber does not distinguish node failure from node congestion
Multiple Description Coding
• A coding technique – fragments a stream into k sub
streams (k>=2)
• The more sub streams received, the higher the quality– roughly proportional to # of sub
streams– any subset of these sub streams
can be decoded8/12
Climber + MDC
• In Climber, only header information are sent via random edges
• Climber’s multipath delivery concept naturally fits with MDC
• What if we send a sub stream as a random edge– Improved resilience with much more
bandwidth consumption
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Need a prediction mechanism
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123
12
I am receiving 1, 2, 3. If I send only 1, 2, will my descendants receive 3 through random edges?
134
4 3
sub stream 1, 2, 3, 4
1,2,3,4
11/12
Summary
• Climber– The 7th International Workshop on
Peer-to-Peer Systems (IPTPS '08)
• MDC• Climber + MDC
• Ongoing work
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