Natural Selection in Peer-to-Peer Streaming: From the Cathedral to the Bazaar Vivek Shrivastava, Suman Banerjee University of Wisconsin-Madison, USA ACM.
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Natural Selection in Peer-to-Peer Streaming: From the Cathedral to
the Bazaar
Vivek Shrivastava, Suman Banerjee
University of Wisconsin-Madison, USA
ACM NOSSDAV’05
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Introduction
Peer altruism (resource contribution) is a key factor of p2p applications
BitTorrent employs a tit-for-tat rule This work exploits scenarios in p2p stream
ing media applications where resource sharing is a natural behavior without external rules and incentives
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Background
not altruistic limited asymmetrical upstream bandwidth of
DSL and cable modems uploading may reduce its access bandwidth and
degrade the network access performance
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This paper
p2p streaming environment has inherent natural incentives for peers to contribute
form efficient overlay tree for data streaming
shift from Cathedral style to Bazaar style, where no rules are imposed on peers and resources sharing takes place naturally as peers try to maintain their perceived data utility
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Utility
Utility benefit(incoming bandwidth, latency) – cost (out
going bandwidth) maybe different in different peers
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An example
Case (a) incoming bandwidth to peer A is 80kbps
Case (b) incoming bandwidth to peer A is 200kbps outgoing bandwidth from peer A is 400kbps
If the increase in A’s perceived data utility offsets the loss, A will do so
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An example
final overlay depends on the mix of utility functions of peers
peer B also has natural incentive to join under A as the streaming bandwidth increases from 80kbps to 200kbps
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This paper
provide a platform to facilitate the formation of such a mutually beneficial overlay without introducing any rules or incentives in the system
based on natural incentive of peer to conserve own incoming bandwidth by attracting the new entrant to join under itself rather than its parent
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Bazaar framework
regular peers strategic, maximize incoming and minimize
outgoing bandwidth
BSE (Boot Strap Entity) ~tracker, provide overlay information to new
node
root (publisher) altruistic, allocates fixed outgoing bandwidth
during the entire streaming session
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Market Quote (M-Quote)
Each node provides a M-Quote of its services to attract peers to join under it rather its parent, so as to preserve its own incoming bandwidth
has the following advertised components: bandwidth latency from root to the peer
kept in BSE
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Bazaar framework
peers can perform join/leave the overlay dynamically advertise their services participate in shuffle operation to improve
overlay structure
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Bazaar in action
1. root enters the system
2. A interested in the contentjoins the system
3. revise M-Quote (250 = 500/2)
4. if A is selfish, it can sendM-Quote of 0 or do notsend at all. However, a newnode will definitely choosesroot as peer which reduce the bandwidth shared by A. This motivates A to offer competitive quote
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Bazaar in action
B choose A if bandwidth outweighs latency
B choose A if latency outweighs bandwidth
Advertising a lower outgoing bandwidth which leads to competition of parent bandwidth, A may participatein a local shuffling operation
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Bazaar in action
shuffle is a periodic operation
if B is attracted by the new quote,the overlay changes accordingly
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Evaluation
Utility function
Y. hua Chum J. Chuang, and H. Zhang, “A case for taxation in peer-to-peer streaming broadcast,” Workshop on Practice and theory of incentives in networked systems (PINS), 2004
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Simulation environment
peer-to-peer network simulator myns, developed at University of Maryland
use Transit Stub topology generated by GT-ITM topology generator
50 peers, all results are averaged over 1000 permutations of peer join order
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Performance metrics
throughput incoming bandwidth of each peer
total system utility sum of perceived data utility of all peers
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Bimodal simulations
all peers are categorized as high or low capacity peers
high capacity: outgoing bandwidth randomly selected from 500Kbps to 1Mbps
low capacity: random [50Kbps, 450Kbps]simulate heterogeneous peer environments
by varying fraction of high capacity peers from 0 to 1
max streaming rate is 500Kbps
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Bimodal simulations – system utility
Observations utility increases with fraction of high capacity,
as cost of forward (fraction of forward bandwidth over max outgoing bandwidth) reduces
strategic is better than random, as random my degrade it own and others utility
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Bimodal simulations – throughput
Observation gap between altruistic and strategic mode
decreases with decrease in fraction of high capacity peers
The fraction of high capacity peers in real life is low, so strategic peers can achieve good throughput in real life
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Trace based simulations
outgoing capacity distribution of peers are based on traces collected from Sigcomm, Slashdot and Gnutella
max streaming rate is 500Kbps
A. Bharambe, S. Rao, V. Padmanabhan, S. Seshan, and H. Zhang, “The impact of heterogeneousbandwidth constraints on DHT-based multicast protocols,” International Workshop on P2P Systems, 2005
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Trace based simulations
Observations Sigcomm: performance of Bazaar degrade subs
tantially as the fraction of strategic peers increases
Slashdot and Gnutella: performance degrade gracefully
infer Bazaar framework is particularly well suited for many p2p streaming scenarios, in which peers are mostly resource poor
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Summary
Bazaar framework make use of the natural inherent incentive facilitate formation of efficient overlay structure improve performance in p2p streaming
applications involving strategic peers optimize by shuffle-k operations works well in environments with low fraction of
high capacity peers
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Cathedral approach
most existing p2p streaming impose rules and incentives to motivate contribution
each peer is expected to follow – Cathedral approach
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Trace-based
Sigcomm: streaming Sigcomm conferences or workshops; most audience were interested in the contents but could not attain in person
Slashdot: a popular web-based discussion forum; audience is either interested in the contents or curious about the system
Gnutella: hosts in the Gnutella system
CHU ET. AL, “Early deployment experience with an overlay based internet broadcasting system,” USENIX Annual Technical Conference, June 2004
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