1. 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

2. 2 Cathedral and Bazaar CathedralBazaar imposed incentive/rulenatural incentive

3. 3 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 streaming media applications where resource sharing is a natural behavior without external rules and incentives

4. 4 Outlines Background Proposed Bazaar framework Evaluation and simulation Summary

5. 5 Background not altruistic  limited asymmetrical upstream bandwidth of DSL and cable modems  uploading may reduce its access bandwidth and degrade the network access performance

6. 6 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

7. 7 Utility  benefit(incoming bandwidth, latency) – cost (outgoing bandwidth)  maybe different in different peers

8. 8 An example all selfish

9. 9 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

10. 10 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

11. 11 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

12. 12 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

13. 13 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

14. 14 Bazaar framework peers can perform  join/leave the overlay dynamically  advertise their services  participate in shuffle operation to improve overlay structure

15. 15 Bazaar in action 1. root enters the system 2. A interested in the content joins the system 3. revise M-Quote (250 = 500/2) 4. if A is selfish, it can send M-Quote of 0 or do not send at all. However, a new node will definitely chooses root as peer which reduce the bandwidth shared by A. This motivates A to offer competitive quote

16. 16 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 participate in a local shuffling operation

17. 17 Bazaar in action shuffle is a periodic operation if B is attracted by the new quote, the overlay changes accordingly

18. 18 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

19. 19 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

20. 20 Evaluate under modes of operation

21. 21 Performance metrics throughput  incoming bandwidth of each peer total system utility  sum of perceived data utility of all peers

22. 22 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

23. 23 Bimodal simulations – system utility

24. 24 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

25. 25 Bimodal simulations – throughput

26. 26 Bimodal simulations – throughput

27. 27 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

28. 28 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 heterogeneous bandwidth constraints on DHT-based multicast protocols,” International Workshop on P2P Systems, 2005

29. 29 Trace based simulations varying the fraction of strategic peers

30. 30 Trace based simulations

31. 31 Trace based simulations Observations  Sigcomm: performance of Bazaar degrade substantially 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

32. 32 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

33. THE END

34. 34 Cathedral approach most existing p2p streaming impose rules and incentives to motivate contribution each peer is expected to follow – Cathedral approach

35. 35 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