1 / 49

TexPoint fonts used in EMF. Read the TexPoint manual before you delete this box.: A A A A A A A

Coping with Selfishness in D istributed Systems. Mechanism Design in Multi-Core and Peer-to-Peer Systems. TexPoint fonts used in EMF. Read the TexPoint manual before you delete this box.: A A A A A A A. Selfishness in Computer Science.

brygid
Download Presentation

TexPoint fonts used in EMF. Read the TexPoint manual before you delete this box.: A A A A A A A

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Coping with Selfishness in Distributed Systems • Mechanism Design in Multi-Core and • Peer-to-Peer Systems TexPoint fonts used in EMF. Read the TexPoint manual before you delete this box.: AAAAAAA

  2. Selfishness in Computer Science „The Internet is unique among all computer systems in that it is built, operated, and used by a multitude of diverse economic interests, in varying relationships of collaboration and competition with each other.“ C. Papadimitriou, STOC 2001 Game theory attempts to mathematically capture behavior in strategic situations (games), in which an individual's success in making choices depends on the choices of others.

  3. Game Theory & Mechanism Design • Game Theory explains/predicts behavior • Mechanism Design Selfishness-aware optimization

  4. Mechanism Design with Payments

  5. Mechanism Design with Payments + = cost = 2 net gain = 2

  6. Optimal Implementations

  7. Optimal Implementations

  8. Complexity Optimal exact implementation NP-hard , , 1 2 , , , ,

  9. Worst-Case Leverage • «maximum worst-case net gain»

  10. Uniform Leverage • «maximum average net gain»

  11. Result Overview

  12. Multi-Core Architecture

  13. The Multicore Revolution

  14. Transactional Memory explicit locks • transactions Which transaction shall I abort?? Timestamp, Polite, Karma, Polka, Randomized, ...

  15. Transactional Memory is a Game • Players = programmers • Strategy space = placing of transactions • Their goal: fast execution • Social goal: maximize system throughput „My thread is the fastest!“

  16. Good Programming incRingCounters(Node start){ var cur = start; transaction{ repeat{ cur.doSomething(); cur = cur.next; } until(cur==start) }} incRingCountersGP(Node start){ var cur = start; repeat{ transaction{cur.doSomething();} cur = cur.next; until(cur==start) }} R1 R1 R2 R2 R3 R3 Rs Rs t t long transactions vs short transactions

  17. Good Programming Incentives • A CM is GPI compatible iff it • punishes unnecessary locking • and rewards partitioning.

  18. Quasi Priority Accumulating CM Thm: Timestamp is not GPI compatible. R1 R2 R3 Rs t R1 R2 R3 Rs t

  19. Randomized CM • Not priority based • „Choose random winner“ • Proof Intuition • Unnecessary Locks: stupid because only risk conflict (no priority gain) • Partitioning: Lemma: Randomized CM is GPI compatible. Ti Ti Ti1 Ti2 Ti1 Ti2

  20. Randomized CM • Not priority based • „Choose random winner“ • Proof Intuition • Unnecessary Locks: stupid because only risk conflict (no priority gain) • Partitioning: Lemma: Randomized CM is GPI compatible. Ti Ti Ti1 Ti2 Ti2

  21. Polka Karma throughput selfish (updates/s) throughput selfish (updates/s) throughput collaborators (updates/s) throughput collaborators (updates/s) Randomized Timestamp throughput selfish (updates/s) throughput selfish (updates/s) throughput collaborators (updates/s) throughput collaborators (updates/s)

  22. Peer-to-Peer Computing

  23. Peer-to-Peer File Sharing • History

  24. Cyclic Tit-for-Tat Trading

  25. Cyclic Tit-for-Tat Trading

  26. BitTorrent: Downloads per Peer

  27. Cross-Swarm Cycles in BitTorrent

  28. Evaluation

  29. Evaluation • Results

  30. Cyclic Trading Protocol CYCT4T outTable inTable Out-neighbors on cycles from : SELECT id FROM outTable INNER JOIN inTable ON outTable.id = inTable.source WHERE via = r; Update: SELECT DISTINCT source, dist FROM inTable WHERE distance < k − 1 AND via q;

  31. Cyclic Trading Protocol CYCT4T …

  32. Established Equilibrium utility ? n T4T

  33. BitThief: Smooth Transition utility ? n

  34. BitThief: Smooth Transition utility ? n

  35. Steganographic Handshake in BitThief • BitThief is a BitTorrent client that • Free rides with BitTorrent clients [1], and • Trades tit-for-tat (T4T) with other BitThiefs [2] • Block request sequence • Hybrid approach using PEX • Order of peer addresses • Forged peer address [1] Locher et al.,Free Riding in Bittorrent is Cheap, HotNets 2006 [2] Locher et al., Rescuing Tit-for-Tat with Source Coding, P2P 2007

  36. Steganographic Handshake ?

  37. Steganographic Handshake ?

  38. Steganographic Channels • P2P File sharing • Block request sequence • Block subset selection • Timing • Bandwidth • Ports

  39. Encoding Bits Into a Permutation • Encode a message M in a permutation • Represent M as a factorial number • because • M is encoded into as the Lehmer Code of is 2210. • Lehmer Code • Counts the # swaps to get to • (1,2,3,4) ..2 swaps.. • (3,1,2,4) ..2 swaps.. • (3,4,1,2) ..1 swap.. • (3,4,2,1) ..0 swaps.. • (3,4,2,1)

  40. Hidden Broadcast • Send a secret message to all conspirers n c n-c

  41. Steganographic Broadcast • Send a message to all conspirers • Bittorrent-like p2p file sharing system k

  42. Efficient Broadcast • If each conspirer randomly connects to peers, then the subnetwork induced by the 𝑐 conspirers is connected w.h.p. Lemma

  43. Efficient Broadcast • Space complexity • Communication complexity w.h.p. • If each conspirer randomly connects to peers, then the subnetwork induced by the 𝑐 conspirers is connected w.h.p. Lemma • Get peer addresses • Acquire blocks • Reveal types of connected peers • Broadcast message in conspirer subnetwork Algorithm

  44. Proof of Theorem 10.1 • If each conspirer randomly connects to peers, then the subnetwork induced by the conspirers is connected w.h.p. • Proof: • For each conspirer , it holds that . • (Chernoff) • If each edge of a graph G with c nodes is present with probability then G is connected with probability (Corollary from [Hofstad 2007]) • In such a graph G, all nodes have less than neighbors w.h.p. • Each conspirer implicitly chooses random neighbors in the conspirer subgraph.

  45. Stronger Authority Models • Individual Monitoring • Authority monitors individual communication links, no correlation • where m is the # of blocks • Complete Monitoring • Authority monitors complete network • Stochastic Monitoring • Trade-off: Hidden communication vs. False positives

  46. Broadcast under Stochastic Monitoring • Regular peers choose their request order permutation according to a distribution C • Authority classifies a peer as a conspirer if it uses a request order permutation with • Trade-off in the choice of threshold • Amount of hidden communication vs. False positives

  47. Broadcast under Stochastic Monitoring • Regular peers choose their request order permutation according to a distribution C • Authority classifies a peer as a conspirer if it uses a request order permutation with • is a deterministic PRG

  48. Conclusion t t

  49. Thank You!Questions & Comments? TexPoint fonts used in EMF. Read the TexPoint manual before you delete this box.: AAAAAAA

More Related