1 / 24

Peer-to-Peer Systems

This survey paper provides a high-level view of various aspects of Peer-to-Peer (P2P) systems, including distributed hash tables. It discusses the history of P2P systems, major applications, system properties, typologies, challenges, and management issues.

dwynn
Télécharger la présentation

Peer-to-Peer Systems

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. Peer-to-Peer Systems Rodrigo Rodrigues Peter Druschel Max Planck Institute for Software Systems

  2. Paper Overview • Survey paper • Long list of references • Presents a high view of various aspects of P2P systems • Describes distributed hash tables in more detail

  3. In the beginning • 1999 • Napster music sharing system • Gave a bad reputation to P2P systems • Freenet anonymous data store • SETI@home volunteer-based distributed computational project

  4. Now • BitTorrent • Skype P2P telephony system • Skinkers enterprise communication management system • P2PLive, CoolStreaming, BBC’s iPlayer

  5. What I think • Previous list mentioned commercial products • Does it mean all major issues have been solved?

  6. Email from Skype To our valued customers:As 2010 draws to a close, I would like to take a moment to thank each of you for your patience, understanding, and support during Skype’s recent outage. … Kind regards, Tony BatesCEOSkype

  7. Defining propertiesof P2P systems • High degree of decentralization • Few or no dedicated central nodes • Multiple administrative domains • Low barriers to deployment • Organic growth • Resilience to faults and attacks • Abundance and diversity of resources

  8. What I think • P2P systems are • Very cheap • Very easy to deploy • Highly scalable

  9. Applications (I) • Sharing and distributing files: • Napster (quickly shutdown) • Gnutella, FastTrack aka Kazaa(all decentralized) • eDonkey, BitTorrent (faster) • Streaming media: • PPLive, Coolstreaming (academia) • BBC’s iPlayer, Skinkers Livestation (industry)

  10. Applications (II) • Telephony: • Skype • Scientific Computing: • SETI@home • BOINC • Other: • Distributed storage systems (Freenet) • Content-delivery networks(CoralCDN, CoDeeN)

  11. Typology (I) • Degree of centralization: • Partly decentralized: • BitTorrent tracker, • Skype billing subsystem • Fully decentralized: • More scalable • Resilient to failure, attacks and legal challenges • Can have supernodes

  12. Typology (II) • Overlay maintenance • Overlay is graph G = (N, E) describing set of links E among members of set N of participating nodes • If there is a link in E between two nodes, they are aware of each other • Overlays can be structured or unstructured

  13. Unstructured overlays • When a node joins, it acquires a set of "neighbors" by • Contacting the tracker (BitTorrent) • Contacting a system participant • Must have a mechanism advertising these nodes

  14. Structured overlays (I) • Use key-based routing • Each node has a unique identifier • 160-bit integer • Identifiers are uniformly distributed • Addressing is based on keys • Each key is mapped into exactly one of the current overlay nodes • Smallest integer "larger" than key value: make identifier space circular

  15. Structured overlays (II) • Key-based routing implements primitiveKBR(no, k) that produces a path going from a node no to the node holding key k • Big tradeoff is between • Keeping paths short • Minimizing state information kept by nodes

  16. Typology (III) • Distributed state • In partly decentralized systems state is maintained by • The central node(s) • The peers assigned by it/them to each node • In decentralized systems, state is kept by • The content providers • Individual peers

  17. Locating data • In unstructured systems, nodes wanting to access a specific object flood their neighbors, which flood their neighbors and so on • Structured systems use distributed hash tables • All data have keys • Stored at node responsible for key value and replicated at its successors

  18. Typology (IV) • Distributed control: • In unstructured systems , it is typically done by epidemic techniques • Can also build a spanning tree among the nodes if membership is fairly stable • In structured systems, it is much easier to build spanning trees

  19. Content distribution • Tree-based protocols • Main disadvantage is that leave nodes ado not contribute anything • Full binary tree of height n has 2n+1- 1 nodes and 2n leaves • Swarm-based protocols • BitTorrent • All nodes can participate

  20. Challenges (I) • Controlling membership: • Preventing Sybil attacks • One node pretending to be many • Can require proof of work or use trusted identities (FARSITE)

  21. Challenges (II) • Protecting data: • Integrity and Authenticity: • Can use digital signatures • Data stored in DHTs can be self-certifying by making DHT keys function of data themselves • Can use voting (LOCKSS) • Availability and Durability • Replicate data and keep system alive

  22. Challenges (III) • Incentives: • Fighting Free riding • Big problem • BitTorrent tit-for-tat • Not always feasible • Managing P2P Systems: • Lack of centralized control can make system hard to manage • Skype collapses

  23. P2P and ISPs • P2P systems consume a lot of bandwidth • Current ISP billing models assume that customers send much less bits than they receive • Flat-rate pricing for residential customers • Bandwidth-based pricing for information providers • ISPs have no way to bill anyone for P2P traffic

  24. Conclusions • P2P is a disruptive technology with great potential • Major strength is lack of centralized control • Also creates new challenges that can be • Technical • Commercial • Legal

More Related