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Distributed Systems Concepts and Design Chapter 10: Peer-to-Peer Systems

Distributed Systems Concepts and Design Chapter 10: Peer-to-Peer Systems. Bruce Hammer, Steve Wallis, Raymond Ho. 10.1: Introduction. Peer-to-Peer Systems Where data and computational resources are contributed by many hosts

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Distributed Systems Concepts and Design Chapter 10: Peer-to-Peer Systems

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  1. Distributed Systems Concepts and Design Chapter 10: Peer-to-Peer Systems Bruce Hammer, Steve Wallis, Raymond Ho

  2. 10.1: Introduction • Peer-to-Peer Systems • Where data and computational resources are contributed by many hosts • Objective to balance network traffic and reduce the load on the primary host • Management requires knowledge of all hosts, their accessibility, (distance in number of hops), availability and performance. • They exploit existing naming, routing, data replication and security techniques in new ways Bruce Hammer, Steve Wallis, Raymond Ho

  3. 10.1: Introduction • Goal of Peer-to-Peer Systems • Sharing data and resources on a very large scale • ‘Applications that exploit resources available at the edges of the Internet – storage, cycles, content, human presence’ (Shirky 2000) • Uses data and computing resources available in the personal computers and workstations Bruce Hammer, Steve Wallis, Raymond Ho

  4. 10.1: Introduction • Characteristics of Peer-to-Peer Systems • Each computer contributes resources • All the nodes have the same functional capabilities and responsibilities • No centrally-administered system • Offers a limited degree of anonymity • Algorithm for placing and accessing the data • Balance workload, ensure availability • Without adding undue overhead Bruce Hammer, Steve Wallis, Raymond Ho

  5. 10.1: Introduction • Evolution of Peer-to-Peer Systems • Napster – download music, return address • Freenet, Gnutella, Kazaa and BitTorrent • More sophisticated – greater scalability, anonymity and fault tolerance • Pastry, Tapestry, CAN, Chord, Kademlia • Peer-to-peer middleware Bruce Hammer, Steve Wallis, Raymond Ho

  6. 10.1: Introduction • Evolution (Continued) • Immutable Files, (music, video) • GUIDs (Globally Unique Identifiers) • Middleware to provide better routing algorithms, react to outages • Evolve to mutable files • Application within one company’s intranet Bruce Hammer, Steve Wallis, Raymond Ho

  7. 10.2: Napster and its Legacy Bruce Hammer, Steve Wallis, Raymond Ho

  8. 10.2: Napster and Its Legacy Bruce Hammer, Steve Wallis, Raymond Ho

  9. 10.3: Peer-to-Peer Middleware Bruce Hammer, Steve Wallis, Raymond Ho

  10. 10.4: Routing Overlays • Routing Overlays • Sub-systems, APIs, within the peer-to-peer middleware • Responsible for locating nodes and objects • Implements a routing mechanism in the application layer • Separate from any other routing mechanisms such as IP routing • Ensures that any node can access any object by routing each request thru a sequence of nodes • Exploits knowledge at each node to locate the destination Bruce Hammer, Steve Wallis, Raymond Ho

  11. 10.4: Routing Overlays • GUIDs • ‘pure’ names or opaque identifiers • Reveal nothing about the locations of the objects • Building blocks for routing overlays • Computed from all or part of the state of the object using a function that deliver a value that is very likely to be unique. Uniqueness is then checked against all other GUIDs • Not human readable Bruce Hammer, Steve Wallis, Raymond Ho

  12. 10.4: Routing Overlays • Tasks of a routing overlay • Client submits a request including the object GUID, routing overlay routes the request to a node at which a replica of the object resides • A node introduces a new object by computing its GUID and announces it to the routing overlay • Clients can remove an object • Nodes may join and leave the service Bruce Hammer, Steve Wallis, Raymond Ho

  13. 10.4: Routing Overlays • Types of Routing Overlays • DHT – Distributed Hash Tables • DOLR – Distributed Object Location and Routing • DOLR is a layer over the DHT that maps GUIDs and address of nodes • DHT – GUIDs are stored based on the hash value • DOLR – GUIDs host address is notified using the Publish() operation Bruce Hammer, Steve Wallis, Raymond Ho

  14. 10.5: Overlay Case Studies: Pastry, Tapestry Bruce Hammer, Steve Wallis, Raymond Ho

  15. 10.6: Application Case Studies: Squirrel, OceanStore, Ivy Squirrel Bruce Hammer, Steve Wallis, Raymond Ho

  16. 10.7: Summary • Napster – immutable data, unsophisticated routing • Current – mutable data, routing overlays, sophisticated algorithms • Internet or company intranet support • Distributed Computing (SETI) Bruce Hammer, Steve Wallis, Raymond Ho

  17. 10.7: Summary • Benefits of Peer-to-Peer Systems • Ability to exploit unused resources (storage, processing) in the host computers • Scalability to support large numbers of clients and hosts with load balancing of network links and host computer resources • Self-organizing properties of the middleware platforms reduces costs Bruce Hammer, Steve Wallis, Raymond Ho

  18. 10.7: Summary • Weaknesses of Peer-to-Peer Systems • Costly for the storage of mutable data compared to trusted, centralized service • Can not yet guarantee anonymity to hosts Bruce Hammer, Steve Wallis, Raymond Ho

  19. 10: Peer-to-Peer Systems • Questions???? • Comments?? Bruce Hammer, Steve Wallis, Raymond Ho

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