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Distributed SYSTEM MODEL

Distributed SYSTEM MODEL. SYSTEM MODEL. Topics. SYSTEM MODEL. Introduction. SYSTEM MODEL. Introduction. SYSTEM MODEL. Introduction. SYSTEM MODEL. Introduction. SYSTEM MODEL. Introduction. Architectural Models-Intro. SYSTEM MODEL. Architectural Models-Intro. SYSTEM MODEL.

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Distributed SYSTEM MODEL

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  1. Distributed SYSTEM MODEL

  2. SYSTEM MODEL Topics

  3. SYSTEM MODEL Introduction

  4. SYSTEM MODEL Introduction

  5. SYSTEM MODEL Introduction

  6. SYSTEM MODEL Introduction

  7. SYSTEM MODEL Introduction

  8. Architectural Models-Intro

  9. SYSTEM MODEL Architectural Models-Intro

  10. SYSTEM MODEL Software Layers

  11. SYSTEM MODEL Software Layers Layer N … Layer 2 (services offered to above layer) Layer 1 Figure 1. Software layers

  12. SYSTEM MODEL Software Layers

  13. SYSTEM MODEL Software Layers Figure 2. Software and hardware service layers in distributed systems

  14. SYSTEM MODEL Software Layers

  15. SYSTEM MODEL Variants of Client Sever Model

  16. SYSTEM MODEL Variants of Client Sever Model Figure 6. A service provided by multiple servers.

  17. SYSTEM MODEL Variants of Client Sever Model

  18. SYSTEM MODEL Variants of Client Sever Model Figure 7. Web proxy server

  19. SYSTEM MODEL Variants of Client Sever Model

  20. SYSTEM MODEL Variants of Client Sever Model Figure 8. Web applets

  21. SYSTEM MODEL Variants of Client Sever Model

  22. SYSTEM MODEL Variants of Client Sever Model

  23. SYSTEM MODEL Variants of Client Sever Model

  24. SYSTEM MODEL Variants of Client Sever Model

  25. SYSTEM MODEL Variants of Client Sever Model

  26. SYSTEM MODEL Variants of Client Sever Model Compute server Network computer or PC Application network Thin Process Client Figure 9. Thin clients and compute servers

  27. Peer-to-Peer Computing

  28. The Peer-to-Peer Model • Applications based on peer processes • Not Client-Server • processes that have largely identical functionality

  29. Definitions • Everything except the client/server model • Network of nodes with equivalent capabilities/responsibilities (symmetrical) • Nodes are both Servers and clients called “Servents” • Direct exchange of information between hosts at the edge of the Internet

  30. Definitions (cont.) • A transient network that allows a group of computer users to connect with each other and collaborate by sharing resources (CPU, storage, content). • The connected peers construct a virtual overlay network on top of the underlying network infrastructure • Examples of overlays: • BGP routers and their peering relationships • Content distribution networks (CDNs) • And P2P apps !

  31. Overlay Networks • An overlay network is a set of logical connections between end hosts • Proximity not necessarily taken into account

  32. Overlays: All in the application layer • Design flexibility • Topology • Protocol • Messaging over TCP, UDP, ICMP Underlying physical net is transparent to developer

  33. P2P Goals • Cost reduction through cost sharing • Client/Server: Server bears most of the cost • P2P: Cost spread over all the peers (+Napster, ++Gnutella,…) • Interoperability • for the aggregation of diverse resources (storage, CPU, …) • Increased autonomy • independence from servers, hence providers (e.g., A way around censorship, licensing restrictions, etc.)

  34. Goals (cont.) • Anonymity/privacy • Difficult to ensure with a central server • Required by users who do not want a server/provider to know their involvement in the system • Dynamism and Ad hoc communications • Resources (e.g., compute nodes) enter and leave the system continuously • P2P systems typically do not rely on an established infrastructure • they build their own, e.g. logical overlay in CAN

  35. P2P Classification • Degree of P2P decentralization • Hybrid decentralized P2P • Purely decentralized P2P • Partially centralized P2P • Degree of P2P structure • Structured P2P • Loosely structured P2P • Unstructured P2P

  36. Hybrid decentralized P2P • Central server facilitates the interaction b/w peers. • Central server performs the lookups and identifies the nodes of the network. • example: Napster • (-) Single point of failure, scalability?, …

  37. Purely decentralized P2P • network nodes perform the same tasks (Servents) • no central coordination activity • examples: original Gnutella, Freenet • (-) data consistency?, Manageability?, Security?, Comm. overhead

  38. Partially centralized P2P • some of the nodes assume a more important role • Supernodes act as local central indexes • examples: Kazaa, recent Gnutella

  39. Unstructured P2P • data is distributed randomly over the peers and broadcasting mechanisms are used for searching. • examples: Napster, Gnutella, KaZaa Reporting a file list

  40. Structured P2P • Network topology is tightly controlled and files are placed at precisely specified locations. • Provide a mapping between the file identifier and location • Examples: Chord, Tapestry, Pastry, etc.

  41. Loosely Structured P2P • Between structured and unstructured • File locations are affected by routing hints, but they are not completely specified. • example: Freenet

  42. P2P Applications • File Sharing • Communication • Collaboration • Computation • Databases • Others

  43. P2P File Sharing (cont.) • Examples of P2P file sharing applications: • Napster • disruptive; proof of concept • Gnutella • open source • KaZaA • at some point, more KaZaAtraffic than Web traffic! • eDonkey • popular in Europe • BitTorrent: • 53% of all P2P traffic in June 2004 was BitTorrent traffic • and many others…

  44. P2P Communication • Instant Messaging (IM) • User A runs IM client on her PC • Intermittently connects to Internet; gets new IP address for each connection • Registers herself with “system” • Learns from “system”that user B in her “buddy list”is active • User A initiates direct TCP connection with User B: P2P • User A and User B chat. • Can also be voice, video and text. • Audio-Video Conferencing • Example: Voice-over-IP (Skype)

  45. P2P Databases • Fragments large database over physically distributed nodes • Overcomes limitations of distributed DBMS • Static topology • Heavy administration work • Dissemination of data sources over the Internet • Each peer is a node with a database • Set of peers changes often (site availability, usage patterns) • Examples: • AmbientDB (http://homepages.cwi.nl/~boncz/ambientdb.html) • XPeer: self-organizing XML DB

  46. What is a DHT? • Hash Table • data structure that maps “keys” to “values” • Interface • put(key, value) • get(key) • Distributed Hash Table (DHT) • similar, but spread across the Internet • challenge: locate content

  47. What is a DHT? (cont.) • Single-node hash table: Key = hash (data) put(key, value) get(key)->value • Distributed Hash Table (DHT): Key = hash (data) Lookup (key) -> node-IP@ Route (node-IP@, PUT, key, value) Route (node-IP@, GET, key) -> value • Idea: • Assign particular nodes to hold particular content (or reference to content) • Every node supports a routing function (given a key, route messages to node holding key)

  48. What is a DHT? (cont.)

  49. DHT in action

  50. DHT in action: put()

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