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Distributed Systems


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Distributed Systems

  1. 1. Distributed Systems A Brief Introduction
  3. 3. OUTLINE (Contd.)  ORGANISATION OF DISTRIBUTED SYSTEM.  GOALS OF D.S. − Resource Sharing. − Openness. − Transparency. − Scalability.
  4. 4. OUTLINE (Contd.) − Concurrency.  TYPES OF DISTRIBUTED SYSTEMS. − Distributed Computing Systems. − Distributed Information Systems. − Distributed Pervasive Systems.  SUMMARY.
  5. 5. HISTORY  1945~1985 − Computers were large and expensive. − No way to connect them. − All systems were Centralized Systems.  Mid-1980s − Powerful microprocessors. − High Speed Computer Networks (LANs , WANs).
  6. 6. HISTORY (Contd.) Then came the DISTRIBUTED SYSTEMS…
  7. 7. What are Distributed Systems ? ?  A distributed system is a piece of software that ensures that:  a collection of independent computers appears to its users as a single coherent system.  Two aspects:  (1) independent computers and (2) single system => middleware.
  8. 8. EXAMPLES  World Wide Web (WWW) is the biggest example of distributed system.  Others are  The internet  An intranet which is a portion of the internet managed by an organization
  9. 9. WHY DISTRIBUTED SYSTEMS ? ?  availability of powerful yet cheap microprocessors (PCs, workstations),  continuing advances in communication technology
  10. 10. ADVANTAGES OF D.S. OVER CENTRALIZED SYSTEM:  Economics: A collection of microprocessors offer a better price/performance than mainframes. Low price/performance ratio: cost effective way to increase computing power.  Reliability: • If one machine crashes, the system as a whole can still survive. Higher availability and improved reliability.
  11. 11. ADVANTAGES (Contd.) Speed: a distributed system may have more total computing power than a mainframe. Ex.: 10,000 CPU chips, each running at 50 MIPS. Not possible to build 500,000 MIPS single processor. Enhanced performance through load distributing.
  12. 12. ADVANTAGES (Contd.)  Incremental growth: Computing power can be added in small increments. This leads to Modular expandability
  13. 13. ADVANTAGES OF D.S. OVER INDEPENDENT PCs:  Data sharing: allow many users to access to a common data base.  Resource Sharing: expensive peripherals like color printers.
  14. 14. ADVANTAGES (Contd.)  Communication: enhance human-to- human communication. E.g.: email, chat.  Flexibility: spread the workload over the available machines
  15. 15. ORGANIZATION OF D.S.: A distributed system organized as middleware. −The middleware layer extends over multiple machines, and offers each application the same interface.
  16. 16. GOALS OF D.S. : − Resource Sharing. − Openness. − Transparency. − Scalability. − Concurrency.
  17. 17. RESOURCE SHARING:  With Distributed Systems, it is easier for users to access remote resources and to share resources with other users. − Examples: printers, files, Web pages, etc  A distributed system should also make it easier for users to exchange information.  Easier resource and data exchange could cause security problems – a distributed system should deal with this problem.
  18. 18. OPENNESS:  The openness of DS is determined primarily by the degree to which new resource- sharing services can be added and be made available for use by a variety of client programs.
  19. 19. TRANSPARENCY:  It hides the fact that the processes and resources are physically distributed across multiple computers.  Transparency is of various forms as follows:
  20. 20. TRANSPARENCY (Contd.)
  21. 21. SCALABILITY:  A system is described as scalable if it remains effective when there is a significant increase in the number of resources and the number of users.  Challenges:  Controlling the cost of resources or money.  Controlling the performance loss.
  22. 22. CONCURRENCY:  There is a possibility that several clients will attempt to access a shared resource at the same time.  Any object that represents a shared resource in a distributed system must be responsible for ensuring that operates correctly in a concurrent environment.
  23. 23. TYPES OF D.S. :  Distributed Computing Systems. − Cluster Computing Systems. − Grid Computing Systems.  Distributed Information Systems.  Distributed Pervasive Systems.
  24. 24. DISTRIBUTED COMPUTING SYSTEMS:  Goal: High performance computing tasks. Cluster Computing Systems: − A “supercomputer” built from “off the shelf” computer in a high-speed network (usually a LAN) − Most common use: a single program is run in parallel on multiple machines
  25. 25. (Contd.) Grid Computing Systems: − Contrary to clusters, grids are usually composed of different types of computers (hardware, OS, network, security, etc.) − Resources from different organizations are brought together to allow collaboration − Examples: SETI@home, WWW…
  26. 26. DISTRIBUTED INFORMATION SYSTEMS:  Goal: Distribute information across several Servers. − Remote processes called Clients access the servers to manipulate the information − Different communication models are used. The most usual are RPC (Remote Procedure Calls) and the object oriented RMI (Remote Method Invocations)
  27. 27. (Contd.) − Often associated with Transaction systems − Examples:  Banks;  Travel agencies;  Rent-a-Cars’;  Etc…
  28. 28. DISTRIBUTED PERVASIVE SYSTEMS: − These are the distributed systems involving mobile and embedded computer devices like Small, wireless, battery-powered devices (PDA’s, smart phones, sensors, wireless surveillance cams, portable ECG monitors, etc.) − These systems characterized by their “instability” when compared to more “traditional” distributed systems
  29. 29. (Contd.) − Pervasive Systems are all around us, and ideally should be able to adapt to the lack of human administrative control:  Automatically connect to a different network;  Discover services and react accordingly;  Automatic self configuration (E.g.: UPnP – Universal Plug and Play)… − Examples: Home Systems, Electronic Health Care Systems, Sensor Networks, etc.
  30. 30. SUMMARY  Distributed systems are everywhere  Internet, intranet, wireless networks.  Resource sharing is the main motivating factor for constructing distributed systems.  The construction of distributed systems produces many challenges like Secure communication over public networks.