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Lecture 4: Sun: 23/4/1435 Distributed Operating Systems

CS- 492 : Distributed system & Parallel Processing. Lecture 4: Sun: 23/4/1435 Distributed Operating Systems. Lecturer/ Kawther Abas k.albasheir@sau.edu.sa. Distributed System is used to describe a system with the following characteristics:.

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Lecture 4: Sun: 23/4/1435 Distributed Operating Systems

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  1. CS- 492 : Distributed system & Parallel Processing Lecture 4: Sun: 23/4/1435Distributed Operating Systems Lecturer/ Kawther Abas k.albasheir@sau.edu.sa

  2. Distributed System is used to describe a system with the following characteristics: • Consists of several computers that do not share a memory or a clock; • The computers communicate with each other by exchanging messages over a communication network. • Each computer has its own memory and runs its own operating system.

  3. Architecture of Distributed OS

  4. Definition of Distributed OS It extends the concepts of resource management and user friendly interface for shared memory computers a step further, encompassing a distributed computing system consisting of several autonomous computers connected by a communicating network.

  5. Issues in Distributed OS • Global Knowledge • Naming • Scalability • Compatibility • Process Synchronization • Resource Management • Security • Structuring

  6. Type of Distributed Operating Systems • Network Operating Systems • Distributed Operating Systems

  7. Network Topology • they are compared with respect to the following criteria: • Basic cost - • Communication cost - • Reliability -

  8. Network Topology

  9. Communication Structure The design of a communication network must address four basic issues: • Naming and name resolutionRouting strategies • Connection strategies • Contention

  10. Communication Processors in a Wide-Area Network

  11. Communication Protocol • Physical layer • Data-link layer • Network layer • Transport layer • Session layer • Presentation layer • Application layer The communication network is partitioned into the following multiple layers:

  12. Communication Via ISO Network Model

  13. Robustness • Failure detection • Reconfiguration

  14. Failure Detection • Detecting hardware failure is difficult • To detect a link failure, a handshaking protocol can be used • Assume Site A and Site B have established a link • If Site A does not receive a message within the fixed interval, it assumes either (a) the other site is not up or (b) the message was lost • Site A can now send an Are-you-up? message to Site B • If Site A does not receive a reply, it can repeat the message or try an alternate route to Site B

  15. Failure Detection (cont) • If Site A does not ultimately receive a reply from Site B, it concludes some type of failure has occurred • Types of failures:- Site B is down - The direct link between A and B is down- The alternate link from A to B is down - The message has been lost • However, Site A cannot determine exactly why the failure has occurred

  16. Reconfiguration • When Site A determines a failure has occurred, it must reconfigure the system: 1. If the link from A to B has failed, this must be broadcast to every site in the system 2. If a site has failed, every other site must also be notified indicating that the services offered by the failed site are no longer availableWhen the link or the site becomes available again, this information must again be broadcast to all other sites

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