distS - Distributed System Chapter 16 Issues in ch 17, ch...

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1 1 Distributed System Chapter 16 Issues in ch 17, ch 18 Chapter 16: Distributed System Structures ! Motivation ! Types of Network-Based Operating Systems ! Network Structure ! Network Topology ! Communication Structure ! Communication Protocols ! Robustness ! Design Issues ! An Example: Networking 2
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2 Motivation ! Distributed system is collection of loosely coupled processors interconnected by a communications network ! Processors variously called nodes, computers, machines, hosts " Site is location of the processor ! Reasons for distributed systems " Resource sharing # sharing and printing files at remote sites # processing information in a distributed database # using remote specialized hardware devices " Computation speedup – load sharing " Reliability – detect and recover from site failure, function transfer, reintegrate failed site " Communication – message passing 3 A Distributed System 4
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3 Network-Operating Systems ! Users are aware of multiplicity of machines. Access to resources of various machines is done explicitly by: " Remote logging into the appropriate remote machine (telnet, ssh) " Remote Desktop (Microsoft Windows) " Transferring data from remote machines to local machines, via the File Transfer Protocol (FTP) mechanism 5 Distributed-Operating Systems ! Users not aware of multiplicity of machines " Access to remote resources similar to access to local resources ! Data Migration – transfer data by transferring entire file, or transferring only those portions of the file necessary for the immediate task ! Computation Migration – transfer the computation, rather than the data, across the system 6
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4 Distributed-Operating Systems (cont’d) ! Process Migration – execute an entire process, or parts of it, at different sites " Load balancing – distribute processes across network to even the workload " Computation speedup – subprocesses can run concurrently on different sites " Hardware preference – process execution may require specialized processor " Software preference – required software may be available at only a particular site " Data access – run process remotely, rather than transfer all data locally 7 Network Structure ! Local-Area Network (LAN) – designed to cover small geographical area. " Multiaccess bus, ring, or star network " Speed 10 – 100 megabits/second " Broadcast is fast and cheap " Nodes: # usually workstations and/or personal computers # a few (usually one or two) mainframes 8
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5 Depiction of typical LAN 9 Network Structure (cont’d) ! Wide-Area Network (WAN) – links geographically separated sites " Point-to-point connections over long-haul lines (often leased from a phone company) " Speed 1.544 – 45 megbits/second " Broadcast usually requires multiple messages " Nodes: # usually a high percentage of mainframes 10
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6 Communication Processors in a Wide-Area Network 11 Network Topology !
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distS - Distributed System Chapter 16 Issues in ch 17, ch...

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