TAILIEUCHUNG - Operating System Concepts ppt (15)
Module 15: Network Structures Background. Topology. Network Types. Communication. Communication Protocol. Robustness. Design Strategies. Silberschatz, Galvin and Gagne 2002A Distributed System. Silberschatz, Galvin and Gagne 2002Motivation 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. Silberschatz, Galvin and Gagne 2002Network-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 Transferring data from remote machines to local machines,. via the File Transfer Protocol (FTP) mechanism Silberschatz, Galvin and Gagne 2002Distributed-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 Silberschatz, Galvin and Gagne 2002Distributed-Operating Systems (Cont.) 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 Silberschatz, Galvin and Gagne 2002Topology Sites in the system can be physically connected in a. variety of ways; they are compared with respect to the. following criteria:. Basic cost. How expensive is it to link the various sites in. the system?. Communication cost. How long does it take to send a. message from site A to site B?. Reliability. If a link or a site in the system fails, can the. remaining sites still communicate with each other?. The various topologies are depicted as graphs whose. nodes correspond to sites. An edge from node A to node. B corresponds to a direct connection between the two. sites The following six items depict various network topologies. Silberschatz, Galvin and Gagne 2002Network Topology. Silberschatz, Galvin and Gagne 2002Network Types Local-Area Network (LAN) – designed to cover small. geographical area Multiaccess bus, ring, or star network Speed 10 megabits/second, or higher Broadcast is fast and cheap Nodes:. usually workstations and/or personal computers. a few (usually one or two) mainframes Silberschatz, Galvin and Gagne 2002 Network Types (Cont.)Depiction of typical LAN:. Silberschatz, Galvin and Gagne 2002Network Types (Cont.) Wide-Area Network (WAN) – links geographically. separated sites Point-to-point connections over long-haul lines (often leased. from a phone company) Speed 100 kilobits/second Broadcast usually requires multiple messages Nodes:. usually a high percentage of mainframes. Silberschatz, Galvin and Gagne 2002Communication Processo
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