Lecture11nFull - Click to edit Master subtitle style 8/1/11...

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Unformatted text preview: Click to edit Master subtitle style 8/1/11 Lecture 11 COT 4600 Operating Systems Spring 2011 Dan C. Marinescu Office: HEC 304 Office hours: Tu-Th 5:00 6:00 PM Lecture 11 8/1/11 n Last time: n URLs n Soft modularity Procedure call conventions and the memory map; the stack Errors Strongly-typed languages help enforce modularity. n Enforced modularity; message passing and the client-server model. Example of a client server system: WWW Today: Today Client-server organization Intermediaries; Trusted Intermediaries; Thin clients Issues Heterogeneity; little-endian and big-endian representation Timing, response time. Examples: Event service, X11; Trusted intermediaries: Email, File Systems, Web Remote Procedure Call Next time n Strategies for name resolution n Case study DNS Lecture 11 Thursday, February 17, 2011 Lecture 11 22 Lecture 11 8/1/11 33 Lecture 11 Lecture 11 8/1/11 44 Client/service organization n Not only separates functions but also enforces this separation!! No globally-shared state (e.g., through the stack) Errors can only propagate from client to service and vice-versa only if the messages are not properly checked. A client can use time-outs to detect a non-responsive service and take another course of action. The separation of abstraction from implementation is clearer; the client needs only to know the format of the message, the implementation of the service may change. Lecture 11 Lecture 11 8/1/11 55 5 Intermediaries n What if the sender and the receiver of a message are not active at the same time? n Intermediaries support buffered communication and allow more flexibility& the intermediary may decide how to sort messages n The sender and the receiver may: Push a message Pull a message n Example: the mail service: The sender pushes a message into his/her outbox The outbox pushes it to the inbox of the recipient The recipient pulls it whenever s(he) wants n The publish/subscribe paradigm & the sender notifies an event service when it produced a message. Recipients subscribe to the events and when the events occur the messages are delivered Lecture 11 Lecture 11 8/1/11 66 Trusted intermediary n Trusted service acting as an intermediary among multiple clients. Enforces modularity a fault of one client does not affect other clients. Examples: n File systems n Mail systems n Supports thin-clients & a significant part of client functionality is transferred to the intermediary. n In a thin client/server system, the only software installed on the thin client is the user interface, certain frequently used applications, and a networked operating system. By simplifying the load on the thin client, it can be a very small, low- powered device giving lower costs to purchase and to operate per seat....
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This note was uploaded on 07/30/2011 for the course COP 4600 taught by Professor Montagne during the Spring '08 term at University of Central Florida.

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Lecture11nFull - Click to edit Master subtitle style 8/1/11...

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