Feb23 - CSE398: Network Systems Design Instructor: Dr....

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CSE398: Network Systems Design Instructor: Dr. Liang Cheng Department of Computer Science and Engineering Lehigh University February 23, 2005
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Instructor: Dr. Liang Cheng CSE398: Network Systems Design 02/23/05 Outline ± Recap ± Packet processing functions ± Protocol software ± Summary and homework
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Instructor: Dr. Liang Cheng CSE398: Network Systems Design 02/23/05 Outline ± Recap ± Protocol software on a conventional processor ± Summary and homework
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Instructor: Dr. Liang Cheng CSE398: Network Systems Design 02/23/05 Possible Implementations of Protocol Software ± In an application program ± Easy to program ± Runs as user-level process ± No direct access to network devices ± High cost to copy data from kernel address space ± Cannot run at wire speed ± In an embedded system ± Special-purpose hardware device ± Dedicated to specific task ± Ideal for stand-alone system ± Software has full control ± In an operating system kernel ± More difficult to program than application ± Runs with kernel privilege ± Direct access to network devices
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Instructor: Dr. Liang Cheng CSE398: Network Systems Design 02/23/05 Processing Priorities ± Determine which code CPU runs at any time ± Hardware devices need highest priority ± Protocol software has medium priority ± Application programs have lowest priority ± Queues provide buffering across priorities ± Why hardware device- related processing has higher priority?
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Instructor: Dr. Liang Cheng CSE398: Network Systems Design 02/23/05 OS Implementation of Priority (1) ± Interrupt mechanism ± Operates asynchronously ± Saves current processing state ± Changes processor status ± Branches to specified location ± Hardware interrupt
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Feb23 - CSE398: Network Systems Design Instructor: Dr....

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