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CS 3204 Operating Systems

This lecture discusses network layering, delay measurement, and implementation issues in operating systems. It also covers advantages of layering, services vs protocols, and the TCP/IP reference model.

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CS 3204 Operating Systems

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  1. CS 3204Operating Systems Godmar Back Lecture 40

  2. Announcements • Project 4 due Wed, May 3, 11:59pm • Read chapter 13 (networking) CS 3204 Spring 2006

  3. Networking (Most slides from Kurose/Ross: Computer Networking – A Top Approach Featuring The Internet)

  4. 3 probes 3 probes 3 probes traceroute Provides delay measurement from source to router along end-end Internet path towards destination • Problem: • Don’t know which route is taken • How: • Send probes to destination • Tell probes to die off after i hops, i = 1..30 • Ask router to send echo packets if packets dies • Measure RTT CS 3204 Spring 2006

  5. application transport network link physical Layered Protocol Architecture • What is a layered architecture? • Motivation • Terminology • Reference Models • Implementation Issues CS 3204 Spring 2006

  6. Advantages of Layering • Decomposition • Masters complexity • Encapsulation • Hiding of implementation details • Evolution • Layers can change/be replaced • Alternative implementations can be added, possibly coexist • Robustness • Testing layers independently increases confidence CS 3204 Spring 2006

  7. Services vs Protocols (horizontal component) • Layer k may interact with peer layer konly via protocols CS 3204 Spring 2006

  8. Interfaces vs Protocols • Duality • Both describe rules regarding order and format of “communication” between entities • Difference: • Interface – vertical: between layers • Protocol – horizontal: between peers • NB: Term “protocol” is sometimes used to describe module implementing a layer CS 3204 Spring 2006

  9. TCP/IP Reference Model CS 3204 Spring 2006

  10. DNS NFS HTTP FTP UDP TCP IP Ethernet ATM Wireless TCP/IP Hourglass View Application Transport Internet Host-To-Network CS 3204 Spring 2006

  11. source network link physical message application transport network link physical segment link physical datagram frame M M Ht Ht M M switch Hn Hn Hn Hn Ht Ht Ht Ht M M M M Hl Hl Hl Hl Hl Hl Hn Hn Hn Hn Hn Hn Ht Ht Ht Ht Ht Ht M M M M M M destination application transport network link physical router Encapsulation CS 3204 Spring 2006

  12. User App user Socket Kernel:“top-half” Kernel:“sw interrupt” TCP Layer IP Layer Kernel:“hw interrupt” Network Device Typical Implementation may cross multiple boundaries! CS 3204 Spring 2006

  13. Queuing Layer k+1 send queues recv queues Layer k Layer k-1 CS 3204 Spring 2006

  14. General Implementation Issues • Who schedules a layer’s processing: • On send: application thread • What if queues are full? Blocking vs. nonblocking • Who does retransmit if necessary? • On receive: interrupt-driven • Not all processing done right away: some delayed processing • Sometimes interrupts can be too slow; polling based approach used instead • Memory management/Protection Issues: • How to you prepend headers? • How do you strip headers? • When are copies needed? • Who allocates and frees packet buffers? CS 3204 Spring 2006

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