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  1. 1. Chapter 2 Network Models2.1
  2. 2. 2-1 LAYERED TASKSWe use the concept of layers in our daily life. As anexample, let us consider two friends who communicatethrough postal mail. The process of sending a letter to afriend would be complex if there were no servicesavailable from the post office. Topics discussed in this section: Sender, Receiver, and Carrier Hierarchy2.2
  3. 3. Figure 2.1 Tasks involved in sending a letter2.3
  4. 4. 2-2 THE OSI MODELEstablished in 1947, the International StandardsOrganization (ISO) is a multinational body dedicated toworldwide agreement on international standards. An ISOstandard that covers all aspects of networkcommunications is the Open Systems Interconnection(OSI) model. It was first introduced in the late 1970s. Topics discussed in this section: Layered Architecture Peer-to-Peer Processes Encapsulation2.4
  5. 5. ISO is the organization. OSI is the model.2.5
  6. 6. Figure 2.2 Seven layers of the OSI model2.6
  7. 7. Figure 2.3 The interaction between layers in the OSI model2.7
  8. 8. Figure 2.4 An exchange using the OSI model2.8
  9. 9. 2-3 LAYERS IN THE OSI MODELIn this section we briefly describe the functions of eachlayer in the OSI model. Topics discussed in this section: Physical Layer Data Link Layer Network Layer Transport Layer Session Layer Presentation Layer Application Layer2.9
  10. 10. Figure 2.5 Physical layer2.10
  11. 11. The physical layer is responsible for movements of individual bits from one hop (node) to the next.2.11
  12. 12. Figure 2.6 Data link layer2.12
  13. 13. The data link layer is responsible for moving frames from one hop (node) to the next.2.13
  14. 14. Figure 2.7 Hop-to-hop delivery2.14
  15. 15. Figure 2.8 Network layer2.15
  16. 16. The network layer is responsible for the delivery of individual packets from the source host to the destination host.2.16
  17. 17. Figure 2.9 Source-to-destination delivery2.17
  18. 18. Figure 2.10 Transport layer2.18
  19. 19. The transport layer is responsible for the delivery of a message from one process to another.2.19
  20. 20. Figure 2.11 Reliable process-to-process delivery of a message2.20
  21. 21. Figure 2.12 Session layer2.21
  22. 22. The session layer is responsible for dialog control and synchronization.2.22
  23. 23. Figure 2.13 Presentation layer2.23
  24. 24. The presentation layer is responsible for translation, compression, and encryption.2.24
  25. 25. Figure 2.14 Application layer2.25
  26. 26. The application layer is responsible for providing services to the user.2.26
  27. 27. Figure 2.15 Summary of layers2.27
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