1. Chapter 2 Network Models Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. Components of Communication Sender Receiver Message Transmission medium Protocol

3. Effectiveness of Communication Delivery (confidentiality) Accuracy (integrity) Timeliness (availability) Jitter – a subset of timeliness 2.3

4. Data Flow Simplex Half-Duplex Duplex 2.4

5. Connection Types Point-to-Point A circuit switch creates a point to point connection. Multi-point Many packet switched networks are multi- point 2.5

6. Physical Topologies Bus Ring Star Mesh Compound 2.6

7. Physical Topology Links Let n=# of nodes. The number of links is: Busn-1 Ringn Starn-1 (includes the hub) Meshn*(n-1)/2 2.7

8. Network Types LAN – nodes belonging to an address space that are part of a well defined domain. WAN – When two or more LANs are linked together. 2.8

9. Chapter 2: Outline 2.1 Protocol Layering 2.1 Protocol Layering 2.2 TCP/IP Protocol Suite 2.2 TCP/IP Protocol Suite 2.3 OSI Model 2.3 OSI Model

10. 2.10 2-1 PROTOCOL LAYERING A protocol defines the rules that the sender, receiver and all intermediate devices must follow to communicate effectively.

11. 2.11 2.1.1 Scenarios Consider two scenarios. Scenario 1: communication is so simple it occurs in one layer. Scenario 2: communication takes place in three layers.

12. 2.12 2-1 PROTOCOL LAYERING When communication is simple, one simple protocol may be enough; When the communication is complex, layers are introduced, and each layer has its own protocol.

13. 2.13 Figure 2.1 : A single-layer protocol

14. 2.14 Figure 2.2 : A three-layer protocol

15. 2.15 2.1.2 Principles of Protocol Layering Consider two principles of protocol layering.

16. 2.16 2.1.2 Principles of Protocol Layering Consider two principles of protocol layering. 1. For half-duplex or full duplex data flow, each layer must perform a forward operation and the corresponding inverse operation.

17. 2.17 2.1.2 Principles of Protocol Layering Consider two principles of protocol layering. 2. The two objects under each logically linked layer at both sites should be identical.

18. 2.18 2.1.2 Principles of Protocol Layering Consider two principles of protocol layering. 1. For half-duplex or full duplex data flow, each layer must perform a forward operation and the corresponding inverse operation. 2. The two objects under each logically linked layer at both sites should be identical.

19. 2.19 Figure 2.2 : A three-layer protocol

20. 2.20 2.1.3 Logical Connections The principles of protocol layering lead to a logical connection between the layers at sending and receiving ends of the communication.

21. 2.21 Figure 2.3 : Logical connection between peer layers

22. 2.22 2-2 TCP/IP PROTOCOL SUITE A protocol defines the rules that both the sender and receiver and all intermediate devices must follow to communicate effectively.

23. 2.23 2-2 TCP/IP PROTOCOL SUITE TCP/IP is a five layer protocol suite.

24. 2.24 2-2 TCP/IP PROTOCOL SUITE TCP/IP is a five layer protocol suite. Application Layer

25. 2.25 2-2 TCP/IP PROTOCOL SUITE TCP/IP is a five layer protocol suite. Application Layer Transport Layer

26. 2.26 2-2 TCP/IP PROTOCOL SUITE TCP/IP is a five layer protocol suite. Application Layer Transport Layer Network Layer

27. 2.27 2-2 TCP/IP PROTOCOL SUITE TCP/IP is a five layer protocol suite. Application Layer Transport Layer Network Layer Data Link Layer

28. 2.28 2-2 TCP/IP PROTOCOL SUITE TCP/IP is a five layer protocol suite. Application Layer Transport Layer Network Layer Data Link Layer Physical Layer

29. 2.29 Figure 2.4 : Layers in the TCP/IP protocol suite

30. 2.30 2.2.1 Layered Architecture TCP/IP protocol suite example: Consider three LANs Each LAN has a group of hosts connected to a switch (aka 2-level switch). Each switch is connected to a router (aka 3-level switch)

31. 2.31 Figure 2.5: Communication through an internet

32. 2.32 2.2.2 Layers in the TCP/IP Protocol Suite Draw a diagram with multiple nodes in each LAN Why is it called a 2-level switch? Why is a router is 3-level switch?

33. 2.33 Figure 2.6 : Logical connections between layers in TCP/IP Logical connections

34. 2.34 Network Data Objects Data objects: message

35. 2.35 Network Data Objects Data objects: message segment

36. 2.36 Network Data Objects Data objects: message segment datagram

37. 2.37 Network Data Objects Data objects: message segment datagram frame

38. 2.38 Network Data Objects Network data object taxonomy: message segment datagram frame signals representing bits

39. 2.39 Figure 2.7 : Identical objects in the TCP/IP protocol suite Identical objects (messages) Identical objects (segment or user datagram) Identical objects (datagram) Identical objects (frame) Identical objects (bits) Identical objects (datagram) Identical objects (frame) Identical objects (bits)

40. 2.40 Network Data Objects Data Object Taxonomy: Application layer - message Transport layer - segment Network layer - datagram Data link layer - frame Physical layer – signals representing bits

41. 2.41 2.2.3 The TCP/IP Layers Descriptions of the TCP/IP layers will come later; next, we will follow a data object through the layers…

42. 2.42 2.2.4 Encapsulation and Decapsulation One of the important concepts in protocol layering in the Internet is encapsulation/ decapsulation.

43. 2.43 2.2.4 Encapsulation and Decapsulation As the object passes through each layer, an information header (and or trailer) is added to the object. The information header is used to assist in any of these tasks: routing of the object, flow control, error detection, error correction, etc. (see next slide)

44. 2.44 Figure 2.8 : Encapsulation / Decapsulation

45. Encapsulation payload Each layer receives an object that is referred to as the payload, and then attaches a data header. Payload can be relative to each layer, or absolute. The absolute case refers to the original object message. 2.45

46. Example Encapsulation Q: What is the efficiency of the link in figure 2.8, between LANs if each header is 60 bytes and the message is 1000 bytes? 2.46

47. Example Encapsulation Q: What is the efficiency of the link in figure 2.8, between LANs if each header is 60 bytes and the message is 1000 bytes? A: 84.7% 2.47

48. Example Encapsulation Q: How does the efficiency change if the message is only 100 bytes? 2.48

49. Example Encapsulation Q: How does the efficiency change if the message is only 100 bytes? A: 35.7% 2.49

50. 2.50 Figure 2.9: Addressing in the TCP/IP protocol suite

51. 2.51 2-3 OSI MODEL A seven layer protocol model. It never really caught on due to the success of TCP/IP

52. 2.52 Figure 2.11: The OSI model

53. 2.53 Figure 2.12 : TCP/IP and OSI model

54. 2.54 2.3.1 OSI versus TCP/IP When we compare the two models, we find that two layers, session and presentation, are missing from the TCP/IP protocol suite. These two layers were not added to the TCP/IP protocol suite after the publication of the OSI model. The application layer in the suite is usually considered to be the combination of three layers in the OSI model, as shown in Figure 2.12.