1. CompTIA Network+ Chapter 2
OSI Model
CompTIA Network+
Chapter 2

2. Exam Objectives
The following 4 exam objectives will be covered in this chapter.
Define the layers of the OSI model and identify the protocols, services, and functions that pertain to each layer.
Identify the OSI Model layers where routing, switching or bridging occurs.
Describe data link layer concepts, including MAC address, bridges and 802.x specifications.
Explain routing and network layer concepts.

3. The Seven Layers of the OSI Model
International
Organization of
Standardization
ISO

4. Layer7
The application layer is the OSI layer that is closest to the user; it provides network services to the user’s applications. It differs from the other layers in that it does not provide services to any other OSI layer, but rather, only to applications outside the OSI model. Examples of such applications are spreadsheet programs, word processing programs, and bank terminal programs. If you want to remember Layer 7 in as few words as possible, think of browsers.

5. Layer 6
The presentation layer ensures that the information that the application layer of one system sends out is readable by the application layer of another system. The presentation layer translates between multiple data formats by using a common format.
Data encryption and compression also takes place at the Presentation layer

6. Layer 5
As its name implies, the session layer establishes, manages, and terminates sessions between two communicating hosts. The session layer provides its services to the presentation layer. It also synchronizes dialogue between the two hosts' presentation layers and manages their data exchange. If you want to remember Layer 5 in as few words as possible, think of dialogues and conversations.

7. Layer 4
The transport layer segments data from the sending host's system and reassembles the data into a data stream on the receiving host's system. Layer 4 is the boundary between media-layer protocols and host-layer protocols. Layer 4 also deals with Flow Control (Windowing), and Reliability of Communication (Acknowledgement).

8. Layer 3
The network layer is a complex layer that provides connectivity and path selection between two host systems that may be located on geographically separated networks. If you want to remember Layer 3 in as few words as possible, think of path selection, routing, and addressing.

9. Layer 2
The data link layer provides reliable transit of data across a physical link. In so doing, the data link layer is concerned with physical (as opposed to logical) addressing, network topology, network access, error notification, ordered delivery of frames. If you want to remember Layer 2 in as few words as possible, think of frames and media access control.

10. Layer 1
The physical layer defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems. Such characteristics as voltage levels, maximum transmission distances, physical connectors, transceivers and other, similar, attributes are defined by physical layer specifications. If you want to remember Layer 1 in as few words as possible, think of signals and media.

11. Encapsulation

12. Summary of the OSI Model
Layer
Description

13. 5 Conversion Steps to Encapsulate Data

15. Devices and layers
Physical layer: Media, transceivers, hubs, and repeaters.
Data link Layer: bridges, switches, NICs and brouters
Network Layer: routers, brouters.

16. Frame Specifications Ethernet Token Ring
Networking technology originally developed in 1970 by Xerox
Token Ring
Networking technology developed by IBM in the 1980s

17. Typical Ethernet Frame
FIGURE 2-5 Ethernet frame as specified by the IEEE standard
802.3 Standard
IEEE standard for Ethernet networking devices and data handling

18. Components of the Ethernet 802.3 Frame
Preamble: announces to the network that data is in rout.
Start of Frame Delimiter (SFD): beginning of the addressing frame
Destination Address
Source Address

19. Components of the Ethernet 802.3 Frame
Length (LEN)
Data
Pad: Minimum frame size is 46 bytes
Frame Check Sequence (FCS)
Cyclic Redundancy Check (CRC)
Algorithm used to verify the accuracy of data contained in a data frame

20. Standardized four Ethernet Frame Types
Ethernet II
Ethernet SNAP
The four frames are not compatible with each other.

21. Typical Token Ring Frame
FIGURE 2-6 Typical Token Ring frame as specified in the IEEE standard
802.5 Standard
IEEE standard for Token Ring networking devices and data handling

22. Components of Token Ring Frame
Start Delimiter (SD)
Access Control (AC)
Frame Control (FC)
Destination Address
Source Address

23. Components of Token Ring Frame
Data
Frame Check Sequence (FCS)
End Delimiter (ED)
Frame Status (FS)

24. Addressing Through the Layers
Data Link Layer Address
Network Layer Address

25. Data Link Layer Address
Also called MAC address, after Media Access Control (MAC) sublayer
Number uniquely defining a network node
Manufacturer-hard codes the address
Block ID
Device ID

26. Network Layer Address Resides at Network level of OSI Model
Follows hierarchical addressing scheme
Can be assigned through operating system software

27. IEEE Networking Specifications
IEEE 802 standards

28. IEEE Networking Specifications
To accommodate shared access for multiple network nodes, the IEEE expanded the OSI Model by separating the Data Link layer into two sublayers
Logical Link Control (LLC) sublayer
Media Access Control (MAC) sublayer

29. Data Link Layer Sublayers
LLC
Upper Sublayers
Provides common interface
Supplies reliability and flow control services
MAC
Lower sub layer
Appends the physical address of the destination computer onto the frame

30. Subdivided Data Link Layer

31. Labs and Homework Labs: Homework 2.2 2.4 2.5
End of chapter review questions (30 Multiple choice questions.)

32. OSI Model Network+ Exam Questions

33. Question 1

34. Question 2

35. Question 3

36. Question 4

37. Question 5

38. Question 6

39. Question 7

40. Question 8

41. Question 9

42. Question 10

43. Question 12

44. Question 13

45. Question 14

46. Question 15

47. Question 16

48. Question 17

49. Question 18

50. Question 19

51. Question 20

52. Question 21

53. Question 22

54. Question 23

55. Question 24

56. Question 25

57. Question 26

58. Question 27

59. Question 28

60. Question 29

61. Question 30

62. Question 31

63. Question 32

64. Question 33

65. Question 34

66. Question 35