1. Network+ Guide to Networks 5 th Edition Chapter 2 Networking Standards and the OSI Model

2. Figure 2.1 Flow of data through the OSI model

3. Mnemonics for the OSI Model Bottom Up –Please –Do –Not –Throw –Sausage –Pizza –Away Top Down –All –People –Seem –To –Need –Data –Processing

4. Application Layer Top (seventh) OSI model layer No software applications Protocol functions –Facilitates communication Between software applications and lower-layer network services –Network interprets application request –Application interprets data sent from network

5. Presentation Layer Protocol functions –Accept Application layer data –Formats data to make it understandable to different applications and hosts Examples –Text encoding methods ASCII and ANSI –Compression methods like JPEG and MP3 –Data encryption and decryption

6. Session Layer Protocol functions –Coordinate and maintain communications between two nodes Session –Connection for ongoing data exchange between two parties Example: between Web browser client and Web server Functions –Establishing and keeping alive communications link For session duration –Determining if communications ended Determining where to restart transmission –Terminating communications

7. Transport Layer Protocol functions –Accept data from Session layer –Provides flow control, segmentation, and error control Primary Transport Layer Protocols: TCP and UDP

8. Transport Layer TCP Connection-oriented –Establishes a connection before transmitting data –Three-way handshake SYN SYN/ACK ACK

9. Transport Layer TCP –Require acknowledgements from receiver to ensure data was received correctly –Checksum Unique character string allowing receiving node to determine if arriving data unit exactly matches data unit sent by source Ensures data integrity Send data, wait for ACK ACK Send more data, wait for ACK

10. Transport Layer UDP: A connectionless protocol –Do not establish connection with another node before transmitting data—no handshake –Make no effort to ensure data is delivered free of errors –Faster than connection-oriented protocol –Useful when data must be transferred quickly, such as streaming music or video

11. Transport Layer Segmentation –Breaking large data units received from Session layer into multiple smaller units called segments –Increases data transmission efficiency MTU (maximum transmission unit) –Largest data unit network will carry –Ethernet default: 1500 bytes –Discovery routine used to determine MTU

12. Transport Layer (cont’d.) Reassembly –Process of reconstructing segmented data units Sequencing –Method of identifying segments belonging to the same group of subdivided data

13. Transport Layer (cont’d.) Figure 2-2 Segmentation and reassembly

14. Network Layer Packet formation –Transport layer segment is encapsulated by a Network layer packet Network layer adds logical addressing information—IP address Routing –Determine path from point A on one network to point B on another network Routing considerations –Delivery priorities, network congestion, quality of service, cost of alternative routes

15. Network Layer Common Network layer protocol –IP (Internet Protocol) Fragmentation –Network layer protocol (IP) subdivides Transport layer segments received into smaller packets –This is usually avoided by adjusting the Maximum Segment Size in the Transport layer, because it makes data transfer inefficient Link Ch 2e

16. Data Link Layer Function of protocols –Divide data received into distinct frames for transmission in Physical layer –Add Physical address to the frame: MAC addresses like 00-30-48-82-11-BD Frame –Structured package for moving data Includes raw data (payload), sender’s and receiver’s physical addresses, error checking and control information

17. Data Link Layer (cont’d.) Frames may be damaged as they pass through the Physical layer, so the Data Link layer has error- checking –Error checking Frame check sequence CRC (cyclic redundancy check) Possible glut of communication requests –Data Link layer controls flow of information Allows NIC to process data without error

18. Data Link Layer (cont’d.) Two Data Link layer sublayers –LLC (Logical Link Control) sublayer –MAC (Media Access Control) sublayer MAC address components –Block ID Six-character sequence unique to each vendor –Device ID Six-character number added at vendor’s factory MAC addresses frequently depicted in hexadecimal format

19. Example of MAC Address Whole MAC address: 00-30-48-82-11-BD –Block ID 00-30-48 Identifies the vendor –Device ID 82-11-BD Different for each NIC from the same vendor If two NICs have the same MAC address, they have problems networking –This can happen with cheaply made refurbished NICs, or with copied virtual machines

20. Data Link Layer (cont’d.) Figure 2-5 The Data Link layer and its sublayers

21. Data Link Layer (cont’d.) Figure 2-6 A NIC’s Mac address

22. Finding Your MAC Address Start, CMD, Enter IPCONFIG /ALL Scroll up to see the first entry MAC Address (also called "Physical Address") IP Address

23. Physical Layer Functions of protocols –Accept frames from Data Link layer –Generate signals as changes in voltage at the NIC Copper transmission medium –Signals issued as voltage Fiber-optic cable transmission medium –Signals issued as light pulses Wireless transmission medium –Signals issued as electromagnetic waves

24. Physical Layer (cont’d.) Physical layer protocols responsibility when receiving data –Detect and accept signals –Pass on to Data Link layer –Set data transmission rate Devices operating at Physical layer –Hubs and repeaters NICs operate at both Physical layer and Data Link layers

25. Applying the OSI Model Table 2-1 Functions of the OSI layers

26. iClicker Questions

27. Which OSI layer creates electrical signals which travel along an Ethernet cable? A.Session, Presentation, or Application B.Transport C.Network D.Data Link E.Physical 1 of 5

28. Which OSI layer tears down a connection after a period of inactivity? A.Application B.Presentation C.Session D.Transport E.Network, Data Link, or Physical 2 of 5

29. Which OSI layer encrypts and decrypts data sent with secure protocols like HTTPS? A.Session, Presentation, or Application B.Transport C.Network D.Data Link E.Physical 3 of 5

30. Which OSI layer assigns addresses like 00-50-56-C0-00-01 to the data? A.Session, Presentation, or Application B.Transport C.Network D.Data Link E.Physical 4 of 5

31. Which OSI layer assigns addresses like 147.144.51.101 to the data? A.Session, Presentation, or Application B.Transport C.Network D.Data Link E.Physical 5 of 5

32. iClicker Questions Review

33. Which item below is a MAC address? A.147.144.1.2 B.94112 C.1005HA D.00-12-11-XY-9Q-01 E.00-11-15-A3-B2-2E 1 of 5

34. Which OSI layer is also called Layer 2? A.Session, Presentation, or Application B.Physical C.Network D.Data Link E.Transport 2 of 5

35. Which OSI layer routes packets across the Internet? A.Layer 5, 6 or 7 B.Layer 4 C.Layer 3 D.Layer 2 E.Layer 1 3 of 5

36. Which OSI layer maintains a list of remote servers that your computer is currently connected to? A.Layer 5, 6 or 7 B.Layer 4 C.Layer 3 D.Layer 2 E.Layer 1 4 of 5

37. Which OSI layer sends radio signals out your Wi-Fi Interface? A.Session, Presentation, or Application B.Transport C.Network D.Data Link E.Physical 5 of 5