2. Open System Interconnection Reference Model (OSI reference model) Prepared by: Eric Hansen and Dean Juola

3. OSI Learning Preparation The following are necessary for understanding: l Lesson 1 & 2 completed, including the review questions l OSI Reference Model vocabulary (completed!) l paper and pencil

4. OSI model OSI Reference model The OSI Reference Model is a “reference guide” for understanding network functionality. Each of the 7 layers (numbered from bottom to top) represents one step in the process of sending data packets from a source to a destination.

5. Data Packets and Encapsulation The contiguous elements of the OSI are only able to communicate with each other (layer 7 can communicate with layer 5 only by communicating with layer 6). As a result, each layer adds a protocol header which is encapsulated for data transfer from source to destination.

6. Data Transfer The transfer of data packets seems simple on the outside but a closer look will reveal the specific process of moving data from source to destination. We will look at this by starting with the OSI layer closest to the user, the Application Layer.

7. Application Layer

8. Presentation Layer

9. Session Layer

10. Transport Layer

11. Network Layer

12. Data Link Layer

13. Physical Layer

14. Group Activity Part 1 In your assigned groups of three complete the following: Each group will be assigned an IP address and a MAC address. Then, each person in each group is assigned one of the 1st three layers of the OSI reference model (choose within the group). The instructor will hand the incoming data packet to the layer 1 person who checks the layer 1 information. If it is good, the encapsulated data is then passed to the next layer. If it is bad, then the data is placed in the “bad” pile. With each new data packet, the student will assume a new layer (take a layer you have not been) and continue the cycle two more times. When everyone understands and is finished, go to part 2.

15. Group Activity Part 2 Next, in your group encapsulate data to send to an assigned group. If you receive a data packet, follow the same procedure as in part 1. Hint: You have a group’s address information but you do not know which group it is. What do you do?