CS475: Computer Networks - Layers
Activity Goals
The goals of this activity are:- To identify the layers of the OSI Reference Model for networking
- To map the TCP/IP model layers to those of the OSI Reference Model
Supplemental Reading
Feel free to visit these resources for supplemental background reading material.The Activity
Directions
Consider the activity models and answer the questions provided. First reflect on these questions on your own briefly, before discussing and comparing your thoughts with your group. Appoint one member of your group to discuss your findings with the class, and the rest of the group should help that member prepare their response. Answer each question individually from the activity, and compare with your group to prepare for our whole-class discussion. After class, think about the questions in the reflective prompt and respond to those individually in your notebook. Report out on areas of disagreement or items for which you and your group identified alternative approaches. Write down and report out questions you encountered along the way for group discussion.Model 1: The OSI Reference Model
| Layer | Layer Name | Protocol Data Unit | Description |
|---|---|---|---|
| 7 | Application | Application-level messages | |
| 6 | Presentation | Encoding, compression, encryption, etc. | |
| 5 | Session | User state to maintain a sense of "connection" at the application, for example, cookies to represent a shopping cart | |
| 4 | Transport | Datagram | Segmentation, robust/reliable communications, including sequencing and acknowledgements |
| 3 | Network | Packet | Addressing and routing information |
| 2 | Link | Frame | Error correction and resubmission between two nodes (or a "hop") on the network path |
| 1 | Physical | Bit | Representing a binary 1 and a 0 over a wired or wireless communication |
Adapted from Wikipedia
Questions
- Describe the functionality of each of the layers for a shopping service over HTTP that employs user accounts and a shopping cart. What functionality exists at each layer?
- What do you think would happen with this shopping service if the user started using a wireless connection to communicate with the web site?
Model 2: The TCP/IP Architecture
Questions
- How do you think the OSI Layers map to the TCP/IP architecture?
- What does TCP stand for?
- Is TCP present in this architecture? What is there in its place in this implementation, and what are some differences between it and TCP?
- What kinds of services might be helpful at each layer to communicate a sentence from one side of the classroom to someone on the other side of the classroom?