Chapter 2: Network Models - buaamer81/IT130-Networking-Wiki GitHub Wiki
Chapter 2: Network Models
Summary
This chapter explains the framework of how data moves in networks using two major models:
- OSI Model (7 Layers)
- TCP/IP Model (4 Layers)
These models help to troubleshoot, design, and understand networking systems.
Key Concepts
OSI Model (Open Systems Interconnection)
A conceptual model with 7 layers, each with a specific function.
| Layer Number | Layer Name | Example |
|---|---|---|
| 7 | Application | HTTP, FTP, DNS |
| 6 | Presentation | Encryption, Data formatting |
| 5 | Session | Session management |
| 4 | Transport | TCP, UDP |
| 3 | Network | IP addressing, Routing |
| 2 | Data Link | MAC address, Switches |
| 1 | Physical | Cables, Hubs, Bits |
TCP/IP Model
A simplified 4-layer model more commonly used in real-world networking.
| Layer | Equivalent OSI Layers | Examples |
|---|---|---|
| Application | OSI Layers 5-7 | HTTP, FTP, DNS |
| Transport | OSI Layer 4 | TCP, UDP |
| Internet | OSI Layer 3 | IP, ICMP |
| Link | OSI Layers 1-2 | Ethernet, MAC Address |
Encapsulation Process
When sending data:
- Each layer adds its own header info (like an envelope around data).
- At the receiving end → The headers are stripped off.
Example Flow:
MAC vs IP Address
| MAC Address | IP Address |
|---|---|
| Physical, Burned into NIC | Logical, Assigned by network |
| Used in LAN | Used for global identification |
| Doesn't change | Can change often |
Protocol Data Units (PDUs)
- Layer 1: Bits
- Layer 2: Frames
- Layer 3: Packets
- Layer 4: Segments
Sample Practice Questions
- Which OSI layer is responsible for routing packets?
- a) Layer 2
- b) Layer 3
- c) Layer 4
- d) Layer 7
Answer: b) Layer 3 (Network Layer)
- What is the main job of Layer 2 in the OSI model?
- a) Routing
- b) IP addressing
- c) MAC addressing & framing
- d) Encryption
Answer: c) MAC addressing & framing