OSI Model - buaamer81/IT130-Networking-Wiki GitHub Wiki
OSI Model Overview
๐ What is the OSI Model?
The OSI Model (Open Systems Interconnection) is a 7-layer conceptual framework developed by the International Organization for Standardization (ISO). It helps explain how different networking protocols and technologies work together to move data between computers.
๐ Purpose of the OSI Model
- Standardize communication across networks
- Simplify troubleshooting by breaking down network functions
- Allow multi-vendor interoperability (Cisco, Juniper, Microsoft, etc.)
- Provide a common language for network engineers
๐งฑ The 7 Layers of OSI (Top to Bottom)
| Layer | Name | Key Function |
|---|---|---|
| Layer 7: Application Layer | User interface for network services | |
| Layer 6: Presentation Layer | Data translation, encryption, compression | |
| Layer 5: Session Layer | Starts and manages sessions | |
| Layer 4: Transport Layer | Reliable delivery (TCP/UDP) | |
| Layer 3: Network Layer | Routing and logical addressing (IP) | |
| Layer 2: Data Link Layer | Framing, MAC addressing, switching | |
| Layer 1: Physical Layer | Transmitting raw bits over media |
๐ง Mnemonics to Remember
From Top (7) to Bottom (1):
โAll People Seem To Need Data Processingโ
From Bottom (1) to Top (7):
โPlease Do Not Throw Sausage Pizza Awayโ
๐ Real-World Example: Sending an Email
| OSI Layer | What Happens |
|---|---|
| 7 | Your email client opens |
| 6 | Message is encoded |
| 5 | Session with email server is established |
| 4 | Message is split into segments |
| 3 | Segments are addressed with IP |
| 2 | Frames are created and sent through MAC |
| 1 | Bits go through cables/Wi-Fi |
๐ Related Concepts
๐ Visual Aid
๐ Quiz Yourself
- Which OSI layer handles encryption?
- What layer is responsible for IP addressing?
- Which layer does a router operate at?
- Where does TCP/UDP operate?
๐ Explore Each Layer
- Layer 1: Physical Layer
- Layer 2: Data Link Layer
- Layer 3: Network Layer
- Layer 4: Transport Layer
- Layer 5: Session Layer
- Layer 6: Presentation Layer
- Layer 7: Application Layer
Return to: Chapter 2