The OSI Model (Open Systems Interconnection Model) is a conceptual framework used to understand and standardize how different networking systems communicate with each other. It divides the networking process into 7 layers, each with specific functions.
🔹 7 Layers of the OSI Model (Top to Bottom):
| Layer | Name | Function | Example Protocols |
|---|---|---|---|
| 7 | Application | Interface for user applications to access network | HTTP, FTP, SMTP |
| 6 | Presentation | Data translation, encryption, compression | SSL/TLS, JPEG |
| 5 | Session | Establishes and maintains sessions | NetBIOS, RPC |
| 4 | Transport | Reliable data delivery (error correction, flow) | TCP, UDP |
| 3 | Network | Routing and addressing | IP, ICMP, IPsec |
| 2 | Data Link | MAC addressing and error detection on LAN | Ethernet, PPP |
| 1 | Physical | Physical transmission of data (bits) | Cables, Hubs |
🔹 Simple Analogy (Postal Service):
- Application (7): You write the letter.
- Presentation (6): You translate the letter if needed.
- Session (5): You start a phone call to say you're sending it.
- Transport (4): You make sure it arrives safely.
- Network (3): You find the best path to the destination.
- Data Link (2): You put the address and stamp on the envelope.
- Physical (1): You drop it into the mailbox.
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